Index: src/analyze.c
==================================================================
--- src/analyze.c
+++ src/analyze.c
@@ -147,10 +147,11 @@
     return;
   }
   assert( sqlite3BtreeHoldsAllMutexes(db) );
   iDb = sqlite3SchemaToIndex(db, pTab->pSchema);
   assert( iDb>=0 );
+  assert( sqlite3SchemaMutexHeld(db, iDb, 0) );
 #ifndef SQLITE_OMIT_AUTHORIZATION
   if( sqlite3AuthCheck(pParse, SQLITE_ANALYZE, pTab->zName, 0,
       db->aDb[iDb].zName ) ){
     return;
   }
@@ -388,10 +389,11 @@
   sqlite3BeginWriteOperation(pParse, 0, iDb);
   iStatCur = pParse->nTab;
   pParse->nTab += 2;
   openStatTable(pParse, iDb, iStatCur, 0, 0);
   iMem = pParse->nMem+1;
+  assert( sqlite3SchemaMutexHeld(db, iDb, 0) );
   for(k=sqliteHashFirst(&pSchema->tblHash); k; k=sqliteHashNext(k)){
     Table *pTab = (Table*)sqliteHashData(k);
     analyzeOneTable(pParse, pTab, 0, iStatCur, iMem);
   }
   loadAnalysis(pParse, iDb);
@@ -598,13 +600,13 @@
   char *zSql;
   int rc;
 
   assert( iDb>=0 && iDb<db->nDb );
   assert( db->aDb[iDb].pBt!=0 );
-  assert( sqlite3BtreeHoldsMutex(db->aDb[iDb].pBt) );
 
   /* Clear any prior statistics */
+  assert( sqlite3SchemaMutexHeld(db, iDb, 0) );
   for(i=sqliteHashFirst(&db->aDb[iDb].pSchema->idxHash);i;i=sqliteHashNext(i)){
     Index *pIdx = sqliteHashData(i);
     sqlite3DefaultRowEst(pIdx);
     sqlite3DeleteIndexSamples(db, pIdx);
     pIdx->aSample = 0;

Index: src/attach.c
==================================================================
--- src/attach.c
+++ src/attach.c
@@ -198,11 +198,11 @@
     if( db->aDb[iDb].pBt ){
       sqlite3BtreeClose(db->aDb[iDb].pBt);
       db->aDb[iDb].pBt = 0;
       db->aDb[iDb].pSchema = 0;
     }
-    sqlite3ResetInternalSchema(db, 0);
+    sqlite3ResetInternalSchema(db, -1);
     db->nDb = iDb;
     if( rc==SQLITE_NOMEM || rc==SQLITE_IOERR_NOMEM ){
       db->mallocFailed = 1;
       sqlite3DbFree(db, zErrDyn);
       zErrDyn = sqlite3MPrintf(db, "out of memory");
@@ -270,11 +270,11 @@
   }
 
   sqlite3BtreeClose(pDb->pBt);
   pDb->pBt = 0;
   pDb->pSchema = 0;
-  sqlite3ResetInternalSchema(db, 0);
+  sqlite3ResetInternalSchema(db, -1);
   return;
 
 detach_error:
   sqlite3_result_error(context, zErr, -1);
 }

Index: src/backup.c
==================================================================
--- src/backup.c
+++ src/backup.c
@@ -399,11 +399,11 @@
      && (rc = sqlite3BtreeUpdateMeta(p->pDest,1,p->iDestSchema+1))==SQLITE_OK
     ){
       int nDestTruncate;
   
       if( p->pDestDb ){
-        sqlite3ResetInternalSchema(p->pDestDb, 0);
+        sqlite3ResetInternalSchema(p->pDestDb, -1);
       }
 
       /* Set nDestTruncate to the final number of pages in the destination
       ** database. The complication here is that the destination page
       ** size may be different to the source page size. 

Index: src/btmutex.c
==================================================================
--- src/btmutex.c
+++ src/btmutex.c
@@ -286,10 +286,35 @@
   }
   return 1;
 }
 #endif /* NDEBUG */
 
+#ifndef NDEBUG
+/*
+** Return true if the correct mutexes are held for accessing the
+** db->aDb[iDb].pSchema structure.  The mutexes required for schema
+** access are:
+**
+**   (1) The mutex on db
+**   (2) if iDb!=1, then the mutex on db->aDb[iDb].pBt.
+**
+** If pSchema is not NULL, then iDb is computed from pSchema and
+** db using sqlite3SchemaToIndex().
+*/
+int sqlite3SchemaMutexHeld(sqlite3 *db, int iDb, Schema *pSchema){
+  Btree *p;
+  assert( db!=0 );
+  if( pSchema ) iDb = sqlite3SchemaToIndex(db, pSchema);
+  assert( iDb>=0 && iDb<db->nDb );
+  if( !sqlite3_mutex_held(db->mutex) ) return 0;
+  if( iDb==1 ) return 1;
+  p = db->aDb[iDb].pBt;
+  assert( p!=0 );
+  return p->sharable==0 || p->locked==1;
+}
+#endif /* NDEBUG */
+
 #else /* SQLITE_THREADSAFE>0 above.  SQLITE_THREADSAFE==0 below */
 /*
 ** The following are special cases for mutex enter routines for use
 ** in single threaded applications that use shared cache.  Except for
 ** these two routines, all mutex operations are no-ops in that case and

Index: src/btree.h
==================================================================
--- src/btree.h
+++ src/btree.h
@@ -218,10 +218,11 @@
   void sqlite3BtreeLeaveAll(sqlite3*);
 #ifndef NDEBUG
   /* These routines are used inside assert() statements only. */
   int sqlite3BtreeHoldsMutex(Btree*);
   int sqlite3BtreeHoldsAllMutexes(sqlite3*);
+  int sqlite3SchemaMutexHeld(sqlite3*,int,Schema*);
   u32 sqlite3BtreeMutexCounter(Btree*);
 #endif
 #else
 
