From d136a8f5edc723899daafb59377930ee7fec3838 Mon Sep 17 00:00:00 2001 From: Amit Langote Date: Tue, 9 Jun 2026 22:11:54 +0900 Subject: [PATCH v1 2/2] Confine RI fast-path batching to the top transaction level The FK fast-path batching added in b7b27eb41a5 buffers rows in a transaction-lived cache (ri_fastpath_cache) keyed by constraint OID. Running user-defined cast and equality functions during a batch flush, together with the cache's lifetime and iteration, exposed two defects reachable by an unprivileged table owner. First, on subtransaction abort ri_FastPathSubXactCallback discarded the entire cache. An entry's batch holds rows buffered by the enclosing transaction, not just the aborting subxact -- the cache is keyed by constraint, so a single entry can mix rows from multiple subxact levels. An internal subxact abort during after-trigger firing (e.g. a PL/pgSQL BEGIN ... EXCEPTION block) therefore dropped buffered rows of the outer transaction without running their FK checks, letting orphan rows commit behind a constraint that still reported itself valid. The discard also left relations opened by the batch unclosed, producing "resource was not closed" warnings. Second, ri_FastPathEndBatch flushes by iterating the cache with hash_seq_search. If flush-time user code inserts into a different fast-path FK table, a new entry is added to the cache mid-scan; it may land in a bucket the scan has already passed and never be reached, and ri_FastPathTeardown then destroys the cache without flushing it, silently dropping that check. Cleanly unwinding the cache on subxact abort would require tracking the originating subxact of each buffered row, since rows from different levels share an entry (the cache is keyed by constraint) and deferred constraints cannot be flushed early at a subxact boundary. Rather than add that bookkeeping, confine batching to the top transaction level: in RI_FKey_check, when GetCurrentTransactionNestLevel() > 1, use the per-row fast path (ri_FastPathCheck) instead of buffering. Rows checked inside a subtransaction are then verified immediately and roll back cleanly with their subtransaction, and the cache only ever holds top-level rows. With the cache confined to the top level, a subtransaction abort has nothing of its own to discard, so ri_FastPathSubXactCallback is removed along with its registration. For the second defect, add a cache-wide flag (ri_fastpath_flushing) set while ri_FastPathEndBatch iterates the cache. A re-entrant FK check arriving while the flag is set takes the per-row path rather than adding an entry to the cache being scanned, so no entry can be missed and torn down unflushed. The flag is cleared in a PG_FINALLY so a flush that throws (a reported violation or an error from user code) does not leave it stuck. The per-row fast path still bypasses SPI and stays well ahead of the pre-19 SPI-based check. A fuller fix that preserves batching across subtransactions -- whether by tracking the originating subxact of each buffered row or by per-subxact cache stacks merged into the parent on commit -- is left for a future release. The subtransaction-abort case is covered by a new regression test. The mid-scan cross-table case depends on hash bucket placement and so is not reliably reproducible in a portable test, but the flag prevents it by construction. Reported-by: Nikolay Samokhvalov Discussion: https://postgr.es/m/CAM527d9exRCdWrhJOnAxk_vACg7sr_yPoaJp_+uCFY0qP8v=aw@mail.gmail.com --- src/backend/utils/adt/ri_triggers.c | 77 +++++++++++++++-------- src/test/regress/expected/foreign_key.out | 24 +++++++ src/test/regress/sql/foreign_key.sql | 23 +++++++ 3 files changed, 97 insertions(+), 27 deletions(-) diff --git a/src/backend/utils/adt/ri_triggers.c b/src/backend/utils/adt/ri_triggers.c index 453b83ce85d..9b49d87279f 100644 --- a/src/backend/utils/adt/ri_triggers.c +++ b/src/backend/utils/adt/ri_triggers.c @@ -267,6 +267,7 @@ static dclist_head ri_constraint_cache_valid_list; static HTAB *ri_fastpath_cache = NULL; static bool ri_fastpath_callback_registered = false; +static bool ri_fastpath_flushing = false; /* * Local function prototypes @@ -469,14 +470,31 @@ RI_FKey_check(TriggerData *trigdata) */ if (ri_fastpath_is_applicable(riinfo)) { - if (AfterTriggerIsActive()) + if (AfterTriggerIsActive() && + GetCurrentTransactionNestLevel() == 1 && + !ri_fastpath_flushing) { /* Batched path: buffer and probe in groups */ ri_FastPathBatchAdd(riinfo, fk_rel, newslot); } else { - /* ALTER TABLE validation: per-row, no cache */ + /* + * Per-row path, used when batching is not safe or not + * applicable: + * + * - ALTER TABLE validation, where no after-trigger firing is + * active; + * + * - any FK check inside a subtransaction, since the batch cache + * is confined to the top transaction level (it cannot be + * cleanly unwound on subxact abort); + * + * - a re-entrant check from user cast/operator code running + * during a batch flush, since adding a cache entry while + * ri_FastPathEndBatch is iterating the cache could leave it + * unflushed. + */ ri_FastPathCheck(riinfo, fk_rel, newslot); } return PointerGetDatum(NULL); @@ -4170,19 +4188,41 @@ ri_FastPathEndBatch(void *arg) if (ri_fastpath_cache == NULL) return; - /* Flush any partial batches -- can throw ERROR */ - hash_seq_init(&status, ri_fastpath_cache); - while ((entry = hash_seq_search(&status)) != NULL) + /* + * Set a flag for the duration of the scan so that any FK check triggered + * by user cast or operator code during a flush takes the per-row path + * instead of adding a new entry to the cache we are iterating. A new + * entry could land in an already-scanned bucket and then be torn down + * unflushed below. + * + * The flush can throw ERROR (a reported constraint violation, or an error + * from the user code it runs). In that case ri_FastPathTeardown below is + * skipped; the ResourceOwner and the transaction-end callback handle + * resource cleanup on the abort path. The PG_FINALLY only resets the + * flag and deliberately does not attempt teardown. + */ + Assert(!ri_fastpath_flushing); + ri_fastpath_flushing = true; + PG_TRY(); { - if (entry->batch_count > 0) + hash_seq_init(&status, ri_fastpath_cache); + while ((entry = hash_seq_search(&status)) != NULL) { - Relation fk_rel = table_open(entry->fk_relid, AccessShareLock); - RI_ConstraintInfo *riinfo = ri_LoadConstraintInfo(entry->conoid); + if (entry->batch_count > 0) + { + Relation fk_rel = table_open(entry->fk_relid, AccessShareLock); + RI_ConstraintInfo *riinfo = ri_LoadConstraintInfo(entry->conoid); - ri_FastPathBatchFlush(entry, fk_rel, riinfo); - table_close(fk_rel, NoLock); + ri_FastPathBatchFlush(entry, fk_rel, riinfo); + table_close(fk_rel, NoLock); + } } } + PG_FINALLY(); + { + ri_fastpath_flushing = false; + } + PG_END_TRY(); ri_FastPathTeardown(); } @@ -4236,22 +4276,6 @@ ri_FastPathXactCallback(XactEvent event, void *arg) ri_fastpath_callback_registered = false; } -static void -ri_FastPathSubXactCallback(SubXactEvent event, SubTransactionId mySubid, - SubTransactionId parentSubid, void *arg) -{ - if (event == SUBXACT_EVENT_ABORT_SUB) - { - /* - * ResourceOwner already released relations. NULL the static pointers - * so the still-registered