Re: BUG #19006: Assert(BufferIsPinned) in BufferGetBlockNumber() is triggered for forwarded buffer

Hi,

On Sun, Aug 3, 2025 at 8:58 PM 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 = s.two
>         WHERE s.twenty < 0;
>
> with
> shared_buffers = 16MB
> triggers:
> TRAP: failed Assert("BufferIsPinned(buffer)"), File: "bufmgr.c", Line: 4233,
> PID: 2785555
>
> Core was generated by `postgres: law regression [local] SELECT
> '.
> Program terminated with signal SIGABRT, Aborted.
> ...
> #0  __pthread_kill_implementation (no_tid=0, signo=6, threadid=<optimized
> out>) at ./nptl/pthread_kill.c:44
> #1  __pthread_kill_internal (signo=6, threadid=<optimized out>) at
> ./nptl/pthread_kill.c:78
> #2  __GI___pthread_kill (threadid=<optimized out>, signo=signo@entry=6) at
> ./nptl/pthread_kill.c:89
> #3  0x000075efce04527e in __GI_raise (sig=sig@entry=6) at
> ../sysdeps/posix/raise.c:26
> #4  0x000075efce0288ff in __GI_abort () at ./stdlib/abort.c:79
> #5  0x00006419a43d5e3f in ExceptionalCondition
> (conditionName=conditionName@entry=0x6419a445bb56 "BufferIsPinned(buffer)",
> fileName=fileName@entry=0x6419a445b9b7 "bufmgr.c",
> lineNumber=lineNumber@entry=4233) at assert.c:66
> #6  0x00006419a423f028 in BufferGetBlockNumber (buffer=<optimized out>) at
> bufmgr.c:4233
> #7  0x00006419a42445c5 in StartReadBuffersImpl (allow_forwarding=true,
> flags=0, nblocks=0x7fff9765ee74, blockNum=710, buffers=0x6419bc3d127c,
> operation=0x6419bc3d1428) at bufmgr.c:1292
> #8  StartReadBuffers (operation=0x6419bc3d1428,
> buffers=buffers@entry=0x6419bc3d127c, blockNum=710,
> nblocks=nblocks@entry=0x7fff9765ee74, flags=flags@entry=0) at bufmgr.c:1500
> #9  0x00006419a423afc4 in read_stream_start_pending_read
> (stream=stream@entry=0x6419bc3d1218) at read_stream.c:335
> #10 0x00006419a423b3df in read_stream_look_ahead
> (stream=stream@entry=0x6419bc3d1218) at read_stream.c:493
> #11 0x00006419a423b7b3 in read_stream_next_buffer (stream=0x6419bc3d1218,
> per_buffer_data=per_buffer_data@entry=0x0) at read_stream.c:971
> #12 0x00006419a3efaede in heap_fetch_next_buffer (dir=<optimized out>,
> scan=0x6419bc3d0cf8) at heapam.c:675
> #13 heapgettup_pagemode (scan=scan@entry=0x6419bc3d0cf8, dir=<optimized
> out>, nkeys=<optimized out>, key=<optimized out>) at heapam.c:1037
> #14 0x00006419a3efb5d2 in heap_getnextslot (sscan=0x6419bc3d0cf8,
> direction=<optimized out>, slot=0x6419bc3c11a8) at heapam.c:1391
> #15 0x00006419a40d1503 in table_scan_getnextslot (slot=0x6419bc3c11a8,
> direction=ForwardScanDirection, sscan=<optimized out>) at
> ../../../src/include/access/tableam.h:1031
> #16 SeqNext (node=node@entry=0x6419bc3c0f88) at nodeSeqscan.c:81
> #17 0x00006419a40d197f in ExecScanFetch (recheckMtd=0x6419a40d1490
> <SeqRecheck>, accessMtd=0x6419a40d14a0 <SeqNext>, epqstate=0x0,
> node=<optimized out>) at ../../../src/include/executor/execScan.h:126
> #18 ExecScanExtended (projInfo=0x0, qual=0x6419bc38a650, epqstate=0x0,
> recheckMtd=0x6419a40d1490 <SeqRecheck>, accessMtd=0x6419a40d14a0 <SeqNext>,
> node=0x6419bc3c0f88) at ../../../src/include/executor/execScan.h:187
> #19 ExecSeqScanWithQual (pstate=0x6419bc3c0f88) at nodeSeqscan.c:138
> #20 0x00006419a40cf97b in ExecProcNode (node=0x6419bc3c0f88) at
> ../../../src/include/executor/executor.h:313
> #21 ExecNestLoop (pstate=<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