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During online checkpoints, insert XLOG_CHECKPOINT_REDO at redo point.

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This allows tools that read the WAL sequentially to identify (possible)
redo points when they're reached, rather than only being able to
detect them in retrospect when XLOG_CHECKPOINT_ONLINE is found, possibly
much later in the WAL stream. There are other possible applications as
well; see the discussion links below.

Any redo location that precedes the checkpoint location should now point
to an XLOG_CHECKPOINT_REDO record, so add a cross-check to verify this.

While adjusting the code in CreateCheckPoint() for this patch, I made it
call WALInsertLockAcquireExclusive a bit later than before, since there
appears to be no need for it to be held while checking whether the system
is idle, whether this is an end-of-recovery checkpoint, or what the current
timeline is.

Bump XLOG_PAGE_MAGIC.

Patch by me, based in part on earlier work from Dilip Kumar. Review by
Dilip Kumar, Amit Kapila, Andres Freund, and Michael Paquier.

Discussion: http://postgr.es/m/CA+TgmoYy-Vc6G9QKcAKNksCa29cv__czr+N9X_QCxEfQVpp_8w@mail.gmail.com
Discussion: http://postgr.es/m/20230614194717.jyuw3okxup4cvtbt%40awork3.anarazel.de
Discussion: http://postgr.es/m/CA+hUKG+b2ego8=YNW2Ohe9QmSiReh1-ogrv8V_WZpJTqP3O+2w@mail.gmail.com
This commit is contained in:
Robert Haas
2023-10-19 14:47:29 -04:00
parent 8483a54b7d
commit afd12774ae
9 changed files with 178 additions and 61 deletions
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10
contrib/pg_walinspect/sql/pg_walinspect.sql
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@ -80,9 +80,17 @@ SELECT pg_current_wal_lsn() AS wal_lsn4 \gset
SELECT COUNT(*) >= 1 AS ok FROM pg_get_wal_block_info(:'wal_lsn3', :'wal_lsn4')
WHERE relfilenode = :'sample_tbl_oid' AND block_data IS NOT NULL;
-- Force full-page image on the next update.
-- Force a checkpoint so that the next update will log a full-page image.
SELECT pg_current_wal_lsn() AS wal_lsn5 \gset
CHECKPOINT;
-- Verify that an XLOG_CHECKPOINT_REDO record begins at precisely the redo LSN
-- of the checkpoint we just performed.
SELECT redo_lsn FROM pg_control_checkpoint() \gset
SELECT start_lsn = :'redo_lsn'::pg_lsn AS same_lsn, resource_manager,
record_type FROM pg_get_wal_record_info(:'redo_lsn');
-- This update should produce a full-page image because of the checkpoint.
UPDATE sample_tbl SET col1 = col1 + 1 WHERE col1 = 2;
SELECT pg_current_wal_lsn() AS wal_lsn6 \gset
-- Check if we get FPI from WAL record.