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Fix memory leak in pgoutput with streamed prepared transactions.

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pgoutput records the toplevel XID in the relation's streamed_txns
list, allocated in CacheMemoryContext, when it sends a relation's
schema during a streamed transaction. We clean up that list at stream
commit and stream abort, but missed stream prepare, so the XIDs stay
around until a relcache invalidation for the relation or until the
walsender exits.

Fix by cleaning up the cache after writing the stream prepare message,
marking the schema as sent as we do at stream commit. The subscriber
applies the spooled relation messages at PREPARE time and its relation
map isn't rolled back by ROLLBACK PREPARED, so we don't need to send
the schema again even if the prepared transaction eventually aborts.

Oversight in commit 63cf61cdeb.

Author: Ayush Tiwari <ayushtiwari.slg01@gmail.com>
Reviewed-by: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Reviewed-by: Masahiko Sawada <sawada.mshk@gmail.com>
Discussion: https://postgr.es/m/CAJTYsWWt5aaKHCnV=jNOwABzspd-WbnhWLndDqtESDQRQ-BkKQ@mail.gmail.com
Backpatch-through: 15
This commit is contained in:
Masahiko Sawada
2026-09-18 10:19:07 -07:00
parent 47c43ffdae
commit 274da088e0
1 changed files with 16 additions and 13 deletions
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29
src/backend/replication/pgoutput/pgoutput.c
View File

@@ -220,7 +220,7 @@ typedef struct PGOutputTxnData
static HTAB *RelationSyncCache = NULL;
static void init_rel_sync_cache(MemoryContext decoding_context);
static void cleanup_rel_sync_cache(TransactionId xid, bool is_commit);
static void cleanup_rel_sync_cache(TransactionId xid, bool mark_schema_sent);
static RelationSyncEntry *get_rel_sync_entry(PGOutputData *data,
Relation relation);
static void rel_sync_cache_relation_cb(Datum arg, Oid relid);
@@ -1936,6 +1936,9 @@ pgoutput_stream_prepare_txn(LogicalDecodingContext *ctx,
OutputPluginPrepareWrite(ctx, true);
logicalrep_write_stream_prepare(ctx->out, txn, prepare_lsn);
OutputPluginWrite(ctx, true);
/* Schema cache updates at PREPARE survive ROLLBACK PREPARED. */
cleanup_rel_sync_cache(txn->xid, true);
}
/*
@@ -2307,16 +2310,16 @@ get_rel_sync_entry(PGOutputData *data, Relation relation)
/*
* Cleanup list of streamed transactions and update the schema_sent flag.
*
* When a streamed transaction commits or aborts, we need to remove the
* toplevel XID from the schema cache. If the transaction aborted, the
* subscriber will simply throw away the schema records we streamed, so
* we don't need to do anything else.
* When a streamed transaction commits, aborts or prepares, we need to remove
* the toplevel XID from the schema cache. If the transaction aborted, the
* subscriber will simply throw away the schema records we streamed, so we
* don't need to do anything else.
*
* If the transaction is committed, the subscriber will update the relation
* cache - so tweak the schema_sent flag accordingly.
* If the transaction is committed or prepared, the subscriber will update
* the relation cache - so tweak the schema_sent flag accordingly.
*/
static void
cleanup_rel_sync_cache(TransactionId xid, bool is_commit)
cleanup_rel_sync_cache(TransactionId xid, bool mark_schema_sent)
{
HASH_SEQ_STATUS hash_seq;
RelationSyncEntry *entry;
@@ -2328,16 +2331,16 @@ cleanup_rel_sync_cache(TransactionId xid, bool is_commit)
while ((entry = hash_seq_search(&hash_seq)) != NULL)
{
/*
* We can set the schema_sent flag for an entry that has committed xid
* in the list as that ensures that the subscriber would have the
* corresponding schema and we don't need to send it unless there is
* any invalidation for that relation.
* We can set the schema_sent flag for an entry that has a committed or
* prepared xid in the list as that ensures that the subscriber would
* have the corresponding schema and we don't need to send it unless
* there is any invalidation for that relation.
*/
foreach(lc, entry->streamed_txns)
{
if (xid == (uint32) lfirst_int(lc))
{
if (is_commit)
if (mark_schema_sent)
entry->schema_sent = true;
entry->streamed_txns =