Index: src/analyze.c
==================================================================
--- src/analyze.c
+++ src/analyze.c
@@ -1852,13 +1852,13 @@
   }
 
   /* Load the statistics from the sqlite_stat4 table. */
 #ifdef SQLITE_ENABLE_STAT4
   if( rc==SQLITE_OK ){
-    db->lookaside.bDisable++;
+    DisableLookaside;
     rc = loadStat4(db, sInfo.zDatabase);
-    db->lookaside.bDisable--;
+    EnableLookaside;
   }
   for(i=sqliteHashFirst(&pSchema->idxHash); i; i=sqliteHashNext(i)){
     Index *pIdx = sqliteHashData(i);
     sqlite3_free(pIdx->aiRowEst);
     pIdx->aiRowEst = 0;

Index: src/build.c
==================================================================
--- src/build.c
+++ src/build.c
@@ -2445,11 +2445,11 @@
     pParse->eParseMode = PARSE_MODE_NORMAL;
 #endif
     n = pParse->nTab;
     sqlite3SrcListAssignCursors(pParse, pSel->pSrc);
     pTable->nCol = -1;
-    db->lookaside.bDisable++;
+    DisableLookaside;
 #ifndef SQLITE_OMIT_AUTHORIZATION
     xAuth = db->xAuth;
     db->xAuth = 0;
     pSelTab = sqlite3ResultSetOfSelect(pParse, pSel, SQLITE_AFF_NONE);
     db->xAuth = xAuth;
@@ -2487,11 +2487,11 @@
       pTable->nCol = 0;
       nErr++;
     }
     sqlite3DeleteTable(db, pSelTab);
     sqlite3SelectDelete(db, pSel);
-    db->lookaside.bDisable--;
+    EnableLookaside;
 #ifndef SQLITE_OMIT_ALTERTABLE
     pParse->eParseMode = eParseMode;
 #endif
   } else {
     nErr++;

Index: src/fkey.c
==================================================================
--- src/fkey.c
+++ src/fkey.c
@@ -1297,11 +1297,11 @@
       );
       pWhere = 0;
     }
 
     /* Disable lookaside memory allocation */
-    db->lookaside.bDisable++;
+    DisableLookaside;
 
     pTrigger = (Trigger *)sqlite3DbMallocZero(db, 
         sizeof(Trigger) +         /* struct Trigger */
         sizeof(TriggerStep) +     /* Single step in trigger program */
         nFrom + 1                 /* Space for pStep->zTarget */
@@ -1319,11 +1319,11 @@
         pTrigger->pWhen = sqlite3ExprDup(db, pWhen, EXPRDUP_REDUCE);
       }
     }
 
     /* Re-enable the lookaside buffer, if it was disabled earlier. */
-    db->lookaside.bDisable--;
+    EnableLookaside;
 
     sqlite3ExprDelete(db, pWhere);
     sqlite3ExprDelete(db, pWhen);
     sqlite3ExprListDelete(db, pList);
     sqlite3SelectDelete(db, pSelect);

Index: src/main.c
==================================================================
--- src/main.c
+++ src/main.c
@@ -713,10 +713,11 @@
   }
   db->lookaside.pStart = pStart;
   db->lookaside.pInit = 0;
   db->lookaside.pFree = 0;
   db->lookaside.sz = (u16)sz;
+  db->lookaside.szTrue = (u16)sz;
   if( pStart ){
     int i;
     LookasideSlot *p;
     assert( sz > (int)sizeof(LookasideSlot*) );
     db->lookaside.nSlot = cnt;
@@ -731,10 +732,11 @@
     db->lookaside.bMalloced = pBuf==0 ?1:0;
   }else{
     db->lookaside.pStart = db;
     db->lookaside.pEnd = db;
     db->lookaside.bDisable = 1;
+    db->lookaside.sz = 0;
     db->lookaside.bMalloced = 0;
     db->lookaside.nSlot = 0;
   }
 #endif /* SQLITE_OMIT_LOOKASIDE */
   return SQLITE_OK;
@@ -3062,10 +3064,11 @@
   db->errMask = 0xff;
   db->nDb = 2;
   db->magic = SQLITE_MAGIC_BUSY;
   db->aDb = db->aDbStatic;
   db->lookaside.bDisable = 1;
+  db->lookaside.sz = 0;
 
   assert( sizeof(db->aLimit)==sizeof(aHardLimit) );
   memcpy(db->aLimit, aHardLimit, sizeof(db->aLimit));
   db->aLimit[SQLITE_LIMIT_WORKER_THREADS] = SQLITE_DEFAULT_WORKER_THREADS;
   db->autoCommit = 1;

