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pgbench: When using pipelining only do PQconsumeInput() when necessary.

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Up to now we did a PQconsumeInput() for each pipelined query, asking the OS
for more input - which it often won't have, as all results might already have
been sent. That turns out to have a noticeable performance impact.

Alvaro Herrera reviewed the idea to add the PQisBusy() check, but not this
concrete patch.

Author: Andres Freund <andres@anarazel.de>
Discussion: https://postgr.es/m/20210720180039.23rivhdft3l4mayn@alap3.anarazel.de
Backpatch: 14, where libpq/pgbench pipelining was introduced.
This commit is contained in:
Andres Freund 2021-08-04 19:19:44 -07:00
parent 1bc8e7b099
commit 87bff68840
1 changed files with 8 additions and 1 deletions
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9
src/bin/pgbench/pgbench.c
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@ -3461,7 +3461,14 @@ advanceConnectionState(TState *thread, CState *st, StatsData *agg)
*/ */
case CSTATE_WAIT_RESULT: case CSTATE_WAIT_RESULT:
pg_log_debug("client %d receiving", st->id); pg_log_debug("client %d receiving", st->id);
if (!PQconsumeInput(st->con))
/*
* Only check for new network data if we processed all data
* fetched prior. Otherwise we end up doing a syscall for each
* individual pipelined query, which has a measurable
* performance impact.
*/
if (PQisBusy(st->con) && !PQconsumeInput(st->con))
{ {
/* there's something wrong */ /* there's something wrong */
commandFailed(st, "SQL", "perhaps the backend died while processing"); commandFailed(st, "SQL", "perhaps the backend died while processing");