batch callback becomes a no-op for the rest - * of this transaction. - */ - ri_fastpath_cache = NULL; - ri_fastpath_callback_registered = false; - } -} - /* * ri_FastPathGetEntry * Look up or create a per-batch cache entry for the given constraint. @@ -4276,7 +4300,6 @@ ri_FastPathGetEntry(const RI_ConstraintInfo *riinfo, Relation fk_rel) if (!ri_fastpath_xact_callback_registered) { RegisterXactCallback(ri_FastPathXactCallback, NULL); - RegisterSubXactCallback(ri_FastPathSubXactCallback, NULL); ri_fastpath_xact_callback_registered = true; } diff --git a/src/test/regress/expected/foreign_key.out b/src/test/regress/expected/foreign_key.out index fa80d9c915f..3f99a4a59cc 100644 --- a/src/test/regress/expected/foreign_key.out +++ b/src/test/regress/expected/foreign_key.out @@ -3768,3 +3768,27 @@ SELECT count(*), max(a) FROM fp_reentry_fk2; -- 64 rows, max 1 (1 row) DROP TABLE fp_reentry_fk2, fp_reentry_pk2; +-- Subtransaction abort during after-trigger firing must not drop FK checks +-- for rows buffered earlier in the same statement. Batching is confined to +-- the top transaction level and the buffered batch is no longer discarded on +-- subxact abort, so the violating rows are detected. +CREATE TABLE fp_subxact_pk (id int PRIMARY KEY); +INSERT INTO fp_subxact_pk SELECT g FROM generate_series(1, 10) g; +CREATE TABLE fp_subxact_fk (a int, tag text); +ALTER TABLE fp_subxact_fk ADD CONSTRAINT fp_subxact_fk_fkey + FOREIGN KEY (a) REFERENCES fp_subxact_pk (id); +CREATE FUNCTION fp_abort_subxact() RETURNS trigger LANGUAGE plpgsql AS $$ +BEGIN + IF NEW.tag = 'boom' THEN + BEGIN PERFORM 1/0; EXCEPTION WHEN division_by_zero THEN NULL; END; + END IF; + RETURN NEW; +END$$; +CREATE TRIGGER fp_subxact_trg AFTER INSERT ON fp_subxact_fk + FOR EACH ROW EXECUTE FUNCTION fp_abort_subxact(); +INSERT INTO fp_subxact_fk VALUES (999, 'bad'), (0, 'boom'), (1, 'ok'); +ERROR: insert or update on table "fp_subxact_fk" violates foreign key constraint "fp_subxact_fk_fkey" +DETAIL: Key (a)=(999) is not present in table "fp_subxact_pk". +DROP TRIGGER fp_subxact_trg ON fp_subxact_fk; +DROP FUNCTION fp_abort_subxact(); +DROP TABLE fp_subxact_fk, fp_subxact_pk; diff --git a/src/test/regress/sql/foreign_key.sql b/src/test/regress/sql/foreign_key.sql index 0f2ce8f76f5..18c3e166f02 100644 --- a/src/test/regress/sql/foreign_key.sql +++ b/src/test/regress/sql/foreign_key.sql @@ -2726,3 +2726,26 @@ BEGIN END$$; SELECT count(*), max(a) FROM fp_reentry_fk2; -- 64 rows, max 1 DROP TABLE fp_reentry_fk2, fp_reentry_pk2; + +-- Subtransaction abort during after-trigger firing must not drop FK checks +-- for rows buffered earlier in the same statement. Batching is confined to +-- the top transaction level and the buffered batch is no longer discarded on +-- subxact abort, so the violating rows are detected. +CREATE TABLE fp_subxact_pk (id int PRIMARY KEY); +INSERT INTO fp_subxact_pk SELECT g FROM generate_series(1, 10) g; +CREATE TABLE fp_subxact_fk (a int, tag text); +ALTER TABLE fp_subxact_fk ADD CONSTRAINT fp_subxact_fk_fkey + FOREIGN KEY (a) REFERENCES fp_subxact_pk (id); +CREATE FUNCTION fp_abort_subxact() RETURNS trigger LANGUAGE plpgsql AS $$ +BEGIN + IF NEW.tag = 'boom' THEN + BEGIN PERFORM 1/0; EXCEPTION WHEN division_by_zero THEN NULL; END; + END IF; + RETURN NEW; +END$$; +CREATE TRIGGER fp_subxact_trg AFTER INSERT ON fp_subxact_fk + FOR EACH ROW EXECUTE FUNCTION fp_abort_subxact(); +INSERT INTO fp_subxact_fk VALUES (999, 'bad'), (0, 'boom'), (1, 'ok'); +DROP TRIGGER fp_subxact_trg ON fp_subxact_fk; +DROP FUNCTION fp_abort_subxact(); +DROP TABLE fp_subxact_fk, fp_subxact_pk; -- 2.47.3