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Subject: BUG #19556: Segmentation fault in test_decoding
To: pgsql-bugs@lists.postgresql.org
From: PG Bug reporting form <noreply@postgresql.org>
Cc: a.kozhemyakin@postgrespro.ru
Reply-To: a.kozhemyakin@postgrespro.ru, pgsql-bugs@lists.postgresql.org
Date: Fri, 17 Jul 2026 06:24:34 +0000
Message-ID: <19556-daa6d7ea65054d48@postgresql.org>
Auto-Submitted: auto-generated
Archived-At: 
 <https://www.postgresql.org/message-id/19556-daa6d7ea65054d48%40postgresql.org>
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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:       =20

Hi,

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

initdb -D data
echo "
max_prepared_transactions =3D '15'
wal_level =3D logical " >> data/postgresql.auto.conf
pg_ctl -D data -l logfile start

psql <<EOF
SELECT 'init' FROM pg_create_logical_replication_slot('regression_slot',
'test_decoding', false, true);
CREATE TABLE test (id int PRIMARY KEY, data text);
INSERT INTO test VALUES (1, 'test data');
BEGIN;
SELECT * FROM test WHERE id =3D 1 FOR SHARE;
PREPARE TRANSACTION 'p1';
SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL,
'include-xids', '0', 'skip-empty-xacts', '1');
EOF


