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Overview
Comment:Begin a series of changes designed to reduce the scope and frequency of invalidating schemas. Design goals are that the internal schema should never be deleted out from under a prepared statement that is running and that all prepared statements should be expired if the schema is invalidated. At the same time, minimize the number of schema invalidations. This change merely revises the sqlite3ResetInternalSchema() function to use -1 as the wildcard for "all" rather than 0, so that we can reset the main schema independently of all the others.
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SHA1: 6a8ad6e31e0d2b8a5ace38faf0efd805155ee5f3
User & Date: drh 2011-04-02 16:28:52
Context
2011-04-02
16:50
When resetting any non-TEMP schema, also reset the TEMP schema since it might be holding references to the non-TEMP schema that just got reset. check-in: 211d5dde user: drh tags: schema-parse-refactor
16:28
Begin a series of changes designed to reduce the scope and frequency of invalidating schemas. Design goals are that the internal schema should never be deleted out from under a prepared statement that is running and that all prepared statements should be expired if the schema is invalidated. At the same time, minimize the number of schema invalidations. This change merely revises the sqlite3ResetInternalSchema() function to use -1 as the wildcard for "all" rather than 0, so that we can reset the main schema independently of all the others. check-in: 6a8ad6e3 user: drh tags: schema-parse-refactor
09:44
Fix a race condition in OP_ParseSchema. check-in: 71a799b0 user: dan tags: trunk
Changes
Hide Diffs Unified Diffs Ignore Whitespace Patch

Changes to src/attach.c. 

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    int iDb = db->nDb - 1;
    assert( iDb>=2 );
    if( db->aDb[iDb].pBt ){
      sqlite3BtreeClose(db->aDb[iDb].pBt);
      db->aDb[iDb].pBt = 0;
      db->aDb[iDb].pSchema = 0;
    }
    sqlite3ResetInternalSchema(db, 0);
    db->nDb = iDb;
    if( rc==SQLITE_NOMEM || rc==SQLITE_IOERR_NOMEM ){
      db->mallocFailed = 1;
      sqlite3DbFree(db, zErrDyn);
      zErrDyn = sqlite3MPrintf(db, "out of memory");
    }else if( zErrDyn==0 ){
      zErrDyn = sqlite3MPrintf(db, "unable to open database: %s", zFile);
................................................................................
    sqlite3_snprintf(sizeof(zErr),zErr, "database %s is locked", zName);
    goto detach_error;
  }

  sqlite3BtreeClose(pDb->pBt);
  pDb->pBt = 0;
  pDb->pSchema = 0;
  sqlite3ResetInternalSchema(db, 0);
  return;

detach_error:
  sqlite3_result_error(context, zErr, -1);
}

/*








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    int iDb = db->nDb - 1;
    assert( iDb>=2 );
    if( db->aDb[iDb].pBt ){
      sqlite3BtreeClose(db->aDb[iDb].pBt);
      db->aDb[iDb].pBt = 0;
      db->aDb[iDb].pSchema = 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");
    }else if( zErrDyn==0 ){
      zErrDyn = sqlite3MPrintf(db, "unable to open database: %s", zFile);
................................................................................
    sqlite3_snprintf(sizeof(zErr),zErr, "database %s is locked", zName);
    goto detach_error;
  }

  sqlite3BtreeClose(pDb->pBt);
  pDb->pBt = 0;
  pDb->pSchema = 0;
  sqlite3ResetInternalSchema(db, -1);
  return;

detach_error:
  sqlite3_result_error(context, zErr, -1);
}

/*

Changes to src/backup.c. 

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    */
    if( rc==SQLITE_DONE 
     && (rc = sqlite3BtreeUpdateMeta(p->pDest,1,p->iDestSchema+1))==SQLITE_OK
    ){
      int nDestTruncate;
  
      if( p->pDestDb ){
        sqlite3ResetInternalSchema(p->pDestDb, 0);
      }

      /* 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. 
      **
      ** If the source page size is smaller than the destination page size, 








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    */
    if( rc==SQLITE_DONE 
     && (rc = sqlite3BtreeUpdateMeta(p->pDest,1,p->iDestSchema+1))==SQLITE_OK
    ){
      int nDestTruncate;
  
      if( p->pDestDb ){
        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. 
      **
      ** If the source page size is smaller than the destination page size,

Changes to src/build.c. 

