Horton

Re: Extension Enhancement: Buffer Invalidation in pg_buffercache

Japin Li <japinli@hotmail.com>

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From: Japin Li <japinli@hotmail.com>
To: jian he <jian.universality@gmail.com>
Cc: Palak Chaturvedi <chaturvedipalak1911@gmail.com>, Thomas Munro <thomas.munro@gmail.com>, pgsql-hackers@postgresql.org, pgsql-hackers@lists.postgresql.org
Date: 2023-07-04T09:45:47Z
Lists: pgsql-hackers

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  1. Add pg_buffercache_evict() function for testing.

On Tue, 04 Jul 2023 at 17:00, jian he <jian.universality@gmail.com> wrote:
> the following will also crash. no idea why.
> begin;
>     select count(*) from onek;
>     select relpages from pg_class where relname = 'onek'; --queryA
>
>     SELECT count(*) FROM pg_buffercache WHERE relfilenode =
> pg_relation_filenode('onek'::regclass); --queryB
>
>     insert into onek values(default);
>
>     select count(pg_buffercache_invalidate(bufferid)) from
>     pg_buffercache where relfilenode =
> pg_relation_filenode('onek'::regclass);
>
> ---------------------------------
> queryA returns 35, queryB returns 37.
> ----------------------------------
> crash info:
> test_dev=*#     insert into onek values(default);
> INSERT 0 1
> test_dev=*#     select count(pg_buffercache_invalidate(bufferid)) from
>     pg_buffercache where relfilenode =
> pg_relation_filenode('onek'::regclass);
> TRAP: failed Assert("resarr->nitems < resarr->maxitems"), File:
> "../../Desktop/pg_sources/main/postgres/src/backend/utils/resowner/resowner.c",
> Line: 275, PID: 1533312

According to the comments of ResourceArrayAdd(), the caller must have previously
done ResourceArrayEnlarge(). I tried to call ResourceOwnerEnlargeBuffers() before
PinBuffer_Locked(), so it can avoid this crash.

		if ((buf_state & BM_DIRTY) == BM_DIRTY)
		{
+			/* make sure we can handle the pin */
+			ResourceOwnerEnlargeBuffers(CurrentResourceOwner);
+
			/*
			 * Try once to flush the dirty buffer.
			 */
			PinBuffer_Locked(bufHdr);

-- 
Regrads,
Japin Li.