From: | Jeff Davis <pgsql(at)j-davis(dot)com> |
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To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | pgsql-committers(at)postgresql(dot)org, pgsql-hackers(at)postgresql(dot)org, Andres Freund <andres(at)anarazel(dot)de>, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> |
Subject: | Re: [COMMITTERS] pgsql: Invent a memory context reset/delete callback mechanism. |
Date: | 2015-02-28 01:26:59 |
Message-ID: | 1425086819.12308.273.camel@jeff-desktop |
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Lists: | pgsql-committers pgsql-hackers |
On Fri, 2015-02-27 at 22:17 +0000, Tom Lane wrote:
> In passing, per discussion, rearrange some boolean fields in struct
> MemoryContextData so as to avoid wasted padding space. For safety,
> this requires making allowInCritSection's existence unconditional;
> but I think that's a better approach than what was there anyway.
I notice that this uses the bytes in MemoryContextData that I was hoping
to use for the memory accounting patch (for memory-bounded HashAgg).
Leaving no space for even a 32-bit value (without AllocSetContext
growing beyond the magical 192-byte number Andres mentioned) removes
most of the options for memory accounting. The only things I can think
of are:
1. Move a few less-frequently-accessed fields out to an auxiliary
structure (Tomas proposed something similar); or
2. Walk the memory contexts, but use some kind of
estimation/extrapolation so that it doesn't need to be done for every
input tuple of HashAgg.
Thoughts?
Regards,
Jeff Davis
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