From: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>
To: Amit Kapila <amit.kapila16@gmail.com>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: VACUUM PARALLEL option vs. max_parallel_maintenance_workers
Date: Sun, 20 Sep 2020 15:46:29 +0200
Message-ID: <4de14d71-7fe9-fa12-121e-a41bd610998e@2ndquadrant.com> (raw)
In-Reply-To: <CAA4eK1Ljgt1V89ua5b=Y02r2c0ch05VXm-F3ew6gyxbqLoVXxA@mail.gmail.com>
References: <36aa8aea-61b7-eb3c-263b-648e0cb117b7@2ndquadrant.com>
<CAA4eK1LQWXS_4RwLo+WT7jusGnBkUvXO73xQOCsydWLYBpLBEg@mail.gmail.com>
<5a8b1b58-30b6-cd9a-5a37-75f1da063429@2ndquadrant.com>
<CAA4eK1Ljgt1V89ua5b=Y02r2c0ch05VXm-F3ew6gyxbqLoVXxA@mail.gmail.com>
On 2020-09-19 13:24, Amit Kapila wrote:
>> I think the implemented behavior is wrong.
>
> It is the same as what we do for other parallel operations, for
> example, we limit the number of parallel workers for parallel create
> index by 'max_parallel_maintenance_workers' and parallel scan
> operations are limited by 'max_parallel_workers_per_gather'.
But in those cases we don't provide user-visible options to specify a
per-command setting, so it's not the same thing, is it?
>> The VACUUM PARALLEL option
>> should override the max_parallel_maintenance_worker setting.
>>
>> Otherwise, what's the point of the command option?
>
> It is for the cases where the user has a better idea of workload. We
> can launch only a limited number of parallel workers
> 'max_parallel_workers' in the system, so sometimes users would like to
> use it as per their requirement.
Right, but my point is, it doesn't actually do that correctly. I can't
just say, oh, I have a maintenance window, I'd like to run a really fast
VACUUM. The PARALLEL option is capped by the setting you'd normally use
anyway, so specifying it is useless.
The only thing it can do right now is if you want to run a manual VACUUM
less parallel than by default. But I don't see how that is often useful.
--
Peter Eisentraut http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-hackers@postgresql.org
Cc: peter.eisentraut@2ndquadrant.com, amit.kapila16@gmail.com
Subject: Re: VACUUM PARALLEL option vs. max_parallel_maintenance_workers
In-Reply-To: <4de14d71-7fe9-fa12-121e-a41bd610998e@2ndquadrant.com>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox