CREATE UNLOGGED TABLE seq faults when debug_discard_caches=1

Hi Hackers,

while testing the developer settings of PSQL (14.5) I came across this
issue:

postgres=# CREATE UNLOGGED TABLE stats (
postgres(# pg_hash BIGINT NOT NULL,
postgres(# category TEXT NOT NULL,
postgres(# PRIMARY KEY (pg_hash, category)
postgres(# );
server closed the connection unexpectedly
This probably means the server terminated abnormally
before or while processing the request.
The connection to the server was lost. Attempting reset: Failed.

Checking the stack trace I found this:
Program received signal SIGSEGV, Segmentation fault.
0x0000000000ab6662 in smgrwrite (reln=0x0, forknum=INIT_FORKNUM,
blocknum=0, buffer=0x2b5eec0 "", skipFsync=true)
at
/opt/postgresql-src/debug-build/../src/backend/storage/smgr/smgr.c:526
526 smgrsw[reln->smgr_which].smgr_write(reln, forknum, blocknum,
(gdb) bt
#0 0x0000000000ab6662 in smgrwrite (reln=0x0, forknum=INIT_FORKNUM,
blocknum=0, buffer=0x2b5eec0 "", skipFsync=true) at
/opt/postgresql-src/debug-build/../src/backend/storage/smgr/smgr.c:526
#1 0x000000000056991b in btbuildempty (index=0x7fe60ac9be60) at
/opt/postgresql-src/debug-build/../src/backend/access/nbtree/nbtree.c:166
#2 0x0000000000623ad9 in index_build (heapRelation=0x7fe60ac9c078,
indexRelation=0x7fe60ac9be60, indexInfo=0x2b4c330, isreindex=false,
parallel=true) at
/opt/postgresql-src/debug-build/../src/backend/catalog/index.c:3028
#3 0x0000000000621886 in index_create (heapRelation=0x7fe60ac9c078,
indexRelationName=0x2b4c448 "stats_pkey", indexRelationId=16954,
parentIndexRelid=0, parentConstraintId=0, relFileNode=0,
indexInfo=0x2b4c330, indexColNames=0x2b4bee8, accessMethodObjectId=403,
tableSpaceId=0, collationObjectId=0x2b4c560, classObjectId=0x2b4c580,
coloptions=0x2b4c5a0, reloptions=0,
flags=3, constr_flags=0, allow_system_table_mods=false,
is_internal=false, constraintId=0x7ffef5cc4a7c) at
/opt/postgresql-src/debug-build/../src/backend/catalog/index.c:1232
#4 0x000000000074af6e in DefineIndex (relationId=16949, stmt=0x2b527a0,
indexRelationId=0, parentIndexId=0, parentConstraintId=0,
is_alter_table=false, check_rights=true, check_not_in_use=true,
skip_build=false, quiet=false) at
/opt/postgresql-src/debug-build/../src/backend/commands/indexcmds.c:1164
#5 0x0000000000ac8d78 in ProcessUtilitySlow (pstate=0x2b49230,
pstmt=0x2b48fe8, queryString=0x2a71650 "CREATE UNLOGGED TABLE stats (\n
pg_hash BIGINT NOT NULL,\n category TEXT NOT NULL,\n PRIMARY KEY
(pg_hash, category)\n);", context=PROCESS_UTILITY_SUBCOMMAND, params=0x0,
queryEnv=0x0, dest=0xe9ceb0 <donothingDR>, qc=0x0)
at /opt/postgresql-src/debug-build/../src/backend/tcop/utility.c:1535
#6 0x0000000000ac6637 in standard_ProcessUtility (pstmt=0x2b48fe8,
queryString=0x2a71650 "CREATE UNLOGGED TABLE stats (\n pg_hash BIGINT
NOT NULL,\n category TEXT NOT NULL,\n PRIMARY KEY (pg_hash,
category)\n);", readOnlyTree=false, context=PROCESS_UTILITY_SUBCOMMAND,
params=0x0, queryEnv=0x0, dest=0xe9ceb0 <donothingDR>, qc=0x0)
at /opt/postgresql-src/debug-build/../src/backend/tcop/utility.c:1066
#7 0x0000000000ac548b in ProcessUtility (pstmt=0x2b48fe8,
queryString=0x2a71650 "CREATE UNLOGGED TABLE stats (\n pg_hash BIGINT
NOT NULL,\n category TEXT NOT NULL,\n PRIMARY KEY (pg_hash,
category)\n);", readOnlyTree=false, context=PROCESS_UTILITY_SUBCOMMAND,