 # define sqlite3BtreeLeave(X)
@@ -230,9 +231,10 @@
 # define sqlite3BtreeLeaveCursor(X)
 # define sqlite3BtreeLeaveAll(X)
 
 # define sqlite3BtreeHoldsMutex(X) 1
 # define sqlite3BtreeHoldsAllMutexes(X) 1
+# define sqlite3BtreeSchemaMutexHeld(X,Y) 1
 #endif
 
 
 #endif /* _BTREE_H_ */

Index: src/build.c
==================================================================
--- src/build.c
+++ src/build.c
@@ -154,10 +154,11 @@
       for(iDb=0, mask=1; iDb<db->nDb; mask<<=1, iDb++){
         if( (mask & pParse->cookieMask)==0 ) continue;
         sqlite3VdbeUsesBtree(v, iDb);
         sqlite3VdbeAddOp2(v,OP_Transaction, iDb, (mask & pParse->writeMask)!=0);
         if( db->init.busy==0 ){
+          assert( sqlite3SchemaMutexHeld(db, iDb, 0) );
           sqlite3VdbeAddOp3(v, OP_VerifyCookie,
                             iDb, pParse->cookieValue[iDb],
                             db->aDb[iDb].pSchema->iGeneration);
         }
       }
@@ -269,13 +270,16 @@
   Table *p = 0;
   int i;
   int nName;
   assert( zName!=0 );
   nName = sqlite3Strlen30(zName);
+  /* All mutexes are required for schema access.  Make sure we hold them. */
+  assert( zDatabase!=0 || sqlite3BtreeHoldsAllMutexes(db) );
   for(i=OMIT_TEMPDB; i<db->nDb; i++){
     int j = (i<2) ? i^1 : i;   /* Search TEMP before MAIN */
     if( zDatabase!=0 && sqlite3StrICmp(zDatabase, db->aDb[j].zName) ) continue;
+    assert( sqlite3SchemaMutexHeld(db, j, 0) );
     p = sqlite3HashFind(&db->aDb[j].pSchema->tblHash, zName, nName);
     if( p ) break;
   }
   return p;
 }
@@ -331,15 +335,18 @@
 */
 Index *sqlite3FindIndex(sqlite3 *db, const char *zName, const char *zDb){
   Index *p = 0;
   int i;
   int nName = sqlite3Strlen30(zName);
+  /* All mutexes are required for schema access.  Make sure we hold them. */
+  assert( zDb!=0 || sqlite3BtreeHoldsAllMutexes(db) );
   for(i=OMIT_TEMPDB; i<db->nDb; i++){
     int j = (i<2) ? i^1 : i;  /* Search TEMP before MAIN */
     Schema *pSchema = db->aDb[j].pSchema;
     assert( pSchema );
     if( zDb && sqlite3StrICmp(zDb, db->aDb[j].zName) ) continue;
+    assert( sqlite3SchemaMutexHeld(db, j, 0) );
     p = sqlite3HashFind(&pSchema->idxHash, zName, nName);
     if( p ) break;
   }
   return p;
 }
@@ -362,12 +369,14 @@
 ** with the index.
 */
 void sqlite3UnlinkAndDeleteIndex(sqlite3 *db, int iDb, const char *zIdxName){
   Index *pIndex;
   int len;
-  Hash *pHash = &db->aDb[iDb].pSchema->idxHash;
+  Hash *pHash;
 
+  assert( sqlite3SchemaMutexHeld(db, iDb, 0) );
+  pHash = &db->aDb[iDb].pSchema->idxHash;
   len = sqlite3Strlen30(zIdxName);
   pIndex = sqlite3HashInsert(pHash, zIdxName, len, 0);
   if( ALWAYS(pIndex) ){
     if( pIndex->pTable->pIndex==pIndex ){
       pIndex->pTable->pIndex = pIndex->pNext;
@@ -391,30 +400,44 @@
 ** a single database.  This routine is called to reclaim memory
 ** before the database closes.  It is also called during a rollback
 ** if there were schema changes during the transaction or if a
 ** schema-cookie mismatch occurs.
 **
-** If iDb==0 then reset the internal schema tables for all database
-** files.  If iDb>=1 then reset the internal schema for only the
+** If iDb<0 then reset the internal schema tables for all database
+** files.  If iDb>=0 then reset the internal schema for only the
 ** single file indicated.
 */
 void sqlite3ResetInternalSchema(sqlite3 *db, int iDb){
   int i, j;
-  assert( iDb>=0 && iDb<db->nDb );
+  assert( iDb<db->nDb );
 
-  if( iDb==0 ){
-    sqlite3BtreeEnterAll(db);
+  if( iDb>=0 ){
+    /* Case 1:  Reset the single schema identified by iDb */
+    Db *pDb = &db->aDb[iDb];
+    assert( sqlite3SchemaMutexHeld(db, iDb, 0) );
+    if( ALWAYS(pDb->pSchema) ){
+      sqlite3SchemaClear(pDb->pSchema);
+    }
+    /* If any database other than TEMP is reset, then also reset TEMP
+    ** since TEMP might be holding triggers that reference tables in the
+    ** other database.
+    */
+    if( iDb!=1 && (pDb = &db->aDb[1])!=0 && ALWAYS(pDb->pSchema) ){
+      sqlite3SchemaClear(pDb->pSchema);
+    }
+    return;
   }
-  for(i=iDb; i<db->nDb; i++){
+  /* Case 2 (from here to the end): Reset all schemas for all attached
+  ** databases. */
+  assert( iDb<0 );
+  sqlite3BtreeEnterAll(db);
+  for(i=0; i<db->nDb; i++){
     Db *pDb = &db->aDb[i];
     if( pDb->pSchema ){
-      assert(i==1 || (pDb->pBt && sqlite3BtreeHoldsMutex(pDb->pBt)));
-      sqlite3SchemaFree(pDb->pSchema);
+      sqlite3SchemaClear(pDb->pSchema);
     }
-    if( iDb>0 ) return;
   }
-  assert( iDb==0 );
   db->flags &= ~SQLITE_InternChanges;
   sqlite3VtabUnlockList(db);
   sqlite3BtreeLeaveAll(db);
 
