Re: 9.5: Better memory accounting, towards memory-bounded HashAgg

From: Michael Paquier <michael(dot)paquier(at)gmail(dot)com>
To: Jeff Davis <pgsql(at)j-davis(dot)com>
Cc: Peter Geoghegan <pg(at)heroku(dot)com>, Andres Freund <andres(at)2ndquadrant(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Robert Haas <robertmhaas(at)gmail(dot)com>, Tomas Vondra <tv(at)fuzzy(dot)cz>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: 9.5: Better memory accounting, towards memory-bounded HashAgg
Date: 2014-12-15 02:26:44
Message-ID: CAB7nPqRQYuMivFScy4F3pCvUx_Aj+VS+Z0qf4bsWpjch5s7K+A@mail.gmail.com
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On Mon, Dec 8, 2014 at 9:39 AM, Michael Paquier
<michael(dot)paquier(at)gmail(dot)com> wrote:
> On Tue, Dec 2, 2014 at 2:14 PM, Jeff Davis <pgsql(at)j-davis(dot)com> wrote:
>> On Sun, 2014-11-30 at 17:49 -0800, Peter Geoghegan wrote:
>>> On Mon, Nov 17, 2014 at 11:39 PM, Jeff Davis <pgsql(at)j-davis(dot)com> wrote:
>>> > I can also just move isReset there, and keep mem_allocated as a uint64.
>>> > That way, if I find later that I want to track the aggregated value for
>>> > the child contexts as well, I can split it into two uint32s. I'll hold
>>> > off any any such optimizations until I see some numbers from HashAgg
>>> > though.
>>>
>>> I took a quick look at memory-accounting-v8.patch.
>>>
>>> Is there some reason why mem_allocated is a uint64? All other things
>>> being equal, I'd follow the example of tuplesort.c's
>>> MemoryContextAllocHuge() API, which (following bugfix commit
>>> 79e0f87a1) uses int64 variables to track available memory and so on.
>>
>> No reason. New version attached; that's the only change.
> Note that I am marking this patch back to "Needs Review" state. I
Moving to CF 2014-12.
--
Michael

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