params=0x0, queryEnv=0x0, dest=0xe9ceb0 <donothingDR>, qc=0x0)
at /opt/postgresql-src/debug-build/../src/backend/tcop/utility.c:527
#8 0x0000000000ac7e5e in ProcessUtilitySlow (pstate=0x2b52b10,
pstmt=0x2a72d28, queryString=0x2a71650 "CREATE UNLOGGED TABLE stats (\n
pg_hash BIGINT NOT NULL,\n category TEXT NOT NULL,\n PRIMARY KEY
(pg_hash, category)\n);", context=PROCESS_UTILITY_TOPLEVEL, params=0x0,
queryEnv=0x0, dest=0x2a72df8, qc=0x7ffef5cc6c10)
at /opt/postgresql-src/debug-build/../src/backend/tcop/utility.c:1244
#9 0x0000000000ac6637 in standard_ProcessUtility (pstmt=0x2a72d28,
queryString=0x2a71650 "CREATE UNLOGGED TABLE stats (\n pg_hash BIGINT
NOT NULL,\n category TEXT NOT NULL,\n PRIMARY KEY (pg_hash,
category)\n);", readOnlyTree=false, context=PROCESS_UTILITY_TOPLEVEL,
params=0x0, queryEnv=0x0, dest=0x2a72df8, qc=0x7ffef5cc6c10)
at /opt/postgresql-src/debug-build/../src/backend/tcop/utility.c:1066
#10 0x0000000000ac548b in ProcessUtility (pstmt=0x2a72d28,
queryString=0x2a71650 "CREATE UNLOGGED TABLE stats (\n pg_hash BIGINT
NOT NULL,\n category TEXT NOT NULL,\n PRIMARY KEY (pg_hash,
category)\n);", readOnlyTree=false, context=PROCESS_UTILITY_TOPLEVEL,
params=0x0, queryEnv=0x0, dest=0x2a72df8, qc=0x7ffef5cc6c10)
at /opt/postgresql-src/debug-build/../src/backend/tcop/utility.c:527
#11 0x0000000000ac4aad in PortalRunUtility (portal=0x2b06bf0,
pstmt=0x2a72d28, isTopLevel=true, setHoldSnapshot=false, dest=0x2a72df8,
qc=0x7ffef5cc6c10) at
/opt/postgresql-src/debug-build/../src/backend/tcop/pquery.c:1155
#12 0x0000000000ac3b57 in PortalRunMulti (portal=0x2b06bf0,
isTopLevel=true, setHoldSnapshot=false, dest=0x2a72df8, altdest=0x2a72df8,
qc=0x7ffef5cc6c10) at
/opt/postgresql-src/debug-build/../src/backend/tcop/pquery.c:1312
#13 0x0000000000ac306f in PortalRun (portal=0x2b06bf0,
count=9223372036854775807, isTopLevel=true, run_once=true, dest=0x2a72df8,
altdest=0x2a72df8, qc=0x7ffef5cc6c10) at
/opt/postgresql-src/debug-build/../src/backend/tcop/pquery.c:788
#14 0x0000000000abdfad in exec_simple_query (query_string=0x2a71650 "CREATE
UNLOGGED TABLE stats (\n pg_hash BIGINT NOT NULL,\n category TEXT NOT
NULL,\n PRIMARY KEY (pg_hash, category)\n);") at
/opt/postgresql-src/debug-build/../src/backend/tcop/postgres.c:1213
#15 0x0000000000abd1fb in PostgresMain (argc=1, argv=0x7ffef5cc6e50,
dbname=0x2a9cb90 "postgres", username=0x2a9cb68 "host_user") at
/opt/postgresql-src/debug-build/../src/backend/tcop/postgres.c:4496
#16 0x00000000009c2b4a in BackendRun (port=0x2a964c0) at
/opt/postgresql-src/debug-build/../src/backend/postmaster/postmaster.c:4530
#17 0x00000000009c2074 in BackendStartup (port=0x2a964c0) at
/opt/postgresql-src/debug-build/../src/backend/postmaster/postmaster.c:4252
#18 0x00000000009c0e27 in ServerLoop () at
/opt/postgresql-src/debug-build/../src/backend/postmaster/postmaster.c:1745
#19 0x00000000009be275 in PostmasterMain (argc=3, argv=0x2a6add0) at
/opt/postgresql-src/debug-build/../src/backend/postmaster/postmaster.c:1417
#20 0x0000000000896dc3 in main (argc=3, argv=0x2a6add0) at
/opt/postgresql-src/debug-build/../src/backend/main/main.c:209

The error does not appear if the table is not defined as UNLOGGED, or if
the primary key is not compound.
Is it that the specific developer option is not used by the community to
run tests?

Kind regards,

--
Spiros
(ServiceNow)