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trigger.c

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    • Tom Lane's avatar
      a210be77
      Fix dangling-pointer problem in before-row update trigger processing. · a210be77
      Tom Lane authored
      ExecUpdate checked for whether ExecBRUpdateTriggers had returned a new
      tuple value by seeing if the returned tuple was pointer-equal to the old
      one.  But the "old one" was in estate->es_junkFilter's result slot, which
      would be scribbled on if we had done an EvalPlanQual update in response to
      a concurrent update of the target tuple; therefore we were comparing a
      dangling pointer to a live one.  Given the right set of circumstances we
      could get a false match, resulting in not forcing the tuple to be stored in
      the slot we thought it was stored in.  In the case reported by Maxim Boguk
      in bug #5798, this led to "cannot extract system attribute from virtual
      tuple" failures when trying to do "RETURNING ctid".  I believe there is a
      very-low-probability chance of more serious errors, such as generating
      incorrect index entries based on the original rather than the
      trigger-modified version of the row.
      
      In HEAD, change all of ExecBRInsertTriggers, ExecIRInsertTriggers,
      ExecBRUpdateTriggers, and ExecIRUpdateTriggers so that they continue to
      have similar APIs.  In the back branches I just changed
      ExecBRUpdateTriggers, since there is no bug in the ExecBRInsertTriggers
      case.
      a210be77
      History
      Fix dangling-pointer problem in before-row update trigger processing.
      Tom Lane authored
      ExecUpdate checked for whether ExecBRUpdateTriggers had returned a new
      tuple value by seeing if the returned tuple was pointer-equal to the old
      one.  But the "old one" was in estate->es_junkFilter's result slot, which
      would be scribbled on if we had done an EvalPlanQual update in response to
      a concurrent update of the target tuple; therefore we were comparing a
      dangling pointer to a live one.  Given the right set of circumstances we
      could get a false match, resulting in not forcing the tuple to be stored in
      the slot we thought it was stored in.  In the case reported by Maxim Boguk
      in bug #5798, this led to "cannot extract system attribute from virtual
      tuple" failures when trying to do "RETURNING ctid".  I believe there is a
      very-low-probability chance of more serious errors, such as generating
      incorrect index entries based on the original rather than the
      trigger-modified version of the row.
      
      In HEAD, change all of ExecBRInsertTriggers, ExecIRInsertTriggers,
      ExecBRUpdateTriggers, and ExecIRUpdateTriggers so that they continue to
      have similar APIs.  In the back branches I just changed
      ExecBRUpdateTriggers, since there is no bug in the ExecBRInsertTriggers
      case.