Re: Buffer locking is special (hints, checksums, AIO writes)

Hi,

On 2026-03-13 11:55:53 -0400, Andres Freund wrote:
> On 2026-03-13 10:00:00 +0200, Alexander Lakhin wrote:
> > Hello Andres,
> >
> > 12.03.2026 00:40, Andres Freund wrote:
> > > I pushed this and many of the later patches in the series. Here are updated
> > > versions of the remaining changes. The last two previously were one commit
> > > with "WIP" in the title. The first one has, I think, not had a lot of review -
> > > but it's also not a complicated change.
> >
> > I've discovered that starting from 82467f627, the following query:
> > SET cpu_operator_cost = 1000;
> > CREATE TABLE t (i INT);
> > INSERT INTO T SELECT 1 FROM generate_series(1, 1000) a;
> > CREATE INDEX hi on t USING HASH (i);
> > DELETE FROM t WHERE i = 1;
> > DELETE FROM t WHERE i = 1;
> >
> > triggers
> > TRAP: failed Assert("BufferIsValid(buffer)"), File: "bufmgr.c", Line: 497, PID: 3942058
> >
> > #4  0x000079a60ae288ff in __GI_abort () at ./stdlib/abort.c:79
> > #5  0x00005a68d9343eef in ExceptionalCondition (conditionName=conditionName(at)entry=0x5a68d93ac27d "BufferIsValid(buffer)",
> >     fileName=fileName(at)entry=0x5a68d93c99ef "bufmgr.c", lineNumber=lineNumber(at)entry=497) at assert.c:65
> > #6  0x00005a68d91a18eb in GetPrivateRefCountEntry (do_move=true, buffer=<optimized out>) at bufmgr.c:497
> > #7  SharedBufferBeginSetHintBits (lockstate=<synthetic pointer>, buf_hdr=0x79e5febbbc40, buffer=<optimized out>)
> >     at bufmgr.c:6830
> > #8  BufferBeginSetHintBits (buffer=<optimized out>) at bufmgr.c:6931
> > #9  0x00005a68d8e3c862 in _hash_kill_items (scan=<optimized out>) at hashutil.c:603
> > #10 0x00005a68d8e3b7c3 in _hash_next (scan=0x5a68e735f938, dir=<optimized out>) at hashsearch.c:69
> > #11 0x00005a68d8e616ce in index_getnext_tid (scan=scan(at)entry=0x5a68e735f938, direction=direction(at)entry=ForwardScanDirection)
> >     at indexam.c:647
> > ...
> > #25 0x00005a68d91eb4ad in exec_simple_query (query_string=0x5a68e7270120 "DELETE FROM t WHERE i = 1;") at postgres.c:1277
> > ...
> >
> > Could you please look at this?
>
> Yea, it's a stupid small mistake. Alexander Kuzmenkov reported it late
> afternoon yesterday, privately as I just noticed, and I was too tired to make
> sure an added test wouldn't have stability issues.
>
> Will fix in the next few hours.

Took longer, sorry. But it's pushed now.

Greetings,

Andres Freund