From: | Bruce Momjian <bruce(at)momjian(dot)us> |
---|---|
To: | Greg Smith <greg(at)2ndquadrant(dot)com> |
Cc: | Josh Berkus <josh(at)agliodbs(dot)com>, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: max_standby_delay considered harmful |
Date: | 2010-05-06 21:32:07 |
Message-ID: | 201005062132.o46LW7I22842@momjian.us |
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Thread: | |
Lists: | pgsql-hackers |
Greg Smith wrote:
> Bruce Momjian wrote:
> > Remember, delaying wal application just delays making the standby a
> > master and makes the slave data appear staler. We can just tell people
> > that the larger their queries are, the larger this delay will be. If
> > they want to control this, they can set 'statement_timeout' already.
> >
>
> While a useful defensive component, statement_timeout is a user setting,
> so it can't provide guaranteed protection against a WAL application
> denial of service from a long running query. A user that overrides the
> system setting and kicks off a long query puts you right back into
> needing a timeout to ensure forward progress of standby replay.
The nice thing about query cancel is that it give predictable behavior.
We could make statement_timeout that can't be changed if it is set in
postgresql.conf. Again, let's think of that for 9.1.
--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com
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