From: | Andres Freund <andres(at)anarazel(dot)de> |
---|---|
To: | Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> |
Cc: | Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr>, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, PostgreSQL Developers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: checkpointer continuous flushing |
Date: | 2016-01-09 13:40:27 |
Message-ID: | 20160109134027.3actwyxyv47ffv6z@alap3.anarazel.de |
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Lists: | pgsql-hackers |
On 2016-01-09 19:05:54 +0530, Amit Kapila wrote:
> Right that won't be acceptable, however I think with your latest
> proposal [1]
Sure, that'd address that problem.
> [...] think that idea will help to mitigate the problem of backend and
> bgwriter writes as well. In that, can't we do it with the help of
> existing infrastructure of *pendingOpsTable* and
> *CheckpointerShmem->requests[]*, as already the flush requests are
> remembered in those structures, we can use those to apply your idea to
> issue flush requests.
Hm, that might be possible. But that might have some bigger implications
- we currently can issue thousands of flush requests a second, without
much chance of merging. I'm not sure it's a good idea to overlay that
into the lower frequency pendingOpsTable. Backends having to issue
fsyncs because the pending fsync queue is full is darn expensive. In
contrast to that a 'flush hint' request getting lost doesn't cost that
much.
Greetings,
Andres Freund
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