From e755cc06bf4943852e7b31429d8481a44ada15d5 Mon Sep 17 00:00:00 2001 From: Bharath Rupireddy Date: Sat, 27 Jun 2026 00:50:23 +0000 Subject: [PATCH v8] PG17 Fix pg_get_publication_tables race with concurrent DROP TABLE The pg_get_publication_tables() SRF collects table OIDs in its first call, and then opens the tables using table_open() for FOR ALL TABLES publications. If a table is dropped in between, the table_open() errors out with "could not open relation with OID". This is common in environments where many tables are being created and dropped while publication tables are being queried. The bug was introduced by b7ae03953690 in PG16. This commit fixes it by using try_table_open(), which returns NULL instead of erroring out if the relation no longer exists. We now open all tables this way regardless of whether a column list is specified, so a concurrently dropped table is consistently skipped. Such tables are simply absent from the result set, which is the expected point-in-time behavior. To skip dropped tables without emitting a row, we track the current index into the table list ourselves rather than relying on funcctx->call_cntr. Author: Bharath Rupireddy bharath.rupireddyforpostgres@gmail.com Reviewed-by: Bertrand Drouvot bertranddrouvot.pg@gmail.com Reviewed-by: shveta malik shveta.malik@gmail.com Reviewed-by: Ajin Cherian itsajin@gmail.com Reviewed-by: Masahiko Sawada sawada.mshk@gmail.com Discussion: https://www.postgresql.org/message-id/CALj2ACVYYooWH-5tJ6cPKkU%2BmutVxwb_z4S%2BqAi-zdrFqxXE2Q%40mail.gmail.com Backpatch-through: 16 --- src/backend/catalog/pg_publication.c | 52 +++++++++++++++++++++++----- src/test/subscription/t/100_bugs.pl | 46 ++++++++++++++++++++++++ src/tools/pgindent/typedefs.list | 1 + 3 files changed, 90 insertions(+), 9 deletions(-) diff --git a/src/backend/catalog/pg_publication.c b/src/backend/catalog/pg_publication.c index 0602398a545..0b21076dbc4 100644 --- a/src/backend/catalog/pg_publication.c +++ b/src/backend/catalog/pg_publication.c @@ -1052,14 +1052,27 @@ Datum pg_get_publication_tables(PG_FUNCTION_ARGS) { #define NUM_PUBLICATION_TABLES_ELEM 4 + + /* + * State carried across SRF calls. We track the index ourselves instead of + * using funcctx->call_cntr, so that concurrently dropped tables can be + * skipped without emitting a row. + */ + typedef struct + { + List *table_infos; /* list of published_rel */ + int curr_idx; /* current index into table_infos */ + } publication_tables_state; + FuncCallContext *funcctx; - List *table_infos = NIL; + publication_tables_state *ptstate = NULL; /* stuff done only on the first call of the function */ if (SRF_IS_FIRSTCALL()) { TupleDesc tupdesc; MemoryContext oldcontext; + List *table_infos = NIL; ArrayType *arr; Datum *elems; int nelems, @@ -1158,26 +1171,47 @@ pg_get_publication_tables(PG_FUNCTION_ARGS) PG_NODE_TREEOID, -1, 0); funcctx->tuple_desc = BlessTupleDesc(tupdesc); - funcctx->user_fctx = (void *) table_infos; + + /* Store the state to be used across SRF calls. */ + ptstate = palloc_object(publication_tables_state); + ptstate->table_infos = table_infos; + ptstate->curr_idx = 0; + funcctx->user_fctx = ptstate; MemoryContextSwitchTo(oldcontext); } /* stuff done on every call of the function */ funcctx = SRF_PERCALL_SETUP(); - table_infos = (List *) funcctx->user_fctx; + ptstate = (publication_tables_state *) funcctx->user_fctx; - if (funcctx->call_cntr < list_length(table_infos)) + while (ptstate->curr_idx < list_length(ptstate->table_infos)) { HeapTuple pubtuple = NULL; HeapTuple rettuple; Publication *pub; - published_rel *table_info = (published_rel *) list_nth(table_infos, funcctx->call_cntr); + published_rel *table_info = (published_rel *) list_nth(ptstate->table_infos, + ptstate->curr_idx); Oid relid = table_info->relid; - Oid schemaid = get_rel_namespace(relid); + Relation rel; + Oid schemaid; Datum