   /* If one or more of the auxiliary database files has been closed,
@@ -496,10 +519,11 @@
     if( !db || db->pnBytesFreed==0 ){
       char *zName = pIndex->zName; 
       TESTONLY ( Index *pOld = ) sqlite3HashInsert(
 	  &pIndex->pSchema->idxHash, zName, sqlite3Strlen30(zName), 0
       );
+      assert( db==0 || sqlite3SchemaMutexHeld(db, 0, pIndex->pSchema) );
       assert( pOld==pIndex || pOld==0 );
     }
     freeIndex(db, pIndex);
   }
 
@@ -530,10 +554,11 @@
   Db *pDb;
 
   assert( db!=0 );
   assert( iDb>=0 && iDb<db->nDb );
   assert( zTabName );
+  assert( sqlite3SchemaMutexHeld(db, iDb, 0) );
   testcase( zTabName[0]==0 );  /* Zero-length table names are allowed */
   pDb = &db->aDb[iDb];
   p = sqlite3HashInsert(&pDb->pSchema->tblHash, zTabName,
                         sqlite3Strlen30(zTabName),0);
   sqlite3DeleteTable(db, p);
@@ -814,10 +839,11 @@
   ** then record a pointer to this table in the main database structure
   ** so that INSERT can find the table easily.
   */
 #ifndef SQLITE_OMIT_AUTOINCREMENT
   if( !pParse->nested && strcmp(zName, "sqlite_sequence")==0 ){
+    assert( sqlite3SchemaMutexHeld(db, iDb, 0) );
     pTable->pSchema->pSeqTab = pTable;
   }
 #endif
 
   /* Begin generating the code that will insert the table record into
@@ -1274,10 +1300,11 @@
 */
 void sqlite3ChangeCookie(Parse *pParse, int iDb){
   int r1 = sqlite3GetTempReg(pParse);
   sqlite3 *db = pParse->db;
   Vdbe *v = pParse->pVdbe;
+  assert( sqlite3SchemaMutexHeld(db, iDb, 0) );
   sqlite3VdbeAddOp2(v, OP_Integer, db->aDb[iDb].pSchema->schema_cookie+1, r1);
   sqlite3VdbeAddOp3(v, OP_SetCookie, iDb, BTREE_SCHEMA_VERSION, r1);
   sqlite3ReleaseTempReg(pParse, r1);
 }
 
@@ -1576,10 +1603,11 @@
     /* Check to see if we need to create an sqlite_sequence table for
     ** keeping track of autoincrement keys.
     */
     if( p->tabFlags & TF_Autoincrement ){
       Db *pDb = &db->aDb[iDb];
+      assert( sqlite3SchemaMutexHeld(db, iDb, 0) );
       if( pDb->pSchema->pSeqTab==0 ){
         sqlite3NestedParse(pParse,
           "CREATE TABLE %Q.sqlite_sequence(name,seq)",
           pDb->zName
         );
@@ -1596,10 +1624,11 @@
   /* Add the table to the in-memory representation of the database.
   */
   if( db->init.busy ){
     Table *pOld;
     Schema *pSchema = p->pSchema;
+    assert( sqlite3SchemaMutexHeld(db, iDb, 0) );
     pOld = sqlite3HashInsert(&pSchema->tblHash, p->zName,
                              sqlite3Strlen30(p->zName),p);
     if( pOld ){
       assert( p==pOld );  /* Malloc must have failed inside HashInsert() */
       db->mallocFailed = 1;
@@ -1780,10 +1809,11 @@
       pTable->nCol = pSelTab->nCol;
       pTable->aCol = pSelTab->aCol;
       pSelTab->nCol = 0;
       pSelTab->aCol = 0;
       sqlite3DeleteTable(db, pSelTab);
+      assert( sqlite3SchemaMutexHeld(db, 0, pTable->pSchema) );
       pTable->pSchema->flags |= DB_UnresetViews;
     }else{
       pTable->nCol = 0;
       nErr++;
     }
@@ -1800,10 +1830,11 @@
 /*
 ** Clear the column names from every VIEW in database idx.
 */
 static void sqliteViewResetAll(sqlite3 *db, int idx){
   HashElem *i;
+  assert( sqlite3SchemaMutexHeld(db, idx, 0) );
   if( !DbHasProperty(db, idx, DB_UnresetViews) ) return;
   for(i=sqliteHashFirst(&db->aDb[idx].pSchema->tblHash); i;i=sqliteHashNext(i)){
     Table *pTab = sqliteHashData(i);
     if( pTab->pSelect ){
       sqliteDeleteColumnNames(db, pTab);
@@ -1833,14 +1864,17 @@
 ** We must continue looping until all tables and indices with
 ** rootpage==iFrom have been converted to have a rootpage of iTo
 ** in order to be certain that we got the right one.
 */
 #ifndef SQLITE_OMIT_AUTOVACUUM
-void sqlite3RootPageMoved(Db *pDb, int iFrom, int iTo){
+void sqlite3RootPageMoved(sqlite3 *db, int iDb, int iFrom, int iTo){
   HashElem *pElem;
   Hash *pHash;
+  Db *pDb;
 
