From: | Jeff Davis <pgsql(at)j-davis(dot)com> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Tomas Vondra <tv(at)fuzzy(dot)cz>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: PATCH: decreasing memory needlessly consumed by array_agg |
Date: | 2015-01-20 07:22:14 |
Message-ID: | 1421738534.12308.5.camel@jeff-desktop |
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Lists: | pgsql-hackers |
On Sun, Dec 28, 2014 at 11:53 PM, Jeff Davis <pgsql(at)j-davis(dot)com> wrote:
> On Tue, 2014-04-01 at 13:08 -0400, Tom Lane wrote:
>> I think a patch that stood a chance of getting committed would need to
>> detect whether the aggregate was being called in simple or grouped
>> contexts, and apply different behaviors in the two cases.
>
> The simple context doesn't seem like a big problem even if we change
> things as Tomas suggests:
>
> "IMNSHO these are the issues we really should fix - by lowering the
> initial element count (64->4) and using a single memory context."
>
> In the simple context, there's only one context regardless, so the only
> cost I see is from reducing the initial allocation from 64 to some lower
> number. But if we're doubling each time, it won't take long to get
> there; and because it's the simple context, we only need to do it once.
Tom (tgl),
Is my reasoning above acceptable?
The current patch, which I am evaluating for commit, does away with
per-group memory contexts (it uses a common context for all groups), and
reduces the initial array allocation from 64 to 8 (but preserves
doubling behavior).
Regards,
Jeff Davis
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