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SQLite training in Houston TX on 2019-11-05 (details)
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Overview
Comment:Critical fix to the previous check-in so that it works when there are BEFORE triggers that move the cursor before the OP_Delete has a chance to be applied.
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SHA1: db2c0960ffb3b396b20e0441d3edb812254c82bc
User & Date: drh 2017-01-07 14:26:28
Context
2017-01-07
14:47
Improvements to the iIdxNoSeek optimization of sqlite3GenerateRowDelete() so that it is automatically disabled for BEFORE triggers but works in all other cases. check-in: 3178ec4c user: drh tags: trunk
14:26
Critical fix to the previous check-in so that it works when there are BEFORE triggers that move the cursor before the OP_Delete has a chance to be applied. check-in: db2c0960 user: drh tags: trunk
03:26
Avoid an unnecessary btree seek while deleting an index entry due to a conflict on a REPLACE operation. check-in: f0495c51 user: drh tags: trunk
Changes
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Changes to src/delete.c.

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      if( eOnePass==ONEPASS_SINGLE && sqlite3IsToplevel(pParse) ){
        pParse->isMultiWrite = 0;
      }
    }else
#endif
    {
      int count = (pParse->nested==0);    /* True to count changes */
      int iIdxNoSeek = -1;
      if( bComplex==0 && aiCurOnePass[1]!=iDataCur ){
        iIdxNoSeek = aiCurOnePass[1];
      }
      sqlite3GenerateRowDelete(pParse, pTab, pTrigger, iDataCur, iIdxCur,
          iKey, nKey, count, OE_Default, eOnePass, iIdxNoSeek);
    }
  
    /* End of the loop over all rowids/primary-keys. */
    if( eOnePass!=ONEPASS_OFF ){
      sqlite3VdbeResolveLabel(v, addrBypass);
................................................................................
**   ONEPASS_MULTI.  If eMode is not ONEPASS_OFF, then the cursor
**   iDataCur already points to the row to delete. If eMode is ONEPASS_OFF
**   then this function must seek iDataCur to the entry identified by iPk
**   and nPk before reading from it.
**
**   If eMode is ONEPASS_MULTI, then this call is being made as part
**   of a ONEPASS delete that affects multiple rows. In this case, if 
**   iIdxNoSeek is a valid cursor number (>=0), then its position should

**   be preserved following the delete operation. Or, if iIdxNoSeek is not
**   a valid cursor number, the position of iDataCur should be preserved
**   instead.
**
** iIdxNoSeek:
**   If iIdxNoSeek is a valid cursor number (>=0), then it identifies an
**   index cursor (from within array of cursors starting at iIdxCur) that
**   already points to the index entry to be deleted.
*/
void sqlite3GenerateRowDelete(
  Parse *pParse,     /* Parsing context */
  Table *pTab,       /* Table containing the row to be deleted */
  Trigger *pTrigger, /* List of triggers to (potentially) fire */
  int iDataCur,      /* Cursor from which column data is extracted */
  int iIdxCur,       /* First index cursor */
................................................................................
    addrStart = sqlite3VdbeCurrentAddr(v);
    sqlite3CodeRowTrigger(pParse, pTrigger, 
        TK_DELETE, 0, TRIGGER_BEFORE, pTab, iOld, onconf, iLabel
    );

    /* If any BEFORE triggers were coded, then seek the cursor to the 
    ** row to be deleted again. It may be that the BEFORE triggers moved
    ** the cursor or of already deleted the row that the cursor was
    ** pointing to.
    */
    if( addrStart<sqlite3VdbeCurrentAddr(v) ){
      sqlite3VdbeAddOp4Int(v, opSeek, iDataCur, iLabel, iPk, nPk);
      VdbeCoverageIf(v, opSeek==OP_NotExists);
      VdbeCoverageIf(v, opSeek==OP_NotFound);
    }







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      if( eOnePass==ONEPASS_SINGLE && sqlite3IsToplevel(pParse) ){
        pParse->isMultiWrite = 0;
      }
    }else
#endif
    {
      int count = (pParse->nested==0);    /* True to count changes */
      int iIdxNoSeek = bComplex ? -1 : aiCurOnePass[1];



      sqlite3GenerateRowDelete(pParse, pTab, pTrigger, iDataCur, iIdxCur,
          iKey, nKey, count, OE_Default, eOnePass, iIdxNoSeek);
    }
  
