/ Check-in [2f3376eb]
Login
SQLite training in Houston TX on 2019-11-05 (details)
Part of the 2019 Tcl Conference

Many hyperlinks are disabled.
Use anonymous login to enable hyperlinks.

Overview
Comment:Delete the OP_VerifySchema opcode. Enhance OP_Transaction to do the schema version checks that OP_VerifySchema used to do.
Downloads: Tarball | ZIP archive | SQL archive
Timelines: family | ancestors | descendants | both | trunk
Files: files | file ages | folders
SHA1: 2f3376ebf13df44e6acf27cb1f07172cd8b34033
User & Date: drh 2014-02-06 23:56:27
Context
2014-02-07
02:29
Update comments in vdbe.c. No changes to code. check-in: 1122b410 user: drh tags: trunk
2014-02-06
23:56
Delete the OP_VerifySchema opcode. Enhance OP_Transaction to do the schema version checks that OP_VerifySchema used to do. check-in: 2f3376eb user: drh tags: trunk
13:18
Change the spellfix1 virtual table to deterministically names its shadow tables. check-in: 5219cdfc user: drh tags: trunk
Changes
Hide Diffs Unified Diffs Ignore Whitespace Patch

Changes to src/alter.c.

465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
    pVTab = sqlite3GetVTable(db, pTab);
    if( pVTab->pVtab->pModule->xRename==0 ){
      pVTab = 0;
    }
  }
#endif

  /* Begin a transaction and code the VerifyCookie for database iDb. 
  ** Then modify the schema cookie (since the ALTER TABLE modifies the
  ** schema). Open a statement transaction if the table is a virtual
  ** table.
  */
  v = sqlite3GetVdbe(pParse);
  if( v==0 ){
    goto exit_rename_table;







|







465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
    pVTab = sqlite3GetVTable(db, pTab);
    if( pVTab->pVtab->pModule->xRename==0 ){
      pVTab = 0;
    }
  }
#endif

  /* Begin a transaction for database iDb. 
  ** Then modify the schema cookie (since the ALTER TABLE modifies the
  ** schema). Open a statement transaction if the table is a virtual
  ** table.
  */
  v = sqlite3GetVdbe(pParse);
  if( v==0 ){
    goto exit_rename_table;

Changes to src/build.c.

152
153
154
155
156
157
158
159
160
161
162
163
164
165


166
167
168
169
170
171
172
    if( pParse->cookieGoto>0 ){
      yDbMask mask;
      int iDb, i, addr;
      sqlite3VdbeJumpHere(v, pParse->cookieGoto-1);
      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);
        }


      }
#ifndef SQLITE_OMIT_VIRTUALTABLE
      for(i=0; i<pParse->nVtabLock; i++){
        char *vtab = (char *)sqlite3GetVTable(db, pParse->apVtabLock[i]);
        sqlite3VdbeAddOp4(v, OP_VBegin, 0, 0, 0, vtab, P4_VTAB);
      }
      pParse->nVtabLock = 0;







|
|
|
|
|
|
<
>
>







152
153
154
155
156
157
158
159
160
161
162
163
164

165
166
167
168
169
170
171
172
173
    if( pParse->cookieGoto>0 ){
      yDbMask mask;
      int iDb, i, addr;
      sqlite3VdbeJumpHere(v, pParse->cookieGoto-1);
      for(iDb=0, mask=1; iDb<db->nDb; mask<<=1, iDb++){
        if( (mask & pParse->cookieMask)==0 ) continue;
        sqlite3VdbeUsesBtree(v, iDb);
        sqlite3VdbeAddOp4Int(v,
          OP_Transaction,                    /* Opcode */
          iDb,                               /* P1 */
          (mask & pParse->writeMask)!=0,     /* P2 */
          pParse->cookieValue[iDb],          /* P3 */
          db->aDb[iDb].pSchema->iGeneration  /* P4 */

        );
        if( db->init.busy==0 ) sqlite3VdbeChangeP5(v, 1);
      }
#ifndef SQLITE_OMIT_VIRTUALTABLE
      for(i=0; i<pParse->nVtabLock; i++){
        char *vtab = (char *)sqlite3GetVTable(db, pParse->apVtabLock[i]);
        sqlite3VdbeAddOp4(v, OP_VBegin, 0, 0, 0, vtab, P4_VTAB);
      }
      pParse->nVtabLock = 0;

Changes to src/expr.c.

