Horton

Re: PG 15 (and to a smaller degree 14) regression due to ExprEvalStep size

Kyotaro Horiguchi <horikyota.ntt@gmail.com>

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From: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
To: andres@anarazel.de
Cc: dgrowleyml@gmail.com, pg@bowt.ie, pgsql-hackers@postgresql.org, n.gluhov@postgrespro.ru, andrew@dunslane.net
Date: 2022-06-17T06:54:13Z
Lists: pgsql-hackers 
At Thu, 16 Jun 2022 23:24:56 -0700, Andres Freund <andres@anarazel.de> wrote in 
> The remaining difference looks like it's largely caused by the
> enable_timeout_after(IDLE_STATS_UPDATE_TIMEOUT, ...) introduced as part of the
> pgstats patch. It's only really visible when I pin a single connection pgbench
> to the same CPU core as the server (which gives a ~16% boost here).
> 
> It's not the timeout itself - that we amortize nicely (via 09cf1d522). It's
> that enable_timeout_after() does a GetCurrentTimestamp().
> 
> Not sure yet what the best way to fix that is.
> 
> We could just leave the timer active and add some gating condition indicating
> idleness to the IdleStatsUpdateTimeoutPending body in ProcessInterrupts()?
> 
> Or we could add a timeout.c API that specifies the timeout?

I sometimes wanted this, But I don't see a simple way to sort multiple
relative timeouts in absolute time order.  Maybe we can skip
GetCurrentTimestamp only when inserting the first timeout, but I don't
think it benefits this case.

> pgstat_report_stat() uses GetCurrentTransactionStopTimestamp(), it seems like
> it'd make sense to use the same for arming the timeout?

This seems like the feasible best fix for this specific issue.

regards.

-- 
Kyotaro Horiguchi
NTT Open Source Software Center

Commits

  1. JSON_TABLE: Add support for NESTED paths and columns

  2. Add basic JSON_TABLE() functionality

  3. Add SQL/JSON query functions

  4. Add soft error handling to some expression nodes

  5. Adjust populate_record_field() to handle errors softly

  6. Refactor code used by jsonpath executor to fetch variables

  7. Add more SQL/JSON constructor functions

  8. SQL/JSON: support the IS JSON predicate

  9. SQL/JSON: add standard JSON constructor functions

  10. Add static assertion ensuring sizeof(ExprEvalStep) <= 64 bytes

  11. Remove size increase in ExprEvalStep caused by hashed saops

  12. pgstat: reduce timer overhead by leaving timer running.

  13. expression eval: Fix EEOP_JSON_CONSTRUCTOR and EEOP_JSONEXPR size.

  14. SQL/JSON query functions

  15. Speedup ScalarArrayOpExpr evaluation