Index: src/attach.c
==================================================================
--- src/attach.c
+++ src/attach.c
@@ -135,10 +135,11 @@
   assert( pVfs );
   flags |= SQLITE_OPEN_MAIN_DB;
   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");
   }else if( rc==SQLITE_OK ){
     Pager *pPager;

Index: src/btmutex.c
==================================================================
--- src/btmutex.c
+++ src/btmutex.c
@@ -181,28 +181,39 @@
 ** Enter the mutexes in accending order by BtShared pointer address
 ** to avoid the possibility of deadlock when two threads with
 ** 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 sqlite3BtreeEnterAll(sqlite3 *db){
+  if( db->skipBtreeMutex==0 ) btreeEnterAll(db);
 }
-void sqlite3BtreeLeaveAll(sqlite3 *db){
+static void SQLITE_NOINLINE btreeLeaveAll(sqlite3 *db){
   int i;
   Btree *p;
   assert( sqlite3_mutex_held(db->mutex) );
   for(i=0; i<db->nDb; i++){
     p = db->aDb[i].pBt;
     if( p ) sqlite3BtreeLeave(p);
   }
 }
+void sqlite3BtreeLeaveAll(sqlite3 *db){
+  if( db->skipBtreeMutex==0 ) btreeLeaveAll(db);
+}
 
 #ifndef NDEBUG
 /*
 ** Return true if the current thread holds the database connection
 ** mutex and all required BtShared mutexes.

Index: src/sqliteInt.h
==================================================================
--- src/sqliteInt.h
+++ src/sqliteInt.h
@@ -1294,10 +1294,11 @@
   signed char nextAutovac;      /* Autovac setting after VACUUM if >=0 */
   u8 suppressErr;               /* Do not issue error messages if true */
   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() */
   int nTotalChange;             /* Value returned by sqlite3_total_changes() */
   int aLimit[SQLITE_N_LIMIT];   /* Limits */