+  assert( sqlite3SchemaMutexHeld(db, iDb, 0) );
+  pDb = &db->aDb[iDb];
   pHash = &pDb->pSchema->tblHash;
   for(pElem=sqliteHashFirst(pHash); pElem; pElem=sqliteHashNext(pElem)){
     Table *pTab = sqliteHashData(pElem);
     if( pTab->tnum==iFrom ){
       pTab->tnum = iTo;
@@ -2210,10 +2244,11 @@
   }
   pFKey->isDeferred = 0;
   pFKey->aAction[0] = (u8)(flags & 0xff);            /* ON DELETE action */
   pFKey->aAction[1] = (u8)((flags >> 8 ) & 0xff);    /* ON UPDATE action */
 
+  assert( sqlite3SchemaMutexHeld(db, 0, p->pSchema) );
   pNextTo = (FKey *)sqlite3HashInsert(&p->pSchema->fkeyHash, 
       pFKey->zTo, sqlite3Strlen30(pFKey->zTo), (void *)pFKey
   );
   if( pNextTo==pFKey ){
     db->mallocFailed = 1;
@@ -2565,10 +2600,11 @@
   pIndex->pTable = pTab;
   pIndex->nColumn = pList->nExpr;
   pIndex->onError = (u8)onError;
   pIndex->autoIndex = (u8)(pName==0);
   pIndex->pSchema = db->aDb[iDb].pSchema;
+  assert( sqlite3SchemaMutexHeld(db, iDb, 0) );
 
   /* Check to see if we should honor DESC requests on index columns
   */
   if( pDb->pSchema->file_format>=4 ){
     sortOrderMask = -1;   /* Honor DESC */
@@ -2694,10 +2730,11 @@
   /* Link the new Index structure to its table and to the other
   ** in-memory database structures. 
   */
   if( db->init.busy ){
     Index *p;
+    assert( sqlite3SchemaMutexHeld(db, 0, pIndex->pSchema) );
     p = sqlite3HashInsert(&pIndex->pSchema->idxHash, 
                           pIndex->zName, sqlite3Strlen30(pIndex->zName),
                           pIndex);
     if( p ){
       assert( p==pIndex );  /* Malloc must have failed */
@@ -3447,10 +3484,11 @@
     yDbMask mask;
 
     assert( iDb<db->nDb );
     assert( db->aDb[iDb].pBt!=0 || iDb==1 );
     assert( iDb<SQLITE_MAX_ATTACHED+2 );
+    assert( sqlite3SchemaMutexHeld(db, iDb, 0) );
     mask = ((yDbMask)1)<<iDb;
     if( (pToplevel->cookieMask & mask)==0 ){
       pToplevel->cookieMask |= mask;
       pToplevel->cookieValue[iDb] = db->aDb[iDb].pSchema->schema_cookie;
       if( !OMIT_TEMPDB && iDb==1 ){
@@ -3574,10 +3612,11 @@
   int iDb;                    /* The database index number */
   sqlite3 *db = pParse->db;   /* The database connection */
   HashElem *k;                /* For looping over tables in pDb */
   Table *pTab;                /* A table in the database */
 
+  assert( sqlite3BtreeHoldsAllMutexes(db) );  /* Needed for schema access */
   for(iDb=0, pDb=db->aDb; iDb<db->nDb; iDb++, pDb++){
     assert( pDb!=0 );
     for(k=sqliteHashFirst(&pDb->pSchema->tblHash);  k; k=sqliteHashNext(k)){
       pTab = (Table*)sqliteHashData(k);
       reindexTable(pParse, pTab, zColl);

Index: src/callback.c
==================================================================
--- src/callback.c
+++ src/callback.c
@@ -398,16 +398,16 @@
 }
 
 /*
 ** Free all resources held by the schema structure. The void* argument points
 ** at a Schema struct. This function does not call sqlite3DbFree(db, ) on the 
-** pointer itself, it just cleans up subsiduary resources (i.e. the contents
+** pointer itself, it just cleans up subsidiary resources (i.e. the contents
 ** of the schema hash tables).
 **
 ** The Schema.cache_size variable is not cleared.
 */
-void sqlite3SchemaFree(void *p){
+void sqlite3SchemaClear(void *p){
   Hash temp1;
   Hash temp2;
   HashElem *pElem;
   Schema *pSchema = (Schema *)p;
 
@@ -438,11 +438,11 @@
 ** a new one if necessary.
 */
 Schema *sqlite3SchemaGet(sqlite3 *db, Btree *pBt){
   Schema * p;
   if( pBt ){
-    p = (Schema *)sqlite3BtreeSchema(pBt, sizeof(Schema), sqlite3SchemaFree);
+    p = (Schema *)sqlite3BtreeSchema(pBt, sizeof(Schema), sqlite3SchemaClear);
   }else{
     p = (Schema *)sqlite3DbMallocZero(0, sizeof(Schema));
   }
   if( !p ){
     db->mallocFailed = 1;

Index: src/fkey.c
==================================================================
--- src/fkey.c
+++ src/fkey.c
@@ -1152,10 +1152,11 @@
 */
 void sqlite3FkDelete(sqlite3 *db, Table *pTab){
   FKey *pFKey;                    /* Iterator variable */
   FKey *pNext;                    /* Copy of pFKey->pNextFrom */
 
+  assert( db==0 || sqlite3SchemaMutexHeld(db, 0, pTab->pSchema) );
   for(pFKey=pTab->pFKey; pFKey; pFKey=pNext){
 
     /* Remove the FK from the fkeyHash hash table. */
     if( !db || db->pnBytesFreed==0 ){
       if( pFKey->pPrevTo ){

