Fix a performance regression: Keep two btree masks in each prepared

statement; one for btrees used and another for btrees that require locks.
Only try to lock the btrees identified by the second mask.

FossilOrigin-Name: 614de91a504d2231009a9de1305e31fce1b1c5a6

src/btmutex.c

@@ -203,6 +203,14 @@ void sqlite3BtreeLeaveAll(sqlite3 *db){
   }
 }
 
+/*
+** Return true if a particular Btree requires a lock.  Return FALSE if
+** no lock is ever required since it is not sharable.
+*/
+int sqlite3BtreeSharable(Btree *p){
+  return p->sharable;
+}
+
 #ifndef NDEBUG
 /*
 ** Return true if the current thread holds the database connection

src/btree.h

@@ -212,6 +212,7 @@ void sqlite3BtreeCursorList(Btree*);
 #endif
 
 #if !defined(SQLITE_OMIT_SHARED_CACHE) && SQLITE_THREADSAFE
+  int sqlite3BtreeSharable(Btree*);
   void sqlite3BtreeLeave(Btree*);
   void sqlite3BtreeEnterCursor(BtCursor*);
   void sqlite3BtreeLeaveCursor(BtCursor*);
@@ -224,6 +225,7 @@ void sqlite3BtreeCursorList(Btree*);
 #endif
 #else
 
+# define sqlite3BtreeSharable(X) 0
 # define sqlite3BtreeLeave(X)
 # define sqlite3BtreeEnterCursor(X)
 # define sqlite3BtreeLeaveCursor(X)

src/vdbe.c

@@ -4645,8 +4645,6 @@ case OP_ParseSchema: {
     assert( iDb==1 || sqlite3BtreeHoldsMutex(db->aDb[iDb].pBt) );
   }
 #endif
-  assert( p->btreeMask == ~(yDbMask)0 );
-
 
   iDb = pOp->p1;
   assert( iDb>=0 && iDb<db->nDb );

src/vdbeInt.h

@@ -303,6 +303,7 @@ struct Vdbe {
   u8 isPrepareV2;         /* True if prepared with prepare_v2() */
   int nChange;            /* Number of db changes made since last reset */
   yDbMask btreeMask;      /* Bitmask of db->aDb[] entries referenced */
+  yDbMask lockMask;       /* Subset of btreeMask that requires a lock */
   int iStatement;         /* Statement number (or 0 if has not opened stmt) */
   int aCounter[3];        /* Counters used by sqlite3_stmt_status() */
 #ifndef SQLITE_OMIT_TRACE

src/vdbeaux.c

@@ -160,7 +160,8 @@ int sqlite3VdbeAddOp3(Vdbe *p, int op, int p1, int p2, int p3){
   if( op==OP_ParseSchema ){
     /* Any program that uses the OP_ParseSchema opcode needs to lock
     ** all btrees. */
-    p->btreeMask = ~(yDbMask)0;
+    int j;
+    for(j=0; j<p->db->nDb; j++) sqlite3VdbeUsesBtree(p, j);
   }
 #ifdef SQLITE_DEBUG
   pOp->zComment = 0;
@@ -958,6 +959,9 @@ void sqlite3VdbeUsesBtree(Vdbe *p, int i){
   assert( i>=0 && i<p->db->nDb && i<(int)sizeof(yDbMask)*8 );
   assert( i<(int)sizeof(p->btreeMask)*8 );
   p->btreeMask |= ((yDbMask)1)<<i;
+  if( i!=1 && sqlite3BtreeSharable(p->db->aDb[i].pBt) ){
+    p->lockMask |= ((yDbMask)1)<<i;
+  }
 }
 
 #if !defined(SQLITE_OMIT_SHARED_CACHE) && SQLITE_THREADSAFE>0
@@ -985,11 +989,15 @@ void sqlite3VdbeUsesBtree(Vdbe *p, int i){
 void sqlite3VdbeEnter(Vdbe *p){
   int i;
   yDbMask mask;
-  sqlite3 *db = p->db;
-  Db *aDb = db->aDb;
-  int nDb = db->nDb;
+  sqlite3 *db;
+  Db *aDb;
+  int nDb;
+  if( p->lockMask==0 ) return;  /* The common case */
+  db = p->db;
+  aDb = db->aDb;
+  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) ){
+    if( i!=1 && (mask & p->lockMask)!=0 && ALWAYS(aDb[i].pBt!=0) ){
       sqlite3BtreeEnter(aDb[i].pBt);
     }
   }
@@ -1003,12 +1011,15 @@ void sqlite3VdbeEnter(Vdbe *p){
 void sqlite3VdbeLeave(Vdbe *p){
   int i;
   yDbMask mask;
-  sqlite3 *db = p->db;
-  Db *aDb = db->aDb;
-  int nDb = db->nDb;
-
+  sqlite3 *db;
+  Db *aDb;
+  int nDb;
+  if( p->lockMask==0 ) return;  /* The common case */
+  db = p->db;
+  aDb = db->aDb;
+  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) ){
+    if( i!=1 && (mask & p->lockMask)!=0 && ALWAYS(aDb[i].pBt!=0) ){
       sqlite3BtreeLeave(aDb[i].pBt);
     }
   }