values[NUM_PUBLICATION_TABLES_ELEM] = {0}; bool nulls[NUM_PUBLICATION_TABLES_ELEM] = {0}; + /* Advance the index for the next call. */ + ptstate->curr_idx++; + + /* + * The table OIDs were collected earlier, so a table may have been + * dropped before we get here. try_table_open() returns NULL if it is + * already gone, in which case we skip it; such tables are simply + * absent from the result set, which is the expected point-in-time + * behavior. + */ + rel = try_table_open(relid, AccessShareLock); + if (rel == NULL) + continue; + /* * Form tuple with appropriate data. */ @@ -1191,6 +1225,7 @@ pg_get_publication_tables(PG_FUNCTION_ARGS) * We don't consider row filters or column lists for FOR ALL TABLES or * FOR TABLES IN SCHEMA publications. */ + schemaid = RelationGetNamespace(rel); if (!pub->alltables && !SearchSysCacheExists2(PUBLICATIONNAMESPACEMAP, ObjectIdGetDatum(schemaid), @@ -1220,7 +1255,6 @@ pg_get_publication_tables(PG_FUNCTION_ARGS) /* Show all columns when the column list is not specified. */ if (nulls[2]) { - Relation rel = table_open(relid, AccessShareLock); int nattnums = 0; int16 *attnums; TupleDesc desc = RelationGetDescr(rel); @@ -1243,10 +1277,10 @@ pg_get_publication_tables(PG_FUNCTION_ARGS) values[2] = PointerGetDatum(buildint2vector(attnums, nattnums)); nulls[2] = false; } - - table_close(rel, AccessShareLock); } + table_close(rel, AccessShareLock); + rettuple = heap_form_tuple(funcctx->tuple_desc, values, nulls); SRF_RETURN_NEXT(funcctx, HeapTupleGetDatum(rettuple)); diff --git a/src/test/subscription/t/100_bugs.pl b/src/test/subscription/t/100_bugs.pl index 7d804e5ff9c..9ac71f4fc56 100644 --- a/src/test/subscription/t/100_bugs.pl +++ b/src/test/subscription/t/100_bugs.pl @@ -642,4 +642,50 @@ $node_publisher->safe_psql('postgres', "DROP TABLE tab_upsert"); $node_publisher->stop('fast'); +# BUG: pg_get_publication_tables() errors with "could not open relation with +# OID" when a table is dropped concurrently. +$node_publisher->start(); + +$node_publisher->safe_psql( + 'postgres', qq{ + CREATE PUBLICATION pub_all FOR ALL TABLES; + CREATE TABLE t_dropme (id int, data text); +}); + +# Hold an ACCESS EXCLUSIVE lock on the table in a separate session, so that +# the pg_publication_tables query will block when it tries to open the table. +my $holder = $node_publisher->background_psql('postgres'); +$holder->query_safe("BEGIN; LOCK TABLE t_dropme IN ACCESS EXCLUSIVE MODE;"); + +# Background session queries pg_publication_tables; it will block waiting for +# the lock on the table. +my $bgpsql = + $node_publisher->background_psql('postgres', on_error_stop => 0); +$bgpsql->query_until( + qr/querying_publication_tables/, + qq{\\echo querying_publication_tables +SELECT count(*) FROM pg_publication_tables WHERE pubname = 'pub_all'; +}); + +# Wait until the querying session is blocked on the lock. +$node_publisher->poll_query_until('postgres', + "SELECT count(*) > 0 FROM pg_stat_activity WHERE wait_event_type = 'Lock' AND query LIKE '%pg_publication_tables%';" +); + +# Drop the table in the lock-holding session and commit, releasing the lock. +$holder->query_safe("DROP TABLE t_dropme; COMMIT;"); +$holder->quit; + +# Verify the background session completed without error. +my $bg_result = $bgpsql->query_safe("SELECT 1"); +$bgpsql->quit; + +ok(defined($bg_result), + "pg_publication_tables handles concurrently dropped tables"); + +# Cleanup. +$node_publisher->safe_psql('postgres', "DROP PUBLICATION pub_all"); + +$node_publisher->stop('fast'); + done_testing(); diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list index e5634ae2969..86b194da8e3 100644 --- a/src/tools/pgindent/typedefs.list +++ b/src/tools/pgindent/typedefs.list @@ -3805,6 +3805,7 @@ pthread_mutex_t pthread_once_t pthread_t ptrdiff_t +publication_tables_state published_rel pull_var_clause_context pull_varattnos_context -- 2.47.3