Index: src/insert.c
==================================================================
--- src/insert.c
+++ src/insert.c
@@ -235,10 +235,11 @@
 
   assert( v );   /* We failed long ago if this is not so */
   for(p = pParse->pAinc; p; p = p->pNext){
     pDb = &db->aDb[p->iDb];
     memId = p->regCtr;
+    assert( sqlite3SchemaMutexHeld(db, 0, pDb->pSchema) );
     sqlite3OpenTable(pParse, 0, p->iDb, pDb->pSchema->pSeqTab, OP_OpenRead);
     addr = sqlite3VdbeCurrentAddr(v);
     sqlite3VdbeAddOp4(v, OP_String8, 0, memId-1, 0, p->pTab->zName, 0);
     sqlite3VdbeAddOp2(v, OP_Rewind, 0, addr+9);
     sqlite3VdbeAddOp3(v, OP_Column, 0, 0, memId);
@@ -285,10 +286,11 @@
     int j1, j2, j3, j4, j5;
     int iRec;
     int memId = p->regCtr;
 
     iRec = sqlite3GetTempReg(pParse);
+    assert( sqlite3SchemaMutexHeld(db, 0, pDb->pSchema) );
     sqlite3OpenTable(pParse, 0, p->iDb, pDb->pSchema->pSeqTab, OP_OpenWrite);
     j1 = sqlite3VdbeAddOp1(v, OP_NotNull, memId+1);
     j2 = sqlite3VdbeAddOp0(v, OP_Rewind);
     j3 = sqlite3VdbeAddOp3(v, OP_Column, 0, 0, iRec);
     j4 = sqlite3VdbeAddOp3(v, OP_Eq, memId-1, 0, iRec);

Index: src/main.c
==================================================================
--- src/main.c
+++ src/main.c
@@ -685,11 +685,12 @@
   if( !sqlite3SafetyCheckSickOrOk(db) ){
     return SQLITE_MISUSE_BKPT;
   }
   sqlite3_mutex_enter(db->mutex);
 
-  sqlite3ResetInternalSchema(db, 0);
+  /* Force xDestroy calls on all virtual tables */
+  sqlite3ResetInternalSchema(db, -1);
 
   /* If a transaction is open, the ResetInternalSchema() call above
   ** will not have called the xDisconnect() method on any virtual
   ** tables in the db->aVTrans[] array. The following sqlite3VtabRollback()
   ** call will do so. We need to do this before the check for active
@@ -728,11 +729,11 @@
       if( j!=1 ){
         pDb->pSchema = 0;
       }
     }
   }
-  sqlite3ResetInternalSchema(db, 0);
+  sqlite3ResetInternalSchema(db, -1);
 
   /* Tell the code in notify.c that the connection no longer holds any
   ** locks and does not require any further unlock-notify callbacks.
   */
   sqlite3ConnectionClosed(db);
@@ -819,11 +820,11 @@
   sqlite3VtabRollback(db);
   sqlite3EndBenignMalloc();
 
   if( db->flags&SQLITE_InternChanges ){
     sqlite3ExpirePreparedStatements(db);
-    sqlite3ResetInternalSchema(db, 0);
+    sqlite3ResetInternalSchema(db, -1);
   }
 
   /* Any deferred constraint violations have now been resolved. */
   db->nDeferredCons = 0;
 

Index: src/pragma.c
==================================================================
--- src/pragma.c
+++ src/pragma.c
@@ -113,11 +113,11 @@
         "from within a transaction");
       return SQLITE_ERROR;
     }
     sqlite3BtreeClose(db->aDb[1].pBt);
     db->aDb[1].pBt = 0;
-    sqlite3ResetInternalSchema(db, 0);
+    sqlite3ResetInternalSchema(db, -1);
   }
   return SQLITE_OK;
 }
 #endif /* SQLITE_PAGER_PRAGMAS */
 
@@ -386,10 +386,11 @@
     }else{
       int size = sqlite3AbsInt32(sqlite3Atoi(zRight));
       sqlite3BeginWriteOperation(pParse, 0, iDb);
       sqlite3VdbeAddOp2(v, OP_Integer, size, 1);
       sqlite3VdbeAddOp3(v, OP_SetCookie, iDb, BTREE_DEFAULT_CACHE_SIZE, 1);
+      assert( sqlite3SchemaMutexHeld(db, iDb, 0) );
       pDb->pSchema->cache_size = size;
       sqlite3BtreeSetCacheSize(pDb->pBt, pDb->pSchema->cache_size);
     }
   }else
 
@@ -688,10 +689,11 @@
   ** to its default value when the database is closed and reopened.
   ** N should be a positive integer.
   */
   if( sqlite3StrICmp(zLeft,"cache_size")==0 ){
     if( sqlite3ReadSchema(pParse) ) goto pragma_out;
+    assert( sqlite3SchemaMutexHeld(db, iDb, 0) );
     if( !zRight ){
       returnSingleInt(pParse, "cache_size", pDb->pSchema->cache_size);
     }else{
       int size = sqlite3AbsInt32(sqlite3Atoi(zRight));
       pDb->pSchema->cache_size = size;
@@ -1108,10 +1110,11 @@
       /* Do an integrity check of the B-Tree
       **
       ** Begin by filling registers 2, 3, ... with the root pages numbers
       ** for all tables and indices in the database.
       */
+      assert( sqlite3SchemaMutexHeld(db, iDb, 0) );
       pTbls = &db->aDb[i].pSchema->tblHash;
       for(x=sqliteHashFirst(pTbls); x; x=sqliteHashNext(x)){
         Table *pTab = sqliteHashData(x);
         Index *pIdx;
         sqlite3VdbeAddOp2(v, OP_Integer, pTab->tnum, 2+cnt);

Index: src/prepare.c
==================================================================
--- src/prepare.c
+++ src/prepare.c
@@ -336,11 +336,11 @@
     }
 #endif
   }
   if( db->mallocFailed ){
     rc = SQLITE_NOMEM;
-    sqlite3ResetInternalSchema(db, 0);
+    sqlite3ResetInternalSchema(db, -1);
   }
   if( rc==SQLITE_OK || (db->flags&SQLITE_RecoveryMode)){
     /* Black magic: If the SQLITE_RecoveryMode flag is set, then consider
     ** the schema loaded, even if errors occurred. In this situation the 
     ** current sqlite3_prepare() operation will fail, but the following one
@@ -468,11 +468,13 @@
 
