BUG #19556: Segmentation fault in test_decoding

The following bug has been logged on the website:

Bug reference:      19556
Logged by:          Alexander Kozhemyakin
Email address:      a.kozhemyakin@postgrespro.ru
PostgreSQL version: 19beta2
Operating system:   ubuntu 26.04
Description:        

Hi,

The following script causes the server to crash with a Segmentation fault.

initdb -D data
echo "
max_prepared_transactions = '15'
wal_level = logical " >> data/postgresql.auto.conf
pg_ctl -D data -l logfile start

psql <skip_empty_xacts && !txndata->xact_wrote_changes)
(gdb) bt
#0  0x0000749f6ee23f54 in pg_decode_prepare_txn (ctx=0x6344c3d7f3f0,
txn=0x6344c3d7d320, prepare_lsn=24628632) at
/pgpro/postgres/contrib/test_decoding/test_decoding.c:378
#1  0x00006344a8e8293c in prepare_cb_wrapper (cache=,
txn=, prepare_lsn=) at
/pgpro/postgres/src/backend/replication/logical/logical.c:985
#2  0x00006344a8e90c24 in ReorderBufferPrepare (rb=0x6344c3cd9e10,
xid=xid@entry=745, gid=gid@entry=0x7ffcb3620ef4 "p1") at
/pgpro/postgres/src/backend/replication/logical/reorderbuffer.c:2934
#3  0x00006344a8e7fa26 in DecodePrepare (ctx=0x6344c3d7f3f0,
buf=0x7ffcb3621030, parsed=0x7ffcb3620ea0) at
/pgpro/postgres/src/backend/replication/logical/decode.c:815
#4  xact_decode (ctx=0x6344c3d7f3f0, buf=0x7ffcb3621030) at
/pgpro/postgres/src/backend/replication/logical/decode.c:347
#5  0x00006344a8e7f223 in LogicalDecodingProcessRecord
(ctx=ctx@entry=0x6344c3d7f3f0, record=0x6344c3d7f788) at
/pgpro/postgres/src/backend/replication/logical/decode.c:116
#6  0x00006344a8e8577b in pg_logical_slot_get_changes_guts
(fcinfo=0x6344c3d83410, confirm=confirm@entry=true,
binary=binary@entry=false) at
/pgpro/postgres/src/backend/replication/logical/logicalfuncs.c:266
#7  0x00006344a8e858f4 in pg_logical_slot_get_changes (fcinfo=) at /pgpro/postgres/src/backend/replication/logical/logicalfuncs.c:333
#8  0x00006344a8d3666d in ExecMakeTableFunctionResult
(setexpr=0x6344c3d5ffc8, econtext=0x6344c3d5fe18, argContext=, expectedDesc=0x6344c3d49868, randomAccess=false)
    at /pgpro/postgres/src/backend/executor/execSRF.c:234
#9  0x00006344a8d4a14b in FunctionNext (node=node@entry=0x6344c3d5fc08) at
/pgpro/postgres/src/backend/executor/nodeFunctionscan.c:94
#10 0x00006344a8d36f4c in ExecScanFetch (node=,
epqstate=, accessMtd=, recheckMtd=) at /pgpro/postgres/src/include/executor/execScan.h:126
#11 ExecScanExtended (node=, accessMtd=0x6344a8d49e10
, recheckMtd=0x6344a8d49e00 , epqstate=0x0,
qual=0x0, projInfo=0x6344c3d49ea8)
    at /pgpro/postgres/src/include/executor/execScan.h:187
#12 ExecScan (node=0x6344c3d5fc08, accessMtd=0x6344a8d49e10 ,
recheckMtd=0x6344a8d49e00 ) at
/pgpro/postgres/src/backend/executor/execScan.c:59
#13 0x00006344a8d2c17b in ExecProcNode (node=0x6344c3d5fc08) at
/pgpro/postgres/src/include/executor/executor.h:272
#14 ExecutePlan (queryDesc=0x6344c3cd55d0, operation=CMD_SELECT,
sendTuples=true, numberTuples=0, direction=,
dest=0x6344c3d8b7b8) at /pgpro/postgres/src/backend/executor/execMain.c:1675
#15 standard_ExecutorRun (queryDesc=0x6344c3cd55d0, direction=, count=0) at /pgpro/postgres/src/backend/executor/execMain.c:364
#16 0x00006344a8f11478 in PortalRunSelect
(portal=portal@entry=0x6344c3d018b0, forward=forward@entry=true, count=0,
count@entry=9223372036854775807, dest=dest@entry=0x6344c3d8b7b8)
    at /pgpro/postgres/src/backend/tcop/pquery.c:920
#17 0x00006344a8f12c5e in PortalRun (portal=portal@entry=0x6344c3d018b0,
count=count@entry=9223372036854775807, isTopLevel=isTopLevel@entry=true,
dest=dest@entry=0x6344c3d8b7b8, altdest=altdest@entry=0x6344c3d8b7b8,
    qc=qc@entry=0x7ffcb3621640) at
/pgpro/postgres/src/backend/tcop/pquery.c:764
#18 0x00006344a8f0e95e in exec_simple_query (query_string=0x6344c3c80f60
"SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL,
'include-xids', '0', 'skip-empty-xacts', '1');")
    at /pgpro/postgres/src/backend/tcop/postgres.c:1271
#19 0x00006344a8f103e5 in PostgresMain (dbname=,
username=) at
/pgpro/postgres/src/backend/tcop/postgres.c:4691
#20 0x00006344a8f0aaa3 in BackendMain (startup_data=,
startup_data_len=) at
/pgpro/postgres/src/backend/tcop/backend_startup.c:107
#21 0x00006344a8e6184f in postmaster_child_launch (child_type=, child_slot=1, startup_data=startup_data@entry=0x7ffcb3621aec "",
startup_data_len=startup_data_len@entry=4,
    client_sock=client_sock@entry=0x7ffcb3621af0) at
/pgpro/postgres/src/backend/postmaster/launch_backend.c:274
#22 0x00006344a8e653ef in BackendStartup (client_sock=0x7ffcb3621af0) at
/pgpro/postgres/src/backend/postmaster/postmaster.c:3519
#23 ServerLoop () at
/pgpro/postgres/src/backend/postmaster/postmaster.c:1688
#24 0x00006344a8e66cbf in PostmasterMain (argc=argc@entry=3,
argv=argv@entry=0x6344c3c7b440) at
/pgpro/postgres/src/backend/postmaster/postmaster.c:1386
#25 0x00006344a8b3b35e in main (argc=3, argv=0x6344c3c7b440) at
/pgpro/postgres/src/backend/main/main.c:230


first bad commit 072ee847ad4c3fb52