1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
    assert( p->pEList!=0 );             /* Because of isCandidateForInOpt(p) */
    assert( p->pEList->a[0].pExpr!=0 ); /* Because of isCandidateForInOpt(p) */
    assert( p->pSrc!=0 );               /* Because of isCandidateForInOpt(p) */
    pTab = p->pSrc->a[0].pTab;
    pExpr = p->pEList->a[0].pExpr;
    iCol = (i16)pExpr->iColumn;
   
    /* Code an OP_VerifyCookie and OP_TableLock for <table>. */
    iDb = sqlite3SchemaToIndex(db, pTab->pSchema);
    sqlite3CodeVerifySchema(pParse, iDb);
    sqlite3TableLock(pParse, iDb, pTab->tnum, 0, pTab->zName);

    /* This function is only called from two places. In both cases the vdbe
    ** has already been allocated. So assume sqlite3GetVdbe() is always
    ** successful here.







|







1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
    assert( p->pEList!=0 );             /* Because of isCandidateForInOpt(p) */
    assert( p->pEList->a[0].pExpr!=0 ); /* Because of isCandidateForInOpt(p) */
    assert( p->pSrc!=0 );               /* Because of isCandidateForInOpt(p) */
    pTab = p->pSrc->a[0].pTab;
    pExpr = p->pEList->a[0].pExpr;
    iCol = (i16)pExpr->iColumn;
   
    /* Code an OP_Transaction and OP_TableLock for <table>. */
    iDb = sqlite3SchemaToIndex(db, pTab->pSchema);
    sqlite3CodeVerifySchema(pParse, iDb);
    sqlite3TableLock(pParse, iDb, pTab->tnum, 0, pTab->zName);

    /* This function is only called from two places. In both cases the vdbe
    ** has already been allocated. So assume sqlite3GetVdbe() is always
    ** successful here.

Changes to src/vdbe.c.

2942
2943
2944
2945
2946
2947
2948
2949
2950
2951
2952
2953
2954
2955
2956
....
2972
2973
2974
2975
2976
2977
2978






2979
2980
2981


2982
2983
2984
2985
2986
2987
2988
....
3018
3019
3020
3021
3022
3023
3024





























3025
3026
3027
3028
3029
3030
3031
....
3089
3090
3091
3092
3093
3094
3095
3096
3097
3098
3099
3100
3101
3102
3103
3104
3105
3106
3107
3108
3109
3110
3111
3112
3113
3114
3115
3116
3117
3118
3119
3120
3121
3122
3123
3124
3125
3126
3127
3128
3129
3130
3131
3132
3133
3134
3135
3136
3137
3138
3139
3140
3141
3142
3143
3144
3145
3146
3147
3148
3149
3150
3151
3152
3153
3154
3155
3156
3157
3158
3159
3160
3161
3162
                   "cannot commit - no transaction is active"));
         
    rc = SQLITE_ERROR;
  }
  break;
}

/* Opcode: Transaction P1 P2 * * *
**
** Begin a transaction.  The transaction ends when a Commit or Rollback
** opcode is encountered.  Depending on the ON CONFLICT setting, the
** transaction might also be rolled back if an error is encountered.
**
** P1 is the index of the database file on which the transaction is
** started.  Index 0 is the main database file and index 1 is the
................................................................................
** connection is currently not in autocommit mode, or if there are other
** active statements. A statement transaction allows the changes made by this
** VDBE to be rolled back after an error without having to roll back the
** entire transaction. If no error is encountered, the statement transaction
** will automatically commit when the VDBE halts.
**
** If P2 is zero, then a read-lock is obtained on the database file.