Index: src/malloc.c
==================================================================
--- src/malloc.c
+++ src/malloc.c
@@ -296,11 +296,11 @@
     }
 #endif
     return sqlite3GlobalConfig.m.xSize(p);
   }else{
     assert( sqlite3_mutex_held(db->mutex) );
-    return db->lookaside.sz;
+    return db->lookaside.szTrue;
   }
 }
 sqlite3_uint64 sqlite3_msize(void *p){
   assert( sqlite3MemdebugNoType(p, (u8)~MEMTYPE_HEAP) );
   assert( sqlite3MemdebugHasType(p, MEMTYPE_HEAP) );
@@ -348,11 +348,11 @@
     }
     if( isLookaside(db, p) ){
       LookasideSlot *pBuf = (LookasideSlot*)p;
 #ifdef SQLITE_DEBUG
       /* Trash all content in the buffer being freed */
-      memset(p, 0xaa, db->lookaside.sz);
+      memset(p, 0xaa, db->lookaside.szTrue);
 #endif
       pBuf->pNext = db->lookaside.pFree;
       db->lookaside.pFree = pBuf;
       return;
     }
@@ -508,27 +508,25 @@
 #ifndef SQLITE_OMIT_LOOKASIDE
   LookasideSlot *pBuf;
   assert( db!=0 );
   assert( sqlite3_mutex_held(db->mutex) );
   assert( db->pnBytesFreed==0 );
-  if( db->lookaside.bDisable==0 ){
-    assert( db->mallocFailed==0 );
-    if( n>db->lookaside.sz ){
-      db->lookaside.anStat[1]++;
-    }else if( (pBuf = db->lookaside.pFree)!=0 ){
-      db->lookaside.pFree = pBuf->pNext;
-      db->lookaside.anStat[0]++;
-      return (void*)pBuf;
-    }else if( (pBuf = db->lookaside.pInit)!=0 ){
-      db->lookaside.pInit = pBuf->pNext;
-      db->lookaside.anStat[0]++;
-      return (void*)pBuf;
-    }else{
-      db->lookaside.anStat[2]++;
+  if( n>db->lookaside.sz ){
+    if( db->lookaside.bDisable ){
+      return db->mallocFailed ? 0 : dbMallocRawFinish(db, n);
     }
-  }else if( db->mallocFailed ){
-    return 0;
+    db->lookaside.anStat[1]++;
+  }else if( (pBuf = db->lookaside.pFree)!=0 ){
+    db->lookaside.pFree = pBuf->pNext;
+    db->lookaside.anStat[0]++;
+    return (void*)pBuf;
+  }else if( (pBuf = db->lookaside.pInit)!=0 ){
+    db->lookaside.pInit = pBuf->pNext;
+    db->lookaside.anStat[0]++;
+    return (void*)pBuf;
+  }else{
+    db->lookaside.anStat[2]++;
   }
 #else
   assert( db!=0 );
   assert( sqlite3_mutex_held(db->mutex) );
   assert( db->pnBytesFreed==0 );
@@ -548,11 +546,11 @@
 */
 void *sqlite3DbRealloc(sqlite3 *db, void *p, u64 n){
   assert( db!=0 );
   if( p==0 ) return sqlite3DbMallocRawNN(db, n);
   assert( sqlite3_mutex_held(db->mutex) );
-  if( isLookaside(db,p) && n<=db->lookaside.sz ) return p;
+  if( isLookaside(db,p) && n<=db->lookaside.szTrue ) return p;
   return dbReallocFinish(db, p, n);
 }
 static SQLITE_NOINLINE void *dbReallocFinish(sqlite3 *db, void *p, u64 n){
   void *pNew = 0;
   assert( db!=0 );
@@ -559,11 +557,11 @@
   assert( p!=0 );
   if( db->mallocFailed==0 ){
     if( isLookaside(db, p) ){
       pNew = sqlite3DbMallocRawNN(db, n);
       if( pNew ){
-        memcpy(pNew, p, db->lookaside.sz);
+        memcpy(pNew, p, db->lookaside.szTrue);
         sqlite3DbFree(db, p);
       }
     }else{
       assert( sqlite3MemdebugHasType(p, (MEMTYPE_LOOKASIDE|MEMTYPE_HEAP)) );
       assert( sqlite3MemdebugNoType(p, (u8)~(MEMTYPE_LOOKASIDE|MEMTYPE_HEAP)) );
@@ -658,11 +656,11 @@
   if( db->mallocFailed==0 && db->bBenignMalloc==0 ){
     db->mallocFailed = 1;
     if( db->nVdbeExec>0 ){
       db->u1.isInterrupted = 1;
     }
-    db->lookaside.bDisable++;
+    DisableLookaside;
     if( db->pParse ){
       db->pParse->rc = SQLITE_NOMEM_BKPT;
     }
   }
 }
@@ -677,11 +675,11 @@
 void sqlite3OomClear(sqlite3 *db){
   if( db->mallocFailed && db->nVdbeExec==0 ){
     db->mallocFailed = 0;
     db->u1.isInterrupted = 0;
     assert( db->lookaside.bDisable>0 );
-    db->lookaside.bDisable--;
+    EnableLookaside;
   }
 }
 
