Merge the latest changes of trunk into the session branch.

FossilOrigin-Name: 95d53c44320b9639f2623aa9cc88d0d3e1a3be8f

16 files changed, 2022 insertions, 400 deletions

diff --git a/src/btmutex.c b/src/btmutex.c
index 201291a3e..42d0bdcbc 100644
--- a/src/btmutex.c
+++ b/src/btmutex.c
@@ -39,15 +39,34 @@ static void lockBtreeMutex(Btree *p){
 ** clear the p->locked boolean.
 */
 static void unlockBtreeMutex(Btree *p){
+  BtShared *pBt = p->pBt;
   assert( p->locked==1 );
-  assert( sqlite3_mutex_held(p->pBt->mutex) );
+  assert( sqlite3_mutex_held(pBt->mutex) );
   assert( sqlite3_mutex_held(p->db->mutex) );
-  assert( p->db==p->pBt->db );
+  assert( p->db==pBt->db );
 
-  sqlite3_mutex_leave(p->pBt->mutex);
+  pBt->iMutexCounter++;
+  sqlite3_mutex_leave(pBt->mutex);
   p->locked = 0;
 }
 
+#ifdef SQLITE_DEBUG
+/*
+** Return the number of times that the mutex has been exited for
+** the given btree.
+**
+** This is a small circular counter that wraps around to zero on
+** overflow.  It is used only for sanity checking - to verify that
+** mutexes are held continously by asserting that the value of
+** this counter at the beginning of a region is the same as at
+** the end.
+*/
+u32 sqlite3BtreeMutexCounter(Btree *p){
+  assert( p->locked==1 || p->sharable==0 );
+  return p->pBt->iMutexCounter;
+}
+#endif
+
 /*
 ** Enter a mutex on the given BTree object.
 **
@@ -92,6 +111,24 @@ void sqlite3BtreeEnter(Btree *p){
   p->wantToLock++;
   if( p->locked ) return;
 
+  /* Increment the mutex counter on all locked btrees in the same
+  ** database connection.  This simulates the unlocking that would
+  ** occur on a worst-case mutex dead-lock avoidance scenario.
+  */
+#ifdef SQLITE_DEBUG
+  {
+    int ii;
+    sqlite3 *db = p->db;
+    Btree *pOther;
+    for(ii=0; ii<db->nDb; ii++){
+      if( ii==1 ) continue;
+      pOther = db->aDb[ii].pBt;
+      if( pOther==0 || pOther->sharable==0 || pOther->locked==0 ) continue;
+      pOther->pBt->iMutexCounter++;
+    }
+  }
+#endif
+
   /* In most cases, we should be able to acquire the lock we
   ** want without having to go throught the ascending lock
   ** procedure that follows.  Just be sure not to block.
@@ -195,7 +232,7 @@ void sqlite3BtreeEnterAll(sqlite3 *db){
       if( !p->locked ){
         assert( p->wantToLock==1 );
         while( p->pPrev ) p = p->pPrev;
-        /* Reason for ALWAYS:  There must be at least on unlocked Btree in
+        /* Reason for ALWAYS:  There must be at least one unlocked Btree in
         ** the chain.  Otherwise the !p->locked test above would have failed */
         while( p->locked && ALWAYS(p->pNext) ) p = p->pNext;
         for(pLater = p->pNext; pLater; pLater=pLater->pNext){
@@ -251,97 +288,17 @@ int sqlite3BtreeHoldsAllMutexes(sqlite3 *db){
 }
 #endif /* NDEBUG */
 
+#else /* SQLITE_THREADSAFE>0 above.  SQLITE_THREADSAFE==0 below */
 /*
-** Add a new Btree pointer to a BtreeMutexArray. 
-** if the pointer can possibly be shared with
-** another database connection.
+** The following are special cases for mutex enter routines for use
+** in single threaded applications that use shared cache.  Except for
+** these two routines, all mutex operations are no-ops in that case and
+** are null #defines in btree.h.
 **
-** The pointers are kept in sorted order by pBtree->pBt.  That
-** way when we go to enter all the mutexes, we can enter them
-** in order without every having to backup and retry and without
-** worrying about deadlock.
-**
-** The number of shared btrees will always be small (usually 0 or 1)
-** so an insertion sort is an adequate algorithm here.
+** If shared cache is disabled, then all btree mutex routines, including
+** the ones below, are no-ops and are null #defines in btree.h.
 */
-void sqlite3BtreeMutexArrayInsert(BtreeMutexArray *pArray, Btree *pBtree){
-  int i, j;
-  BtShared *pBt;
-  if( pBtree==0 || pBtree->sharable==0 ) return;
-#ifndef NDEBUG
-  {
-    for(i=0; i<pArray->nMutex; i++){
-      assert( pArray->aBtree[i]!=pBtree );
-    }
-  }
-#endif
-  assert( pArray->nMutex>=0 );
-  assert( pArray->nMutex<ArraySize(pArray->aBtree)-1 );
-  pBt = pBtree->pBt;
-  for(i=0; i<pArray->nMutex; i++){
-    assert( pArray->aBtree[i]!=pBtree );
-    if( pArray->aBtree[i]->pBt>pBt ){
-      for(j=pArray->nMutex; j>i; j--){
-        pArray->aBtree[j] = pArray->aBtree[j-1];
-      }
-      pArray->aBtree[i] = pBtree;
-      pArray->nMutex++;
-      return;
-    }
-  }
-  pArray->aBtree[pArray->nMutex++] = pBtree;
-}
-
-/*
-** Enter the mutex of every btree in the array.  This routine is
-** called at the beginning of sqlite3VdbeExec().  The mutexes are
-** exited at the end of the same function.
-*/
-void sqlite3BtreeMutexArrayEnter(BtreeMutexArray *pArray){
-  int i;
-  for(i=0; i<pArray->nMutex; i++){
-    Btree *p = pArray->aBtree[i];
-    /* Some basic sanity checking */
-    assert( i==0 || pArray->aBtree[i-1]->pBt<p->pBt );
-    assert( !p->locked || p->wantToLock>0 );
-
-    /* We should already hold a lock on the database connection */
-    assert( sqlite3_mutex_held(p->db->mutex) );
-
-    /* The Btree is sharable because only sharable Btrees are entered
-    ** into the array in the first place. */
-    assert( p->sharable );
-
-    p->wantToLock++;
-    if( !p->locked ){
-      lockBtreeMutex(p);
-    }
-  }
-}
-
-/*
-** Leave the mutex of every btree in the group.
-*/
-void sqlite3BtreeMutexArrayLeave(BtreeMutexArray *pArray){
-  int i;
-  for(i=0; i<pArray->nMutex; i++){
-    Btree *p = pArray->aBtree[i];
-    /* Some basic sanity checking */
-    assert( i==0 || pArray->aBtree[i-1]->pBt<p->pBt );
-    assert( p->locked );
-    assert( p->wantToLock>0 );
-
-    /* We should already hold a lock on the database connection */
-    assert( sqlite3_mutex_held(p->db->mutex) );
-
-    p->wantToLock--;
-    if( p->wantToLock==0 ){
-      unlockBtreeMutex(p);
-    }
-  }
-}
 
-#else
 void sqlite3BtreeEnter(Btree *p){
   p->pBt->db = p->db;
 }
diff --git a/src/btree.c b/src/btree.c
index 088c555fc..d86b9edad 100644
--- a/src/btree.c
+++ b/src/btree.c
@@ -7990,7 +7990,7 @@ int sqlite3BtreeIsInBackup(Btree *p){
 **
 ** Just before the shared-btree is closed, the function passed as the 
 ** xFree argument when the memory allocation was made is invoked on the 
-** blob of allocated memory. This function should not call sqlite3_free()
+** blob of allocated memory. The xFree function should not call sqlite3_free()
 ** on the memory, the btree layer does that.
 */
 void *sqlite3BtreeSchema(Btree *p, int nBytes, void(*xFree)(void *)){
diff --git a/src/btree.h b/src/btree.h
index 468723b33..4fd4f6768 100644
--- a/src/btree.h
+++ b/src/btree.h
@@ -39,18 +39,6 @@
 typedef struct Btree Btree;
 typedef struct BtCursor BtCursor;
 typedef struct BtShared BtShared;
-typedef struct BtreeMutexArray BtreeMutexArray;
-
-/*
-** This structure records all of the Btrees that need to hold
-** a mutex before we enter sqlite3VdbeExec().  The Btrees are
-** are placed in aBtree[] in order of aBtree[]->pBt.  That way,
-** we can always lock and unlock them all quickly.
-*/
-struct BtreeMutexArray {
-  int nMutex;
-  Btree *aBtree[SQLITE_MAX_ATTACHED+1];
-};
 
 
 int sqlite3BtreeOpen(
@@ -228,23 +216,19 @@ void sqlite3BtreeCursorList(Btree*);
   void sqlite3BtreeEnterCursor(BtCursor*);
   void sqlite3BtreeLeaveCursor(BtCursor*);
   void sqlite3BtreeLeaveAll(sqlite3*);
-  void sqlite3BtreeMutexArrayEnter(BtreeMutexArray*);
-  void sqlite3BtreeMutexArrayLeave(BtreeMutexArray*);
-  void sqlite3BtreeMutexArrayInsert(BtreeMutexArray*, Btree*);
 #ifndef NDEBUG
   /* These routines are used inside assert() statements only. */
   int sqlite3BtreeHoldsMutex(Btree*);
   int sqlite3BtreeHoldsAllMutexes(sqlite3*);
+  u32 sqlite3BtreeMutexCounter(Btree*);
 #endif
 #else
 
 # define sqlite3BtreeLeave(X)
+# define sqlite3BtreeMutexCounter(X) 0
 # define sqlite3BtreeEnterCursor(X)
 # define sqlite3BtreeLeaveCursor(X)
 # define sqlite3BtreeLeaveAll(X)
-# define sqlite3BtreeMutexArrayEnter(X)
-# define sqlite3BtreeMutexArrayLeave(X)
-# define sqlite3BtreeMutexArrayInsert(X,Y)
 
 # define sqlite3BtreeHoldsMutex(X) 1
 # define sqlite3BtreeHoldsAllMutexes(X) 1
diff --git a/src/btreeInt.h b/src/btreeInt.h
index 0e71195b0..2aee063d3 100644
--- a/src/btreeInt.h
+++ b/src/btreeInt.h
@@ -336,7 +336,7 @@ struct BtLock {
 ** All fields in this structure are accessed under sqlite3.mutex.
 ** The pBt pointer itself may not be changed while there exists cursors 
 ** in the referenced BtShared that point back to this Btree since those
-** cursors have to do go through this Btree to find their BtShared and
+** cursors have to go through this Btree to find their BtShared and
 ** they often do so without holding sqlite3.mutex.
 */
 struct Btree {
@@ -426,7 +426,7 @@ struct BtShared {
   u32 nPage;            /* Number of pages in the database */
   void *pSchema;        /* Pointer to space allocated by sqlite3BtreeSchema() */
   void (*xFreeSchema)(void*);  /* Destructor for BtShared.pSchema */
-  sqlite3_mutex *mutex; /* Non-recursive mutex required to access this struct */
+  sqlite3_mutex *mutex; /* Non-recursive mutex required to access this object */
   Bitvec *pHasContent;  /* Set of pages moved to free-list this transaction */
 #ifndef SQLITE_OMIT_SHARED_CACHE
   int nRef;             /* Number of references to this structure */
@@ -435,6 +435,7 @@ struct BtShared {
   Btree *pWriter;       /* Btree with currently open write transaction */
   u8 isExclusive;       /* True if pWriter has an EXCLUSIVE lock on the db */
   u8 isPending;         /* If waiting for read-locks to clear */
+  u16 iMutexCounter;    /* The number of mutex_leave(mutex) calls */
 #endif
   u8 *pTmpSpace;        /* BtShared.pageSize bytes of space for tmp use */
 };
diff --git a/src/build.c b/src/build.c
index bf3273fc8..b4528347d 100644
--- a/src/build.c
+++ b/src/build.c
@@ -148,7 +148,7 @@ void sqlite3FinishCoding(Parse *pParse){
     ** on each used database.
     */
     if( pParse->cookieGoto>0 ){
-      tAttachMask mask;
+      yDbMask mask;
       int iDb;
       sqlite3VdbeJumpHere(v, pParse->cookieGoto-1);
       for(iDb=0, mask=1; iDb<db->nDb; mask<<=1, iDb++){
@@ -3444,12 +3444,12 @@ void sqlite3CodeVerifySchema(Parse *pParse, int iDb){
   }
   if( iDb>=0 ){
     sqlite3 *db = pToplevel->db;
-    tAttachMask mask;
+    yDbMask mask;
 
     assert( iDb<db->nDb );
     assert( db->aDb[iDb].pBt!=0 || iDb==1 );
     assert( iDb<SQLITE_MAX_ATTACHED+2 );
-    mask = ((tAttachMask)1)<<iDb;
+    mask = ((yDbMask)1)<<iDb;
     if( (pToplevel->cookieMask & mask)==0 ){
       pToplevel->cookieMask |= mask;
       pToplevel->cookieValue[iDb] = db->aDb[iDb].pSchema->schema_cookie;
@@ -3476,7 +3476,7 @@ void sqlite3CodeVerifySchema(Parse *pParse, int iDb){
 void sqlite3BeginWriteOperation(Parse *pParse, int setStatement, int iDb){
   Parse *pToplevel = sqlite3ParseToplevel(pParse);
   sqlite3CodeVerifySchema(pParse, iDb);
-  pToplevel->writeMask |= ((tAttachMask)1)<<iDb;
+  pToplevel->writeMask |= ((yDbMask)1)<<iDb;
   pToplevel->isMultiWrite |= setStatement;
 }
 
diff --git a/src/os_unix.c b/src/os_unix.c
index f04b6af27..67dd06fc1 100644
--- a/src/os_unix.c
+++ b/src/os_unix.c
@@ -394,10 +394,10 @@ static int unixSetSystemCall(
     /* If no zName is given, restore all system calls to their default
     ** settings and return NULL
     */
+    rc = SQLITE_OK;
     for(i=0; i<sizeof(aSyscall)/sizeof(aSyscall[0]); i++){
       if( aSyscall[i].pDefault ){
         aSyscall[i].pCurrent = aSyscall[i].pDefault;
-        rc = SQLITE_OK;
       }
     }
   }else{
diff --git a/src/sqliteInt.h b/src/sqliteInt.h
index d31ed4ae6..ce1e106df 100644
--- a/src/sqliteInt.h
+++ b/src/sqliteInt.h
@@ -2133,11 +2133,13 @@ struct TriggerPrg {
   TriggerPrg *pNext;      /* Next entry in Parse.pTriggerPrg list */
 };
 
-/* Datatype for the bitmask of all attached databases */
+/*
+** The yDbMask datatype for the bitmask of all attached databases.
+*/
 #if SQLITE_MAX_ATTACHED>30
-  typedef sqlite3_uint64 tAttachMask;
+  typedef sqlite3_uint64 yDbMask;
 #else
-  typedef unsigned int tAttachMask;
+  typedef unsigned int yDbMask;
 #endif
 