*/
case OP_Transaction: {
  Btree *pBt;



  assert( p->bIsReader );
  assert( p->readOnly==0 || pOp->p2==0 );
  assert( pOp->p1>=0 && pOp->p1<db->nDb );
  assert( (p->btreeMask & (((yDbMask)1)<<pOp->p1))!=0 );
  if( pOp->p2 && (db->flags & SQLITE_QueryOnly)!=0 ){
    rc = SQLITE_READONLY;
................................................................................

      /* Store the current value of the database handles deferred constraint
      ** counter. If the statement transaction needs to be rolled back,
      ** the value of this counter needs to be restored too.  */
      p->nStmtDefCons = db->nDeferredCons;
      p->nStmtDefImmCons = db->nDeferredImmCons;
    }





























  }
  break;
}

/* Opcode: ReadCookie P1 P2 P3 * *
**
** Read cookie number P3 from database P1 and write it into register P2.
................................................................................
  }
  if( pOp->p1==1 ){
    /* Invalidate all prepared statements whenever the TEMP database
    ** schema is changed.  Ticket #1644 */
    sqlite3ExpirePreparedStatements(db);
    p->expired = 0;
  }
  break;
}

/* Opcode: VerifyCookie P1 P2 P3 * *
**
** Check the value of global database parameter number 0 (the
** schema version) and make sure it is equal to P2 and that the
** generation counter on the local schema parse equals P3.
**
** P1 is the database number which is 0 for the main database file
** and 1 for the file holding temporary tables and some higher number
** for auxiliary databases.
**
** The cookie changes its value whenever the database schema changes.
** This operation is used to detect when that the cookie has changed
** and that the current process needs to reread the schema.
**
** Either a transaction needs to have been started or an OP_Open needs
** to be executed (to establish a read lock) before this opcode is
** invoked.
*/
case OP_VerifyCookie: {
  int iMeta;
  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) );
  assert( p->bIsReader );
  pBt = db->aDb[pOp->p1].pBt;
  if( pBt ){
    sqlite3BtreeGetMeta(pBt, BTREE_SCHEMA_VERSION, (u32 *)&iMeta);
    iGen = db->aDb[pOp->p1].pSchema->iGeneration;
  }else{
    iGen = iMeta = 0;
  }
  if( iMeta!=pOp->p2 || iGen!=pOp->p3 ){
    sqlite3DbFree(db, p->zErrMsg);
    p->zErrMsg = sqlite3DbStrDup(db, "database schema has changed");
    /* If the schema-cookie from the database file matches the cookie 
    ** stored with the in-memory representation of the schema, do
    ** not reload the schema from the database file.
    **
    ** If virtual-tables are in use, this is not just an optimization.
    ** Often, v-tables store their data in other SQLite tables, which
    ** are queried from within xNext() and other v-table methods using
    ** prepared queries. If such a query is out-of-date, we do not want to
    ** discard the database schema, as the user code implementing the
    ** v-table would have to be ready for the sqlite3_vtab structure itself
    ** to be invalidated whenever sqlite3_step() is called from within 
    ** a v-table method.
    */
    if( db->aDb[pOp->p1].pSchema->schema_cookie!=iMeta ){
      sqlite3ResetOneSchema(db, pOp->p1);
    }

    p->expired = 1;
    rc = SQLITE_SCHEMA;
  }
  break;
}

/* Opcode: OpenRead P1 P2 P3 P4 P5
** Synopsis: root=P2 iDb=P3
**
** Open a read-only cursor for the database table whose root page is







|







 







>
>
>
>
>
>



>
>







 







>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>







 







<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<







2942
2943
2944
2945
2946
2947
2948
2949
2950
2951
2952
2953
2954
2955
2956
....
2972
2973
2974
2975
2976
2977
2978
2979
2980
2981
2982
2983
2984
2985
2986
2987
2988
2989
2990
2991
2992
2993
2994
2995
2996
....
3026
3027
3028
3029
3030
3031
3032
3033
3034
3035
3036
3037
3038
3039
3040
3041
3042
3043
3044
3045
3046
3047
3048
3049
3050
3051
3052
3053
3054
3055
3056
3057
3058
3059
3060
3061
3062
3063
3064
3065
3066
3067
3068
....
3126
3127
3128
3129
3130
3131
3132




























