     /* Read the schema cookie from the database. If it does not match the 
     ** value stored as part of the in-memory schema representation,
     ** set Parse.rc to SQLITE_SCHEMA. */
     sqlite3BtreeGetMeta(pBt, BTREE_SCHEMA_VERSION, (u32 *)&cookie);
+    assert( sqlite3SchemaMutexHeld(db, iDb, 0) );
     if( cookie!=db->aDb[iDb].pSchema->schema_cookie ){
+      sqlite3ResetInternalSchema(db, iDb);
       pParse->rc = SQLITE_SCHEMA;
     }
 
     /* Close the transaction, if one was opened. */
     if( openedTransaction ){
@@ -610,13 +612,10 @@
   }
   if( pParse->rc==SQLITE_DONE ) pParse->rc = SQLITE_OK;
   if( pParse->checkSchema ){
     schemaIsValid(pParse);
   }
-  if( pParse->rc==SQLITE_SCHEMA ){
-    sqlite3ResetInternalSchema(db, 0);
-  }
   if( db->mallocFailed ){
     pParse->rc = SQLITE_NOMEM;
   }
   if( pzTail ){
     *pzTail = pParse->zTail;

Index: src/sqliteInt.h
==================================================================
--- src/sqliteInt.h
+++ src/sqliteInt.h
@@ -666,10 +666,24 @@
   Schema *pSchema;     /* Pointer to database schema (possibly shared) */
 };
 
 /*
 ** An instance of the following structure stores a database schema.
+**
+** Most Schema objects are associated with a Btree.  The exception is
+** the Schema for the TEMP databaes (sqlite3.aDb[1]) which is free-standing.
+** In shared cache mode, a single Schema object can be shared by multiple
+** Btrees that refer to the same underlying BtShared object.
+** 
+** Schema objects are automatically deallocated when the last Btree that
+** references them is destroyed.   The TEMP Schema is manually freed by
+** sqlite3_close().
+*
+** A thread must be holding a mutex on the corresponding Btree in order
+** to access Schema content.  This implies that the thread must also be
+** holding a mutex on the sqlite3 connection pointer that owns the Btree.
+** For a TEMP Schema, on the connection mutex is required.
 */
 struct Schema {
   int schema_cookie;   /* Database schema version number for this file */
   int iGeneration;     /* Generation counter.  Incremented with each change */
   Hash tblHash;        /* All tables indexed by name */
@@ -1182,11 +1196,11 @@
 ** implementation. sqlite3_vtab* handles can not be shared between 
 ** database connections, even when the rest of the in-memory database 
 ** schema is shared, as the implementation often stores the database
 ** connection handle passed to it via the xConnect() or xCreate() method
 ** during initialization internally. This database connection handle may
-** then used by the virtual table implementation to access real tables 
+** then be used by the virtual table implementation to access real tables 
 ** within the database. So that they appear as part of the callers 
 ** transaction, these accesses need to be made via the same database 
 ** connection as that used to execute SQL operations on the virtual table.
 **
 ** All VTable objects that correspond to a single table in a shared
@@ -2940,11 +2954,11 @@
 extern SQLITE_WSD FuncDefHash sqlite3GlobalFunctions;
 #ifndef SQLITE_OMIT_WSD
 extern int sqlite3PendingByte;
 #endif
 #endif
-void sqlite3RootPageMoved(Db*, int, int);
+void sqlite3RootPageMoved(sqlite3*, int, int, int);
 void sqlite3Reindex(Parse*, Token*, Token*);
 void sqlite3AlterFunctions(void);
 void sqlite3AlterRenameTable(Parse*, SrcList*, Token*);
 int sqlite3GetToken(const unsigned char *, int *);
 void sqlite3NestedParse(Parse*, const char*, ...);
@@ -2967,11 +2981,11 @@
 void sqlite3DeleteIndexSamples(sqlite3*,Index*);
 void sqlite3DefaultRowEst(Index*);
 void sqlite3RegisterLikeFunctions(sqlite3*, int);
 int sqlite3IsLikeFunction(sqlite3*,Expr*,int*,char*);
 void sqlite3MinimumFileFormat(Parse*, int, int);
-void sqlite3SchemaFree(void *);
+void sqlite3SchemaClear(void *);
 Schema *sqlite3SchemaGet(sqlite3 *, Btree *);
 int sqlite3SchemaToIndex(sqlite3 *db, Schema *);
 KeyInfo *sqlite3IndexKeyinfo(Parse *, Index *);
 int sqlite3CreateFunc(sqlite3 *, const char *, int, int, void *, 
   void (*)(sqlite3_context*,int,sqlite3_value **),

Index: src/status.c
==================================================================
--- src/status.c
+++ src/status.c
@@ -161,10 +161,11 @@
     */
     case SQLITE_DBSTATUS_SCHEMA_USED: {
       int i;                      /* Used to iterate through schemas */
       int nByte = 0;              /* Used to accumulate return value */
 
+      sqlite3BtreeEnterAll(db);
       db->pnBytesFreed = &nByte;
       for(i=0; i<db->nDb; i++){
         Schema *pSchema = db->aDb[i].pSchema;
         if( ALWAYS(pSchema!=0) ){
           HashElem *p;
@@ -187,10 +188,11 @@
             sqlite3DeleteTable(db, (Table *)sqliteHashData(p));
           }
         }
       }
       db->pnBytesFreed = 0;
+      sqlite3BtreeLeaveAll(db);
 
