From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
---|---|
To: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> |
Cc: | Amit Langote <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp>, Bruno Wolff III <bruno(at)wolff(dot)to>, pgsql-general(at)lists(dot)postgresql(dot)org, pgsql-hackers(at)lists(dot)postgresql(dot)org |
Subject: | Re: Should pg 11 use a lot more memory building an spgist index? |
Date: | 2018-10-26 14:20:02 |
Message-ID: | 26004.1540563602@sss.pgh.pa.us |
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Alvaro Herrera <alvherre(at)2ndquadrant(dot)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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