Fix header check for continuation records where standbys could be stuck XLogPageRead() checks immediately for an invalid WAL record header on a standby, to be able to handle the case of continuation records that need to be read across two different sources. As written, the check was too generic, applying to any target LSN. Based on an analysis by Kyotaro Horiguchi, what really matters is to make sure that the page header is checked when attempting to read a LSN at the boundary of a segment, to handle the case of a continuation record that spawns across multiple pages when dealing with multiple segments, as WAL receivers are spawned they request WAL from the beginning of a segment. This fix has been proposed by Kyotaro Horiguchi.
This could cause standbys to loop infinitely when dealing with a continuation record during a timeline jump, in the case where the contents of the record in the follow-up page are invalid. Some regression tests are added to check such scenarios, able to reproduce the original problem. In the test, the contents of a continuation record are overwritten with junk zeros on its follow-up page, and replayed on standbys. This is inspired by 039_end_of_wal.pl, and is enough to show how standbys should react on promotion by not being stuck. Without the fix, the test would fail with a timeout. The test to reproduce the problem has been written by Alexander Kukushkin. The original check has been introduced in 066871980183, for a similar problem. Author: Kyotaro Horiguchi, Alexander Kukushkin Reviewed-by: Michael Paquier Discussion: https://postgr.es/m/CAFh8B=mozC+e1wGJq0H=0o65gozju+6ab5au7dewcsua2ot...@mail.gmail.com Backpatch-through: 13 Branch ------ master Details ------- https://git.postgresql.org/pg/commitdiff/6cf1647d87e7cd423d71525a8759b75c4e4a47ec Modified Files -------------- src/backend/access/transam/xlogrecovery.c | 13 +- src/test/recovery/meson.build | 1 + src/test/recovery/t/043_no_contrecord_switch.pl | 154 ++++++++++++++++++++++++ 3 files changed, 162 insertions(+), 6 deletions(-)