       *pHighwater = 0;
       *pCurrent = nByte;
       break;
     }

Index: src/trigger.c
==================================================================
--- src/trigger.c
+++ src/trigger.c
@@ -52,10 +52,11 @@
     return 0;
   }
 
   if( pTmpSchema!=pTab->pSchema ){
     HashElem *p;
+    assert( sqlite3SchemaMutexHeld(pParse->db, 0, pTmpSchema) );
     for(p=sqliteHashFirst(&pTmpSchema->trigHash); p; p=sqliteHashNext(p)){
       Trigger *pTrig = (Trigger *)sqliteHashData(p);
       if( pTrig->pTabSchema==pTab->pSchema
        && 0==sqlite3StrICmp(pTrig->table, pTab->zName) 
       ){
@@ -163,10 +164,11 @@
   ** specified name exists */
   zName = sqlite3NameFromToken(db, pName);
   if( !zName || SQLITE_OK!=sqlite3CheckObjectName(pParse, zName) ){
     goto trigger_cleanup;
   }
+  assert( sqlite3SchemaMutexHeld(db, iDb, 0) );
   if( sqlite3HashFind(&(db->aDb[iDb].pSchema->trigHash),
                       zName, sqlite3Strlen30(zName)) ){
     if( !noErr ){
       sqlite3ErrorMsg(pParse, "trigger %T already exists", pName);
     }
@@ -302,10 +304,11 @@
   }
 
   if( db->init.busy ){
     Trigger *pLink = pTrig;
     Hash *pHash = &db->aDb[iDb].pSchema->trigHash;
+    assert( sqlite3SchemaMutexHeld(db, iDb, 0) );
     pTrig = sqlite3HashInsert(pHash, zName, sqlite3Strlen30(zName), pTrig);
     if( pTrig ){
       db->mallocFailed = 1;
     }else if( pLink->pSchema==pLink->pTabSchema ){
       Table *pTab;
@@ -483,13 +486,15 @@
 
   assert( pName->nSrc==1 );
   zDb = pName->a[0].zDatabase;
   zName = pName->a[0].zName;
   nName = sqlite3Strlen30(zName);
+  assert( zDb!=0 || sqlite3BtreeHoldsAllMutexes(db) );
   for(i=OMIT_TEMPDB; i<db->nDb; i++){
     int j = (i<2) ? i^1 : i;  /* Search TEMP before MAIN */
     if( zDb && sqlite3StrICmp(db->aDb[j].zName, zDb) ) continue;
+    assert( sqlite3SchemaMutexHeld(db, j, 0) );
     pTrigger = sqlite3HashFind(&(db->aDb[j].pSchema->trigHash), zName, nName);
     if( pTrigger ) break;
   }
   if( !pTrigger ){
     if( !noErr ){
@@ -574,12 +579,15 @@
 
 /*
 ** Remove a trigger from the hash tables of the sqlite* pointer.
 */
 void sqlite3UnlinkAndDeleteTrigger(sqlite3 *db, int iDb, const char *zName){
-  Hash *pHash = &(db->aDb[iDb].pSchema->trigHash);
   Trigger *pTrigger;
+  Hash *pHash;
+
+  assert( sqlite3SchemaMutexHeld(db, iDb, 0) );
+  pHash = &(db->aDb[iDb].pSchema->trigHash);
   pTrigger = sqlite3HashInsert(pHash, zName, sqlite3Strlen30(zName), 0);
   if( ALWAYS(pTrigger) ){
     if( pTrigger->pSchema==pTrigger->pTabSchema ){
       Table *pTab = tableOfTrigger(pTrigger);
       Trigger **pp;

Index: src/vacuum.c
==================================================================
--- src/vacuum.c
+++ src/vacuum.c
@@ -333,10 +333,13 @@
     sqlite3BtreeClose(pDb->pBt);
     pDb->pBt = 0;
     pDb->pSchema = 0;
   }
 
-  sqlite3ResetInternalSchema(db, 0);
+  /* This both clears the schemas and reduces the size of the db->aDb[]
+  ** array. */ 
+  sqlite3ResetInternalSchema(db, -1);
 
   return rc;
 }
+
 #endif  /* SQLITE_OMIT_VACUUM && SQLITE_OMIT_ATTACH */

Index: src/vdbe.c
==================================================================
--- src/vdbe.c
+++ src/vdbe.c
@@ -549,11 +549,11 @@
   int pc=0;                  /* The program counter */
   Op *aOp = p->aOp;          /* Copy of p->aOp */
   Op *pOp;                   /* Current operation */
   int rc = SQLITE_OK;        /* Value to return */
   sqlite3 *db = p->db;       /* The database */
-  u8 resetSchemaOnFault = 0; /* Reset schema after an error if true */
+  u8 resetSchemaOnFault = 0; /* Reset schema after an error if positive */
   u8 encoding = ENC(db);     /* The database encoding */
 #ifndef SQLITE_OMIT_PROGRESS_CALLBACK
   int checkProgress;         /* True if progress callbacks are enabled */
   int nProgressOps = 0;      /* Opcodes executed since progress callback. */
 #endif
@@ -2657,11 +2657,11 @@
             goto abort_due_to_error;
           }
         }
         if( p1==SAVEPOINT_ROLLBACK && (db->flags&SQLITE_InternChanges)!=0 ){
           sqlite3ExpirePreparedStatements(db);
-          sqlite3ResetInternalSchema(db, 0);
+          sqlite3ResetInternalSchema(db, -1);
           sqlite3VdbeMutexResync(p);
           db->flags = (db->flags | SQLITE_InternChanges);
         }
       }
   
