From: Tom Lane <tgl@sss.pgh.pa.us>
To: Alexander Lakhin <exclusion@gmail.com>
cc: Pavel Borisov <pashkin.elfe@gmail.com>, pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #18616: Long-running hash index build can not be interrupted
In-reply-to: <122464.1726255346@sss.pgh.pa.us>
References: <18616-acbb9e5caf41e964@postgresql.org>
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 <122464.1726255346@sss.pgh.pa.us>
Comments: In-reply-to Tom Lane <tgl@sss.pgh.pa.us>
	message dated "Fri, 13 Sep 2024 15:22:26 -0400"
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Date: Fri, 13 Sep 2024 15:45:11 -0400
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I wrote:
> Looking at hashbuild, the effective sort_threshold depends on
> NBuffers, so maybe if you have that set to a high enough value
> it fails to go into the sort path?  If I use
> SET maintenance_work_mem = '128MB';
> instead of the suggested 1GB, I don't see the problem.

Oh, false alarm: that test in hashbuild takes basically the
min of maintenance_work_mem and NBuffers, so that with
default NBuffers of 128MB, there's no difference here between
those two settings.

The reason I see a difference in behavior seems to be that
with maintenance_work_mem = 1GB, the tuple sorting step
completes faster, allowing control to reach _h_indexbuild
before the 10sec timeout I was testing with.  With the
smaller maintenance_work_mem setting, we're still sorting
when it times out --- and there are CHECK_FOR_INTERRUPTS
calls in the sort code.

			regards, tom lane