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/*
** Erase all schema information from the in-memory hash tables of
** 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
** single file indicated.
*/
void sqlite3ResetInternalSchema(sqlite3 *db, int iDb){
  int i, j;
  assert( iDb>=0 && iDb<db->nDb );

  if( iDb==0 ){
    sqlite3BtreeEnterAll(db);




  }






  for(i=iDb; i<db->nDb; i++){
    Db *pDb = &db->aDb[i];
    if( pDb->pSchema ){
      assert(i==1 || (pDb->pBt && sqlite3BtreeHoldsMutex(pDb->pBt)));
      sqlite3SchemaFree(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,
  ** then remove them from the auxiliary database list.  We take the
  ** opportunity to do this here since we have just deleted all of the








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<

<








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/*
** Erase all schema information from the in-memory hash tables of
** 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>=0 then reset the internal schema for only the
** single file indicated.
*/
void sqlite3ResetInternalSchema(sqlite3 *db, int iDb){
  int i, j;
  assert( iDb<db->nDb );

  if( iDb>=0 ){
    /* Case 1:  Reset the single schema identified by iDb */
    Db *pDb = &db->aDb[iDb];
    if( pDb->pSchema ){
      assert(iDb==1 || (pDb->pBt && sqlite3BtreeHoldsMutex(pDb->pBt)));
      sqlite3SchemaFree(pDb->pSchema);
    }
    return;
  }
  /* 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);
    }

  }

  db->flags &= ~SQLITE_InternChanges;
  sqlite3VtabUnlockList(db);
  sqlite3BtreeLeaveAll(db);

  /* If one or more of the auxiliary database files has been closed,
  ** then remove them from the auxiliary database list.  We take the
  ** opportunity to do this here since we have just deleted all of the

Changes to src/main.c. 

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    return SQLITE_OK;
  }
  if( !sqlite3SafetyCheckSickOrOk(db) ){
    return SQLITE_MISUSE_BKPT;
  }
  sqlite3_mutex_enter(db->mutex);

  sqlite3ResetInternalSchema(db, 0);

  /* 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
  ** SQL statements below, as the v-table implementation may be storing
  ** some prepared statements internally.
................................................................................
      sqlite3BtreeClose(pDb->pBt);
      pDb->pBt = 0;
      if( j!=1 ){
        pDb->pSchema = 0;
      }
    }
  }
  sqlite3ResetInternalSchema(db, 0);

  /* 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);

  assert( db->nDb<=2 );
................................................................................
    }
  }
  sqlite3VtabRollback(db);
  sqlite3EndBenignMalloc();

  if( db->flags&SQLITE_InternChanges ){
    sqlite3ExpirePreparedStatements(db);
    sqlite3ResetInternalSchema(db, 0);
  }

  /* Any deferred constraint violations have now been resolved. */
  db->nDeferredCons = 0;

  /* If one has been configured, invoke the rollback-hook callback */
  if( db->xRollbackCallback && (inTrans || !db->autoCommit) ){








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    return SQLITE_OK;
  }
  if( !sqlite3SafetyCheckSickOrOk(db) ){
    return SQLITE_MISUSE_BKPT;
  }
  sqlite3_mutex_enter(db->mutex);

  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
  ** SQL statements below, as the v-table implementation may be storing
  ** some prepared statements internally.
................................................................................
      sqlite3BtreeClose(pDb->pBt);
      pDb->pBt = 0;
      if( j!=1 ){
        pDb->pSchema = 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);

  assert( db->nDb<=2 );
................................................................................
    }
  }
  sqlite3VtabRollback(db);
  sqlite3EndBenignMalloc();

  if( db->flags&SQLITE_InternChanges ){
    sqlite3ExpirePreparedStatements(db);
    sqlite3ResetInternalSchema(db, -1);
  }

  /* Any deferred constraint violations have now been resolved. */
  db->nDeferredCons = 0;

  /* If one has been configured, invoke the rollback-hook callback */
  if( db->xRollbackCallback && (inTrans || !db->autoCommit) ){

Changes to src/pragma.c. 