backtrace
Program terminated with signal SIGSEGV, Segmentation fault.
#0  0x0000749f6ee23f54 in pg_decode_prepare_txn (ctx=3D0x6344c3d7f3f0,
txn=3D0x6344c3d7d320, prepare_lsn=3D24628632) at
/pgpro/postgres/contrib/test_decoding/test_decoding.c:378
378             if (data->skip_empty_xacts && !txndata->xact_wrote_changes)
(gdb) bt
#0  0x0000749f6ee23f54 in pg_decode_prepare_txn (ctx=3D0x6344c3d7f3f0,
txn=3D0x6344c3d7d320, prepare_lsn=3D24628632) at
/pgpro/postgres/contrib/test_decoding/test_decoding.c:378
#1  0x00006344a8e8293c in prepare_cb_wrapper (cache=3D<optimized out>,
txn=3D<optimized out>, prepare_lsn=3D<optimized out>) at
/pgpro/postgres/src/backend/replication/logical/logical.c:985
#2  0x00006344a8e90c24 in ReorderBufferPrepare (rb=3D0x6344c3cd9e10,
xid=3Dxid@entry=3D745, gid=3Dgid@entry=3D0x7ffcb3620ef4 "p1") at
/pgpro/postgres/src/backend/replication/logical/reorderbuffer.c:2934
#3  0x00006344a8e7fa26 in DecodePrepare (ctx=3D0x6344c3d7f3f0,
buf=3D0x7ffcb3621030, parsed=3D0x7ffcb3620ea0) at
/pgpro/postgres/src/backend/replication/logical/decode.c:815
#4  xact_decode (ctx=3D0x6344c3d7f3f0, buf=3D0x7ffcb3621030) at
/pgpro/postgres/src/backend/replication/logical/decode.c:347
#5  0x00006344a8e7f223 in LogicalDecodingProcessRecord
(ctx=3Dctx@entry=3D0x6344c3d7f3f0, record=3D0x6344c3d7f788) at
/pgpro/postgres/src/backend/replication/logical/decode.c:116
#6  0x00006344a8e8577b in pg_logical_slot_get_changes_guts
(fcinfo=3D0x6344c3d83410, confirm=3Dconfirm@entry=3Dtrue,
binary=3Dbinary@entry=3Dfalse) at
/pgpro/postgres/src/backend/replication/logical/logicalfuncs.c:266
#7  0x00006344a8e858f4 in pg_logical_slot_get_changes (fcinfo=3D<optimized
out>) at /pgpro/postgres/src/backend/replication/logical/logicalfuncs.c:333
#8  0x00006344a8d3666d in ExecMakeTableFunctionResult
(setexpr=3D0x6344c3d5ffc8, econtext=3D0x6344c3d5fe18, argContext=3D<optimiz=
ed
out>, expectedDesc=3D0x6344c3d49868, randomAccess=3Dfalse)
    at /pgpro/postgres/src/backend/executor/execSRF.c:234
#9  0x00006344a8d4a14b in FunctionNext (node=3Dnode@entry=3D0x6344c3d5fc08)=
 at
/pgpro/postgres/src/backend/executor/nodeFunctionscan.c:94
#10 0x00006344a8d36f4c in ExecScanFetch (node=3D<optimized out>,
epqstate=3D<optimized out>, accessMtd=3D<optimized out>, recheckMtd=3D<opti=
mized
out>) at /pgpro/postgres/src/include/executor/execScan.h:126
#11 ExecScanExtended (node=3D<optimized out>, accessMtd=3D0x6344a8d49e10
<FunctionNext>, recheckMtd=3D0x6344a8d49e00 <FunctionRecheck>, epqstate=3D0=
x0,
qual=3D0x0, projInfo=3D0x6344c3d49ea8)
    at /pgpro/postgres/src/include/executor/execScan.h:187
#12 ExecScan (node=3D0x6344c3d5fc08, accessMtd=3D0x6344a8d49e10 <FunctionNe=
xt>,
recheckMtd=3D0x6344a8d49e00 <FunctionRecheck>) at
/pgpro/postgres/src/backend/executor/execScan.c:59
#13 0x00006344a8d2c17b in ExecProcNode (node=3D0x6344c3d5fc08) at
/pgpro/postgres/src/include/executor/executor.h:272
#14 ExecutePlan (queryDesc=3D0x6344c3cd55d0, operation=3DCMD_SELECT,
sendTuples=3Dtrue, numberTuples=3D0, direction=3D<optimized out>,
dest=3D0x6344c3d8b7b8) at /pgpro/postgres/src/backend/executor/execMain.c:1=
675
#15 standard_ExecutorRun (queryDesc=3D0x6344c3cd55d0, direction=3D<optimized
out>, count=3D0) at /pgpro/postgres/src/backend/executor/execMain.c:364
#16 0x00006344a8f11478 in PortalRunSelect
(portal=3Dportal@entry=3D0x6344c3d018b0, forward=3Dforward@entry=3Dtrue, co=
unt=3D0,
count@entry=3D9223372036854775807, dest=3Ddest@entry=3D0x6344c3d8b7b8)
    at /pgpro/postgres/src/backend/tcop/pquery.c:920
#17 0x00006344a8f12c5e in PortalRun (portal=3Dportal@entry=3D0x6344c3d018b0,
count=3Dcount@entry=3D9223372036854775807, isTopLevel=3DisTopLevel@entry=3D=
true,
dest=3Ddest@entry=3D0x6344c3d8b7b8, altdest=3Daltdest@entry=3D0x6344c3d8b7b=
8,
    qc=3Dqc@entry=3D0x7ffcb3621640) at
/pgpro/postgres/src/backend/tcop/pquery.c:764
#18 0x00006344a8f0e95e in exec_simple_query (query_string=3D0x6344c3c80f60
"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=3D<optimized out>,
username=3D<optimized out>) at
/pgpro/postgres/src/backend/tcop/postgres.c:4691
#20 0x00006344a8f0aaa3 in BackendMain (startup_data=3D<optimized out>,
startup_data_len=3D<optimized out>) at
/pgpro/postgres/src/backend/tcop/backend_startup.c:107
#21 0x00006344a8e6184f in postmaster_child_launch (child_type=3D<optimized
out>, child_slot=3D1, startup_data=3Dstartup_data@entry=3D0x7ffcb3621aec "",
startup_data_len=3Dstartup_data_len@entry=3D4,
    client_sock=3Dclient_sock@entry=3D0x7ffcb3621af0) at
/pgpro/postgres/src/backend/postmaster/launch_backend.c:274
#22 0x00006344a8e653ef in BackendStartup (client_sock=3D0x7ffcb3621af0) 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=3Dargc@entry=3D3,
argv=3Dargv@entry=3D0x6344c3c7b440) at
/pgpro/postgres/src/backend/postmaster/postmaster.c:1386
#25 0x00006344a8b3b35e in main (argc=3D3, argv=3D0x6344c3c7b440) at
/pgpro/postgres/src/backend/main/main.c:230


first bad commit 072ee847ad4c3fb52