From 5bcb9c7104b03b9dd7db7ca64296891a868d42a5 Mon Sep 17 00:00:00 2001 From: Zsolt Parragi Date: Thu, 15 Oct 2026 10:10:44 +0000 Subject: [PATCH v1] Fix Parallel TID Range Scan rescans with a different TID range 0ca3b1697 added support for parallel TID Range Scans. The range of blocks to scan is stored in the shared phs_startblock and phs_numblock fields by the first participant to start the scan, but table_block_parallelscan_reinitialize() didn't reset these, so every rescan of the Gather reused the block range of the first execution. This caused rows to be silently missed when a rescan used a different TID range, e.g: SELECT r.lo, (SELECT count(*) FROM t WHERE ctid >= (SELECT r.lo)) FROM (VALUES ('(30,0)'::tid), ('(10,0)'), ('(0,0)')) r(lo); Here we fix this by resetting both fields in table_block_parallelscan_reinitialize(). As a side effect, a rescanned Parallel Seq Scan using synchronized scans now gets a new start location, which is what a new scan would do anyway. The existing rescan test didn't exercise this, so add one that does. This was introduced in 0ca3b1697, so backpatch to v19. Author: Zsolt Parragi Backpatch-through: 19 --- src/backend/access/table/tableam.c | 8 ++++++ src/test/regress/expected/tidrangescan.out | 31 ++++++++++++++++++++++ src/test/regress/sql/tidrangescan.sql | 12 +++++++++ 3 files changed, 51 insertions(+) diff --git a/src/backend/access/table/tableam.c b/src/backend/access/table/tableam.c index 7aaa8d87150..3a1ff9a1d46 100644 --- a/src/backend/access/table/tableam.c +++ b/src/backend/access/table/tableam.c @@ -395,6 +395,14 @@ table_block_parallelscan_reinitialize(Relation rel, ParallelTableScanDesc pscan) { ParallelBlockTableScanDesc bpscan = (ParallelBlockTableScanDesc) pscan; + /* + * Reset the start block and block limit too. These are set by the first + * participant to call table_block_parallelscan_startblock_init(), and a + * rescan may want to scan a different range of blocks, e.g. a TID Range + * Scan with different TID bounds. + */ + pg_atomic_write_u32(&bpscan->phs_startblock, InvalidBlockNumber); + pg_atomic_write_u32(&bpscan->phs_numblock, InvalidBlockNumber); pg_atomic_write_u64(&bpscan->phs_nallocated, 0); } diff --git a/src/test/regress/expected/tidrangescan.out b/src/test/regress/expected/tidrangescan.out index 41f3ba06c3b..e478dfb32ad 100644 --- a/src/test/regress/expected/tidrangescan.out +++ b/src/test/regress/expected/tidrangescan.out @@ -427,5 +427,36 @@ WHERE t.ctid < '(1,0)'; (0,5) | 5 (5 rows) +-- Parallel rescans with a different TID range on each rescan +EXPLAIN (COSTS OFF) +SELECT r.lo, + (SELECT count(*) FROM parallel_tidrangescan t + WHERE t.ctid >= (SELECT r.lo)) c +FROM (VALUES ('(30,0)'::tid), ('(10,0)'), ('(0,0)')) r(lo); + QUERY PLAN +------------------------------------------------------------------------------ + Values Scan on "*VALUES*" + SubPlan expr_1 + -> Finalize Aggregate + InitPlan expr_2 + -> Result + -> Gather + Workers Planned: 4 + -> Partial Aggregate + -> Parallel Tid Range Scan on parallel_tidrangescan t + TID Cond: (ctid >= (InitPlan expr_2).col1) +(10 rows) + +SELECT r.lo, + (SELECT count(*) FROM parallel_tidrangescan t + WHERE t.ctid >= (SELECT r.lo)) c +FROM (VALUES ('(30,0)'::tid), ('(10,0)'), ('(0,0)')) r(lo); + lo | c +--------+----- + (30,0) | 50 + (10,0) | 150 + (0,0) | 200 +(3 rows) + ROLLBACK; RESET enable_seqscan; diff --git a/src/test/regress/sql/tidrangescan.sql b/src/test/regress/sql/tidrangescan.sql index 79f9e2b32be..f8cee41f92c 100644 --- a/src/test/regress/sql/tidrangescan.sql +++ b/src/test/regress/sql/tidrangescan.sql @@ -153,5 +153,17 @@ SELECT t.ctid,t2.c FROM parallel_tidrangescan t, LATERAL (SELECT count(*) c FROM parallel_tidrangescan t2 WHERE t2.ctid <= t.ctid) t2 WHERE t.ctid < '(1,0)'; +-- Parallel rescans with a different TID range on each rescan +EXPLAIN (COSTS OFF) +SELECT r.lo, + (SELECT count(*) FROM parallel_tidrangescan t + WHERE t.ctid >= (SELECT r.lo)) c +FROM (VALUES ('(30,0)'::tid), ('(10,0)'), ('(0,0)')) r(lo); + +SELECT r.lo, + (SELECT count(*) FROM parallel_tidrangescan t + WHERE t.ctid >= (SELECT r.lo)) c +FROM (VALUES ('(30,0)'::tid), ('(10,0)'), ('(0,0)')) r(lo); + ROLLBACK; RESET enable_seqscan; -- 2.56.0