 /*
@@ -2188,8 +2190,8 @@ struct Parse {
     int iReg;             /* Reg with value of this column. 0 means none. */
     int lru;              /* Least recently used entry has the smallest value */
   } aColCache[SQLITE_N_COLCACHE];  /* One for each column cache entry */
-  tAttachMask writeMask;  /* Start a write transaction on these databases */
-  tAttachMask cookieMask; /* Bitmask of schema verified databases */
+  yDbMask writeMask;   /* Start a write transaction on these databases */
+  yDbMask cookieMask;  /* Bitmask of schema verified databases */
   u8 isMultiWrite;     /* True if statement may affect/insert multiple rows */
   u8 mayAbort;         /* True if statement may throw an ABORT exception */
   int cookieGoto;      /* Address of OP_Goto to cookie verifier subroutine */
diff --git a/src/tclsqlite.c b/src/tclsqlite.c
index de0e992bd..e1f451541 100644
--- a/src/tclsqlite.c
+++ b/src/tclsqlite.c
@@ -3728,6 +3728,8 @@ static void init_all(Tcl_Interp *interp){
     extern int Sqlitemultiplex_Init(Tcl_Interp*);
     extern int SqliteSuperlock_Init(Tcl_Interp*);
     extern int SqlitetestSyscall_Init(Tcl_Interp*);
+    extern int Sqlitetestfuzzer_Init(Tcl_Interp*);
+    extern int Sqlitetestwholenumber_Init(Tcl_Interp*);
 #if defined(SQLITE_ENABLE_SESSION) && defined(SQLITE_ENABLE_PREUPDATE_HOOK)
     extern int TestSession_Init(Tcl_Interp*);
 #endif
@@ -3768,6 +3770,8 @@ static void init_all(Tcl_Interp *interp){
     Sqlitemultiplex_Init(interp);
     SqliteSuperlock_Init(interp);
     SqlitetestSyscall_Init(interp);
+    Sqlitetestfuzzer_Init(interp);
+    Sqlitetestwholenumber_Init(interp);
 #if defined(SQLITE_ENABLE_SESSION) && defined(SQLITE_ENABLE_PREUPDATE_HOOK)
     TestSession_Init(interp);
 #endif
diff --git a/src/test_fuzzer.c b/src/test_fuzzer.c
new file mode 100644
index 000000000..cf5925717
--- /dev/null
+++ b/src/test_fuzzer.c
@@ -0,0 +1,944 @@
+/*
+** 2011 March 24
+**
+** The author disclaims copyright to this source code.  In place of
+** a legal notice, here is a blessing:
+**
+**    May you do good and not evil.
+**    May you find forgiveness for yourself and forgive others.
+**    May you share freely, never taking more than you give.
+**
+*************************************************************************
+**
+** Code for demonstartion virtual table that generates variations
+** on an input word at increasing edit distances from the original.
+**
+** A fuzzer virtual table is created like this:
+**
+**     CREATE VIRTUAL TABLE temp.f USING fuzzer;
+**
+** The name of the new virtual table in the example above is "f".
+** Note that all fuzzer virtual tables must be TEMP tables.  The
+** "temp." prefix in front of the table name is required when the
+** table is being created.  The "temp." prefix can be omitted when
+** using the table as long as the name is unambiguous.
+**
+** Before being used, the fuzzer needs to be programmed by giving it
+** character transformations and a cost associated with each transformation.
+** Examples:
+**
+**    INSERT INTO f(cFrom,cTo,Cost) VALUES('','a',100);
+**
+** The above statement says that the cost of inserting a letter 'a' is
+** 100.  (All costs are integers.  We recommend that costs be scaled so
+** that the average cost is around 100.)
+**
+**    INSERT INTO f(cFrom,cTo,Cost) VALUES('b','',87);
+**
+** The above statement says that the cost of deleting a single letter
+** 'b' is 87.
+**
+**    INSERT INTO f(cFrom,cTo,Cost) VALUES('o','oe',38);
+**    INSERT INTO f(cFrom,cTo,Cost) VALUES('oe','o',40);
+**
+** This third example says that the cost of transforming the single
+** letter "o" into the two-letter sequence "oe" is 38 and that the
+** cost of transforming "oe" back into "o" is 40.
+**
+** After all the transformation costs have been set, the fuzzer table
+** can be queried as follows:
+**
+**    SELECT word, distance FROM f
+**     WHERE word MATCH 'abcdefg'
+**       AND distance<200;
+**
+** This first query outputs the string "abcdefg" and all strings that
+** can be derived from that string by appling the specified transformations.
+** The strings are output together with their total transformation cost
+** (called "distance") and appear in order of increasing cost.  No string
+** is output more than once.  If there are multiple ways to transform the
+** target string into the output string then the lowest cost transform is
+** the one that is returned.  In the example, the search is limited to 
+** strings with a total distance of less than 200.
+**
+** It is important to put some kind of a limit on the fuzzer output.  This
+** can be either in the form of a LIMIT clause at the end of the query,
+** or better, a "distance<NNN" constraint where NNN is some number.  The
+** running time and memory requirement is exponential in the value of NNN 
+** so you want to make sure that NNN is not too big.  A value of NNN that
+** is about twice the average transformation cost seems to give good results.
+**
+** The fuzzer table can be useful for tasks such as spelling correction.
+** Suppose there is a second table vocabulary(w) where the w column contains
+** all correctly spelled words.   Let $word be a word you want to look up.
+**
+**   SELECT vocabulary.w FROM f, vocabulary
+**    WHERE f.word MATCH $word
+**      AND f.distance<=200
+**      AND f.word=vocabulary.w
+**    LIMIT 20
+**
+** The query above gives the 20 closest words to the $word being tested.
+** (Note that for good performance, the vocubulary.w column should be
+** indexed.)
+**
+** A similar query can be used to find all words in the dictionary that
+** begin with some prefix $prefix:
+**
+**   SELECT vocabulary.w FROM f, vocabulary
+**    WHERE f.word MATCH $prefix
+**      AND f.distance<=200
+**      AND vocabulary.w BETWEEN f.word AND (f.word || x'F7BFBFBF')
+**    LIMIT 50
+**
+** This last query will show up to 50 words out of the vocabulary that
+** match or nearly match the $prefix.
+*/
+#include "sqlite3.h"
+#include <stdlib.h>
+#include <string.h>
+#include <assert.h>
+#include <stdio.h>
+
+#ifndef SQLITE_OMIT_VIRTUALTABLE
+
+/*
+** Forward declaration of objects used by this implementation
+*/
+typedef struct fuzzer_vtab fuzzer_vtab;
+typedef struct fuzzer_cursor fuzzer_cursor;
+typedef struct fuzzer_rule fuzzer_rule;
+typedef struct fuzzer_seen fuzzer_seen;
+typedef struct fuzzer_stem fuzzer_stem;
+
+/*
+** Type of the "cost" of an edit operation.  Might be changed to
+** "float" or "double" or "sqlite3_int64" in the future.
+*/
+typedef int fuzzer_cost;
+
+
+/*
+** Each transformation rule is stored as an instance of this object.
+** All rules are kept on a linked list sorted by rCost.
+*/
+struct fuzzer_rule {
+  fuzzer_rule *pNext;        /* Next rule in order of increasing rCost */
+  fuzzer_cost rCost;         /* Cost of this transformation */
+  int nFrom, nTo;            /* Length of the zFrom and zTo strings */
+  char *zFrom;               /* Transform from */
+  char zTo[4];               /* Transform to (extra space appended) */
+};
+
+/*
+** A stem object is used to generate variants.  It is also used to record
+** previously generated outputs.
+**
+** Every stem is added to a hash table as it is output.  Generation of
+** duplicate stems is suppressed.
+**
+** Active stems (those that might generate new outputs) are kepts on a linked
+** list sorted by increasing cost.  The cost is the sum of rBaseCost and
+** pRule->rCost.
+*/
+struct fuzzer_stem {
+  char *zBasis;              /* Word being fuzzed */
+  int nBasis;                /* Length of the zBasis string */
+  const fuzzer_rule *pRule;  /* Current rule to apply */
+  int n;                     /* Apply pRule at this character offset */
+  fuzzer_cost rBaseCost;     /* Base cost of getting to zBasis */
+  fuzzer_cost rCostX;        /* Precomputed rBaseCost + pRule->rCost */
+  fuzzer_stem *pNext;        /* Next stem in rCost order */
+  fuzzer_stem *pHash;        /* Next stem with same hash on zBasis */
+};
+
+/* 
+** A fuzzer virtual-table object 
+*/
+struct fuzzer_vtab {
+  sqlite3_vtab base;         /* Base class - must be first */
+  char *zClassName;          /* Name of this class.  Default: "fuzzer" */
+  fuzzer_rule *pRule;        /* All active rules in this fuzzer */
+  fuzzer_rule *pNewRule;     /* New rules to add when last cursor expires */
+  int nCursor;               /* Number of active cursors */
+};
+
+#define FUZZER_HASH  4001    /* Hash table size */
+#define FUZZER_NQUEUE  20    /* Number of slots on the stem queue */
+
+/* A fuzzer cursor object */
+struct fuzzer_cursor {
+  sqlite3_vtab_cursor base;  /* Base class - must be first */
+  sqlite3_int64 iRowid;      /* The rowid of the current word */
+  fuzzer_vtab *pVtab;        /* The virtual table this cursor belongs to */
+  fuzzer_cost rLimit;        /* Maximum cost of any term */
+  fuzzer_stem *pStem;        /* Stem with smallest rCostX */
+  fuzzer_stem *pDone;        /* Stems already processed to completion */
+  fuzzer_stem *aQueue[FUZZER_NQUEUE];  /* Queue of stems with higher rCostX */
+  int mxQueue;               /* Largest used index in aQueue[] */
+  char *zBuf;                /* Temporary use buffer */
+  int nBuf;                  /* Bytes allocated for zBuf */
+  int nStem;                 /* Number of stems allocated */
+  fuzzer_rule nullRule;      /* Null rule used first */
+  fuzzer_stem *apHash[FUZZER_HASH]; /* Hash of previously generated terms */
+};
+
+/* Methods for the fuzzer module */
+static int fuzzerConnect(
+  sqlite3 *db,
+  void *pAux,
+  int argc, const char *const*argv,
+  sqlite3_vtab **ppVtab,
+  char **pzErr
+){
+  fuzzer_vtab *pNew;
+  int n;
+  if( strcmp(argv[1],"temp")!=0 ){
+    *pzErr = sqlite3_mprintf("%s virtual tables must be TEMP", argv[0]);
+    return SQLITE_ERROR;
+  }
+  n = strlen(argv[0]) + 1;
+  pNew = sqlite3_malloc( sizeof(*pNew) + n );
+  if( pNew==0 ) return SQLITE_NOMEM;
+  pNew->zClassName = (char*)&pNew[1];
+  memcpy(pNew->zClassName, argv[0], n);
+  sqlite3_declare_vtab(db, "CREATE TABLE x(word,distance,cFrom,cTo,cost)");
+  memset(pNew, 0, sizeof(*pNew));
+  *ppVtab = &pNew->base;
+  return SQLITE_OK;
+}
+/* Note that for this virtual table, the xCreate and xConnect
+** methods are identical. */
+
+static int fuzzerDisconnect(sqlite3_vtab *pVtab){
+  fuzzer_vtab *p = (fuzzer_vtab*)pVtab;
+  assert( p->nCursor==0 );
+  do{
+    while( p->pRule ){
+      fuzzer_rule *pRule = p->pRule;
+      p->pRule = pRule->pNext;
+      sqlite3_free(pRule);
+    }
+    p->pRule = p->pNewRule;
+    p->pNewRule = 0;
+  }while( p->pRule );
+  sqlite3_free(p);
+  return SQLITE_OK;
+}
+/* The xDisconnect and xDestroy methods are also the same */
+
+/*
+** The two input rule lists are both sorted in order of increasing
+** cost.  Merge them together into a single list, sorted by cost, and
+** return a pointer to the head of that list.
+*/
+static fuzzer_rule *fuzzerMergeRules(fuzzer_rule *pA, fuzzer_rule *pB){
+  fuzzer_rule head;
+  fuzzer_rule *pTail;
+
+  pTail =  &head;
+  while( pA && pB ){
+    if( pA->rCost<=pB->rCost ){
+      pTail->pNext = pA;
+      pTail = pA;
+      pA = pA->pNext;
+    }else{
+      pTail->pNext = pB;
+      pTail = pB;
+      pB = pB->pNext;
+    }
+  }
+  if( pA==0 ){
+    pTail->pNext = pB;
+  }else{
+    pTail->pNext = pA;
+  }
+  return head.pNext;
+}
+
+
+/*
+** Open a new fuzzer cursor.
+*/
+static int fuzzerOpen(sqlite3_vtab *pVTab, sqlite3_vtab_cursor **ppCursor){
+  fuzzer_vtab *p = (fuzzer_vtab*)pVTab;
+  fuzzer_cursor *pCur;
+  pCur = sqlite3_malloc( sizeof(*pCur) );
+  if( pCur==0 ) return SQLITE_NOMEM;
+  memset(pCur, 0, sizeof(*pCur));
+  pCur->pVtab = p;
+  *ppCursor = &pCur->base;
+  if( p->nCursor==0 && p->pNewRule ){
+    unsigned int i;
+    fuzzer_rule *pX;
+    fuzzer_rule *a[15];
+    for(i=0; i<sizeof(a)/sizeof(a[0]); i++) a[i] = 0;
+    while( (pX = p->pNewRule)!=0 ){
+      p->pNewRule = pX->pNext;
+      pX->pNext = 0;
+      for(i=0; a[i] && i<sizeof(a)/sizeof(a[0])-1; i++){
+        pX = fuzzerMergeRules(a[i], pX);
+        a[i] = 0;
+      }
+      a[i] = fuzzerMergeRules(a[i], pX);
+    }
+    for(pX=a[0], i=1; i<sizeof(a)/sizeof(a[0]); i++){
+      pX = fuzzerMergeRules(a[i], pX);
+    }
+    p->pRule = fuzzerMergeRules(p->pRule, pX);
+  }
+  p->nCursor++;
+  return SQLITE_OK;
+}
+
+/*
+** Free all stems in a list.
+*/
+static void fuzzerClearStemList(fuzzer_stem *pStem){
+  while( pStem ){
+    fuzzer_stem *pNext = pStem->pNext;
+    sqlite3_free(pStem);
+    pStem = pNext;
+  }
+}
+
+/*
+** Free up all the memory allocated by a cursor.  Set it rLimit to 0
+** to indicate that it is at EOF.
+*/
+static void fuzzerClearCursor(fuzzer_cursor *pCur, int clearHash){
+  int i;
+  fuzzerClearStemList(pCur->pStem);
+  fuzzerClearStemList(pCur->pDone);
+  for(i=0; i<FUZZER_NQUEUE; i++) fuzzerClearStemList(pCur->aQueue[i]);
+  pCur->rLimit = (fuzzer_cost)0;
+  if( clearHash && pCur->nStem ){
+    pCur->mxQueue = 0;
+    pCur->pStem = 0;
+    pCur->pDone = 0;
+    memset(pCur->aQueue, 0, sizeof(pCur->aQueue));
+    memset(pCur->apHash, 0, sizeof(pCur->apHash));
+  }
+  pCur->nStem = 0;
+}
+
+/*
+** Close a fuzzer cursor.
+*/
+static int fuzzerClose(sqlite3_vtab_cursor *cur){
+  fuzzer_cursor *pCur = (fuzzer_cursor *)cur;
+  fuzzerClearCursor(pCur, 0);
+  sqlite3_free(pCur->zBuf);
+  pCur->pVtab->nCursor--;
+  sqlite3_free(pCur);
+  return SQLITE_OK;
+}
+
+/*
+** Compute the current output term for a fuzzer_stem.
+*/
+static int fuzzerRender(
+  fuzzer_stem *pStem,   /* The stem to be rendered */
+  char **pzBuf,         /* Write results into this buffer.  realloc if needed */
+  int *pnBuf            /* Size of the buffer */
+){
+  const fuzzer_rule *pRule = pStem->pRule;
+  int n;
+  char *z;
+
+  n = pStem->nBasis + pRule->nTo - pRule->nFrom;
+  if( (*pnBuf)<n+1 ){
+    (*pzBuf) = sqlite3_realloc((*pzBuf), n+100);
+    if( (*pzBuf)==0 ) return SQLITE_NOMEM;
+    (*pnBuf) = n+100;
+  }
+  n = pStem->n;
+  z = *pzBuf;
+  if( n<0 ){
+    memcpy(z, pStem->zBasis, pStem->nBasis+1);
+  }else{
+    memcpy(z, pStem->zBasis, n);
+    memcpy(&z[n], pRule->zTo, pRule->nTo);
+    memcpy(&z[n+pRule->nTo], &pStem->zBasis[n+pRule->nFrom], 
+           pStem->nBasis-n-pRule->nFrom+1);
+  }
+  return SQLITE_OK;
+}
+
+/*
+** Compute a hash on zBasis.
+*/
+static unsigned int fuzzerHash(const char *z){
+  unsigned int h = 0;
+  while( *z ){ h = (h<<3) ^ (h>>29) ^ *(z++); }
+  return h % FUZZER_HASH;
+}
+
+/*
+** Current cost of a stem
+*/
+static fuzzer_cost fuzzerCost(fuzzer_stem *pStem){
+  return pStem->rCostX = pStem->rBaseCost + pStem->pRule->rCost;
+}
+
+#if 0
+/*
+** Print a description of a fuzzer_stem on stderr.
+*/
+static void fuzzerStemPrint(
+  const char *zPrefix,
+  fuzzer_stem *pStem,
+  const char *zSuffix
+){
+  if( pStem->n<0 ){
+    fprintf(stderr, "%s[%s](%d)-->self%s",
+       zPrefix,
+       pStem->zBasis, pStem->rBaseCost,
+       zSuffix
+    );
+  }else{
+    char *zBuf = 0;
+    int nBuf = 0;
+    if( fuzzerRender(pStem, &zBuf, &nBuf)!=SQLITE_OK ) return;
+    fprintf(stderr, "%s[%s](%d)-->{%s}(%d)%s",
+      zPrefix,
+      pStem->zBasis, pStem->rBaseCost, zBuf, pStem->,
+      zSuffix
+    );
+    sqlite3_free(zBuf);
+  }
+}
+#endif
+
+/*
+** Return 1 if the string to which the cursor is point has already
+** been emitted.  Return 0 if not.  Return -1 on a memory allocation
+** failures.
+*/
+static int fuzzerSeen(fuzzer_cursor *pCur, fuzzer_stem *pStem){
+  unsigned int h;
+  fuzzer_stem *pLookup;
+
+  if( fuzzerRender(pStem, &pCur->zBuf, &pCur->nBuf)==SQLITE_NOMEM ){
