At Wed, 29 Mar 2023 13:21:55 +0900 (JST), Kyotaro Horiguchi <horikyota....@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