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    if( !db->autoCommit || sqlite3BtreeIsInReadTrans(db->aDb[1].pBt) ){
      sqlite3ErrorMsg(pParse, "temporary storage cannot be changed "
        "from within a transaction");
      return SQLITE_ERROR;
    }
    sqlite3BtreeClose(db->aDb[1].pBt);
    db->aDb[1].pBt = 0;
    sqlite3ResetInternalSchema(db, 0);
  }
  return SQLITE_OK;
}
#endif /* SQLITE_PAGER_PRAGMAS */

#ifndef SQLITE_OMIT_PAGER_PRAGMAS
/*








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    if( !db->autoCommit || sqlite3BtreeIsInReadTrans(db->aDb[1].pBt) ){
      sqlite3ErrorMsg(pParse, "temporary storage cannot be changed "
        "from within a transaction");
      return SQLITE_ERROR;
    }
    sqlite3BtreeClose(db->aDb[1].pBt);
    db->aDb[1].pBt = 0;
    sqlite3ResetInternalSchema(db, -1);
  }
  return SQLITE_OK;
}
#endif /* SQLITE_PAGER_PRAGMAS */

#ifndef SQLITE_OMIT_PAGER_PRAGMAS
/*

Changes to src/prepare.c. 

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    if( rc==SQLITE_OK ){
      sqlite3AnalysisLoad(db, iDb);
    }
#endif
  }
  if( db->mallocFailed ){
    rc = SQLITE_NOMEM;
    sqlite3ResetInternalSchema(db, 0);
  }
  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
    ** will attempt to compile the supplied statement against whatever subset
    ** of the schema was loaded before the error occurred. The primary
................................................................................
    pParse->rc = SQLITE_NOMEM;
  }
  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;
  }








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    if( rc==SQLITE_OK ){
      sqlite3AnalysisLoad(db, iDb);
    }
#endif
  }
  if( db->mallocFailed ){
    rc = SQLITE_NOMEM;
    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
    ** will attempt to compile the supplied statement against whatever subset
    ** of the schema was loaded before the error occurred. The primary
................................................................................
    pParse->rc = SQLITE_NOMEM;
  }
  if( pParse->rc==SQLITE_DONE ) pParse->rc = SQLITE_OK;
  if( pParse->checkSchema ){
    schemaIsValid(pParse);
  }
  if( pParse->rc==SQLITE_SCHEMA ){
    sqlite3ResetInternalSchema(db, -1);
  }
  if( db->mallocFailed ){
    pParse->rc = SQLITE_NOMEM;
  }
  if( pzTail ){
    *pzTail = pParse->zTail;
  }

Changes to src/vacuum.c. 

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342


  if( pDb ){
    sqlite3BtreeClose(pDb->pBt);
    pDb->pBt = 0;
    pDb->pSchema = 0;
  }

  sqlite3ResetInternalSchema(db, 0);

  return rc;
}

#endif  /* SQLITE_OMIT_VACUUM && SQLITE_OMIT_ATTACH */








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>


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  if( pDb ){
    sqlite3BtreeClose(pDb->pBt);
    pDb->pBt = 0;
    pDb->pSchema = 0;
  }

  sqlite3ResetInternalSchema(db, -1);

  return rc;
}

#endif  /* SQLITE_OMIT_VACUUM && SQLITE_OMIT_ATTACH */

Changes to src/vdbe.c. 

