At Wed, 29 Mar 2023 13:21:55 +0900 (JST), Kyotaro Horiguchi <horikyota.ntt@gmail.com> wrote in
> autovacuum.c:2893
> /*
> * If any of the cost delay parameters has been set individually for
> * this table, disable the balancing algorithm.
> */
> tab->at_dobalance =
> !(avopts && (avopts->vacuum_cost_limit > 0 ||
> avopts->vacuum_cost_delay > 0));
>
> So, sorry for the noise. I'll review it while this into cnosideration.
Then I found that the code is quite confusing as it is.
For the tables that don't have cost_delay and cost_limit specified
indificually, at_vacuum_cost_limit and _delay store the system global
values detemined by GUCs. wi_cost_delay, _limit and _limit_base stores
the same values with them. As the result I concluded tha
autovac_balance_cost() does exactly what Melanie's patch does, except
that nworkers_for_balance is not stored in shared memory.
I discovered that commit 1021bd6a89 brought in do_balance.
> Since the mechanism is already complicated, just disable it for those
> cases rather than trying to make it cope. There are undesirable
After reading this, I get why the code is so complex. It is a remnant
of when balancing was done with tables that had individually specified
cost parameters. And I found the following description in the doc.
https://www.postgresql.org/docs/devel/routine-vacuuming.html
> When multiple workers are running, the autovacuum cost delay
> parameters (see Section 20.4.4) are “balanced” among all the running
> workers, so that the total I/O impact on the system is the same
> regardless of the number of workers actually running. However, any
> workers processing tables whose per-table
> autovacuum_vacuum_cost_delay or autovacuum_vacuum_cost_limit storage
> parameters have been set are not considered in the balancing
> algorithm.
The initial balancing mechanism was brought in by e2a186b03c back in
2007. The balancing code has had that unnecessarily complexity ever
since.
Since I can't think of a better idea than Melanie's proposal for
handling this code, I'll keep reviewing it with that approach in mind.
regards.
--
Kyotaro Horiguchi
NTT Open Source Software Center
