Re: WAL Rate Limiting

On 2014-01-16 09:06:30 -0500, Robert Haas wrote:
> > Seems like a really bad name if we are only slowing down some commands -
> > that seems to indicate we're slowing down all of them. I think it should be
> > something that indicates that it only affects the maintenance commands.
> 
> And why should it only affect the maintenance commands anyway, and who
> decides what's a maintenance command?

I think implementing it for everything might have some use, but it's a
much, much more complex task. You can't simply do rate limiting in
XLogInsert() or somesuch - we're holding page locks, buffer pins, other
locks... I don't see why that needs to be done in the same feature.

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.

> I thought Heroku suggested something like this previously, and their
> use case was something along the lines of "we need to slow the system
> down enough to do a backup so we can delete some stuff before the disk
> fills".  For that, it seems likely to me that you would just want to
> slow everything down.

I think the usecase for this more along the lines of not slowing normal
operations or cause replication delays to standbys unduly, while
performing maintenance operations on relations.

Greetings,

Andres Freund

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