+    return -1;
+  }
+  h = fuzzerHash(pCur->zBuf);
+  pLookup = pCur->apHash[h];
+    while( pLookup && strcmp(pLookup->zBasis, pCur->zBuf)!=0 ){
+    pLookup = pLookup->pHash;
+  }
+  return pLookup!=0;
+}
+
+/*
+** Advance a fuzzer_stem to its next value.   Return 0 if there are
+** no more values that can be generated by this fuzzer_stem.  Return
+** -1 on a memory allocation failure.
+*/
+static int fuzzerAdvance(fuzzer_cursor *pCur, fuzzer_stem *pStem){
+  const fuzzer_rule *pRule;
+  while( (pRule = pStem->pRule)!=0 ){
+    while( pStem->n < pStem->nBasis - pRule->nFrom ){
+      pStem->n++;
+      if( pRule->nFrom==0
+       || memcmp(&pStem->zBasis[pStem->n], pRule->zFrom, pRule->nFrom)==0
+      ){
+        /* Found a rewrite case.  Make sure it is not a duplicate */
+        int rc = fuzzerSeen(pCur, pStem);
+        if( rc<0 ) return -1;
+        if( rc==0 ){
+          fuzzerCost(pStem);
+          return 1;
+        }
+      }
+    }
+    pStem->n = -1;
+    pStem->pRule = pRule->pNext;
+    if( pStem->pRule && fuzzerCost(pStem)>pCur->rLimit ) pStem->pRule = 0;
+  }
+  return 0;
+}
+
+/*
+** The two input stem lists are both sorted in order of increasing
+** rCostX.  Merge them together into a single list, sorted by rCostX, and
+** return a pointer to the head of that new list.
+*/
+static fuzzer_stem *fuzzerMergeStems(fuzzer_stem *pA, fuzzer_stem *pB){
+  fuzzer_stem head;
+  fuzzer_stem *pTail;
+
+  pTail =  &head;
+  while( pA && pB ){
+    if( pA->rCostX<=pB->rCostX ){
+      pTail->pNext = pA;
+      pTail = pA;
+      pA = pA->pNext;
+    }else{
+      pTail->pNext = pB;
+      pTail = pB;
+      pB = pB->pNext;
+    }
+  }
+  if( pA==0 ){
+    pTail->pNext = pB;
+  }else{
+    pTail->pNext = pA;
+  }
+  return head.pNext;
+}
+
+/*
+** Load pCur->pStem with the lowest-cost stem.  Return a pointer
+** to the lowest-cost stem.
+*/
+static fuzzer_stem *fuzzerLowestCostStem(fuzzer_cursor *pCur){
+  fuzzer_stem *pBest, *pX;
+  int iBest;
+  int i;
+
+  if( pCur->pStem==0 ){
+    iBest = -1;
+    pBest = 0;
+    for(i=0; i<=pCur->mxQueue; i++){
+      pX = pCur->aQueue[i];
+      if( pX==0 ) continue;
+      if( pBest==0 || pBest->rCostX>pX->rCostX ){
+        pBest = pX;
+        iBest = i;
+      }
+    } 
+    if( pBest ){
+      pCur->aQueue[iBest] = pBest->pNext;
+      pBest->pNext = 0;
+      pCur->pStem = pBest;
+    }
+  }
+  return pCur->pStem;
+}
+
+/*
+** Insert pNew into queue of pending stems.  Then find the stem
+** with the lowest rCostX and move it into pCur->pStem.
+** list.  The insert is done such the pNew is in the correct order
+** according to fuzzer_stem.zBaseCost+fuzzer_stem.pRule->rCost.
+*/
+static fuzzer_stem *fuzzerInsert(fuzzer_cursor *pCur, fuzzer_stem *pNew){
+  fuzzer_stem *pX;
+  int i;
+
+  /* If pCur->pStem exists and is greater than pNew, then make pNew
+  ** the new pCur->pStem and insert the old pCur->pStem instead.
+  */
+  if( (pX = pCur->pStem)!=0 && pX->rCostX>pNew->rCostX ){
+    pNew->pNext = 0;
+    pCur->pStem = pNew;
+    pNew = pX;
+  }
+
+  /* Insert the new value */
+  pNew->pNext = 0;
+  pX = pNew;
+  for(i=0; i<=pCur->mxQueue; i++){
+    if( pCur->aQueue[i] ){
+      pX = fuzzerMergeStems(pX, pCur->aQueue[i]);
+      pCur->aQueue[i] = 0;
+    }else{
+      pCur->aQueue[i] = pX;
+      break;
+    }
+  }
+  if( i>pCur->mxQueue ){
+    if( i<FUZZER_NQUEUE ){
+      pCur->mxQueue = i;
+      pCur->aQueue[i] = pX;
+    }else{
+      assert( pCur->mxQueue==FUZZER_NQUEUE-1 );
+      pX = fuzzerMergeStems(pX, pCur->aQueue[FUZZER_NQUEUE-1]);
+      pCur->aQueue[FUZZER_NQUEUE-1] = pX;
+    }
+  }
+
+  return fuzzerLowestCostStem(pCur);
+}
+
+/*
+** Allocate a new fuzzer_stem.  Add it to the hash table but do not
+** link it into either the pCur->pStem or pCur->pDone lists.
+*/
+static fuzzer_stem *fuzzerNewStem(
+  fuzzer_cursor *pCur,
+  const char *zWord,
+  fuzzer_cost rBaseCost
+){
+  fuzzer_stem *pNew;
+  unsigned int h;
+
+  pNew = sqlite3_malloc( sizeof(*pNew) + strlen(zWord) + 1 );
+  if( pNew==0 ) return 0;
+  memset(pNew, 0, sizeof(*pNew));
+  pNew->zBasis = (char*)&pNew[1];
+  pNew->nBasis = strlen(zWord);
+  memcpy(pNew->zBasis, zWord, pNew->nBasis+1);
+  pNew->pRule = pCur->pVtab->pRule;
+  pNew->n = -1;
+  pNew->rBaseCost = pNew->rCostX = rBaseCost;
+  h = fuzzerHash(pNew->zBasis);
+  pNew->pHash = pCur->apHash[h];
+  pCur->apHash[h] = pNew;
+  pCur->nStem++;
+  return pNew;
+}
+
+
+/*
+** Advance a cursor to its next row of output
+*/
+static int fuzzerNext(sqlite3_vtab_cursor *cur){
+  fuzzer_cursor *pCur = (fuzzer_cursor*)cur;
+  int rc;
+  fuzzer_stem *pStem, *pNew;
+
+  pCur->iRowid++;
+
+  /* Use the element the cursor is currently point to to create
+  ** a new stem and insert the new stem into the priority queue.
+  */
+  pStem = pCur->pStem;
+  if( pStem->rCostX>0 ){
+    rc = fuzzerRender(pStem, &pCur->zBuf, &pCur->nBuf);
+    if( rc==SQLITE_NOMEM ) return SQLITE_NOMEM;
+    pNew = fuzzerNewStem(pCur, pCur->zBuf, pStem->rCostX);
+    if( pNew ){
+      if( fuzzerAdvance(pCur, pNew)==0 ){
+        pNew->pNext = pCur->pDone;
+        pCur->pDone = pNew;
+      }else{
+        if( fuzzerInsert(pCur, pNew)==pNew ){
+          return SQLITE_OK;
+        }
+      }
+    }else{
+      return SQLITE_NOMEM;
+    }
+  }
+
+  /* Adjust the priority queue so that the first element of the
+  ** stem list is the next lowest cost word.
+  */
+  while( (pStem = pCur->pStem)!=0 ){
+    if( fuzzerAdvance(pCur, pStem) ){
+      pCur->pStem = 0;
+      pStem = fuzzerInsert(pCur, pStem);
+      if( (rc = fuzzerSeen(pCur, pStem))!=0 ){
+        if( rc<0 ) return SQLITE_NOMEM;
+        continue;
+      }
+      return SQLITE_OK;  /* New word found */
+    }
+    pCur->pStem = 0;
+    pStem->pNext = pCur->pDone;
+    pCur->pDone = pStem;
+    if( fuzzerLowestCostStem(pCur) ){
+      rc = fuzzerSeen(pCur, pCur->pStem);
+      if( rc<0 ) return SQLITE_NOMEM;
+      if( rc==0 ){
+        return SQLITE_OK;
+      }
+    }
+  }
+
+  /* Reach this point only if queue has been exhausted and there is
+  ** nothing left to be output. */
+  pCur->rLimit = (fuzzer_cost)0;
+  return SQLITE_OK;
+}
+
+/*
+** Called to "rewind" a cursor back to the beginning so that
+** it starts its output over again.  Always called at least once
+** prior to any fuzzerColumn, fuzzerRowid, or fuzzerEof call.
+*/
+static int fuzzerFilter(
+  sqlite3_vtab_cursor *pVtabCursor, 
+  int idxNum, const char *idxStr,
+  int argc, sqlite3_value **argv
+){
+  fuzzer_cursor *pCur = (fuzzer_cursor *)pVtabCursor;
+  const char *zWord = 0;
+  fuzzer_stem *pStem;
+
+  fuzzerClearCursor(pCur, 1);
+  pCur->rLimit = 2147483647;
+  if( idxNum==1 ){
+    zWord = (const char*)sqlite3_value_text(argv[0]);
+  }else if( idxNum==2 ){
+    pCur->rLimit = (fuzzer_cost)sqlite3_value_int(argv[0]);
+  }else if( idxNum==3 ){
+    zWord = (const char*)sqlite3_value_text(argv[0]);
+    pCur->rLimit = (fuzzer_cost)sqlite3_value_int(argv[1]);
+  }
+  if( zWord==0 ) zWord = "";
+  pCur->pStem = pStem = fuzzerNewStem(pCur, zWord, (fuzzer_cost)0);
+  if( pStem==0 ) return SQLITE_NOMEM;
+  pCur->nullRule.pNext = pCur->pVtab->pRule;
+  pCur->nullRule.rCost = 0;
+  pCur->nullRule.nFrom = 0;
+  pCur->nullRule.nTo = 0;
+  pCur->nullRule.zFrom = "";
+  pStem->pRule = &pCur->nullRule;
+  pStem->n = pStem->nBasis;
+  pCur->iRowid = 1;
+  return SQLITE_OK;
+}
+
+/*
+** Only the word and distance columns have values.  All other columns
+** return NULL
+*/
+static int fuzzerColumn(sqlite3_vtab_cursor *cur, sqlite3_context *ctx, int i){
+  fuzzer_cursor *pCur = (fuzzer_cursor*)cur;
+  if( i==0 ){
+    /* the "word" column */
+    if( fuzzerRender(pCur->pStem, &pCur->zBuf, &pCur->nBuf)==SQLITE_NOMEM ){
+      return SQLITE_NOMEM;
+    }
+    sqlite3_result_text(ctx, pCur->zBuf, -1, SQLITE_TRANSIENT);
+  }else if( i==1 ){
+    /* the "distance" column */
+    sqlite3_result_int(ctx, pCur->pStem->rCostX);
+  }else{
+    /* All other columns are NULL */
+    sqlite3_result_null(ctx);
+  }
+  return SQLITE_OK;
+}
+
+/*
+** The rowid.
+*/
+static int fuzzerRowid(sqlite3_vtab_cursor *cur, sqlite_int64 *pRowid){
+  fuzzer_cursor *pCur = (fuzzer_cursor*)cur;
+  *pRowid = pCur->iRowid;
+  return SQLITE_OK;
+}
+
+/*
+** When the fuzzer_cursor.rLimit value is 0 or less, that is a signal
+** that the cursor has nothing more to output.
+*/
+static int fuzzerEof(sqlite3_vtab_cursor *cur){
+  fuzzer_cursor *pCur = (fuzzer_cursor*)cur;
+  return pCur->rLimit<=(fuzzer_cost)0;
+}
+
+/*
+** Search for terms of these forms:
+**
+**       word MATCH $str
+**       distance < $value
+**       distance <= $value
+**
+** The distance< and distance<= are both treated as distance<=.
+** The query plan number is as follows:
+**
+**   0:    None of the terms above are found
+**   1:    There is a "word MATCH" term with $str in filter.argv[0].
+**   2:    There is a "distance<" term with $value in filter.argv[0].
+**   3:    Both "word MATCH" and "distance<" with $str in argv[0] and
+**         $value in argv[1].
+*/
+static int fuzzerBestIndex(sqlite3_vtab *tab, sqlite3_index_info *pIdxInfo){
+  int iPlan = 0;
+  int iDistTerm = -1;
+  int i;
+  const struct sqlite3_index_constraint *pConstraint;
+  pConstraint = pIdxInfo->aConstraint;
+  for(i=0; i<pIdxInfo->nConstraint; i++, pConstraint++){
+    if( pConstraint->usable==0 ) continue;
+    if( (iPlan & 1)==0 
+     && pConstraint->iColumn==0
+     && pConstraint->op==SQLITE_INDEX_CONSTRAINT_MATCH
+    ){
+      iPlan |= 1;
+      pIdxInfo->aConstraintUsage[i].argvIndex = 1;
+      pIdxInfo->aConstraintUsage[i].omit = 1;
+    }
+    if( (iPlan & 2)==0
+     && pConstraint->iColumn==1
+     && (pConstraint->op==SQLITE_INDEX_CONSTRAINT_LT
+           || pConstraint->op==SQLITE_INDEX_CONSTRAINT_LE)
+    ){
+      iPlan |= 2;
+      iDistTerm = i;
+    }
+  }
+  if( iPlan==2 ){
+    pIdxInfo->aConstraintUsage[iDistTerm].argvIndex = 1;
+  }else if( iPlan==3 ){
+    pIdxInfo->aConstraintUsage[iDistTerm].argvIndex = 2;
+  }
+  pIdxInfo->idxNum = iPlan;
+  if( pIdxInfo->nOrderBy==1
+   && pIdxInfo->aOrderBy[0].iColumn==1
+   && pIdxInfo->aOrderBy[0].desc==0
+  ){
+    pIdxInfo->orderByConsumed = 1;
+  }
+  pIdxInfo->estimatedCost = (double)10000;
+   
+  return SQLITE_OK;
+}
+
+/*
+** Disallow all attempts to DELETE or UPDATE.  Only INSERTs are allowed.
+**
+** On an insert, the cFrom, cTo, and cost columns are used to construct
+** a new rule.   All other columns are ignored.  The rule is ignored
+** if cFrom and cTo are identical.  A NULL value for cFrom or cTo is
+** interpreted as an empty string.  The cost must be positive.
+*/
+static int fuzzerUpdate(
+  sqlite3_vtab *pVTab,
+  int argc,
+  sqlite3_value **argv,
+  sqlite_int64 *pRowid
+){
+  fuzzer_vtab *p = (fuzzer_vtab*)pVTab;
+  fuzzer_rule *pRule;
+  const char *zFrom;
+  int nFrom;
+  const char *zTo;
+  int nTo;
+  fuzzer_cost rCost;
+  if( argc!=7 ){
+    sqlite3_free(pVTab->zErrMsg);
+    pVTab->zErrMsg = sqlite3_mprintf("cannot delete from a %s virtual table",
+                                     p->zClassName);
+    return SQLITE_CONSTRAINT;
+  }
+  if( sqlite3_value_type(argv[0])!=SQLITE_NULL ){
+    sqlite3_free(pVTab->zErrMsg);
+    pVTab->zErrMsg = sqlite3_mprintf("cannot update a %s virtual table",
+                                     p->zClassName);
+    return SQLITE_CONSTRAINT;
+  }
+  zFrom = (char*)sqlite3_value_text(argv[4]);
+  if( zFrom==0 ) zFrom = "";
+  zTo = (char*)sqlite3_value_text(argv[5]);
+  if( zTo==0 ) zTo = "";
+  if( strcmp(zFrom,zTo)==0 ){
+    /* Silently ignore null transformations */
+    return SQLITE_OK;
+  }
+  rCost = sqlite3_value_int(argv[6]);
+  if( rCost<=0 ){
+    sqlite3_free(pVTab->zErrMsg);
+    pVTab->zErrMsg = sqlite3_mprintf("cost must be positive");
+    return SQLITE_CONSTRAINT;    
+  }
+  nFrom = strlen(zFrom);
+  nTo = strlen(zTo);
+  pRule = sqlite3_malloc( sizeof(*pRule) + nFrom + nTo );
+  if( pRule==0 ){
+    return SQLITE_NOMEM;
+  }
+  pRule->zFrom = &pRule->zTo[nTo+1];
+  pRule->nFrom = nFrom;
+  memcpy(pRule->zFrom, zFrom, nFrom+1);
+  memcpy(pRule->zTo, zTo, nTo+1);
+  pRule->nTo = nTo;
+  pRule->rCost = rCost;
+  pRule->pNext = p->pNewRule;
+  p->pNewRule = pRule;
+  return SQLITE_OK;
+}
+
+/*
+** A virtual table module that provides read-only access to a
+** Tcl global variable namespace.
+*/
+static sqlite3_module fuzzerModule = {
+  0,                           /* iVersion */
+  fuzzerConnect,
+  fuzzerConnect,
+  fuzzerBestIndex,
+  fuzzerDisconnect, 
+  fuzzerDisconnect,
+  fuzzerOpen,                  /* xOpen - open a cursor */
+  fuzzerClose,                 /* xClose - close a cursor */
+  fuzzerFilter,                /* xFilter - configure scan constraints */
+  fuzzerNext,                  /* xNext - advance a cursor */
+  fuzzerEof,                   /* xEof - check for end of scan */
+  fuzzerColumn,                /* xColumn - read data */
+  fuzzerRowid,                 /* xRowid - read data */
+  fuzzerUpdate,                /* xUpdate - INSERT */
+  0,                           /* xBegin */
+  0,                           /* xSync */
+  0,                           /* xCommit */
+  0,                           /* xRollback */
+  0,                           /* xFindMethod */
+  0,                           /* xRename */
+};
+
+#endif /* SQLITE_OMIT_VIRTUALTABLE */
+
+
+/*
+** Register the fuzzer virtual table
+*/
+int fuzzer_register(sqlite3 *db){
+  int rc = SQLITE_OK;
+#ifndef SQLITE_OMIT_VIRTUALTABLE
+  rc = sqlite3_create_module(db, "fuzzer", &fuzzerModule, 0);
+#endif
+  return rc;
+}
+
+#ifdef SQLITE_TEST
+#include <tcl.h>
+/*
+** Decode a pointer to an sqlite3 object.
+*/
+extern int getDbPointer(Tcl_Interp *interp, const char *zA, sqlite3 **ppDb);
+
+/*
+** Register the echo virtual table module.
+*/
+static int register_fuzzer_module(
+  ClientData clientData, /* Pointer to sqlite3_enable_XXX function */
+  Tcl_Interp *interp,    /* The TCL interpreter that invoked this command */
+  int objc,              /* Number of arguments */
+  Tcl_Obj *CONST objv[]  /* Command arguments */
+){
+  sqlite3 *db;
+  if( objc!=2 ){
+    Tcl_WrongNumArgs(interp, 1, objv, "DB");
+    return TCL_ERROR;
+  }
+  if( getDbPointer(interp, Tcl_GetString(objv[1]), &db) ) return TCL_ERROR;
+  fuzzer_register(db);
+  return TCL_OK;
+}
+
+
+/*
+** Register commands with the TCL interpreter.
+*/
+int Sqlitetestfuzzer_Init(Tcl_Interp *interp){
+  static struct {
+     char *zName;
+     Tcl_ObjCmdProc *xProc;
+     void *clientData;
+  } aObjCmd[] = {
+     { "register_fuzzer_module",   register_fuzzer_module, 0 },
+  };
+  int i;
+  for(i=0; i<sizeof(aObjCmd)/sizeof(aObjCmd[0]); i++){
+    Tcl_CreateObjCommand(interp, aObjCmd[i].zName, 
+        aObjCmd[i].xProc, aObjCmd[i].clientData, 0);
+  }
+  return TCL_OK;
+}
+
+#endif /* SQLITE_TEST */
diff --git a/src/test_multiplex.c b/src/test_multiplex.c
index 72a71621b..d8a7db86e 100644
--- a/src/test_multiplex.c
+++ b/src/test_multiplex.c
@@ -22,7 +22,22 @@
 #include "sqlite3.h"
 #include <string.h>
 #include <assert.h>
-#include "sqliteInt.h"
+#include "test_multiplex.h"
+
+#ifndef SQLITE_CORE
+  #define SQLITE_CORE 1  /* Disable the API redefinition in sqlite3ext.h */
+#endif
+#include "sqlite3ext.h"
+
+/* 
+** These should be defined to be the same as the values in 
+** sqliteInt.h.  They are defined seperately here so that
+** the multiplex VFS shim can be built as a loadable 
+** module.
+*/
+#define UNUSED_PARAMETER(x) (void)(x)
+#define MAX_PAGE_SIZE       0x10000
+#define DEFAULT_SECTOR_SIZE 0x1000
 
