Re: on_error table, saving error info to a table

On Wed, May 6, 2026 at 4:08 PM jian he <jian.universality@gmail.com> wrote:
>
> v9-0002: Introduce a (ModifyTableContext *) field in CopyFromStateData.
> Initialize all useful subordinate structures, including such as
> ModifyTableState, EState, and ModifyTableState->ResultRelInfo.  Set
> cstate->escontext->details_wanted to true to ensure that all input conversion
> error metadata is captured in cstate->escontext.  Use this metadata to construct
> a TupleTableSlot, and then delegate the remaining processing to ExecInsert.
>
> Before calling ExecInsert() to insert error metadata into the ERROR_TABLE, we
> must first populate a ModifyTableState, similar to how it is done in
> ExecInitModifyTable.
>
> By comparing side-by-side with ExecInitModifyTable, it is ok to populate the
> necessary information for the ERROR_TABLE using the following functions:
> ExecInitRangeTable, ExecInitResultRelation, ExecOpenIndices, and
> CheckValidResultRel.
> This will allow the ERROR_TABLE to safely use ExecInsert().
>

example
CREATE TABLE t(a int);
INSERT INTO t VALUES (1);

Execution flow:
ProcessQuery:
    queryDesc = CreateQueryDesc(plan, sourceText,
                                GetActiveSnapshot(), InvalidSnapshot,
                                dest, params, queryEnv, 0);

CreateQueryDesc:
    qd->snapshot = RegisterSnapshot(snapshot);

standard_ExecutorStart:
    estate->es_snapshot = RegisterSnapshot(queryDesc->snapshot);

For COPY FROM, PortalRunUtility -> ProcessUtility ->
standard_ProcessUtility -> DoCopy ensures that an ActiveSnapshot
is available through PortalRunUtility()->PlannedStmtRequiresSnapshot().

Therefore, I think it is OK for the CopyFrom function to register a
active snapshot
(EState->es_snapshot) during constructing the EState, in case snapshot access is
needed later.

    EState *estate = CreateExecutorState(); /* for ExecConstraints() */

Add:
    estate->es_snapshot =
        RegisterSnapshot(GetActiveSnapshot());
    estate->es_crosscheck_snapshot =
        RegisterSnapshot(InvalidSnapshot);

Similarly, it would be better let
CopyFromStateData->ModifyTableContext->EState->es_snapshot
also Register the current ActiveSnapshot.
Just in case the ExecInsert function needs to use it.

In the attached v10, the code flow for inserting content into the error-saving
table involves constructing an EState, while the population and release of its
subfields align more closely with how ExecutorStart, ExecutorFinish,
and ExecutorEnd deal with EState.



--
jian
https://www.enterprisedb.com/