3 files changed, 16 insertions, 3 deletions
diff --git a/src/attach.c b/src/attach.c
index 4fe97bace..393c46ccb 100644
--- a/src/attach.c
+++ b/src/attach.c
@@ -137,6 +137,7 @@ static void attachFunc(
   rc = sqlite3BtreeOpen(pVfs, zPath, db, &aNew->pBt, 0, flags);
   sqlite3_free( zPath );
   db->nDb++;
+  db->skipBtreeMutex = 0;
   if( rc==SQLITE_CONSTRAINT ){
     rc = SQLITE_ERROR;
     zErrDyn = sqlite3MPrintf(db, "database is already attached");
diff --git a/src/btmutex.c b/src/btmutex.c
index c1ebff960..ddffb67fa 100644
--- a/src/btmutex.c
+++ b/src/btmutex.c
@@ -183,16 +183,24 @@ int sqlite3BtreeHoldsMutex(Btree *p){
 ** two or more btrees in common both try to lock all their btrees
 ** at the same instant.
 */
-void sqlite3BtreeEnterAll(sqlite3 *db){
+static void SQLITE_NOINLINE btreeEnterAll(sqlite3 *db){
   int i;
+  int skipOk = 1;
   Btree *p;
   assert( sqlite3_mutex_held(db->mutex) );
   for(i=0; i<db->nDb; i++){
     p = db->aDb[i].pBt;
-    if( p ) sqlite3BtreeEnter(p);
+    if( p && p->sharable ){
+      sqlite3BtreeEnter(p);
+      skipOk = 0;
+    }
   }
+  db->skipBtreeMutex = skipOk;
 }
-void sqlite3BtreeLeaveAll(sqlite3 *db){
+void sqlite3BtreeEnterAll(sqlite3 *db){
+  if( db->skipBtreeMutex==0 ) btreeEnterAll(db);
+}
+static void SQLITE_NOINLINE btreeLeaveAll(sqlite3 *db){
   int i;
   Btree *p;
   assert( sqlite3_mutex_held(db->mutex) );
@@ -201,6 +209,9 @@ void sqlite3BtreeLeaveAll(sqlite3 *db){
     if( p ) sqlite3BtreeLeave(p);
   }
 }
+void sqlite3BtreeLeaveAll(sqlite3 *db){
+  if( db->skipBtreeMutex==0 ) btreeLeaveAll(db);
+}
 
 #ifndef NDEBUG
 /*
diff --git a/src/sqliteInt.h b/src/sqliteInt.h
index d78d2072d..6a01029b8 100644
--- a/src/sqliteInt.h
+++ b/src/sqliteInt.h
@@ -1296,6 +1296,7 @@ struct sqlite3 {
   u8 vtabOnConflict;            /* Value to return for s3_vtab_on_conflict() */
   u8 isTransactionSavepoint;    /* True if the outermost savepoint is a TS */
   u8 mTrace;                    /* zero or more SQLITE_TRACE flags */
+  u8 skipBtreeMutex;            /* True if no shared-cache backends */
   int nextPagesize;             /* Pagesize after VACUUM if >0 */
   u32 magic;                    /* Magic number for detect library misuse */
   int nChange;                  /* Value returned by sqlite3_changes() */