 /*
 ** For a build without mutexes, no-op the mutex calls.
@@ -40,14 +55,18 @@
 
 /************************ Shim Definitions ******************************/
 
+#define SQLITE_MULTIPLEX_VFS_NAME "multiplex"
+
 /* This is the limit on the chunk size.  It may be changed by calling
-** the sqlite3_multiplex_set() interface.
+** the xFileControl() interface.  It will be rounded up to a 
+** multiple of MAX_PAGE_SIZE.  We default it here to 1GB.
 */
-#define SQLITE_MULTIPLEX_CHUNK_SIZE 0x40000000
+#define SQLITE_MULTIPLEX_CHUNK_SIZE (MAX_PAGE_SIZE*16384)
+
 /* Default limit on number of chunks.  Care should be taken
 ** so that values for chunks numbers fit in the SQLITE_MULTIPLEX_EXT_FMT
 ** format specifier. It may be changed by calling
-** the sqlite3_multiplex_set() interface.
+** the xFileControl() interface.
 */
 #define SQLITE_MULTIPLEX_MAX_CHUNKS 32
 
@@ -82,6 +101,9 @@ struct multiplexGroup {
   char *zName;                     /* Base filename of this group */
   int nName;                       /* Length of base filename */
   int flags;                       /* Flags used for original opening */
+  int nChunkSize;                  /* Chunk size used for this group */
+  int nMaxChunks;                  /* Max number of chunks for this group */
+  int bEnabled;                    /* TRUE to use Multiplex VFS for this file */
   multiplexGroup *pNext, *pPrev;   /* Doubly linked list of all group objects */
 };
 
@@ -140,11 +162,6 @@ static struct {
   */
   multiplexGroup *pGroups;
 
-  /* Chunk params.
-  */
-  int nChunkSize;
-  int nMaxChunks;
-
   /* Storage for temp file names.  Allocated during 
   ** initialization to the max pathname of the underlying VFS.
   */
@@ -160,13 +177,28 @@ static struct {
 static void multiplexEnter(void){ sqlite3_mutex_enter(gMultiplex.pMutex); }
 static void multiplexLeave(void){ sqlite3_mutex_leave(gMultiplex.pMutex); }
 
+/*
+** Compute a string length that is limited to what can be stored in
+** lower 30 bits of a 32-bit signed integer.
+**
+** The value returned will never be negative.  Nor will it ever be greater
+** than the actual length of the string.  For very long strings (greater
+** than 1GiB) the value returned might be less than the true string length.
+*/
+int multiplexStrlen30(const char *z){
+  const char *z2 = z;
+  if( z==0 ) return 0;
+  while( *z2 ){ z2++; }
+  return 0x3fffffff & (int)(z2 - z);
+}
+
 /* Translate an sqlite3_file* that is really a multiplexGroup* into
 ** the sqlite3_file* for the underlying original VFS.
 */
 static sqlite3_file *multiplexSubOpen(multiplexConn *pConn, int iChunk, int *rc, int *pOutFlags){
   multiplexGroup *pGroup = pConn->pGroup;
   sqlite3_vfs *pOrigVfs = gMultiplex.pOrigVfs;        /* Real VFS */
-  if( iChunk<gMultiplex.nMaxChunks ){
+  if( iChunk<pGroup->nMaxChunks ){
     sqlite3_file *pSubOpen = pGroup->pReal[iChunk];    /* Real file descriptor */
     if( !pGroup->bOpen[iChunk] ){
       memcpy(gMultiplex.zName, pGroup->zName, pGroup->nName+1);
@@ -191,6 +223,62 @@ static sqlite3_file *multiplexSubOpen(multiplexConn *pConn, int iChunk, int *rc,
   return NULL;
 }
 
+/*
+** This is the implementation of the multiplex_control() SQL function.
+*/
+static void multiplexControlFunc(
+  sqlite3_context *context,
+  int argc,
+  sqlite3_value **argv
+){
+  int rc = SQLITE_OK;
+  sqlite3 *db = sqlite3_context_db_handle(context);
+  int op;
+  int iVal;
+
+  if( !db || argc!=2 ){ 
+    rc = SQLITE_ERROR; 
+  }else{
+    /* extract params */
+    op = sqlite3_value_int(argv[0]);
+    iVal = sqlite3_value_int(argv[1]);
+    /* map function op to file_control op */
+    switch( op ){
+      case 1: 
+        op = MULTIPLEX_CTRL_ENABLE; 
+        break;
+      case 2: 
+        op = MULTIPLEX_CTRL_SET_CHUNK_SIZE; 
+        break;
+      case 3: 
+        op = MULTIPLEX_CTRL_SET_MAX_CHUNKS; 
+        break;
+      default:
+        rc = SQLITE_NOTFOUND;
+        break;
+    }
+  }
+  if( rc==SQLITE_OK ){
+    rc = sqlite3_file_control(db, 0, op, &iVal);
+  }
+  sqlite3_result_error_code(context, rc);
+}
+
+/*
+** This is the entry point to register the auto-extension for the 
+** multiplex_control() function.
+*/
+static int multiplexFuncInit(
+  sqlite3 *db, 
+  char **pzErrMsg, 
+  const sqlite3_api_routines *pApi
+){
+  int rc;
+  rc = sqlite3_create_function(db, "multiplex_control", 2, SQLITE_ANY, 
+      0, multiplexControlFunc, 0, 0);
+  return rc;
+}
+
 /************************* VFS Method Wrappers *****************************/
 
 /*
@@ -212,7 +300,7 @@ static int multiplexOpen(
   multiplexGroup *pGroup;                        /* Corresponding multiplexGroup object */
   sqlite3_file *pSubOpen;                        /* Real file descriptor */
   sqlite3_vfs *pOrigVfs = gMultiplex.pOrigVfs;   /* Real VFS */
-  int nName = sqlite3Strlen30(zName);
+  int nName = multiplexStrlen30(zName);
   int i;
   int sz;
 
@@ -224,11 +312,11 @@ static int multiplexOpen(
   multiplexEnter();
   pMultiplexOpen = (multiplexConn*)pConn;
   /* allocate space for group */
-  sz = sizeof(multiplexGroup)                         /* multiplexGroup */
-     + (sizeof(sqlite3_file *)*gMultiplex.nMaxChunks) /* pReal[] */
-     + (pOrigVfs->szOsFile*gMultiplex.nMaxChunks)     /* *pReal */
-     + gMultiplex.nMaxChunks                          /* bOpen[] */
-     + nName + 1;                                     /* zName */
+  sz = sizeof(multiplexGroup)                                /* multiplexGroup */
+     + (sizeof(sqlite3_file *)*SQLITE_MULTIPLEX_MAX_CHUNKS)  /* pReal[] */
+     + (pOrigVfs->szOsFile*SQLITE_MULTIPLEX_MAX_CHUNKS)      /* *pReal */
+     + SQLITE_MULTIPLEX_MAX_CHUNKS                           /* bOpen[] */
+     + nName + 1;                                            /* zName */
 #ifndef SQLITE_MULTIPLEX_EXT_OVWR
   sz += SQLITE_MULTIPLEX_EXT_SZ;
   assert(nName+SQLITE_MULTIPLEX_EXT_SZ < pOrigVfs->mxPathname);
@@ -244,14 +332,18 @@ static int multiplexOpen(
     char *p = (char *)&pGroup[1];
     pMultiplexOpen->pGroup = pGroup;
     memset(pGroup, 0, sz);
+    pGroup->bEnabled = -1;
+    pGroup->nChunkSize = SQLITE_MULTIPLEX_CHUNK_SIZE;
+    pGroup->nMaxChunks = SQLITE_MULTIPLEX_MAX_CHUNKS;
     pGroup->pReal = (sqlite3_file **)p;
-    p += (sizeof(sqlite3_file *)*gMultiplex.nMaxChunks);
-    for(i=0; i<gMultiplex.nMaxChunks; i++){
+    p += (sizeof(sqlite3_file *)*pGroup->nMaxChunks);
+    for(i=0; i<pGroup->nMaxChunks; i++){
       pGroup->pReal[i] = (sqlite3_file *)p;
       p += pOrigVfs->szOsFile;
     }
+    /* bOpen[] vals should all be zero from memset above */
     pGroup->bOpen = p;
-    p += gMultiplex.nMaxChunks;
+    p += pGroup->nMaxChunks;
     pGroup->zName = p;
     /* save off base filename, name length, and original open flags  */
     memcpy(pGroup->zName, zName, nName+1);
@@ -259,6 +351,14 @@ static int multiplexOpen(
     pGroup->flags = flags;
     pSubOpen = multiplexSubOpen(pMultiplexOpen, 0, &rc, pOutFlags);
     if( pSubOpen ){
+      /* if this file is already larger than chunk size, disable 
+      ** the multiplex feature.
+      */
+      sqlite3_int64 sz;
+      int rc2 = pSubOpen->pMethods->xFileSize(pSubOpen, &sz);
+      if( (rc2==SQLITE_OK) && (sz>pGroup->nChunkSize) ){
+        pGroup->bEnabled = 0;
+      }
       if( pSubOpen->pMethods->iVersion==1 ){
         pMultiplexOpen->base.pMethods = &gMultiplex.sIoMethodsV1;
       }else{
@@ -288,24 +388,29 @@ static int multiplexDelete(
 ){
   sqlite3_vfs *pOrigVfs = gMultiplex.pOrigVfs;   /* Real VFS */
   int rc = SQLITE_OK;
-  int nName = sqlite3Strlen30(zName);
+  int nName = multiplexStrlen30(zName);
   int i;
 
   UNUSED_PARAMETER(pVfs);
 
