Re: WAL Rate Limiting

From: Andres Freund <andres(at)2ndquadrant(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, Magnus Hagander <magnus(at)hagander(dot)net>, Simon Riggs <simon(at)2ndquadrant(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: WAL Rate Limiting
Date: 2014-01-16 15:39:11
Message-ID: 20140116153911.GA21170@alap3.anarazel.de
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On 2014-01-16 10:35:20 -0500, Tom Lane wrote:
> Andres Freund <andres(at)2ndquadrant(dot)com> writes:
> > I don't really see much difficulty in determining what's a utility
> > command and what not for the purpose of this? All utility commands which
> > create WAL in O(table_size) or worse.
>
> By that definition, INSERT, UPDATE, and DELETE can all be "utility
> commands". So would a full-table-scan SELECT, if it's unfortunate
> enough to run into a lot of hint-setting or HOT-pruning work.

Well, I said *utility* command. So everything processed by
ProcessUtility() generating WAL like that.

> I think possibly a more productive approach to this would be to treat
> it as a session-level GUC setting, rather than hard-wiring it to affect
> certain commands and not others.

Do you see a reasonable way to implement this generically for all
commands? I don't.
We shouldn't let the the need for generic resource control stop us from
providing some for of resource control for a consistent subset of
commands.

Greetings,

Andres Freund

--
Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services

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