3133
3134
3135
3136
3137
3138
3139
                   "cannot commit - no transaction is active"));
         
    rc = SQLITE_ERROR;
  }
  break;
}

/* Opcode: Transaction P1 P2 P3 P4 P5
**
** Begin a transaction.  The transaction ends when a Commit or Rollback
** opcode is encountered.  Depending on the ON CONFLICT setting, the
** transaction might also be rolled back if an error is encountered.
**
** P1 is the index of the database file on which the transaction is
** started.  Index 0 is the main database file and index 1 is the
................................................................................
** connection is currently not in autocommit mode, or if there are other
** active statements. A statement transaction allows the changes made by this
** VDBE to be rolled back after an error without having to roll back the
** entire transaction. If no error is encountered, the statement transaction
** will automatically commit when the VDBE halts.
**
** If P2 is zero, then a read-lock is obtained on the database file.
**
** If P5!=0 then this opcode also checks the schema cookie against P3
** and the schema generation counter against P4.
** The cookie changes its value whenever the database schema changes.
** This operation is used to detect when that the cookie has changed
** and that the current process needs to reread the schema.
*/
case OP_Transaction: {
  Btree *pBt;
  int iMeta;
  int iGen;

  assert( p->bIsReader );
  assert( p->readOnly==0 || pOp->p2==0 );
  assert( pOp->p1>=0 && pOp->p1<db->nDb );
  assert( (p->btreeMask & (((yDbMask)1)<<pOp->p1))!=0 );
  if( pOp->p2 && (db->flags & SQLITE_QueryOnly)!=0 ){
    rc = SQLITE_READONLY;
................................................................................

      /* Store the current value of the database handles deferred constraint
      ** counter. If the statement transaction needs to be rolled back,
      ** the value of this counter needs to be restored too.  */
      p->nStmtDefCons = db->nDeferredCons;
      p->nStmtDefImmCons = db->nDeferredImmCons;
    }

    /* Gather the schema version number for checking */
    sqlite3BtreeGetMeta(pBt, BTREE_SCHEMA_VERSION, (u32 *)&iMeta);
    iGen = db->aDb[pOp->p1].pSchema->iGeneration;
  }else{
    iGen = iMeta = 0;
  }
  assert( pOp->p5==0 || pOp->p4type==P4_INT32 );
  if( pOp->p5 && (iMeta!=pOp->p3 || iGen!=pOp->p4.i) ){
    sqlite3DbFree(db, p->zErrMsg);
    p->zErrMsg = sqlite3DbStrDup(db, "database schema has changed");
    /* If the schema-cookie from the database file matches the cookie 
    ** stored with the in-memory representation of the schema, do
    ** not reload the schema from the database file.
    **
    ** If virtual-tables are in use, this is not just an optimization.
    ** Often, v-tables store their data in other SQLite tables, which
    ** are queried from within xNext() and other v-table methods using
    ** prepared queries. If such a query is out-of-date, we do not want to
    ** discard the database schema, as the user code implementing the
    ** v-table would have to be ready for the sqlite3_vtab structure itself
    ** to be invalidated whenever sqlite3_step() is called from within 
    ** a v-table method.
    */
    if( db->aDb[pOp->p1].pSchema->schema_cookie!=iMeta ){
      sqlite3ResetOneSchema(db, pOp->p1);
    }
    p->expired = 1;
    rc = SQLITE_SCHEMA;
  }
  break;
}

/* Opcode: ReadCookie P1 P2 P3 * *
**
** Read cookie number P3 from database P1 and write it into register P2.
................................................................................
  }
  if( pOp->p1==1 ){
    /* Invalidate all prepared statements whenever the TEMP database
    ** schema is changed.  Ticket #1644 */
    sqlite3ExpirePreparedStatements(db);
    p->expired = 0;
  }




























































  break;
}

/* Opcode: OpenRead P1 P2 P3 P4 P5
** Synopsis: root=P2 iDb=P3
**
** Open a read-only cursor for the database table whose root page is

Changes to src/vdbeblob.c.

130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
...
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272

273
274


275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
  ** blob_bytes() functions.
  **
  ** The sqlite3_blob_close() function finalizes the vdbe program,
  ** which closes the b-tree cursor and (possibly) commits the 
  ** transaction.
  */
  static const VdbeOpList openBlob[] = {
    {OP_Transaction, 0, 0, 0},     /* 0: Start a transaction */
    {OP_VerifyCookie, 0, 0, 0},    /* 1: Check the schema cookie */
    {OP_TableLock, 0, 0, 0},       /* 2: Acquire a read or write lock */

    /* One of the following two instructions is replaced by an OP_Noop. */
    {OP_OpenRead, 0, 0, 0},        /* 3: Open cursor 0 for reading */
    {OP_OpenWrite, 0, 0, 0},       /* 4: Open cursor 0 for read/write */

    {OP_Variable, 1, 1, 1},        /* 5: Push the rowid to the stack */
    {OP_NotExists, 0, 10, 1},      /* 6: Seek the cursor */
    {OP_Column, 0, 0, 1},          /* 7  */
    {OP_ResultRow, 1, 0, 0},       /* 8  */
    {OP_Goto, 0, 5, 0},            /* 9  */
    {OP_Close, 0, 0, 0},           /* 10 */
    {OP_Halt, 0, 0, 0},            /* 11 */
  };

  int rc = SQLITE_OK;
  char *zErr = 0;
  Table *pTab;
  Parse *pParse = 0;
  Incrblob *pBlob = 0;
................................................................................

    pBlob->pStmt = (sqlite3_stmt *)sqlite3VdbeCreate(pParse);
    assert( pBlob->pStmt || db->mallocFailed );
    if( pBlob->pStmt ){
      Vdbe *v = (Vdbe *)pBlob->pStmt;
      int iDb = sqlite3SchemaToIndex(db, pTab->pSchema);

      sqlite3VdbeAddOpList(v, sizeof(openBlob)/sizeof(VdbeOpList), openBlob);


      /* Configure the OP_Transaction */
      sqlite3VdbeChangeP1(v, 0, iDb);
      sqlite3VdbeChangeP2(v, 0, flags);

      /* Configure the OP_VerifyCookie */
      sqlite3VdbeChangeP1(v, 1, iDb);

      sqlite3VdbeChangeP2(v, 1, pTab->pSchema->schema_cookie);
      sqlite3VdbeChangeP3(v, 1, pTab->pSchema->iGeneration);



      /* Make sure a mutex is held on the table to be accessed */
      sqlite3VdbeUsesBtree(v, iDb); 

      /* Configure the OP_TableLock instruction */
#ifdef SQLITE_OMIT_SHARED_CACHE
      sqlite3VdbeChangeToNoop(v, 2);
#else
      sqlite3VdbeChangeP1(v, 2, iDb);
      sqlite3VdbeChangeP2(v, 2, pTab->tnum);
      sqlite3VdbeChangeP3(v, 2, flags);
      sqlite3VdbeChangeP4(v, 2, pTab->zName, P4_TRANSIENT);
#endif

      /* Remove either the OP_OpenWrite or OpenRead. Set the P2 
      ** parameter of the other to pTab->tnum.  */
      sqlite3VdbeChangeToNoop(v, 4 - flags);
      sqlite3VdbeChangeP2(v, 3 + flags, pTab->tnum);
      sqlite3VdbeChangeP3(v, 3 + flags, iDb);

      /* Configure the number of columns. Configure the cursor to
      ** think that the table has one more column than it really
      ** does. An OP_Column to retrieve this imaginary column will
      ** always return an SQL NULL. This is useful because it means
      ** we can invoke OP_Column to fill in the vdbe cursors type 
      ** and offset cache without causing any IO.
      */
      sqlite3VdbeChangeP4(v, 3+flags, SQLITE_INT_TO_PTR(pTab->nCol+1),P4_INT32);
      sqlite3VdbeChangeP2(v, 7, pTab->nCol);
      if( !db->mallocFailed ){
        pParse->nVar = 1;
        pParse->nMem = 1;
        pParse->nTab = 1;
        sqlite3VdbeMakeReady(v, pParse);
      }
    }







|
<
|


|
|

|
|
|
|
|
|
|







 