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          rc = sqlite3BtreeSavepoint(db->aDb[ii].pBt, p1, iSavepoint);
          if( rc!=SQLITE_OK ){
            goto abort_due_to_error;
          }
        }
        if( p1==SAVEPOINT_ROLLBACK && (db->flags&SQLITE_InternChanges)!=0 ){
          sqlite3ExpirePreparedStatements(db);
          sqlite3ResetInternalSchema(db, 0);
          db->flags = (db->flags | SQLITE_InternChanges);
        }
      }
  
      /* Regardless of whether this is a RELEASE or ROLLBACK, destroy all 
      ** savepoints nested inside of the savepoint being operated on. */
      while( db->pSavepoint!=pSavepoint ){
................................................................................
  p->rc = rc;
  testcase( sqlite3GlobalConfig.xLog!=0 );
  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);

  /* This is the only way out of this procedure.  We have to
  ** release the mutexes on btrees that were acquired at the
  ** top. */
vdbe_return:
  sqlite3BtreeMutexArrayLeave(&p->aMutex);
  return rc;








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          rc = sqlite3BtreeSavepoint(db->aDb[ii].pBt, p1, iSavepoint);
          if( rc!=SQLITE_OK ){
            goto abort_due_to_error;
          }
        }
        if( p1==SAVEPOINT_ROLLBACK && (db->flags&SQLITE_InternChanges)!=0 ){
          sqlite3ExpirePreparedStatements(db);
          sqlite3ResetInternalSchema(db, -1);
          db->flags = (db->flags | SQLITE_InternChanges);
        }
      }
  
      /* Regardless of whether this is a RELEASE or ROLLBACK, destroy all 
      ** savepoints nested inside of the savepoint being operated on. */
      while( db->pSavepoint!=pSavepoint ){
................................................................................
  p->rc = rc;
  testcase( sqlite3GlobalConfig.xLog!=0 );
  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, -1);

  /* This is the only way out of this procedure.  We have to
  ** release the mutexes on btrees that were acquired at the
  ** top. */
vdbe_return:
  sqlite3BtreeMutexArrayLeave(&p->aMutex);
  return rc;

Changes to src/vdbeaux.c. 

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        sqlite3VdbeSetChanges(db, 0);
      }
      p->nChange = 0;
    }
  
    /* Rollback or commit any schema changes that occurred. */
    if( p->rc!=SQLITE_OK && db->flags&SQLITE_InternChanges ){
      sqlite3ResetInternalSchema(db, 0);
      db->flags = (db->flags | SQLITE_InternChanges);
    }

    /* Release the locks */
    sqlite3BtreeMutexArrayLeave(&p->aMutex);
  }









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        sqlite3VdbeSetChanges(db, 0);
      }
      p->nChange = 0;
    }
  
    /* Rollback or commit any schema changes that occurred. */
    if( p->rc!=SQLITE_OK && db->flags&SQLITE_InternChanges ){
      sqlite3ResetInternalSchema(db, -1);
      db->flags = (db->flags | SQLITE_InternChanges);
    }

    /* Release the locks */
    sqlite3BtreeMutexArrayLeave(&p->aMutex);
  }

Changes to src/vtab.c. 

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    if( pDel && pDel->xDestroy ){
      pDel->xDestroy(pDel->pAux);
    }
    sqlite3DbFree(db, pDel);
    if( pDel==pMod ){
      db->mallocFailed = 1;
    }
    sqlite3ResetInternalSchema(db, 0);
  }else if( xDestroy ){
    xDestroy(pAux);
  }
  rc = sqlite3ApiExit(db, SQLITE_OK);
  sqlite3_mutex_leave(db->mutex);
  return rc;
}








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    if( pDel && pDel->xDestroy ){
      pDel->xDestroy(pDel->pAux);
    }
    sqlite3DbFree(db, pDel);
    if( pDel==pMod ){
      db->mallocFailed = 1;
    }
    sqlite3ResetInternalSchema(db, -1);
  }else if( xDestroy ){
    xDestroy(pAux);
  }
  rc = sqlite3ApiExit(db, SQLITE_OK);
  sqlite3_mutex_leave(db->mutex);
  return rc;
}

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