Index: src/btmutex.c
==================================================================
--- src/btmutex.c
+++ src/btmutex.c
@@ -200,10 +200,18 @@
   for(i=0; i<db->nDb; i++){
     p = db->aDb[i].pBt;
     if( p ) sqlite3BtreeLeave(p);
   }
 }
+
+/*
+** 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
 ** mutex and all required BtShared mutexes.

Index: src/btree.h
==================================================================
--- src/btree.h
+++ src/btree.h
@@ -210,10 +210,11 @@
 # define sqlite3BtreeEnter(X) 
 # define sqlite3BtreeEnterAll(X)
 #endif
 
 #if !defined(SQLITE_OMIT_SHARED_CACHE) && SQLITE_THREADSAFE
+  int sqlite3BtreeSharable(Btree*);
   void sqlite3BtreeLeave(Btree*);
   void sqlite3BtreeEnterCursor(BtCursor*);
   void sqlite3BtreeLeaveCursor(BtCursor*);
   void sqlite3BtreeLeaveAll(sqlite3*);
 #ifndef NDEBUG
@@ -222,10 +223,11 @@
   int sqlite3BtreeHoldsAllMutexes(sqlite3*);
   int sqlite3SchemaMutexHeld(sqlite3*,int,Schema*);
 #endif
 #else
 
+# define sqlite3BtreeSharable(X) 0
 # define sqlite3BtreeLeave(X)
 # define sqlite3BtreeEnterCursor(X)
 # define sqlite3BtreeLeaveCursor(X)
 # define sqlite3BtreeLeaveAll(X)
 

Index: src/vdbe.c
==================================================================
--- src/vdbe.c
+++ src/vdbe.c
@@ -4643,12 +4643,10 @@
 #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 );
   assert( DbHasProperty(db, iDb, DB_SchemaLoaded) );
   /* Used to be a conditional */ {

Index: src/vdbeInt.h
==================================================================
--- src/vdbeInt.h
+++ src/vdbeInt.h
@@ -301,10 +301,11 @@
   u8 usesStmtJournal;     /* True if uses a statement journal */
   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 */
   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
   i64 startTime;          /* Time when query started - used for profiling */
 #endif

Index: src/vdbeaux.c
==================================================================
--- src/vdbeaux.c
+++ src/vdbeaux.c
@@ -158,11 +158,12 @@
   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;
+    int j;
+    for(j=0; j<p->db->nDb; j++) sqlite3VdbeUsesBtree(p, j);
   }
 #ifdef SQLITE_DEBUG
   pOp->zComment = 0;
   if( sqlite3VdbeAddopTrace ) sqlite3VdbePrintOp(0, i, &p->aOp[i]);
 #endif
@@ -956,10 +957,13 @@
 */
 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
 /*
 ** If SQLite is compiled to support shared-cache mode and to be threadsafe,
@@ -983,15 +987,19 @@
 ** be a problem.
 */
 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);
     }
   }
 }
 #endif
@@ -1001,16 +1009,19 @@
 ** Unlock all of the btrees previously locked by a call to sqlite3VdbeEnter().
 */
 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);
     }
   }
 }
 #endif