The PRAGMA journal_mode=WAL; command now makes WAL the default journal mode

for new databases added with ATTACH, so the behavior is consistent with the
other journal modes.

FossilOrigin-Name: c3520460a4a39fc5e981c3033068ffbb422a4af2

4 files changed, 43 insertions, 9 deletions

diff --git a/src/attach.c b/src/attach.c
index 6f0acef94..2b57793f9 100644
--- a/src/attach.c
+++ b/src/attach.c
@@ -143,7 +143,8 @@ static void attachFunc(
     }
     pPager = sqlite3BtreePager(aNew->pBt);
     sqlite3PagerLockingMode(pPager, db->dfltLockMode);
-    sqlite3PagerJournalMode(pPager, db->dfltJournalMode);
+    /* journal_mode set by the OP_JournalMode opcode that will following
+    ** the OP_Function opcode that invoked this function. */
     sqlite3BtreeSecureDelete(aNew->pBt,
                              sqlite3BtreeSecureDelete(db->aDb[0].pBt,-1) );
   }
@@ -339,6 +340,16 @@ static void codeAttach(
     sqlite3VdbeChangeP5(v, (u8)(pFunc->nArg));
     sqlite3VdbeChangeP4(v, -1, (char *)pFunc, P4_FUNCDEF);
 
+    if( type==SQLITE_ATTACH ){
+      /* On an attach, also set the journal mode.  Note that
+      ** sqlite3VdbeUsesBtree() is not call here since the iDb index
+      ** will be out of range prior to the new database being attached.
+      ** The OP_JournalMode opcode will all sqlite3VdbeUsesBtree() for us.
+      */
+      sqlite3VdbeAddOp3(v, OP_JournalMode, db->nDb, regArgs+3, 
+                           db->dfltJournalMode);
+    }
+
     /* Code an OP_Expire. For an ATTACH statement, set P1 to true (expire this
     ** statement only). For DETACH, set it to false (expire all existing
     ** statements).
diff --git a/src/pragma.c b/src/pragma.c
index c3aaaf9b3..d98b68055 100644
--- a/src/pragma.c
+++ b/src/pragma.c
@@ -531,7 +531,8 @@ void sqlite3Pragma(
 
   /*
   **  PRAGMA [database.]journal_mode
-  **  PRAGMA [database.]journal_mode = (delete|persist|off|truncate|memory)
+  **  PRAGMA [database.]journal_mode =
+  **                      (delete|persist|off|truncate|memory|wal|off)
   */
   if( sqlite3StrICmp(zLeft,"journal_mode")==0 ){
     int eMode;                    /* One of the PAGER_JOURNALMODE_XXX symbols */
@@ -562,15 +563,14 @@ void sqlite3Pragma(
     }else{
       int ii;
 
-      if( pId2->n==0 && eMode!=PAGER_JOURNALMODE_WAL ){
-        /* This indicates that no database name was specified as part
-        ** of the PRAGMA command. In this case the journal-mode must be
-        ** set on all attached databases, as well as the main db file.
+      if( pId2->n==0 ){
+        /* When there is no database name before the "journal_mode" keyword
+        ** in the PRAGMA, then the journal-mode will be set on
+        ** all attached databases, as well as the main db file.
         **
         ** Also, the sqlite3.dfltJournalMode variable is set so that
         ** any subsequently attached databases also use the specified
-        ** journal mode. Except, the default journal mode is never set
-        ** to WAL.
+        ** journal mode.
         */
         db->dfltJournalMode = (u8)eMode;
       }
diff --git a/src/vdbe.c b/src/vdbe.c
index a5fe803f0..4e7cedb96 100644
--- a/src/vdbe.c
+++ b/src/vdbe.c
@@ -5227,7 +5227,25 @@ case OP_JournalMode: {    /* out2-prerelease */
        || eNew==PAGER_JOURNALMODE_QUERY
   );
   assert( pOp->p1>=0 && pOp->p1<db->nDb );
-  assert( (p->btreeMask & (1<<pOp->p1))!=0 );
+
+  /* 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
+  ** 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
+  ** yet been attached so that index is unavailable.  We have to wait
+  ** until runtime (now) to get the mutex on the newly attached database.
+  ** 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 ){
+    /* This occurs right after ATTACH.  Get a mutex on the newly ATTACHed
+    ** database. */
+    sqlite3VdbeUsesBtree(p, pOp->p1);
+    sqlite3VdbeMutexArrayEnter(p);
+  }
 
   pBt = db->aDb[pOp->p1].pBt;
   pPager = sqlite3BtreePager(pBt);
diff --git a/src/vdbeaux.c b/src/vdbeaux.c
index 9aeb50250..155a1ae89 100644
--- a/src/vdbeaux.c
+++ b/src/vdbeaux.c
@@ -950,6 +950,11 @@ 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.
 */
 void sqlite3VdbeUsesBtree(Vdbe *p, int i){
   int mask;