   multiplexEnter();
   memcpy(gMultiplex.zName, zName, nName+1);
-  for(i=0; i<gMultiplex.nMaxChunks; i++){
+  for(i=0; i<SQLITE_MULTIPLEX_MAX_CHUNKS; i++){
     int rc2;
     int exists = 0;
     if( i ){
 #ifdef SQLITE_MULTIPLEX_EXT_OVWR
-        sqlite3_snprintf(SQLITE_MULTIPLEX_EXT_SZ+1, gMultiplex.zName+nName-SQLITE_MULTIPLEX_EXT_SZ, SQLITE_MULTIPLEX_EXT_FMT, i);
+        sqlite3_snprintf(SQLITE_MULTIPLEX_EXT_SZ+1, 
+            gMultiplex.zName+nName-SQLITE_MULTIPLEX_EXT_SZ, 
+            SQLITE_MULTIPLEX_EXT_FMT, i);
 #else
-        sqlite3_snprintf(SQLITE_MULTIPLEX_EXT_SZ+1, gMultiplex.zName+nName, SQLITE_MULTIPLEX_EXT_FMT, i);
+        sqlite3_snprintf(SQLITE_MULTIPLEX_EXT_SZ+1, 
+            gMultiplex.zName+nName, 
+            SQLITE_MULTIPLEX_EXT_FMT, i);
 #endif
     }
-    rc2 = pOrigVfs->xAccess(pOrigVfs, gMultiplex.zName, SQLITE_ACCESS_EXISTS, &exists);
+    rc2 = pOrigVfs->xAccess(pOrigVfs, gMultiplex.zName, 
+        SQLITE_ACCESS_EXISTS, &exists);
     if( rc2==SQLITE_OK && exists){
       /* if it exists, delete it */
       rc2 = pOrigVfs->xDelete(pOrigVfs, gMultiplex.zName, syncDir);
@@ -367,7 +472,7 @@ static int multiplexClose(sqlite3_file *pConn){
   int i;
   multiplexEnter();
   /* close any open handles */
-  for(i=0; i<gMultiplex.nMaxChunks; i++){
+  for(i=0; i<pGroup->nMaxChunks; i++){
     if( pGroup->bOpen[i] ){
       sqlite3_file *pSubOpen = pGroup->pReal[i];
       int rc2 = pSubOpen->pMethods->xClose(pSubOpen);
@@ -398,23 +503,29 @@ static int multiplexRead(
   sqlite3_int64 iOfst
 ){
   multiplexConn *p = (multiplexConn*)pConn;
+  multiplexGroup *pGroup = p->pGroup;
   int rc = SQLITE_OK;
   multiplexEnter();
-  while( iAmt > 0 ){
-    int i = (int)(iOfst/gMultiplex.nChunkSize);
-    sqlite3_file *pSubOpen = multiplexSubOpen(p, i, &rc, NULL);
-    if( pSubOpen ){
-      int extra = ((int)(iOfst % gMultiplex.nChunkSize) + iAmt) - gMultiplex.nChunkSize;
-      if( extra<0 ) extra = 0;
-      iAmt -= extra;
-      rc = pSubOpen->pMethods->xRead(pSubOpen, pBuf, iAmt, iOfst%gMultiplex.nChunkSize);
-      if( rc!=SQLITE_OK ) break;
-      pBuf = (char *)pBuf + iAmt;
-      iOfst += iAmt;
-      iAmt = extra;
-    }else{
-      rc = SQLITE_IOERR_READ;
-      break;
+  if( !pGroup->bEnabled ){
+    sqlite3_file *pSubOpen = multiplexSubOpen(p, 0, &rc, NULL);
+    rc = ( !pSubOpen ) ? SQLITE_IOERR_READ : pSubOpen->pMethods->xRead(pSubOpen, pBuf, iAmt, iOfst);
+  }else{
+    while( iAmt > 0 ){
+      int i = (int)(iOfst / pGroup->nChunkSize);
+      sqlite3_file *pSubOpen = multiplexSubOpen(p, i, &rc, NULL);
+      if( pSubOpen ){
+        int extra = ((int)(iOfst % pGroup->nChunkSize) + iAmt) - pGroup->nChunkSize;
+        if( extra<0 ) extra = 0;
+        iAmt -= extra;
+        rc = pSubOpen->pMethods->xRead(pSubOpen, pBuf, iAmt, iOfst % pGroup->nChunkSize);
+        if( rc!=SQLITE_OK ) break;
+        pBuf = (char *)pBuf + iAmt;
+        iOfst += iAmt;
+        iAmt = extra;
+      }else{
+        rc = SQLITE_IOERR_READ;
+        break;
+      }
     }
   }
   multiplexLeave();
@@ -432,23 +543,29 @@ static int multiplexWrite(
   sqlite3_int64 iOfst
 ){
   multiplexConn *p = (multiplexConn*)pConn;
+  multiplexGroup *pGroup = p->pGroup;
   int rc = SQLITE_OK;
   multiplexEnter();
-  while( iAmt > 0 ){
-    int i = (int)(iOfst/gMultiplex.nChunkSize);
-    sqlite3_file *pSubOpen = multiplexSubOpen(p, i, &rc, NULL);
-    if( pSubOpen ){
-      int extra = ((int)(iOfst % gMultiplex.nChunkSize) + iAmt) - gMultiplex.nChunkSize;
-      if( extra<0 ) extra = 0;
-      iAmt -= extra;
-      rc = pSubOpen->pMethods->xWrite(pSubOpen, pBuf, iAmt, iOfst%gMultiplex.nChunkSize);
-      if( rc!=SQLITE_OK ) break;
-      pBuf = (char *)pBuf + iAmt;
-      iOfst += iAmt;
-      iAmt = extra;
-    }else{
-      rc = SQLITE_IOERR_WRITE;
-      break;
+  if( !pGroup->bEnabled ){
+    sqlite3_file *pSubOpen = multiplexSubOpen(p, 0, &rc, NULL);
+    rc = ( !pSubOpen ) ? SQLITE_IOERR_WRITE : pSubOpen->pMethods->xWrite(pSubOpen, pBuf, iAmt, iOfst);
+  }else{
+    while( iAmt > 0 ){
+      int i = (int)(iOfst / pGroup->nChunkSize);
+      sqlite3_file *pSubOpen = multiplexSubOpen(p, i, &rc, NULL);
+      if( pSubOpen ){
+        int extra = ((int)(iOfst % pGroup->nChunkSize) + iAmt) - pGroup->nChunkSize;
+        if( extra<0 ) extra = 0;
+        iAmt -= extra;
+        rc = pSubOpen->pMethods->xWrite(pSubOpen, pBuf, iAmt, iOfst % pGroup->nChunkSize);
+        if( rc!=SQLITE_OK ) break;
+        pBuf = (char *)pBuf + iAmt;
+        iOfst += iAmt;
+        iAmt = extra;
+      }else{
+        rc = SQLITE_IOERR_WRITE;
+        break;
+      }
     }
   }
   multiplexLeave();
@@ -463,35 +580,44 @@ static int multiplexTruncate(sqlite3_file *pConn, sqlite3_int64 size){
   multiplexConn *p = (multiplexConn*)pConn;
   multiplexGroup *pGroup = p->pGroup;
   int rc = SQLITE_OK;
-  int rc2;
-  int i;
-  sqlite3_file *pSubOpen;
-  sqlite3_vfs *pOrigVfs = gMultiplex.pOrigVfs;   /* Real VFS */
   multiplexEnter();
-  memcpy(gMultiplex.zName, pGroup->zName, pGroup->nName+1);
-  /* delete the chunks above the truncate limit */
-  for(i=(int)(size/gMultiplex.nChunkSize)+1; i<gMultiplex.nMaxChunks; i++){
-    /* close any open chunks before deleting them */
-    if( pGroup->bOpen[i] ){
-      pSubOpen = pGroup->pReal[i];
-      rc2 = pSubOpen->pMethods->xClose(pSubOpen);
-      if( rc2!=SQLITE_OK ) rc = SQLITE_IOERR_TRUNCATE;
-      pGroup->bOpen[i] = 0;
-    }
+  if( !pGroup->bEnabled ){
+    sqlite3_file *pSubOpen = multiplexSubOpen(p, 0, &rc, NULL);
+    rc = ( !pSubOpen ) ? SQLITE_IOERR_TRUNCATE : pSubOpen->pMethods->xTruncate(pSubOpen, size);
+  }else{
+    int rc2;
+    int i;
+    sqlite3_file *pSubOpen;
+    sqlite3_vfs *pOrigVfs = gMultiplex.pOrigVfs;   /* Real VFS */
+    memcpy(gMultiplex.zName, pGroup->zName, pGroup->nName+1);
+    /* delete the chunks above the truncate limit */
+    for(i=(int)(size / pGroup->nChunkSize)+1; i<pGroup->nMaxChunks; i++){
+      /* close any open chunks before deleting them */
+      if( pGroup->bOpen[i] ){
+        pSubOpen = pGroup->pReal[i];
+        rc2 = pSubOpen->pMethods->xClose(pSubOpen);
+        if( rc2!=SQLITE_OK ) rc = SQLITE_IOERR_TRUNCATE;
+        pGroup->bOpen[i] = 0;
+      }
 #ifdef SQLITE_MULTIPLEX_EXT_OVWR
-    sqlite3_snprintf(SQLITE_MULTIPLEX_EXT_SZ+1, gMultiplex.zName+pGroup->nName-SQLITE_MULTIPLEX_EXT_SZ, SQLITE_MULTIPLEX_EXT_FMT, i);
+      sqlite3_snprintf(SQLITE_MULTIPLEX_EXT_SZ+1, 
+          gMultiplex.zName+pGroup->nName-SQLITE_MULTIPLEX_EXT_SZ, 
+          SQLITE_MULTIPLEX_EXT_FMT, i);
 #else
-    sqlite3_snprintf(SQLITE_MULTIPLEX_EXT_SZ+1, gMultiplex.zName+pGroup->nName, SQLITE_MULTIPLEX_EXT_FMT, i);
+      sqlite3_snprintf(SQLITE_MULTIPLEX_EXT_SZ+1, 
+          gMultiplex.zName+pGroup->nName, 
+          SQLITE_MULTIPLEX_EXT_FMT, i);
 #endif
-    rc2 = pOrigVfs->xDelete(pOrigVfs, gMultiplex.zName, 0);
-    if( rc2!=SQLITE_OK ) rc = SQLITE_IOERR_TRUNCATE;
-  }
-  pSubOpen = multiplexSubOpen(p, (int)(size/gMultiplex.nChunkSize), &rc2, NULL);
-  if( pSubOpen ){
-    rc2 = pSubOpen->pMethods->xTruncate(pSubOpen, size%gMultiplex.nChunkSize);
-    if( rc2!=SQLITE_OK ) rc = rc2;
-  }else{
-    rc = SQLITE_IOERR_TRUNCATE;
+      rc2 = pOrigVfs->xDelete(pOrigVfs, gMultiplex.zName, 0);
+      if( rc2!=SQLITE_OK ) rc = SQLITE_IOERR_TRUNCATE;
+    }
+    pSubOpen = multiplexSubOpen(p, (int)(size / pGroup->nChunkSize), &rc2, NULL);
+    if( pSubOpen ){
+      rc2 = pSubOpen->pMethods->xTruncate(pSubOpen, size % pGroup->nChunkSize);
+      if( rc2!=SQLITE_OK ) rc = rc2;
+    }else{
+      rc = SQLITE_IOERR_TRUNCATE;
+    }
   }
   multiplexLeave();
   return rc;
@@ -505,7 +631,7 @@ static int multiplexSync(sqlite3_file *pConn, int flags){
   int rc = SQLITE_OK;
   int i;
   multiplexEnter();
-  for(i=0; i<gMultiplex.nMaxChunks; i++){
+  for(i=0; i<pGroup->nMaxChunks; i++){
     /* if we don't have it open, we don't need to sync it */
     if( pGroup->bOpen[i] ){
       sqlite3_file *pSubOpen = pGroup->pReal[i];
@@ -527,46 +653,56 @@ static int multiplexFileSize(sqlite3_file *pConn, sqlite3_int64 *pSize){
   int rc2;
   int i;
   multiplexEnter();
-  *pSize = 0;
-  for(i=0; i<gMultiplex.nMaxChunks; i++){
-    sqlite3_file *pSubOpen = NULL;
-    /* if not opened already, check to see if the chunk exists */
-    if( pGroup->bOpen[i] ){
-      pSubOpen = pGroup->pReal[i];
-    }else{
-      sqlite3_vfs *pOrigVfs = gMultiplex.pOrigVfs;   /* Real VFS */
-      int exists = 0;
-      memcpy(gMultiplex.zName, pGroup->zName, pGroup->nName+1);
-      if( i ){
+  if( !pGroup->bEnabled ){
+    sqlite3_file *pSubOpen = multiplexSubOpen(p, 0, &rc, NULL);
+    rc = ( !pSubOpen ) ? SQLITE_IOERR_FSTAT : pSubOpen->pMethods->xFileSize(pSubOpen, pSize);
+  }else{
+    *pSize = 0;
+    for(i=0; i<pGroup->nMaxChunks; i++){
+      sqlite3_file *pSubOpen = NULL;
+      /* if not opened already, check to see if the chunk exists */
+      if( pGroup->bOpen[i] ){
+        pSubOpen = pGroup->pReal[i];
+      }else{
+        sqlite3_vfs *pOrigVfs = gMultiplex.pOrigVfs;   /* Real VFS */
+        int exists = 0;
+        memcpy(gMultiplex.zName, pGroup->zName, pGroup->nName+1);
+        if( i ){
 #ifdef SQLITE_MULTIPLEX_EXT_OVWR
-        sqlite3_snprintf(SQLITE_MULTIPLEX_EXT_SZ+1, gMultiplex.zName+pGroup->nName-SQLITE_MULTIPLEX_EXT_SZ, SQLITE_MULTIPLEX_EXT_FMT, i);
+          sqlite3_snprintf(SQLITE_MULTIPLEX_EXT_SZ+1, 
+              gMultiplex.zName+pGroup->nName-SQLITE_MULTIPLEX_EXT_SZ, 
+              SQLITE_MULTIPLEX_EXT_FMT, i);
 #else
-        sqlite3_snprintf(SQLITE_MULTIPLEX_EXT_SZ+1, gMultiplex.zName+pGroup->nName, SQLITE_MULTIPLEX_EXT_FMT, i);
+          sqlite3_snprintf(SQLITE_MULTIPLEX_EXT_SZ+1, 
+              gMultiplex.zName+pGroup->nName, 
+              SQLITE_MULTIPLEX_EXT_FMT, i);
 #endif
+        }
+        rc2 = pOrigVfs->xAccess(pOrigVfs, gMultiplex.zName, 
+            SQLITE_ACCESS_EXISTS, &exists);
+        if( rc2==SQLITE_OK && exists){
+          /* if it exists, open it */
+          pSubOpen = multiplexSubOpen(p, i, &rc, NULL);
+        }else{
+          /* stop at first "gap" */
+          break;
+        }
       }
-      rc2 = pOrigVfs->xAccess(pOrigVfs, gMultiplex.zName, SQLITE_ACCESS_EXISTS, &exists);
-      if( rc2==SQLITE_OK && exists){
-        /* if it exists, open it */
-        pSubOpen = multiplexSubOpen(p, i, &rc, NULL);
+      if( pSubOpen ){
+        sqlite3_int64 sz;
+        rc2 = pSubOpen->pMethods->xFileSize(pSubOpen, &sz);
+        if( rc2!=SQLITE_OK ){
+          rc = rc2;
+        }else{
+          if( sz>pGroup->nChunkSize ){
+            rc = SQLITE_IOERR_FSTAT;
+          }
+          *pSize += sz;
+        }
       }else{
-        /* stop at first "gap" */
         break;
       }
     }
-    if( pSubOpen ){
-      sqlite3_int64 sz;
-      rc2 = pSubOpen->pMethods->xFileSize(pSubOpen, &sz);
-      if( rc2!=SQLITE_OK ){
-        rc = rc2;
-      }else{
-        if( sz>gMultiplex.nChunkSize ){
-          rc = SQLITE_IOERR_FSTAT;
-        }
-        *pSize += sz;
-      }
-    }else{
-      break;
-    }
   }
   multiplexLeave();
   return rc;
@@ -608,18 +744,62 @@ static int multiplexCheckReservedLock(sqlite3_file *pConn, int *pResOut){
   return SQLITE_IOERR_CHECKRESERVEDLOCK;
 }
 
-/* Pass xFileControl requests through to the original VFS unchanged.
+/* Pass xFileControl requests through to the original VFS unchanged,
+** except for any MULTIPLEX_CTRL_* requests here.
 */
 static int multiplexFileControl(sqlite3_file *pConn, int op, void *pArg){
   multiplexConn *p = (multiplexConn*)pConn;
-  int rc;
+  multiplexGroup *pGroup = p->pGroup;
+  int rc = SQLITE_ERROR;
   sqlite3_file *pSubOpen;
-  if ( op==SQLITE_FCNTL_SIZE_HINT || op==SQLITE_FCNTL_CHUNK_SIZE ) return SQLITE_OK;
-  pSubOpen = multiplexSubOpen(p, 0, &rc, NULL);
-  if( pSubOpen ){
-    return pSubOpen->pMethods->xFileControl(pSubOpen, op, pArg);
+
+  if( !gMultiplex.isInitialized ) return SQLITE_MISUSE;
+  switch( op ){
+    case MULTIPLEX_CTRL_ENABLE:
+      if( pArg ) {
+        int bEnabled = *(int *)pArg;
+        pGroup->bEnabled = bEnabled;
+        rc = SQLITE_OK;
+      }
+      break;
+    case MULTIPLEX_CTRL_SET_CHUNK_SIZE:
+      if( pArg ) {
+        int nChunkSize = *(int *)pArg;
+        if( nChunkSize<1 ){
+          rc = SQLITE_MISUSE;
+        }else{
+          /* Round up to nearest multiple of MAX_PAGE_SIZE. */
+          nChunkSize = (nChunkSize + (MAX_PAGE_SIZE-1));
+          nChunkSize &= ~(MAX_PAGE_SIZE-1);
+          pGroup->nChunkSize = nChunkSize;
+          rc = SQLITE_OK;
+        }
+      }
+      break;
+    case MULTIPLEX_CTRL_SET_MAX_CHUNKS:
+      if( pArg ) {
+        int nMaxChunks = *(int *)pArg;
+        if(( nMaxChunks<1 ) || ( nMaxChunks>SQLITE_MULTIPLEX_MAX_CHUNKS )){
+          rc = SQLITE_MISUSE;
+        }else{
+          pGroup->nMaxChunks = nMaxChunks;
+          rc = SQLITE_OK;
+        }
+      }
+      break;
+    case SQLITE_FCNTL_SIZE_HINT:
+    case SQLITE_FCNTL_CHUNK_SIZE:
+      /* no-op these */
+      rc = SQLITE_OK;
+      break;
+    default:
+      pSubOpen = multiplexSubOpen(p, 0, &rc, NULL);
+      if( pSubOpen ){
+        rc = pSubOpen->pMethods->xFileControl(pSubOpen, op, pArg);
+      }
+      break;
   }
-  return SQLITE_ERROR;
+  return rc;
 }
 
 /* Pass xSectorSize requests through to the original VFS unchanged.
@@ -631,7 +811,7 @@ static int multiplexSectorSize(sqlite3_file *pConn){
   if( pSubOpen ){
     return pSubOpen->pMethods->xSectorSize(pSubOpen);
   }
-  return SQLITE_DEFAULT_SECTOR_SIZE;
+  return DEFAULT_SECTOR_SIZE;
 }
 
 /* Pass xDeviceCharacteristics requests through to the original VFS unchanged.
@@ -706,9 +886,10 @@ static int multiplexShmUnmap(sqlite3_file *pConn, int deleteFlag){
 
 /************************** Public Interfaces *****************************/
 /*
-** Initialize the multiplex VFS shim.  Use the VFS named zOrigVfsName
-** as the VFS that does the actual work.  Use the default if
-** zOrigVfsName==NULL.  
+** CAPI: Initialize the multiplex VFS shim - sqlite3_multiplex_initialize()
+**
+** Use the VFS named zOrigVfsName as the VFS that does the actual work.  
+** Use the default if zOrigVfsName==NULL.  
 **
 ** The multiplex VFS shim is named "multiplex".  It will become the default
 ** VFS if makeDefault is non-zero.
@@ -731,14 +912,12 @@ int sqlite3_multiplex_initialize(const char *zOrigVfsName, int makeDefault){
     sqlite3_mutex_free(gMultiplex.pMutex);
     return SQLITE_NOMEM;
   }
-  gMultiplex.nChunkSize = SQLITE_MULTIPLEX_CHUNK_SIZE;
-  gMultiplex.nMaxChunks = SQLITE_MULTIPLEX_MAX_CHUNKS;
   gMultiplex.pGroups = NULL;
   gMultiplex.isInitialized = 1;
   gMultiplex.pOrigVfs = pOrigVfs;
   gMultiplex.sThisVfs = *pOrigVfs;
   gMultiplex.sThisVfs.szOsFile += sizeof(multiplexConn);
-  gMultiplex.sThisVfs.zName = "multiplex";
+  gMultiplex.sThisVfs.zName = SQLITE_MULTIPLEX_VFS_NAME;
   gMultiplex.sThisVfs.xOpen = multiplexOpen;
   gMultiplex.sThisVfs.xDelete = multiplexDelete;
   gMultiplex.sThisVfs.xAccess = multiplexAccess;
@@ -773,11 +952,14 @@ int sqlite3_multiplex_initialize(const char *zOrigVfsName, int makeDefault){
   gMultiplex.sIoMethodsV2.xShmBarrier = multiplexShmBarrier;
   gMultiplex.sIoMethodsV2.xShmUnmap = multiplexShmUnmap;
   sqlite3_vfs_register(&gMultiplex.sThisVfs, makeDefault);
+
+  sqlite3_auto_extension((void*)multiplexFuncInit);
+
   return SQLITE_OK;
 }
 