<

<
<
<
<
<
<
<
>
|
|
>
>






|

|
|
|
|




|
|
|








|
|







130
131
132
133
134
135
136
137

138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
...
256
257
258
259
260
261
262

263







264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
  ** blob_bytes() functions.
  **
  ** The sqlite3_blob_close() function finalizes the vdbe program,
  ** which closes the b-tree cursor and (possibly) commits the 
  ** transaction.
  */
  static const VdbeOpList openBlob[] = {
    /* {OP_Transaction, 0, 0, 0},  // 0: Inserted separately */

    {OP_TableLock, 0, 0, 0},       /* 1: Acquire a read or write lock */

    /* One of the following two instructions is replaced by an OP_Noop. */
    {OP_OpenRead, 0, 0, 0},        /* 2: Open cursor 0 for reading */
    {OP_OpenWrite, 0, 0, 0},       /* 3: Open cursor 0 for read/write */

    {OP_Variable, 1, 1, 1},        /* 4: Push the rowid to the stack */
    {OP_NotExists, 0, 10, 1},      /* 5: Seek the cursor */
    {OP_Column, 0, 0, 1},          /* 6  */
    {OP_ResultRow, 1, 0, 0},       /* 7  */
    {OP_Goto, 0, 4, 0},            /* 8  */
    {OP_Close, 0, 0, 0},           /* 9  */
    {OP_Halt, 0, 0, 0},            /* 10 */
  };

  int rc = SQLITE_OK;
  char *zErr = 0;
  Table *pTab;
  Parse *pParse = 0;
  Incrblob *pBlob = 0;
................................................................................

    pBlob->pStmt = (sqlite3_stmt *)sqlite3VdbeCreate(pParse);
    assert( pBlob->pStmt || db->mallocFailed );
    if( pBlob->pStmt ){
      Vdbe *v = (Vdbe *)pBlob->pStmt;
      int iDb = sqlite3SchemaToIndex(db, pTab->pSchema);










      sqlite3VdbeAddOp4Int(v, OP_Transaction, iDb, flags, 
                           pTab->pSchema->schema_cookie,
                           pTab->pSchema->iGeneration);
      sqlite3VdbeChangeP5(v, 1);     
      sqlite3VdbeAddOpList(v, sizeof(openBlob)/sizeof(VdbeOpList), openBlob);

      /* Make sure a mutex is held on the table to be accessed */
      sqlite3VdbeUsesBtree(v, iDb); 

      /* Configure the OP_TableLock instruction */
#ifdef SQLITE_OMIT_SHARED_CACHE
      sqlite3VdbeChangeToNoop(v, 1);
#else
      sqlite3VdbeChangeP1(v, 1, iDb);
      sqlite3VdbeChangeP2(v, 1, pTab->tnum);
      sqlite3VdbeChangeP3(v, 1, flags);
      sqlite3VdbeChangeP4(v, 1, pTab->zName, P4_TRANSIENT);
#endif

      /* Remove either the OP_OpenWrite or OpenRead. Set the P2 
      ** parameter of the other to pTab->tnum.  */
      sqlite3VdbeChangeToNoop(v, 3 - flags);
      sqlite3VdbeChangeP2(v, 2 + flags, pTab->tnum);
      sqlite3VdbeChangeP3(v, 2 + flags, iDb);

      /* Configure the number of columns. Configure the cursor to
      ** think that the table has one more column than it really
      ** does. An OP_Column to retrieve this imaginary column will
      ** always return an SQL NULL. This is useful because it means
      ** we can invoke OP_Column to fill in the vdbe cursors type 
      ** and offset cache without causing any IO.
      */
      sqlite3VdbeChangeP4(v, 2+flags, SQLITE_INT_TO_PTR(pTab->nCol+1),P4_INT32);
      sqlite3VdbeChangeP2(v, 6, pTab->nCol);
      if( !db->mallocFailed ){
        pParse->nVar = 1;
        pParse->nMem = 1;
        pParse->nTab = 1;
        sqlite3VdbeMakeReady(v, pParse);
      }
    }