On Mon, Feb 3, 2020 at 6:20 PM Kasahara Tatsuhito <kasahara.tatsuh...@gmail.com> wrote: > Therefore, from v12, Tid scan not only increases the value of > seq_scan, but also acquires a predicate lock.
Based on further investigation and Fujii's advice, I've summarized this issue as follows. >From commit 147e3722f7, Tid Scan came to (A) increments num of seq_scan on pg_stat_*_tables and (B) take a predicate lock on the entire relation. (A) may be confusing to users, so I think it is better to fix it. For (B), an unexpected serialization error has occurred as follows, so I think it should be fix. ========================================================================= [Preparation] CREATE TABLE tid_test (c1 int, c2 int); INSERT INTO tid_test SELECT generate_series(1,1000), 0; [Session-1:] BEGIN TRANSACTION ISOLATION LEVEL SERIALIZABLE ; [Session-2:] BEGIN TRANSACTION ISOLATION LEVEL SERIALIZABLE ; [Session-1:] SELECT * FROM tid_test WHERE ctid = '(0,1)'; [Session-2:] SELECT * FROM tid_test WHERE ctid = '(1,1)'; [Session-1:] INSERT INTO tid_test SELECT 1001, 10; [Session-2:] INSERT INTO tid_test SELECT 1001, 10; [Session-1:] COMMIT; [Session-2:] COMMIT; Result: (-v11): Both session could commit. (v12-): Session-2 raised error as following because of taking a predicate lock on the entire table... -------- ERROR: could not serialize access due to read/write dependencies among transactions DETAIL: Reason code: Canceled on identification as a pivot, during commit attempt. HINT: The transaction might succeed if retried. -------- ========================================================================= Attached patch fix both (A) and (B), so that the behavior of Tid Scan back to the same as before v11. (As a result, this patch is the same as the one that first attached.) Best regards, -- Tatsuhito Kasahara kasahara.tatsuhito _at_ gmail.com
fix_tidscan_issues.patch
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