From 0ffe2975c37473981113fc461990c7533bbcf26d Mon Sep 17 00:00:00 2001 From: Michael Paquier Date: Fri, 21 Jan 2022 14:54:59 +0900 Subject: [PATCH] Fix one-off bug causing missing commit timestamps for subtransactions The logic in charge of writing commit timestamps (enabled with track_commit_timestamp) for subtransactions had a one-bug bug, where it would be possible that commit timestamps go missing for the last subtransaction committed. While on it, simplify a bit the iteration logic in the loop writing the commit timestamps, as per suggestions from Kyotaro Horiguchi and Tom Lane, so as some variable initializations are not part of the loop itself. Issue introduced in 73c986a. Analyzed-by: Alex Kingsborough Author: Alex Kingsborough, Kyotaro Horiguchi Discussion: https://postgr.es/m/73A66172-4050-4F2A-B7F1-13508EDA2144@amazon.com Backpatch-through: 10 --- src/backend/access/transam/commit_ts.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/src/backend/access/transam/commit_ts.c b/src/backend/access/transam/commit_ts.c index 030740fcf3..4cc878997a 100644 --- a/src/backend/access/transam/commit_ts.c +++ b/src/backend/access/transam/commit_ts.c @@ -184,7 +184,9 @@ TransactionTreeSetCommitTsData(TransactionId xid, int nsubxids, * subxid not on the previous page as head. This way, we only have to * lock/modify each SLRU page once. */ - for (i = 0, headxid = xid;;) + headxid = xid; + i = 0; + for (;;) { int pageno = TransactionIdToCTsPage(headxid); int j; @@ -200,7 +202,7 @@ TransactionTreeSetCommitTsData(TransactionId xid, int nsubxids, pageno); /* if we wrote out all subxids, we're done. */ - if (j + 1 >= nsubxids) + if (j >= nsubxids) break; /* @@ -208,7 +210,7 @@ TransactionTreeSetCommitTsData(TransactionId xid, int nsubxids, * just wrote. */ headxid = subxids[j]; - i += j - i + 1; + i = j + 1; } /* update the cached value in shared memory */