    /* End of the loop over all rowids/primary-keys. */
    if( eOnePass!=ONEPASS_OFF ){
      sqlite3VdbeResolveLabel(v, addrBypass);
................................................................................
**   ONEPASS_MULTI.  If eMode is not ONEPASS_OFF, then the cursor
**   iDataCur already points to the row to delete. If eMode is ONEPASS_OFF
**   then this function must seek iDataCur to the entry identified by iPk
**   and nPk before reading from it.
**
**   If eMode is ONEPASS_MULTI, then this call is being made as part
**   of a ONEPASS delete that affects multiple rows. In this case, if 
**   iIdxNoSeek is a valid cursor number (>=0) and is not the same as
**   iDataCur, then its position should be preserved following the delete
**   operation. Or, if iIdxNoSeek is not a valid cursor number, the
**   position of iDataCur should be preserved instead.

**
** iIdxNoSeek:
**   If iIdxNoSeek is a valid cursor number (>=0) not equal to iDataCur,
**   then it identifies an index cursor (from within array of cursors
**   starting at iIdxCur) that already points to the index entry to be deleted.
*/
void sqlite3GenerateRowDelete(
  Parse *pParse,     /* Parsing context */
  Table *pTab,       /* Table containing the row to be deleted */
  Trigger *pTrigger, /* List of triggers to (potentially) fire */
  int iDataCur,      /* Cursor from which column data is extracted */
  int iIdxCur,       /* First index cursor */
................................................................................
    addrStart = sqlite3VdbeCurrentAddr(v);
    sqlite3CodeRowTrigger(pParse, pTrigger, 
        TK_DELETE, 0, TRIGGER_BEFORE, pTab, iOld, onconf, iLabel
    );

    /* If any BEFORE triggers were coded, then seek the cursor to the 
    ** row to be deleted again. It may be that the BEFORE triggers moved
    ** the cursor or already deleted the row that the cursor was
    ** pointing to.
    */
    if( addrStart<sqlite3VdbeCurrentAddr(v) ){
      sqlite3VdbeAddOp4Int(v, opSeek, iDataCur, iLabel, iPk, nPk);
      VdbeCoverageIf(v, opSeek==OP_NotExists);
      VdbeCoverageIf(v, opSeek==OP_NotFound);
    }

Changes to src/insert.c.

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        assert( onError==OE_Replace );
        sqlite3MultiWrite(pParse);
        if( db->flags&SQLITE_RecTriggers ){
          pTrigger = sqlite3TriggersExist(pParse, pTab, TK_DELETE, 0, 0);
        }
        sqlite3GenerateRowDelete(pParse, pTab, pTrigger, iDataCur, iIdxCur,
            regR, nPkField, 0, OE_Replace,
            (pIdx==pPk ? ONEPASS_SINGLE : ONEPASS_OFF), iThisCur);

        seenReplace = 1;
        break;
      }
    }
    sqlite3VdbeResolveLabel(v, addrUniqueOk);
    if( regR!=regIdx ) sqlite3ReleaseTempRange(pParse, regR, nPkField);
  }







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        assert( onError==OE_Replace );
        sqlite3MultiWrite(pParse);
        if( db->flags&SQLITE_RecTriggers ){
          pTrigger = sqlite3TriggersExist(pParse, pTab, TK_DELETE, 0, 0);
        }
        sqlite3GenerateRowDelete(pParse, pTab, pTrigger, iDataCur, iIdxCur,
            regR, nPkField, 0, OE_Replace,
            (pIdx==pPk ? ONEPASS_SINGLE : ONEPASS_OFF),
            (pTrigger ? -1 : iThisCur));
        seenReplace = 1;
        break;
      }
    }
    sqlite3VdbeResolveLabel(v, addrUniqueOk);
    if( regR!=regIdx ) sqlite3ReleaseTempRange(pParse, regR, nPkField);
  }