 /*
 ** Take actions at the end of an API call to indicate an OOM error

Index: src/parse.y
==================================================================
--- src/parse.y
+++ src/parse.y
@@ -104,12 +104,13 @@
 /*
 ** Disable lookaside memory allocation for objects that might be
 ** shared across database connections.
 */
 static void disableLookaside(Parse *pParse){
+  sqlite3 *db = pParse->db;
   pParse->disableLookaside++;
-  pParse->db->lookaside.bDisable++;
+  DisableLookaside;
 }
 
 } // end %include
 
 // Input is a single SQL command

Index: src/prepare.c
==================================================================
--- src/prepare.c
+++ src/prepare.c
@@ -525,10 +525,11 @@
   sqlite3DbFree(db, pParse->aLabel);
   sqlite3ExprListDelete(db, pParse->pConstExpr);
   if( db ){
     assert( db->lookaside.bDisable >= pParse->disableLookaside );
     db->lookaside.bDisable -= pParse->disableLookaside;
+    db->lookaside.sz = db->lookaside.bDisable ? 0 : db->lookaside.szTrue;
   }
   pParse->disableLookaside = 0;
 }
 
 /*
@@ -558,11 +559,11 @@
   /* For a long-term use prepared statement avoid the use of
   ** lookaside memory.
   */
   if( prepFlags & SQLITE_PREPARE_PERSISTENT ){
     sParse.disableLookaside++;
-    db->lookaside.bDisable++;
+    DisableLookaside;
   }
   sParse.disableVtab = (prepFlags & SQLITE_PREPARE_NO_VTAB)!=0;
 
   /* Check to verify that it is possible to get a read lock on all
   ** database schemas.  The inability to get a read lock indicates that

Index: src/sqliteInt.h
==================================================================
--- src/sqliteInt.h
+++ src/sqliteInt.h
@@ -1269,14 +1269,21 @@
 ** with a particular database connection.  Hence, schema information cannot
 ** be stored in lookaside because in shared cache mode the schema information
 ** is shared by multiple database connections.  Therefore, while parsing
 ** schema information, the Lookaside.bEnabled flag is cleared so that
 ** lookaside allocations are not used to construct the schema objects.
+**
+** New lookaside allocations are only allowed if bDisable==0.  When
+** bDisable is greater than zero, sz is set to zero which effectively
+** disables lookaside without adding a new test for the bDisable flag
+** in a performance-critical path.  sz should be set by to szTrue whenever
+** bDisable changes back to zero.
 */
 struct Lookaside {
   u32 bDisable;           /* Only operate the lookaside when zero */
   u16 sz;                 /* Size of each buffer in bytes */
+  u16 szTrue;             /* True value of sz, even if disabled */
   u8 bMalloced;           /* True if pStart obtained from sqlite3_malloc() */
   u32 nSlot;              /* Number of lookaside slots allocated */
   u32 anStat[3];          /* 0: hits.  1: size misses.  2: full misses */
   LookasideSlot *pInit;   /* List of buffers not previously used */
   LookasideSlot *pFree;   /* List of available buffers */
@@ -1284,10 +1291,14 @@
   void *pEnd;             /* First byte past end of available space */
 };
 struct LookasideSlot {
   LookasideSlot *pNext;    /* Next buffer in the list of free buffers */
 };
+
+#define DisableLookaside  db->lookaside.bDisable++;db->lookaside.sz=0
+#define EnableLookaside   db->lookaside.bDisable--;\
+   db->lookaside.sz=db->lookaside.bDisable?0:db->lookaside.szTrue
 
 /*
 ** A hash table for built-in function definitions.  (Application-defined
 ** functions use a regular table table from hash.h.)
 **