> On Nov 10, 2025, at 12:45, Fujii Masao <[email protected]> wrote:
>
> On Mon, Nov 10, 2025 at 11:07 AM Chao Li <[email protected]> wrote:
>> I just did a test. In the test, I inserted a tuple with the same primary key
>> so that the inserts fails by the unique key constraint which breaks the
>> pipeline, and some random select statements followed. And I added some debug
>> messages in discardAvailableResults(), which showed me that the function
>> will discard rest of statements’ results until \endpipeline. As there are
>> anyway limited number of statements before \endpipeline, my concern is
>> actually not valid. So, now I am good with this patch.
>
> Thanks a lot for testing!
>
Hi Fujii-san,
I just did more tests on both pipeline mode and non-pipeline mode, I think the
main purpose of discardAvailableResults() is to drain results for pipeline
mode. In non-pipeline mode, a NULL res indicates no more result to read; while
in pipeline mode, when a pipeline is aborted, either a valid result or NULL
could still be returned, thus we need to wait until pipeline state switch to
PQ_PIPELINE_OK. From this perspective, the current inline comment is correct,
but I feel it’s not clear enough.
So I am proposing the function comment and inline comment like the following:
```
/*
* Read and discard all available results from the connection.
*
* Non-pipeline mode:
* ------------------
* PQgetResult() returns each PGresult in order for the last command sent.
* When it returns NULL, that definitively means there are no more results
* for that command. We stop on NULL (or on CONNECTION_BAD).
*
* Pipeline mode:
* --------------
* If an earlier command in the pipeline errors, libpq enters the
* PQ_PIPELINE_ABORTED state. In this state, PQgetResult() may return
* either a valid PGresult or NULL, and a NULL return does NOT mean
* that the connection is drained. More results for later commands (or
* protocol housekeeping such as the pipeline sync result) can still
* arrive afterward. Therefore we must continue calling PQgetResult()
* while PQpipelineStatus(conn) == PQ_PIPELINE_ABORTED, even if we see
* intermittent NULLs.
*/
static void
discardAvailableResults(CState *st)
{
PGresult *res = NULL;
for (;;)
{
res = PQgetResult(st->con);
/*
* Stop when there are no more results *and* the pipeline is not
* in the aborted state, or if the connection has failed.
*/
if ((res == NULL && PQpipelineStatus(st->con) !=
PQ_PIPELINE_ABORTED) ||
PQstatus(st->con) == CONNECTION_BAD)
break;
PQclear(res);
}
PQclear(res);
}
```
What do you think?
Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/
