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In-Reply-To: <19006-80fcaaf69000377e@postgresql.org>
From: Xuneng Zhou <xunengzhou@gmail.com>
Date: Mon, 4 Aug 2025 21:13:47 +0800
Message-ID: <CABPTF7VaW0Hw2-KXoiYFTH40LeUgr06gE5q09sq9LXQPH-vjPA@mail.gmail.com>
Subject: Re: BUG #19006: Assert(BufferIsPinned) in BufferGetBlockNumber() is
 triggered for forwarded buffer
To: exclusion@gmail.com, pgsql-bugs@lists.postgresql.org
Cc: thomas.munro@gmail.com, Michael Paquier <michael@paquier.xyz>
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Hi,

On Sun, Aug 3, 2025 at 8:58=E2=80=AFPM PG Bug reporting form
<noreply@postgresql.org> wrote:
>
> The following bug has been logged on the website:
>
> Bug reference:      19006
> Logged by:          Alexander Lakhin
> Email address:      exclusion@gmail.com
> PostgreSQL version: 18beta2
> Operating system:   Ubuntu 24.04
> Description:
>
> The following script (based on the regress scripts):
> CREATE TABLE public.tenk1 (
>     unique1 integer,
>     unique2 integer,
>     two integer,
>     four integer,
>     ten integer,
>     twenty integer,
>     hundred integer,
>     thousand integer,
>     twothousand integer,
>     fivethous integer,
>     tenthous integer,
>     odd integer,
>     even integer,
>     stringu1 name,
>     stringu2 name,
>     string4 name
> );
>
> COPY tenk1 FROM '.../src/test/regress/data/tenk.data';
> COPY tenk1 FROM '.../src/test/regress/data/tenk.data';
> DELETE FROM tenk1;
> COPY tenk1 FROM '.../src/test/regress/data/tenk.data';
>
> SELECT COUNT(*) FROM tenk1 t1 LEFT JOIN
>         LATERAL (SELECT t1.twenty, t2.two FROM tenk1 t2) s
>         ON t1.two =3D s.two
>         WHERE s.twenty < 0;
>
> with
> shared_buffers =3D 16MB
> triggers:
> TRAP: failed Assert("BufferIsPinned(buffer)"), File: "bufmgr.c", Line: 42=
33,
> PID: 2785555
>
> Core was generated by `postgres: law regression [local] SELECT
> '.
> Program terminated with signal SIGABRT, Aborted.
> ...
> #0  __pthread_kill_implementation (no_tid=3D0, signo=3D6, threadid=3D<opt=
imized
> out>) at ./nptl/pthread_kill.c:44
> #1  __pthread_kill_internal (signo=3D6, threadid=3D<optimized out>) at
> ./nptl/pthread_kill.c:78
> #2  __GI___pthread_kill (threadid=3D<optimized out>, signo=3Dsigno@entry=
=3D6) at
> ./nptl/pthread_kill.c:89
> #3  0x000075efce04527e in __GI_raise (sig=3Dsig@entry=3D6) at
> ../sysdeps/posix/raise.c:26
> #4  0x000075efce0288ff in __GI_abort () at ./stdlib/abort.c:79
> #5  0x00006419a43d5e3f in ExceptionalCondition
> (conditionName=3DconditionName@entry=3D0x6419a445bb56 "BufferIsPinned(buf=
fer)",
> fileName=3DfileName@entry=3D0x6419a445b9b7 "bufmgr.c",
> lineNumber=3DlineNumber@entry=3D4233) at assert.c:66
> #6  0x00006419a423f028 in BufferGetBlockNumber (buffer=3D<optimized out>)=
 at
> bufmgr.c:4233
> #7  0x00006419a42445c5 in StartReadBuffersImpl (allow_forwarding=3Dtrue,
> flags=3D0, nblocks=3D0x7fff9765ee74, blockNum=3D710, buffers=3D0x6419bc3d=
127c,
> operation=3D0x6419bc3d1428) at bufmgr.c:1292
> #8  StartReadBuffers (operation=3D0x6419bc3d1428,
> buffers=3Dbuffers@entry=3D0x6419bc3d127c, blockNum=3D710,
> nblocks=3Dnblocks@entry=3D0x7fff9765ee74, flags=3Dflags@entry=3D0) at buf=
mgr.c:1500
> #9  0x00006419a423afc4 in read_stream_start_pending_read
> (stream=3Dstream@entry=3D0x6419bc3d1218) at read_stream.c:335
> #10 0x00006419a423b3df in read_stream_look_ahead
> (stream=3Dstream@entry=3D0x6419bc3d1218) at read_stream.c:493
> #11 0x00006419a423b7b3 in read_stream_next_buffer (stream=3D0x6419bc3d121=
8,
> per_buffer_data=3Dper_buffer_data@entry=3D0x0) at read_stream.c:971
> #12 0x00006419a3efaede in heap_fetch_next_buffer (dir=3D<optimized out>,
> scan=3D0x6419bc3d0cf8) at heapam.c:675
> #13 heapgettup_pagemode (scan=3Dscan@entry=3D0x6419bc3d0cf8, dir=3D<optim=
ized
> out>, nkeys=3D<optimized out>, key=3D<optimized out>) at heapam.c:1037
> #14 0x00006419a3efb5d2 in heap_getnextslot (sscan=3D0x6419bc3d0cf8,
> direction=3D<optimized out>, slot=3D0x6419bc3c11a8) at heapam.c:1391
> #15 0x00006419a40d1503 in table_scan_getnextslot (slot=3D0x6419bc3c11a8,
> direction=3DForwardScanDirection, sscan=3D<optimized out>) at
> ../../../src/include/access/tableam.h:1031
> #16 SeqNext (node=3Dnode@entry=3D0x6419bc3c0f88) at nodeSeqscan.c:81
> #17 0x00006419a40d197f in ExecScanFetch (recheckMtd=3D0x6419a40d1490
> <SeqRecheck>, accessMtd=3D0x6419a40d14a0 <SeqNext>, epqstate=3D0x0,
> node=3D<optimized out>) at ../../../src/include/executor/execScan.h:126
> #18 ExecScanExtended (projInfo=3D0x0, qual=3D0x6419bc38a650, epqstate=3D0=
x0,
> recheckMtd=3D0x6419a40d1490 <SeqRecheck>, accessMtd=3D0x6419a40d14a0 <Seq=
Next>,
> node=3D0x6419bc3c0f88) at ../../../src/include/executor/execScan.h:187
> #19 ExecSeqScanWithQual (pstate=3D0x6419bc3c0f88) at nodeSeqscan.c:138
> #20 0x00006419a40cf97b in ExecProcNode (node=3D0x6419bc3c0f88) at
> ../../../src/include/executor/executor.h:313
> #21 ExecNestLoop (pstate=3D<optimized out>) at nodeNestloop.c:159
> ...
>
> Reproduced starting from 12ce89fd0.
>

Thanks for reporting this. I can reproduce this issue reliably when
shared_buffers is set to 16 MB; raising the value allows the query to
complete normally. However, I don't have the expertise to investigate
and fix it. Perhaps we could CC Thomas on this thread to see whether
he might have time to look into it.

Best,
Xuneng