 /*
-** Shutdown the multiplex system.
+** CAPI: Shutdown the multiplex system - sqlite3_multiplex_shutdown()
 **
 ** All SQLite database connections must be closed before calling this
 ** routine.
@@ -796,31 +978,9 @@ int sqlite3_multiplex_shutdown(void){
   return SQLITE_OK;
 }
 
-/*
-** Adjust chunking params.  VFS should be initialized first.
-** No files should be open.  Re-intializing will reset these
-** to the default.
-*/
-int sqlite3_multiplex_set(
-  int nChunkSize,                 /* Max chunk size */
-  int nMaxChunks                  /* Max number of chunks */
-){
-  if( !gMultiplex.isInitialized ) return SQLITE_MISUSE;
-  if( gMultiplex.pGroups ) return SQLITE_MISUSE;
-  if( nChunkSize<32 ) return SQLITE_MISUSE;
-  if( nMaxChunks<1 ) return SQLITE_MISUSE;
-  if( nMaxChunks>99 ) return SQLITE_MISUSE;
-  multiplexEnter();
-  gMultiplex.nChunkSize = nChunkSize;
-  gMultiplex.nMaxChunks = nMaxChunks;
-  multiplexLeave();
-  return SQLITE_OK;
-}
-
 /***************************** Test Code ***********************************/
 #ifdef SQLITE_TEST
 #include <tcl.h>
-
 extern const char *sqlite3TestErrorName(int);
 
 
@@ -881,36 +1041,6 @@ static int test_multiplex_shutdown(
 }
 
 /*
-** tclcmd: sqlite3_multiplex_set CHUNK_SIZE MAX_CHUNKS
-*/
-static int test_multiplex_set(
-  void * clientData,
-  Tcl_Interp *interp,
-  int objc,
-  Tcl_Obj *CONST objv[]
-){
-  int nChunkSize;                 /* Max chunk size */
-  int nMaxChunks;                 /* Max number of chunks */
-  int rc;                         /* Value returned by sqlite3_multiplex_set() */
-
-  UNUSED_PARAMETER(clientData);
-
-  /* Process arguments */
-  if( objc!=3 ){
-    Tcl_WrongNumArgs(interp, 1, objv, "CHUNK_SIZE MAX_CHUNKS");
-    return TCL_ERROR;
-  }
-  if( Tcl_GetIntFromObj(interp, objv[1], &nChunkSize) ) return TCL_ERROR;
-  if( Tcl_GetIntFromObj(interp, objv[2], &nMaxChunks) ) return TCL_ERROR;
-
-  /* Invoke sqlite3_multiplex_set() */
-  rc = sqlite3_multiplex_set(nChunkSize, nMaxChunks);
-
-  Tcl_SetResult(interp, (char *)sqlite3TestErrorName(rc), TCL_STATIC);
-  return TCL_OK;
-}
-
-/*
 ** tclcmd:  sqlite3_multiplex_dump
 */
 static int test_multiplex_dump(
@@ -943,16 +1073,16 @@ static int test_multiplex_dump(
           Tcl_NewIntObj(pGroup->flags));
 
     /* count number of chunks with open handles */
-    for(i=0; i<gMultiplex.nMaxChunks; i++){
+    for(i=0; i<pGroup->nMaxChunks; i++){
       if( pGroup->bOpen[i] ) nChunks++;
     }
     Tcl_ListObjAppendElement(interp, pGroupTerm,
           Tcl_NewIntObj(nChunks));
 
     Tcl_ListObjAppendElement(interp, pGroupTerm,
-          Tcl_NewIntObj(gMultiplex.nChunkSize));
+          Tcl_NewIntObj(pGroup->nChunkSize));
     Tcl_ListObjAppendElement(interp, pGroupTerm,
-          Tcl_NewIntObj(gMultiplex.nMaxChunks));
+          Tcl_NewIntObj(pGroup->nMaxChunks));
 
     Tcl_ListObjAppendElement(interp, pResult, pGroupTerm);
   }
@@ -962,6 +1092,68 @@ static int test_multiplex_dump(
 }
 
 /*
+** Tclcmd: test_multiplex_control HANDLE DBNAME SUB-COMMAND ?INT-VALUE?
+*/
+static int test_multiplex_control(
+  ClientData cd,
+  Tcl_Interp *interp,
+  int objc,
+  Tcl_Obj *CONST objv[]
+){
+  int rc;                         /* Return code from file_control() */
+  int idx;                        /* Index in aSub[] */
+  Tcl_CmdInfo cmdInfo;            /* Command info structure for HANDLE */
+  sqlite3 *db;                    /* Underlying db handle for HANDLE */
+  int iValue = 0;
+  void *pArg = 0;
+
+  struct SubCommand {
+    const char *zName;
+    int op;
+    int argtype;
+  } aSub[] = {
+    { "enable",       MULTIPLEX_CTRL_ENABLE,           1 },
+    { "chunk_size",   MULTIPLEX_CTRL_SET_CHUNK_SIZE,   1 },
+    { "max_chunks",   MULTIPLEX_CTRL_SET_MAX_CHUNKS,   1 },
+    { 0, 0, 0 }
+  };
+
+  if( objc!=5 ){
+    Tcl_WrongNumArgs(interp, 1, objv, "HANDLE DBNAME SUB-COMMAND INT-VALUE");
+    return TCL_ERROR;
+  }
+
+  if( 0==Tcl_GetCommandInfo(interp, Tcl_GetString(objv[1]), &cmdInfo) ){
+    Tcl_AppendResult(interp, "expected database handle, got \"", 0);
+    Tcl_AppendResult(interp, Tcl_GetString(objv[1]), "\"", 0);
+    return TCL_ERROR;
+  }else{
+    db = *(sqlite3 **)cmdInfo.objClientData;
+  }
+
+  rc = Tcl_GetIndexFromObjStruct(
+      interp, objv[3], aSub, sizeof(aSub[0]), "sub-command", 0, &idx
+  );
+  if( rc!=TCL_OK ) return rc;
+
+  switch( aSub[idx].argtype ){
+    case 1:
+      if( Tcl_GetIntFromObj(interp, objv[4], &iValue) ){
+        return TCL_ERROR;
+      }
+      pArg = (void *)&iValue;
+      break;
+    default:
+      Tcl_WrongNumArgs(interp, 4, objv, "SUB-COMMAND");
+      return TCL_ERROR;
+  }
+
+  rc = sqlite3_file_control(db, Tcl_GetString(objv[2]), aSub[idx].op, pArg);
+  Tcl_SetResult(interp, (char *)sqlite3TestErrorName(rc), TCL_STATIC);
+  return (rc==SQLITE_OK) ? TCL_OK : TCL_ERROR;
+}
+
+/*
 ** This routine registers the custom TCL commands defined in this
 ** module.  This should be the only procedure visible from outside
 ** of this module.
@@ -973,8 +1165,8 @@ int Sqlitemultiplex_Init(Tcl_Interp *interp){
   } aCmd[] = {
     { "sqlite3_multiplex_initialize", test_multiplex_initialize },
     { "sqlite3_multiplex_shutdown", test_multiplex_shutdown },
-    { "sqlite3_multiplex_set", test_multiplex_set },
     { "sqlite3_multiplex_dump", test_multiplex_dump },
+    { "sqlite3_multiplex_control", test_multiplex_control },
   };
   int i;
 
diff --git a/src/test_multiplex.h b/src/test_multiplex.h
new file mode 100644
index 000000000..ec1ba9bb2
--- /dev/null
+++ b/src/test_multiplex.h
@@ -0,0 +1,91 @@
+/*
+** 2011 March 18
+**
+** The author disclaims copyright to this source code.  In place of
+** a legal notice, here is a blessing:
+**
+**    May you do good and not evil.
+**    May you find forgiveness for yourself and forgive others.
+**    May you share freely, never taking more than you give.
+**
+*************************************************************************
+**
+** This file contains a VFS "shim" - a layer that sits in between the
+** pager and the real VFS.
+**
+** This particular shim enforces a multiplex system on DB files.  
+** This shim shards/partitions a single DB file into smaller 
+** "chunks" such that the total DB file size may exceed the maximum
+** file size of the underlying file system.
+**
+*/
+
+#ifndef _TEST_MULTIPLEX_H
+#define _TEST_MULTIPLEX_H
+
+/*
+** CAPI: File-control Operations Supported by Multiplex VFS
+**
+** Values interpreted by the xFileControl method of a Multiplex VFS db file-handle.
+**
+** MULTIPLEX_CTRL_ENABLE:
+**   This file control is used to enable or disable the multiplex
+**   shim.
+**
+** MULTIPLEX_CTRL_SET_CHUNK_SIZE:
+**   This file control is used to set the maximum allowed chunk 
+**   size for a multiplex file set.  The chunk size should be 
+**   a multiple of SQLITE_MAX_PAGE_SIZE, and will be rounded up
+**   if not.
+**
+** MULTIPLEX_CTRL_SET_MAX_CHUNKS:
+**   This file control is used to set the maximum number of chunks
+**   allowed to be used for a mutliplex file set.
+*/
+#define MULTIPLEX_CTRL_ENABLE          214014
+#define MULTIPLEX_CTRL_SET_CHUNK_SIZE  214015
+#define MULTIPLEX_CTRL_SET_MAX_CHUNKS  214016
+
+/*
+** CAPI: Initialize the multiplex VFS shim - sqlite3_multiplex_initialize()
+**
+** Use the VFS named zOrigVfsName as the VFS that does the actual work.  
+** Use the default if zOrigVfsName==NULL.  
+**
+** The multiplex VFS shim is named "multiplex".  It will become the default
+** VFS if makeDefault is non-zero.
+**
+** An auto-extension is registered which will make the function 
+** multiplex_control() available to database connections.  This
+** function gives access to the xFileControl interface of the 
+** multiplex VFS shim.
+**
+** SELECT multiplex_control(<op>,<val>);
+** 
+**   <op>=1 MULTIPLEX_CTRL_ENABLE
+**   <val>=0 disable
+**   <val>=1 enable
+** 
+**   <op>=2 MULTIPLEX_CTRL_SET_CHUNK_SIZE
+**   <val> int, chunk size
+** 
+**   <op>=3 MULTIPLEX_CTRL_SET_MAX_CHUNKS
+**   <val> int, max chunks
+**
+** THIS ROUTINE IS NOT THREADSAFE.  Call this routine exactly once
+** during start-up.
+*/
+extern int sqlite3_multiplex_initialize(const char *zOrigVfsName, int makeDefault);
+
+/*
+** CAPI: Shutdown the multiplex system - sqlite3_multiplex_shutdown()
+**
+** All SQLite database connections must be closed before calling this
+** routine.
+**
+** THIS ROUTINE IS NOT THREADSAFE.  Call this routine exactly once while
+** shutting down in order to free all remaining multiplex groups.
+*/
+extern int sqlite3_multiplex_shutdown(void);
+
+#endif
diff --git a/src/test_syscall.c b/src/test_syscall.c
index dbac01d69..c570b71e8 100644
--- a/src/test_syscall.c
+++ b/src/test_syscall.c
@@ -214,6 +214,12 @@ static int ts_open(const char *zFile, int flags, int mode){
 */
 static int ts_close(int fd){
   if( tsIsFail() ){
+    /* Even if simulating an error, close the original file-descriptor. 
+    ** This is to stop the test process from running out of file-descriptors
+    ** when running a long test. If a call to close() appears to fail, SQLite
+    ** never attempts to use the file-descriptor afterwards (or even to close
+    ** it a second time).  */
+    orig_close(fd);
     return -1;
   }
   return orig_close(fd);
@@ -593,6 +599,24 @@ static int test_syscall_list(
   return TCL_OK;
 }
 
