From: Joe Conway <mail@joeconway.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-patches@postgreSQL.org
Subject: Re: Values list-of-targetlists patch for comments (was Re:
Date: Wed, 02 Aug 2006 11:10:11 -0700
Message-ID: <44D0EA83.7050702@joeconway.com> (raw)
In-Reply-To: <17704.1154534183@sss.pgh.pa.us>
References: <44B69778.5050104@dunslane.net>
<50461.84.63.113.55.1152832991.squirrel@pezone.net>
<ECCAAC0A3182895D3D12B0E8@[172.26.14.247]>
<44B7ADFC.90205@dunslane.net>
<44D03D9F.80203@joeconway.com>
<15263.1154526181@sss.pgh.pa.us>
<44D0AF87.2030304@joeconway.com>
<16892.1154528708@sss.pgh.pa.us>
<44D0B9C1.2020608@joeconway.com>
<17704.1154534183@sss.pgh.pa.us>
Tom Lane wrote:
> Yeah, I've just been doing that and some hand analysis too. What I get
> (on a 64-bit machine) is that essentially all the space goes into
>
> lists of A_Const lists: 320000000
> lists of Const lists: 320000000
> transformInsertRow extra lists: 144000000
>
> I think we could safely list_free the input list in transformInsertRow
> as your patch suggests, which would buy back the 144M part. But I don't
> believe it's safe at all to free the raw_parser output --- the grammar
> sometimes makes multiple links to the same subtree, eg in BETWEEN.
> In any case the patch as proposed wouldn't catch all the detritus for
> any case more complicated than a simple integer constant.
:-(
> The way that the list memory usage works (again, 64-bit machine) is
>
> sizeof(List) = 24
> sizeof(ListCell) = 16
> sizeof(A_Const) = 32
>
> Each of these nodes will have 16 bytes palloc overhead, and the List
> header will be rounded up to 32 bytes as well, so we have total space
> for a 3-element integer list of
> 32+16 + (16+16 + 32+16) * 3
> Add in 16+16 for the associated ListCell of the top list-of-lists,
> and you come to 320 bytes per sublist. Const happens to also be
> 32 bytes so the transformed lists are the same size.
What if we built an array of A_Const nodes instead of a List? Maybe we
could use something akin to appendStringInfo()/enlargeStringInfo() to
build the array of nodes and enlarge it in chunks.
Joe
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Cc: mail@joeconway.com, tgl@sss.pgh.pa.us, pgsql-patches@postgreSQL.org
Subject: Re: Values list-of-targetlists patch for comments (was Re:
In-Reply-To: <44D0EA83.7050702@joeconway.com>
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