3 files changed, 17 insertions, 3 deletions
diff --git a/src/btree.c b/src/btree.c
index cbf93d222..c02f070e0 100644
--- a/src/btree.c
+++ b/src/btree.c
@@ -3278,8 +3278,8 @@ int sqlite3BtreeSavepoint(Btree *p, int op, int iSavepoint){
 ** root page of a b-tree.  If it is not, then the cursor acquired
 ** will not work correctly.
 **
-** It is assumed that the sqlite3BtreeCursorSize() bytes of memory 
-** pointed to by pCur have been zeroed by the caller.
+** It is assumed that the sqlite3BtreeCursorZero() has been called
+** on pCur to initialize the memory space prior to invoking this routine.
 */
 static int btreeCursor(
   Btree *p,                              /* The btree */
@@ -3356,6 +3356,18 @@ int sqlite3BtreeCursorSize(void){
 }
 
 /*
+** Initialize memory that will be converted into a BtCursor object.
+**
+** The simple approach here would be to memset() the entire object
+** to zero.  But it turns out that the apPage[] and aiIdx[] arrays
+** do not need to be zeroed and they are large, so we can save a lot
+** of run-time by skipping the initialization of those elements.
+*/
+void sqlite3BtreeCursorZero(BtCursor *p){
+  memset(p, 0, offsetof(BtCursor, iPage));
+}
+
+/*
 ** Set the cached rowid value of every cursor in the same database file
 ** as pCur and having the same root page number as pCur.  The value is
 ** set to iRowid.
diff --git a/src/btree.h b/src/btree.h
index 93de4d1c3..7852d4ae6 100644
--- a/src/btree.h
+++ b/src/btree.h
@@ -148,6 +148,7 @@ int sqlite3BtreeCursor(
   BtCursor *pCursor                    /* Space to write cursor structure */
 );
 int sqlite3BtreeCursorSize(void);
+void sqlite3BtreeCursorZero(BtCursor*);
 
 int sqlite3BtreeCloseCursor(BtCursor*);
 int sqlite3BtreeMovetoUnpacked(
diff --git a/src/vdbe.c b/src/vdbe.c
index 4ea20b752..90dd90e67 100644
--- a/src/vdbe.c
+++ b/src/vdbe.c
@@ -215,7 +215,7 @@ static VdbeCursor *allocateCursor(
   }
   if( SQLITE_OK==sqlite3VdbeMemGrow(pMem, nByte, 0) ){
     p->apCsr[iCur] = pCx = (VdbeCursor*)pMem->z;
-    memset(pCx, 0, nByte);
+    memset(pCx, 0, sizeof(VdbeCursor));
     pCx->iDb = iDb;
     pCx->nField = nField;
     if( nField ){
@@ -224,6 +224,7 @@ static VdbeCursor *allocateCursor(
     if( isBtreeCursor ){
       pCx->pCursor = (BtCursor*)
           &pMem->z[ROUND8(sizeof(VdbeCursor))+2*nField*sizeof(u32)];
+      sqlite3BtreeCursorZero(pCx->pCursor);
     }
   }
   return pCx;