@@ -2878,10 +2878,11 @@
   assert( pOp->p2<SQLITE_N_BTREE_META );
   assert( pOp->p1>=0 && pOp->p1<db->nDb );
   assert( (p->btreeMask & (((yDbMask)1)<<pOp->p1))!=0 );
   pDb = &db->aDb[pOp->p1];
   assert( pDb->pBt!=0 );
+  assert( sqlite3SchemaMutexHeld(db, pOp->p1, 0) );
   pIn3 = &aMem[pOp->p3];
   sqlite3VdbeMemIntegerify(pIn3);
   /* See note about index shifting on OP_ReadCookie */
   rc = sqlite3BtreeUpdateMeta(pDb->pBt, pOp->p2, (int)pIn3->u.i);
   if( pOp->p2==BTREE_SCHEMA_VERSION ){
@@ -2924,10 +2925,11 @@
   int iGen;
   Btree *pBt;
 
   assert( pOp->p1>=0 && pOp->p1<db->nDb );
   assert( (p->btreeMask & (((yDbMask)1)<<pOp->p1))!=0 );
+  assert( sqlite3SchemaMutexHeld(db, pOp->p1, 0) );
   pBt = db->aDb[pOp->p1].pBt;
   if( pBt ){
     sqlite3BtreeGetMeta(pBt, BTREE_SCHEMA_VERSION, (u32 *)&iMeta);
     iGen = db->aDb[pOp->p1].pSchema->iGeneration;
   }else{
@@ -2949,11 +2951,10 @@
     ** to be invalidated whenever sqlite3_step() is called from within 
     ** a v-table method.
     */
     if( db->aDb[pOp->p1].pSchema->schema_cookie!=iMeta ){
       sqlite3ResetInternalSchema(db, pOp->p1);
-      sqlite3VdbeMutexResync(p);
     }
 
     p->expired = 1;
     rc = SQLITE_SCHEMA;
   }
@@ -3034,10 +3035,11 @@
   pDb = &db->aDb[iDb];
   pX = pDb->pBt;
   assert( pX!=0 );
   if( pOp->opcode==OP_OpenWrite ){
     wrFlag = 1;
+    assert( sqlite3SchemaMutexHeld(db, iDb, 0) );
     if( pDb->pSchema->file_format < p->minWriteFileFormat ){
       p->minWriteFileFormat = pDb->pSchema->file_format;
     }
   }else{
     wrFlag = 0;
@@ -4529,12 +4531,14 @@
     rc = sqlite3BtreeDropTable(db->aDb[iDb].pBt, pOp->p1, &iMoved);
     pOut->flags = MEM_Int;
     pOut->u.i = iMoved;
 #ifndef SQLITE_OMIT_AUTOVACUUM
     if( rc==SQLITE_OK && iMoved!=0 ){
-      sqlite3RootPageMoved(&db->aDb[iDb], iMoved, pOp->p1);
-      resetSchemaOnFault = 1;
+      sqlite3RootPageMoved(db, iDb, iMoved, pOp->p1);
+      /* All OP_Destroy operations occur on the same btree */
+      assert( resetSchemaOnFault==0 || resetSchemaOnFault==iDb+1 );
+      resetSchemaOnFault = iDb+1;
     }
 #endif
   }
   break;
 }
@@ -5964,13 +5968,12 @@
   sqlite3_log(rc, "statement aborts at %d: [%s] %s", 
                    pc, p->zSql, p->zErrMsg);
   sqlite3VdbeHalt(p);
   if( rc==SQLITE_IOERR_NOMEM ) db->mallocFailed = 1;
   rc = SQLITE_ERROR;
-  if( resetSchemaOnFault ){
-    sqlite3ResetInternalSchema(db, 0);
-    sqlite3VdbeMutexResync(p);
+  if( resetSchemaOnFault>0 ){
+    sqlite3ResetInternalSchema(db, resetSchemaOnFault-1);
   }
 
   /* This is the only way out of this procedure.  We have to
   ** release the mutexes on btrees that were acquired at the
   ** top. */

Index: src/vdbeaux.c
==================================================================
--- src/vdbeaux.c
+++ src/vdbeaux.c
@@ -2276,11 +2276,11 @@
       p->nChange = 0;
     }
   
     /* Rollback or commit any schema changes that occurred. */
     if( p->rc!=SQLITE_OK && db->flags&SQLITE_InternChanges ){
-      sqlite3ResetInternalSchema(db, 0);
+      sqlite3ResetInternalSchema(db, -1);
       db->flags = (db->flags | SQLITE_InternChanges);
     }
 
     /* Release the locks */
     sqlite3VdbeMutexResync(p);

Index: src/vtab.c
==================================================================
--- src/vtab.c
+++ src/vtab.c
@@ -46,11 +46,11 @@
     }
     sqlite3DbFree(db, pDel);
     if( pDel==pMod ){
       db->mallocFailed = 1;
     }
-    sqlite3ResetInternalSchema(db, 0);
+    sqlite3ResetInternalSchema(db, -1);
   }else if( xDestroy ){
     xDestroy(pAux);
   }
   rc = sqlite3ApiExit(db, SQLITE_OK);
   sqlite3_mutex_leave(db->mutex);
@@ -143,14 +143,13 @@
 
   /* Assert that the mutex (if any) associated with the BtShared database 
   ** that contains table p is held by the caller. See header comments 
   ** above function sqlite3VtabUnlockList() for an explanation of why
   ** this makes it safe to access the sqlite3.pDisconnect list of any
-  ** database connection that may have an entry in the p->pVTable list.  */
-  assert( db==0 ||
-    sqlite3BtreeHoldsMutex(db->aDb[sqlite3SchemaToIndex(db, p->pSchema)].pBt) 
-  );
+  ** database connection that may have an entry in the p->pVTable list.
+  */
+  assert( db==0 || sqlite3SchemaMutexHeld(db, 0, p->pSchema) );
 
   while( pVTable ){
     sqlite3 *db2 = pVTable->db;
     VTable *pNext = pVTable->pNext;
     assert( db2 );
@@ -385,10 +384,11 @@
   else {
     Table *pOld;
     Schema *pSchema = pTab->pSchema;
     const char *zName = pTab->zName;
     int nName = sqlite3Strlen30(zName);
+    assert( sqlite3SchemaMutexHeld(db, 0, pSchema) );
     pOld = sqlite3HashInsert(&pSchema->tblHash, zName, nName, pTab);
     if( pOld ){
       db->mallocFailed = 1;
       assert( pTab==pOld );  /* Malloc must have failed inside HashInsert() */
       return;