Automatically close ephemeral b-trees when their last cursor is closed.

FossilOrigin-Name: 39b5af18c0580c8e92516d410f8c465bfec31b2d0be9df1cfd6a1d1a19b4fc14

src/btree.c

@@ -2742,6 +2742,7 @@ int sqlite3BtreeClose(Btree *p){
   /* Close all cursors opened via this handle.  */
   assert( sqlite3_mutex_held(p->db->mutex) );
   sqlite3BtreeEnter(p);
+  pBt->openFlags &= ~BTREE_SINGLE;
   pCur = pBt->pCursor;
   while( pCur ){
     BtCursor *pTmp = pCur;
@@ -4541,7 +4542,14 @@ int sqlite3BtreeCloseCursor(BtCursor *pCur){
     unlockBtreeIfUnused(pBt);
     sqlite3_free(pCur->aOverflow);
     sqlite3_free(pCur->pKey);
-    sqlite3BtreeLeave(pBtree);
+    if( (pBt->openFlags & BTREE_SINGLE) && pBt->pCursor==0 ){
+      /* Since the BtShared is not sharable, there is no need to
+      ** worry about the missing sqlite3BtreeLeave() call here.  */
+      assert( pBtree->sharable==0 );
+      sqlite3BtreeClose(pBtree);
+    }else{
+      sqlite3BtreeLeave(pBtree);
+    }
     pCur->pBtree = 0;
   }
   return SQLITE_OK;
@@ -10705,14 +10713,6 @@ int sqlite3BtreeIsReadonly(Btree *p){
 */
 int sqlite3HeaderSizeBtree(void){ return ROUND8(sizeof(MemPage)); }
 
-/*
-** Return the Btree object used to open the cursor provided as an
-** argument.
-*/
-Btree *sqlite3BtreeGetBtree(BtCursor *pCsr){
-  return pCsr->pBtree;
-}
-
 #if !defined(SQLITE_OMIT_SHARED_CACHE)
 /*
 ** Return true if the Btree passed as the only argument is sharable.