+static int test_syscall_defaultvfs(
+  void * clientData,
+  Tcl_Interp *interp,
+  int objc,
+  Tcl_Obj *CONST objv[]
+){
+  sqlite3_vfs *pVfs; 
+
+  if( objc!=2 ){
+    Tcl_WrongNumArgs(interp, 2, objv, "");
+    return TCL_ERROR;
+  }
+
+  pVfs = sqlite3_vfs_find(0);
+  Tcl_SetObjResult(interp, Tcl_NewStringObj(pVfs->zName, -1));
+  return TCL_OK;
+}
+
 static int test_syscall(
   void * clientData,
   Tcl_Interp *interp,
@@ -603,13 +627,14 @@ static int test_syscall(
     const char *zName;
     Tcl_ObjCmdProc *xCmd;
   } aCmd[] = {
-    { "fault",     test_syscall_fault },
-    { "install",   test_syscall_install },
-    { "uninstall", test_syscall_uninstall },
-    { "reset",     test_syscall_reset },
-    { "errno",     test_syscall_errno },
-    { "exists",    test_syscall_exists },
-    { "list",      test_syscall_list },
+    { "fault",      test_syscall_fault },
+    { "install",    test_syscall_install },
+    { "uninstall",  test_syscall_uninstall },
+    { "reset",      test_syscall_reset },
+    { "errno",      test_syscall_errno },
+    { "exists",     test_syscall_exists },
+    { "list",       test_syscall_list },
+    { "defaultvfs", test_syscall_defaultvfs },
     { 0, 0 }
   };
   int iCmd;
diff --git a/src/test_wholenumber.c b/src/test_wholenumber.c
new file mode 100644
index 000000000..150dc95ac
--- /dev/null
+++ b/src/test_wholenumber.c
@@ -0,0 +1,311 @@
+/*
+** 2011 April 02
+**
+** The author disclaims copyright to this source code.  In place of
+** a legal notice, here is a blessing:
+**
+**    May you do good and not evil.
+**    May you find forgiveness for yourself and forgive others.
+**    May you share freely, never taking more than you give.
+**
+*************************************************************************
+**
+** This file implements a virtual table that returns the whole numbers
+** between 1 and 4294967295, inclusive.
+**
+** Example:
+**
+**     CREATE VIRTUAL TABLE nums USING wholenumber;
+**     SELECT value FROM nums WHERE value<10;
+**
+** Results in:
+**
+**     1 2 3 4 5 6 7 8 9
+*/
+#include "sqlite3.h"
+#include <assert.h>
+#include <string.h>
+
+#ifndef SQLITE_OMIT_VIRTUALTABLE
+
+
+/* A wholenumber cursor object */
+typedef struct wholenumber_cursor wholenumber_cursor;
+struct wholenumber_cursor {
+  sqlite3_vtab_cursor base;  /* Base class - must be first */
+  unsigned iValue;           /* Current value */
+  unsigned mxValue;          /* Maximum value */
+};
+
+/* Methods for the wholenumber module */
+static int wholenumberConnect(
+  sqlite3 *db,
+  void *pAux,
+  int argc, const char *const*argv,
+  sqlite3_vtab **ppVtab,
+  char **pzErr
+){
+  sqlite3_vtab *pNew;
+  pNew = *ppVtab = sqlite3_malloc( sizeof(*pNew) );
+  if( pNew==0 ) return SQLITE_NOMEM;
+  sqlite3_declare_vtab(db, "CREATE TABLE x(value)");
+  memset(pNew, 0, sizeof(*pNew));
+  return SQLITE_OK;
+}
+/* Note that for this virtual table, the xCreate and xConnect
+** methods are identical. */
+
+static int wholenumberDisconnect(sqlite3_vtab *pVtab){
+  sqlite3_free(pVtab);
+  return SQLITE_OK;
+}
+/* The xDisconnect and xDestroy methods are also the same */
+
+
+/*
+** Open a new wholenumber cursor.
+*/
+static int wholenumberOpen(sqlite3_vtab *p, sqlite3_vtab_cursor **ppCursor){
+  wholenumber_cursor *pCur;
+  pCur = sqlite3_malloc( sizeof(*pCur) );
+  if( pCur==0 ) return SQLITE_NOMEM;
+  memset(pCur, 0, sizeof(*pCur));
+  *ppCursor = &pCur->base;
+  return SQLITE_OK;
+}
+
+/*
+** Close a wholenumber cursor.
+*/
+static int wholenumberClose(sqlite3_vtab_cursor *cur){
+  sqlite3_free(cur);
+  return SQLITE_OK;
+}
+
+
+/*
+** Advance a cursor to its next row of output
+*/
+static int wholenumberNext(sqlite3_vtab_cursor *cur){
+  wholenumber_cursor *pCur = (wholenumber_cursor*)cur;
+  pCur->iValue++;
+  return SQLITE_OK;
+}
+
+/*
+** Return the value associated with a wholenumber.
+*/
+static int wholenumberColumn(
+  sqlite3_vtab_cursor *cur,
+  sqlite3_context *ctx,
+  int i
+){
+  wholenumber_cursor *pCur = (wholenumber_cursor*)cur;
+  sqlite3_result_int64(ctx, pCur->iValue);
+  return SQLITE_OK;
+}
+
+/*
+** The rowid.
+*/
+static int wholenumberRowid(sqlite3_vtab_cursor *cur, sqlite_int64 *pRowid){
+  wholenumber_cursor *pCur = (wholenumber_cursor*)cur;
+  *pRowid = pCur->iValue;
+  return SQLITE_OK;
+}
+
+/*
+** When the wholenumber_cursor.rLimit value is 0 or less, that is a signal
+** that the cursor has nothing more to output.
+*/
+static int wholenumberEof(sqlite3_vtab_cursor *cur){
+  wholenumber_cursor *pCur = (wholenumber_cursor*)cur;
+  return pCur->iValue>pCur->mxValue || pCur->iValue==0;
+}
+
+/*
+** Called to "rewind" a cursor back to the beginning so that
+** it starts its output over again.  Always called at least once
+** prior to any wholenumberColumn, wholenumberRowid, or wholenumberEof call.
+**
+**    idxNum   Constraints
+**    ------   ---------------------
+**      0      (none)
+**      1      value > $argv0
+**      2      value >= $argv0
+**      4      value < $argv0
+**      8      value <= $argv0
+**
+**      5      value > $argv0 AND value < $argv1
+**      6      value >= $argv0 AND value < $argv1
+**      9      value > $argv0 AND value <= $argv1
+**     10      value >= $argv0 AND value <= $argv1
+*/
+static int wholenumberFilter(
+  sqlite3_vtab_cursor *pVtabCursor, 
+  int idxNum, const char *idxStr,
+  int argc, sqlite3_value **argv
+){
+  wholenumber_cursor *pCur = (wholenumber_cursor *)pVtabCursor;
+  sqlite3_int64 v;
+  int i = 0;
+  pCur->iValue = 1;
+  pCur->mxValue = 0xffffffff;  /* 4294967295 */
+  if( idxNum & 3 ){
+    v = sqlite3_value_int64(argv[0]) + (idxNum&1);
+    if( v>pCur->iValue && v<=pCur->mxValue ) pCur->iValue = v;
+    i++;
+  }
+  if( idxNum & 12 ){
+    v = sqlite3_value_int64(argv[i]) - ((idxNum>>2)&1);
+    if( v>=pCur->iValue && v<pCur->mxValue ) pCur->mxValue = v;
+  }
+  return SQLITE_OK;
+}
+
+/*
+** Search for terms of these forms:
+**
+**  (1)  value > $value
+**  (2)  value >= $value
+**  (4)  value < $value
+**  (8)  value <= $value
+**
+** idxNum is an ORed combination of 1 or 2 with 4 or 8.
+*/
+static int wholenumberBestIndex(
+  sqlite3_vtab *tab,
+  sqlite3_index_info *pIdxInfo
+){
+  int i;
+  int idxNum = 0;
+  int argvIdx = 1;
+  int ltIdx = -1;
+  int gtIdx = -1;
+  const struct sqlite3_index_constraint *pConstraint;
+  pConstraint = pIdxInfo->aConstraint;
+  for(i=0; i<pIdxInfo->nConstraint; i++, pConstraint++){
+    if( pConstraint->usable==0 ) continue;
+    if( (idxNum & 3)==0 && pConstraint->op==SQLITE_INDEX_CONSTRAINT_GT ){
+      idxNum |= 1;
+      ltIdx = i;
+    }
+    if( (idxNum & 3)==0 && pConstraint->op==SQLITE_INDEX_CONSTRAINT_GE ){
+      idxNum |= 2;
+      ltIdx = i;
+    }
+    if( (idxNum & 12)==0 && pConstraint->op==SQLITE_INDEX_CONSTRAINT_LT ){
+      idxNum |= 4;
+      gtIdx = i;
+    }
+    if( (idxNum & 12)==0 && pConstraint->op==SQLITE_INDEX_CONSTRAINT_LE ){
+      idxNum |= 8;
+      gtIdx = i;
+    }
+  }
+  pIdxInfo->idxNum = idxNum;
+  if( ltIdx>=0 ){
+    pIdxInfo->aConstraintUsage[ltIdx].argvIndex = argvIdx++;
+    pIdxInfo->aConstraintUsage[ltIdx].omit = 1;
+  }
+  if( gtIdx>=0 ){
+    pIdxInfo->aConstraintUsage[gtIdx].argvIndex = argvIdx;
+    pIdxInfo->aConstraintUsage[gtIdx].omit = 1;
+  }
+  if( pIdxInfo->nOrderBy==1
+   && pIdxInfo->aOrderBy[0].desc==0
+  ){
+    pIdxInfo->orderByConsumed = 1;
+  }
+  pIdxInfo->estimatedCost = (double)1;
+  return SQLITE_OK;
+}
+
+/*
+** A virtual table module that provides read-only access to a
+** Tcl global variable namespace.
+*/
+static sqlite3_module wholenumberModule = {
+  0,                         /* iVersion */
+  wholenumberConnect,
+  wholenumberConnect,
+  wholenumberBestIndex,
+  wholenumberDisconnect, 
+  wholenumberDisconnect,
+  wholenumberOpen,           /* xOpen - open a cursor */
+  wholenumberClose,          /* xClose - close a cursor */
+  wholenumberFilter,         /* xFilter - configure scan constraints */
+  wholenumberNext,           /* xNext - advance a cursor */
+  wholenumberEof,            /* xEof - check for end of scan */
+  wholenumberColumn,         /* xColumn - read data */
+  wholenumberRowid,          /* xRowid - read data */
+  0,                         /* xUpdate */
+  0,                         /* xBegin */
+  0,                         /* xSync */
+  0,                         /* xCommit */
+  0,                         /* xRollback */
+  0,                         /* xFindMethod */
+  0,                         /* xRename */
+};
+
+#endif /* SQLITE_OMIT_VIRTUALTABLE */
+
+
+/*
+** Register the wholenumber virtual table
+*/
+int wholenumber_register(sqlite3 *db){
+  int rc = SQLITE_OK;
+#ifndef SQLITE_OMIT_VIRTUALTABLE
+  rc = sqlite3_create_module(db, "wholenumber", &wholenumberModule, 0);
+#endif
+  return rc;
+}
+
+#ifdef SQLITE_TEST
+#include <tcl.h>
+/*
+** Decode a pointer to an sqlite3 object.
+*/
+extern int getDbPointer(Tcl_Interp *interp, const char *zA, sqlite3 **ppDb);
+
+/*
+** Register the echo virtual table module.
+*/
+static int register_wholenumber_module(
+  ClientData clientData, /* Pointer to sqlite3_enable_XXX function */
+  Tcl_Interp *interp,    /* The TCL interpreter that invoked this command */
+  int objc,              /* Number of arguments */
+  Tcl_Obj *CONST objv[]  /* Command arguments */
+){
+  sqlite3 *db;
+  if( objc!=2 ){
+    Tcl_WrongNumArgs(interp, 1, objv, "DB");
+    return TCL_ERROR;
+  }
+  if( getDbPointer(interp, Tcl_GetString(objv[1]), &db) ) return TCL_ERROR;
+  wholenumber_register(db);
+  return TCL_OK;
+}
+
+
+/*
+** Register commands with the TCL interpreter.
+*/
+int Sqlitetestwholenumber_Init(Tcl_Interp *interp){
+  static struct {
+     char *zName;
+     Tcl_ObjCmdProc *xProc;
+     void *clientData;
+  } aObjCmd[] = {
+     { "register_wholenumber_module",   register_wholenumber_module, 0 },
+  };
+  int i;
+  for(i=0; i<sizeof(aObjCmd)/sizeof(aObjCmd[0]); i++){
+    Tcl_CreateObjCommand(interp, aObjCmd[i].zName, 
+        aObjCmd[i].xProc, aObjCmd[i].clientData, 0);
+  }
+  return TCL_OK;
+}
+
+#endif /* SQLITE_TEST */
diff --git a/src/vdbe.c b/src/vdbe.c
index e85dc85f6..b0e66317c 100644
--- a/src/vdbe.c
+++ b/src/vdbe.c
@@ -581,7 +581,7 @@ int sqlite3VdbeExec(
   /*** INSERT STACK UNION HERE ***/
 
   assert( p->magic==VDBE_MAGIC_RUN );  /* sqlite3_step() verifies this */
-  sqlite3VdbeMutexArrayEnter(p);
+  sqlite3VdbeEnter(p);
   if( p->rc==SQLITE_NOMEM ){
     /* This happens if a malloc() inside a call to sqlite3_column_text() or
     ** sqlite3_column_text16() failed.  */
@@ -1404,6 +1404,7 @@ case OP_Function: {
     ctx.pColl = pOp[-1].p4.pColl;
   }
   (*ctx.pFunc->xFunc)(&ctx, n, apVal); /* IMP: R-24505-23230 */
+  sqlite3VdbeMutexResync(p);
   if( db->mallocFailed ){
     /* Even though a malloc() has failed, the implementation of the
     ** user function may have called an sqlite3_result_XXX() function
@@ -1435,6 +1436,15 @@ case OP_Function: {
   if( sqlite3VdbeMemTooBig(pOut) ){
     goto too_big;
   }
+
+#if 0
+  /* The app-defined function has done something that as caused this
+  ** statement to expire.  (Perhaps the function called sqlite3_exec()
+  ** with a CREATE TABLE statement.)
+  */
+  if( p->expired ) rc = SQLITE_ABORT;
+#endif
+
   REGISTER_TRACE(pOp->p3, pOut);
   UPDATE_MAX_BLOBSIZE(pOut);
   break;
@@ -2660,6 +2670,7 @@ case OP_Savepoint: {
         if( p1==SAVEPOINT_ROLLBACK && (db->flags&SQLITE_InternChanges)!=0 ){
           sqlite3ExpirePreparedStatements(db);
           sqlite3ResetInternalSchema(db, 0);
+          sqlite3VdbeMutexResync(p);
           db->flags = (db->flags | SQLITE_InternChanges);
         }
       }
@@ -2799,7 +2810,7 @@ case OP_Transaction: {
   Btree *pBt;
 
   assert( pOp->p1>=0 && pOp->p1<db->nDb );
-  assert( (p->btreeMask & (1<<pOp->p1))!=0 );
+  assert( (p->btreeMask & (((yDbMask)1)<<pOp->p1))!=0 );
   pBt = db->aDb[pOp->p1].pBt;
 
   if( pBt ){
@@ -2855,7 +2866,7 @@ case OP_ReadCookie: {               /* out2-prerelease */
   assert( pOp->p3<SQLITE_N_BTREE_META );
   assert( iDb>=0 && iDb<db->nDb );
   assert( db->aDb[iDb].pBt!=0 );
-  assert( (p->btreeMask & (1<<iDb))!=0 );
+  assert( (p->btreeMask & (((yDbMask)1)<<iDb))!=0 );
 
   sqlite3BtreeGetMeta(db->aDb[iDb].pBt, iCookie, (u32 *)&iMeta);
   pOut->u.i = iMeta;
@@ -2876,7 +2887,7 @@ case OP_SetCookie: {       /* in3 */
   Db *pDb;
   assert( pOp->p2<SQLITE_N_BTREE_META );
   assert( pOp->p1>=0 && pOp->p1<db->nDb );
-  assert( (p->btreeMask & (1<<pOp->p1))!=0 );
+  assert( (p->btreeMask & (((yDbMask)1)<<pOp->p1))!=0 );
   pDb = &db->aDb[pOp->p1];
   assert( pDb->pBt!=0 );
   pIn3 = &aMem[pOp->p3];
@@ -2924,7 +2935,7 @@ case OP_VerifyCookie: {
   Btree *pBt;
 
   assert( pOp->p1>=0 && pOp->p1<db->nDb );
-  assert( (p->btreeMask & (1<<pOp->p1))!=0 );
+  assert( (p->btreeMask & (((yDbMask)1)<<pOp->p1))!=0 );
   pBt = db->aDb[pOp->p1].pBt;
   if( pBt ){
     sqlite3BtreeGetMeta(pBt, BTREE_SCHEMA_VERSION, (u32 *)&iMeta);
@@ -2950,6 +2961,7 @@ case OP_VerifyCookie: {
     */
     if( db->aDb[pOp->p1].pSchema->schema_cookie!=iMeta ){
       sqlite3ResetInternalSchema(db, pOp->p1);
+      sqlite3VdbeMutexResync(p);
     }
 
     p->expired = 1;
@@ -3028,7 +3040,7 @@ case OP_OpenWrite: {
   p2 = pOp->p2;
   iDb = pOp->p3;
   assert( iDb>=0 && iDb<db->nDb );
-  assert( (p->btreeMask & (1<<iDb))!=0 );
+  assert( (p->btreeMask & (((yDbMask)1)<<iDb))!=0 );
   pDb = &db->aDb[iDb];
   pX = pDb->pBt;
   assert( pX!=0 );
@@ -4565,7 +4577,7 @@ case OP_Destroy: {     /* out2-prerelease */
   }else{
     iDb = pOp->p3;
     assert( iCnt==1 );
-    assert( (p->btreeMask & (1<<iDb))!=0 );
+    assert( (p->btreeMask & (((yDbMask)1)<<iDb))!=0 );
     rc = sqlite3BtreeDropTable(db->aDb[iDb].pBt, pOp->p1, &iMoved);
     pOut->flags = MEM_Int;
     pOut->u.i = iMoved;
@@ -4601,7 +4613,7 @@ case OP_Clear: {
   int nChange;
  
   nChange = 0;
-  assert( (p->btreeMask & (1<<pOp->p2))!=0 );
+  assert( (p->btreeMask & (((yDbMask)1)<<pOp->p2))!=0 );
   rc = sqlite3BtreeClearTable(
       db->aDb[pOp->p2].pBt, pOp->p1, (pOp->p3 ? &nChange : 0)
   );
@@ -4646,7 +4658,7 @@ case OP_CreateTable: {          /* out2-prerelease */
 
   pgno = 0;
   assert( pOp->p1>=0 && pOp->p1<db->nDb );
-  assert( (p->btreeMask & (1<<pOp->p1))!=0 );
+  assert( (p->btreeMask & (((yDbMask)1)<<pOp->p1))!=0 );
   pDb = &db->aDb[pOp->p1];
   assert( pDb->pBt!=0 );
   if( pOp->opcode==OP_CreateTable ){
@@ -4674,26 +4686,22 @@ case OP_ParseSchema: {
   char *zSql;
   InitData initData;
 
+  /* Any prepared statement that invokes this opcode will hold mutexes
+  ** on every btree.  This is a prerequisite for invoking 
+  ** sqlite3InitCallback().
+  */
+#ifdef SQLITE_DEBUG
+  for(iDb=0; iDb<db->nDb; iDb++){
+    assert( iDb==1 || sqlite3BtreeHoldsMutex(db->aDb[iDb].pBt) );
+  }
+#endif
+  assert( p->btreeMask == ~(yDbMask)0 );
+
+
   iDb = pOp->p1;
   assert( iDb>=0 && iDb<db->nDb );
-
-  /* Although the mutex on the BtShared object that corresponds to
-  ** database iDb (the database containing the sqlite_master table
-  ** read by this instruction) is currently held, it is necessary to
-  ** obtain the mutexes on all attached databases before checking if
-  ** the schema of iDb is loaded. This is because, at the start of
-  ** the sqlite3_exec() call below, SQLite will invoke 
-  ** sqlite3BtreeEnterAll(). If all mutexes are not already held, the
-  ** iDb mutex may be temporarily released to avoid deadlock. If 
-  ** this happens, then some other thread may delete the in-memory 
-  ** schema of database iDb before the SQL statement runs. The schema
-  ** will not be reloaded becuase the db->init.busy flag is set. This
-  ** can result in a "no such table: sqlite_master" or "malformed
-  ** database schema" error being returned to the user.
-  */
-  assert( sqlite3BtreeHoldsMutex(db->aDb[iDb].pBt) );
-  sqlite3BtreeEnterAll(db);
-  if( ALWAYS(DbHasProperty(db, iDb, DB_SchemaLoaded)) ){
+  assert( DbHasProperty(db, iDb, DB_SchemaLoaded) );
+  /* Used to be a conditional */ {
     zMaster = SCHEMA_TABLE(iDb);
     initData.db = db;
     initData.iDb = pOp->p1;
@@ -4714,7 +4722,6 @@ case OP_ParseSchema: {
       db->init.busy = 0;
     }
   }
-  sqlite3BtreeLeaveAll(db);
   if( rc==SQLITE_NOMEM ){
     goto no_mem;
   }
@@ -4815,7 +4822,7 @@ case OP_IntegrityCk: {
   }
   aRoot[j] = 0;
   assert( pOp->p5<db->nDb );
-  assert( (p->btreeMask & (1<<pOp->p5))!=0 );
+  assert( (p->btreeMask & (((yDbMask)1)<<pOp->p5))!=0 );
   z = sqlite3BtreeIntegrityCheck(db->aDb[pOp->p5].pBt, aRoot, nRoot,
                                  (int)pnErr->u.i, &nErr);
   sqlite3DbFree(db, aRoot);
@@ -5239,11 +5246,25 @@ case OP_AggStep: {
     ctx.pColl = pOp[-1].p4.pColl;
   }
   (ctx.pFunc->xStep)(&ctx, n, apVal); /* IMP: R-24505-23230 */
+  sqlite3VdbeMutexResync(p);
   if( ctx.isError ){
     sqlite3SetString(&p->zErrMsg, db, "%s", sqlite3_value_text(&ctx.s));
     rc = ctx.isError;
   }
+
+  /* The app-defined function has done something that as caused this
+  ** statement to expire.  (Perhaps the function called sqlite3_exec()
+  ** with a CREATE TABLE statement.)
+  */
+#if 0
+  if( p->expired ){
+    rc = SQLITE_ABORT;
+    break;
+  }
+#endif
+
   sqlite3VdbeMemRelease(&ctx.s);
+
   break;
 }
 
