From: Tom Lane <tgl@sss.pgh.pa.us>
To: Alvaro Herrera <alvherre@2ndquadrant.com>
Cc: Amit Langote <Langote_Amit_f8@lab.ntt.co.jp>
Cc: Bruno Wolff III <bruno@wolff.to>
Cc: pgsql-general@lists.postgresql.org
Cc: pgsql-hackers@lists.postgresql.org
Subject: Re: Should pg 11 use a lot more memory building an spgist index?
Date: Fri, 26 Oct 2018 15:20:02 +0100
Message-ID: <26004.1540563602@sss.pgh.pa.us> (raw)
In-Reply-To: <20181026140927.oh4gd367st47li6h@alvherre.pgsql>
References: <20181026140927.oh4gd367st47li6h@alvherre.pgsql>
Alvaro Herrera <alvherre@2ndquadrant.com> writes:
> On 2018-Oct-26, Tom Lane wrote:
>> After a quick look around, I think that making systable_begin/endscan
>> do this is a nonstarter; there are just too many call sites that would
>> be affected. Now, you could imagine specifying that indexes on system
>> catalogs (in practice, only btree) have to clean up at endscan time
>> but other index types don't, so that only operations that might be
>> scanning user indexes need to have suitable wrapping contexts. Not sure
>> there's a lot of benefit to that, though.
> How about modifying SysScanDescData to have a memory context member,
> which is created by systable_beginscan and destroyed by endscan?
I think it would still have problems, in that it would affect in which
context index_getnext delivers its output. We could reasonably make
these sorts of changes in places where the entire index_beginscan/
index_getnext/index_endscan call structure is in one place, but that
doesn't apply for the systable functions.
Also, going in that direction would imply an additional memory context
switch / switch-back per tuple processed (around the index_getnext call),
which would create questions about whether it has a negative performance
impact.
regards, tom lane
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To: pgsql-general@postgresql.org
Cc: tgl@sss.pgh.pa.us, alvherre@2ndquadrant.com, Langote_Amit_f8@lab.ntt.co.jp, bruno@wolff.to, pgsql-general@lists.postgresql.org, pgsql-hackers@lists.postgresql.org
Subject: Re: Should pg 11 use a lot more memory building an spgist index?
In-Reply-To: <26004.1540563602@sss.pgh.pa.us>
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