Re: [HACKERS] Block level parallel vacuum

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От Mahendra Singh
Тема Re: [HACKERS] Block level parallel vacuum
Дата
Msg-id CAKYtNAoyZMsoQTK7saUYYXfs4Yh=2mkHj6knNux3CF1PvNFudA@mail.gmail.com
обсуждение исходный текст
Ответ на Re: [HACKERS] Block level parallel vacuum  (Masahiko Sawada <masahiko.sawada@2ndquadrant.com>)
Список pgsql-hackers
Дерево обсуждения
On Thu, 28 Nov 2019 at 13:32, Masahiko Sawada <masahiko.sawada@2ndquadrant.com> wrote:
On Wed, 27 Nov 2019 at 19:21, Mahendra Singh <mahi6run@gmail.com> wrote:
>
>
> Thanks for the re-based patches.
>
> On the top of v35 patch, I can see one compilation warning.
>>
>> parallel.c: In function ‘LaunchParallelWorkers’:
>> parallel.c:502:2: warning: ISO C90 forbids mixed declarations and code [-Wdeclaration-after-statement]
>>   int   i;
>>   ^
>
>
> Above warning is due to one extra semicolon added at the end of declaration line in v35-0003 patch. Please fix this in next version.
> +   int         nworkers_to_launch = Min(nworkers, pcxt->nworkers);;

Thanks. I will fix it in the next version patch.

>
> I will continue my testing on the top of v35 patch set and will post results.

While reviewing v35 patch set and doing testing, I found that if we disable leader participation, then we are launching 1 less parallel worker than total number of indexes. (I am using max_parallel_workers = 20, max_parallel_maintenance_workers = 20)

For example: If table have 3 indexes and we gave 6 parallel vacuum degree(leader participation is disabled), then I think, we should launch 3 parallel workers but we are launching 2 workers due to below check.
+       nworkers = lps->nindexes_parallel_bulkdel - 1;
+
+   /* Cap by the worker we computed at the beginning of parallel lazy vacuum */
+   nworkers = Min(nworkers, lps->pcxt->nworkers);

Please let me know your thoughts for this.

Thanks and Regards
Mahendra Thalor

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