@@ -5265,8 +5286,11 @@ case OP_AggFinal: {
   pMem = &aMem[pOp->p1];
   assert( (pMem->flags & ~(MEM_Null|MEM_Agg))==0 );
   rc = sqlite3VdbeMemFinalize(pMem, pOp->p4.pFunc);
+  sqlite3VdbeMutexResync(p);
   if( rc ){
     sqlite3SetString(&p->zErrMsg, db, "%s", sqlite3_value_text(pMem));
+  }else if( p->expired ){
+    rc = SQLITE_ABORT;
   }
   sqlite3VdbeChangeEncoding(pMem, encoding);
   UPDATE_MAX_BLOBSIZE(pMem);
@@ -5343,7 +5367,7 @@ case OP_JournalMode: {    /* out2-prerelease */
 
   /* This opcode is used in two places: PRAGMA journal_mode and ATTACH.
   ** In PRAGMA journal_mode, the sqlite3VdbeUsesBtree() routine is called
-  ** when the statment is prepared and so p->aMutex.nMutex>0.  All mutexes
+  ** when the statement is prepared and so p->btreeMask!=0.  All mutexes
   ** are already acquired.  But when used in ATTACH, sqlite3VdbeUsesBtree()
   ** is not called when the statement is prepared because it requires the
   ** iDb index of the database as a parameter, and the database has not
@@ -5352,12 +5376,11 @@ case OP_JournalMode: {    /* out2-prerelease */
   ** No other mutexes are required by the ATTACH command so this is safe
   ** to do.
   */
-  assert( (p->btreeMask & (1<<pOp->p1))!=0 || p->aMutex.nMutex==0 );
-  if( p->aMutex.nMutex==0 ){
+  if( p->btreeMask==0 ){
     /* This occurs right after ATTACH.  Get a mutex on the newly ATTACHed
     ** database. */
     sqlite3VdbeUsesBtree(p, pOp->p1);
-    sqlite3VdbeMutexArrayEnter(p);
+    sqlite3VdbeEnter(p);
   }
 
   pBt = db->aDb[pOp->p1].pBt;
@@ -5457,7 +5480,7 @@ case OP_IncrVacuum: {        /* jump */
   Btree *pBt;
 
   assert( pOp->p1>=0 && pOp->p1<db->nDb );
-  assert( (p->btreeMask & (1<<pOp->p1))!=0 );
+  assert( (p->btreeMask & (((yDbMask)1)<<pOp->p1))!=0 );
   pBt = db->aDb[pOp->p1].pBt;
   rc = sqlite3BtreeIncrVacuum(pBt);
   if( rc==SQLITE_DONE ){
@@ -5506,7 +5529,7 @@ case OP_TableLock: {
   if( isWriteLock || 0==(db->flags&SQLITE_ReadUncommitted) ){
     int p1 = pOp->p1; 
     assert( p1>=0 && p1<db->nDb );
-    assert( (p->btreeMask & (1<<p1))!=0 );
+    assert( (p->btreeMask & (((yDbMask)1)<<p1))!=0 );
     assert( isWriteLock==0 || isWriteLock==1 );
     rc = sqlite3BtreeLockTable(db->aDb[p1].pBt, pOp->p2, isWriteLock);
     if( (rc&0xFF)==SQLITE_LOCKED ){
@@ -5995,13 +6018,16 @@ vdbe_error_halt:
   sqlite3VdbeHalt(p);
   if( rc==SQLITE_IOERR_NOMEM ) db->mallocFailed = 1;
   rc = SQLITE_ERROR;
-  if( resetSchemaOnFault ) sqlite3ResetInternalSchema(db, 0);
+  if( resetSchemaOnFault ){
+    sqlite3ResetInternalSchema(db, 0);
+    sqlite3VdbeMutexResync(p);
+  }
 
   /* This is the only way out of this procedure.  We have to
   ** release the mutexes on btrees that were acquired at the
   ** top. */
 vdbe_return:
-  sqlite3BtreeMutexArrayLeave(&p->aMutex);
+  sqlite3VdbeLeave(p);
   return rc;
 
   /* Jump to here if a string or blob larger than SQLITE_MAX_LENGTH
diff --git a/src/vdbeInt.h b/src/vdbeInt.h
index 911c29faf..05136cbeb 100644
--- a/src/vdbeInt.h
+++ b/src/vdbeInt.h
@@ -302,10 +302,10 @@ struct Vdbe {
   u8 readOnly;            /* True for read-only statements */
   u8 isPrepareV2;         /* True if prepared with prepare_v2() */
   int nChange;            /* Number of db changes made since last reset */
-  tAttachMask btreeMask;  /* Bitmask of db->aDb[] entries referenced */
+  yDbMask btreeMask;      /* Bitmask of db->aDb[] entries referenced */
+  u32 iMutexCounter;      /* Mutex counter upon sqlite3VdbeEnter() */
   int iStatement;         /* Statement number (or 0 if has not opened stmt) */
   int aCounter[3];        /* Counters used by sqlite3_stmt_status() */
-  BtreeMutexArray aMutex; /* An array of Btree used here and needing locks */
 #ifndef SQLITE_OMIT_TRACE
   i64 startTime;          /* Time when query started - used for profiling */
 #endif
@@ -408,6 +408,9 @@ int sqlite3VdbeFrameRestore(VdbeFrame *);
 void sqlite3VdbeMemStoreType(Mem *pMem);
 void sqlite3VdbePreUpdateHook(
     Vdbe *, VdbeCursor *, int, const char*, Table *, i64, int);
+void sqlite3VdbeEnter(Vdbe*);
+void sqlite3VdbeLeave(Vdbe*);
+void sqlite3VdbeMutexResync(Vdbe*);
 
 #ifdef SQLITE_DEBUG
 void sqlite3VdbeMemPrepareToChange(Vdbe*,Mem*);
@@ -419,12 +422,6 @@ int sqlite3VdbeCheckFk(Vdbe *, int);
 # define sqlite3VdbeCheckFk(p,i) 0
 #endif
 
-#ifndef SQLITE_OMIT_SHARED_CACHE
-void sqlite3VdbeMutexArrayEnter(Vdbe *p);
-#else
-# define sqlite3VdbeMutexArrayEnter(p)
-#endif
-
 int sqlite3VdbeMemTranslate(Mem*, u8);
 #ifdef SQLITE_DEBUG
   void sqlite3VdbePrintSql(Vdbe*);
diff --git a/src/vdbeaux.c b/src/vdbeaux.c
index a4b0df8f4..16eeb5ce1 100644
--- a/src/vdbeaux.c
+++ b/src/vdbeaux.c
@@ -158,6 +158,11 @@ int sqlite3VdbeAddOp3(Vdbe *p, int op, int p1, int p2, int p3){
   pOp->p4.p = 0;
   pOp->p4type = P4_NOTUSED;
   p->expired = 0;
+  if( op==OP_ParseSchema ){
+    /* Any program that uses the OP_ParseSchema opcode needs to lock
+    ** all btrees. */
+    p->btreeMask = ~(yDbMask)0;
+  }
 #ifdef SQLITE_DEBUG
   pOp->zComment = 0;
   if( sqlite3VdbeAddopTrace ) sqlite3VdbePrintOp(0, i, &p->aOp[i]);
@@ -458,7 +463,7 @@ VdbeOp *sqlite3VdbeTakeOpArray(Vdbe *p, int *pnOp, int *pnMaxArg){
   assert( aOp && !p->db->mallocFailed );
 
   /* Check that sqlite3VdbeUsesBtree() was not called on this VM */
-  assert( p->aMutex.nMutex==0 );
+  assert( p->btreeMask==0 );
 
   resolveP2Values(p, pnMaxArg);
   *pnOp = p->nOp;
@@ -946,22 +951,131 @@ static char *displayP4(Op *pOp, char *zTemp, int nTemp){
 /*
 ** Declare to the Vdbe that the BTree object at db->aDb[i] is used.
 **
-** The prepared statement has to know in advance which Btree objects
-** will be used so that it can acquire mutexes on them all in sorted
-** order (via sqlite3VdbeMutexArrayEnter().  Mutexes are acquired
-** in order (and released in reverse order) to avoid deadlocks.
+** The prepared statements need to know in advance the complete set of
+** attached databases that they will be using.  A mask of these databases
+** is maintained in p->btreeMask and is used for locking and other purposes.
 */
 void sqlite3VdbeUsesBtree(Vdbe *p, int i){
-  tAttachMask mask;
-  assert( i>=0 && i<p->db->nDb && i<sizeof(tAttachMask)*8 );
+  assert( i>=0 && i<p->db->nDb && i<sizeof(yDbMask)*8 );
   assert( i<(int)sizeof(p->btreeMask)*8 );
-  mask = ((u32)1)<<i;
-  if( (p->btreeMask & mask)==0 ){
-    p->btreeMask |= mask;
-    sqlite3BtreeMutexArrayInsert(&p->aMutex, p->db->aDb[i].pBt);
+  p->btreeMask |= ((yDbMask)1)<<i;
+}
+
+/*
+** Compute the sum of all mutex counters for all btrees in the
+** given prepared statement.
+*/
+#ifndef SQLITE_OMIT_SHARED_CACHE
+static u32 mutexCounterSum(Vdbe *p){
+  u32 cntSum = 0;
+#ifdef SQLITE_DEBUG
+  int i;
+  yDbMask mask;
+  sqlite3 *db = p->db;
+  Db *aDb = db->aDb;
+  int nDb = db->nDb;
+  for(i=0, mask=1; i<nDb; i++, mask += mask){
+    if( i!=1 && (mask & p->btreeMask)!=0 && ALWAYS(aDb[i].pBt!=0) ){
+      cntSum += sqlite3BtreeMutexCounter(aDb[i].pBt);
+    }
+  }
+#else
+  UNUSED_PARAMETER(p);
+#endif
+  return cntSum;
+}
+#endif
+
+/*
+** If SQLite is compiled to support shared-cache mode and to be threadsafe,
+** this routine obtains the mutex associated with each BtShared structure
+** that may be accessed by the VM passed as an argument. In doing so it also
+** sets the BtShared.db member of each of the BtShared structures, ensuring
+** that the correct busy-handler callback is invoked if required.
+**
+** If SQLite is not threadsafe but does support shared-cache mode, then
+** sqlite3BtreeEnter() is invoked to set the BtShared.db variables
+** of all of BtShared structures accessible via the database handle 
+** associated with the VM.
+**
+** If SQLite is not threadsafe and does not support shared-cache mode, this
+** function is a no-op.
+**
+** The p->btreeMask field is a bitmask of all btrees that the prepared 
+** statement p will ever use.  Let N be the number of bits in p->btreeMask
+** corresponding to btrees that use shared cache.  Then the runtime of
+** this routine is N*N.  But as N is rarely more than 1, this should not
+** be a problem.
+*/
+void sqlite3VdbeEnter(Vdbe *p){
+#ifndef SQLITE_OMIT_SHARED_CACHE
+  int i;
+  yDbMask mask;
+  sqlite3 *db = p->db;
+  Db *aDb = db->aDb;
+  int nDb = db->nDb;
+  for(i=0, mask=1; i<nDb; i++, mask += mask){
+    if( i!=1 && (mask & p->btreeMask)!=0 && ALWAYS(aDb[i].pBt!=0) ){
+      sqlite3BtreeEnter(aDb[i].pBt);
+    }
+  }
+  p->iMutexCounter = mutexCounterSum(p);
+#else
+  UNUSED_PARAMETER(p);
+#endif
+}
+
+/*
+** Unlock all of the btrees previously locked by a call to sqlite3VdbeEnter().
+*/
+void sqlite3VdbeLeave(Vdbe *p){
+#ifndef SQLITE_OMIT_SHARED_CACHE
+  int i;
+  yDbMask mask;
+  sqlite3 *db = p->db;
+  Db *aDb = db->aDb;
+  int nDb = db->nDb;
+
+  /* Assert that the all mutexes have been held continously since
+  ** the most recent sqlite3VdbeEnter() or sqlite3VdbeMutexResync().
+  */
+  assert( mutexCounterSum(p) == p->iMutexCounter );
+
+  for(i=0, mask=1; i<nDb; i++, mask += mask){
+    if( i!=1 && (mask & p->btreeMask)!=0 && ALWAYS(aDb[i].pBt!=0) ){
+      sqlite3BtreeLeave(aDb[i].pBt);
+    }
   }
+#else
+  UNUSED_PARAMETER(p);
+#endif
 }
 
+/*
+** Recompute the sum of the mutex counters on all btrees used by the
+** prepared statement p.
+**
+** Call this routine while holding a sqlite3VdbeEnter() after doing something
+** that might cause one or more of the individual mutexes held by the
+** prepared statement to be released.  Calling sqlite3BtreeEnter() on 
+** any BtShared mutex which is not used by the prepared statement is one
+** way to cause one or more of the mutexes in the prepared statement
+** to be temporarily released.  The anti-deadlocking logic in
+** sqlite3BtreeEnter() can cause mutexes to be released temporarily then
+** reacquired.
+**
+** Calling this routine is an acknowledgement that some of the individual
+** mutexes in the prepared statement might have been released and reacquired.
+** So checks to verify that mutex-protected content did not change
+** unexpectedly should accompany any call to this routine.
+*/
+void sqlite3VdbeMutexResync(Vdbe *p){
+#if !defined(SQLITE_OMIT_SHARED_CACHE) && defined(SQLITE_DEBUG)
+  p->iMutexCounter = mutexCounterSum(p);
+#else
+  UNUSED_PARAMETER(p);
+#endif
+}
 
 #if defined(VDBE_PROFILE) || defined(SQLITE_DEBUG)
 /*
@@ -1961,33 +2075,6 @@ int sqlite3VdbeCloseStatement(Vdbe *p, int eOp){
 }
 
 /*
-** If SQLite is compiled to support shared-cache mode and to be threadsafe,
-** this routine obtains the mutex associated with each BtShared structure
-** that may be accessed by the VM passed as an argument. In doing so it
-** sets the BtShared.db member of each of the BtShared structures, ensuring
-** that the correct busy-handler callback is invoked if required.
-**
-** If SQLite is not threadsafe but does support shared-cache mode, then
-** sqlite3BtreeEnterAll() is invoked to set the BtShared.db variables
-** of all of BtShared structures accessible via the database handle 
-** associated with the VM. Of course only a subset of these structures
-** will be accessed by the VM, and we could use Vdbe.btreeMask to figure
-** that subset out, but there is no advantage to doing so.
-**
-** If SQLite is not threadsafe and does not support shared-cache mode, this
-** function is a no-op.
-*/
-#ifndef SQLITE_OMIT_SHARED_CACHE
-void sqlite3VdbeMutexArrayEnter(Vdbe *p){
-#if SQLITE_THREADSAFE
-  sqlite3BtreeMutexArrayEnter(&p->aMutex);
-#else
-  sqlite3BtreeEnterAll(p->db);
-#endif
-}
-#endif
-
-/*
 ** This function is called when a transaction opened by the database 
 ** handle associated with the VM passed as an argument is about to be 
 ** committed. If there are outstanding deferred foreign key constraint
@@ -2059,7 +2146,7 @@ int sqlite3VdbeHalt(Vdbe *p){
     int isSpecialError;            /* Set to true if a 'special' error */
 
     /* Lock all btrees used by the statement */
-    sqlite3VdbeMutexArrayEnter(p);
+    sqlite3VdbeEnter(p);
 
     /* Check for one of the special errors */
     mrc = p->rc & 0xff;
@@ -2113,7 +2200,7 @@ int sqlite3VdbeHalt(Vdbe *p){
         rc = sqlite3VdbeCheckFk(p, 1);
         if( rc!=SQLITE_OK ){
           if( NEVER(p->readOnly) ){
-            sqlite3BtreeMutexArrayLeave(&p->aMutex);
+            sqlite3VdbeLeave(p);
             return SQLITE_ERROR;
           }
           rc = SQLITE_CONSTRAINT;
@@ -2125,7 +2212,7 @@ int sqlite3VdbeHalt(Vdbe *p){
           rc = vdbeCommit(db, p);
         }
         if( rc==SQLITE_BUSY && p->readOnly ){
-          sqlite3BtreeMutexArrayLeave(&p->aMutex);
+          sqlite3VdbeLeave(p);
           return SQLITE_BUSY;
         }else if( rc!=SQLITE_OK ){
           p->rc = rc;
@@ -2197,7 +2284,8 @@ int sqlite3VdbeHalt(Vdbe *p){
     }
 
     /* Release the locks */
-    sqlite3BtreeMutexArrayLeave(&p->aMutex);
+    sqlite3VdbeMutexResync(p);
+    sqlite3VdbeLeave(p);
   }
 
   /* We have successfully halted and closed the VM.  Record this fact. */