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Continuation of work started in commit 15a79c73, after initial trial.
Author: Thomas Munro <thomas.munro@gmail.com>
Discussion: https://postgr.es/m/b936d2fb-590d-49c3-a615-92c3a88c6c19%40eisentraut.org
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Backpatch-through: 13
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Previously, pg_wal_summary_contents() had two issues,
causing discrepancies between pg_wal_summary_contents()
and the pg_walsummary command on the same WAL summary file:
(1) It did not emit the limit block when that's the only data for
a particular relation fork.
(2) It emitted the same limit block multiple times if the list of
block numbers was long enough.
This commit fixes these issues.
Backpatch to v17 where pg_wal_summary_contents() was added.
Author: Fujii Masao
Reviewed-by: Robert Haas
Discussion: https://postgr.es/m/90980ee6-2da6-42f6-a7b0-b7bae62ae279@oss.nttdata.com
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This makes it possible to access information about the progress
of WAL summarization from SQL. The previously-added functions
pg_available_wal_summaries() and pg_wal_summary_contents() only
examine on-disk state, but this function exposes information from
the server's shared memory.
Discussion: http://postgr.es/m/CA+Tgmobvqqj-DW9F7uUzT-cQqs6wcVb-Xhs=w=hzJnXSE-kRGw@mail.gmail.com
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Reported-by: Michael Paquier
Discussion: https://postgr.es/m/ZZKTDPxBBMt3C0J9@paquier.xyz
Backpatch-through: 12
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Apparently, spell check would have been a really good idea.
Alexander Lakhin, with a few additions as per an off-list report
from Andres Freund.
Discussion: http://postgr.es/m/f08f7c60-1ad3-0b57-d580-54b11f07cddf@gmail.com
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When active, this process writes WAL summary files to
$PGDATA/pg_wal/summaries. Each summary file contains information for a
certain range of LSNs on a certain TLI. For each relation, it stores a
"limit block" which is 0 if a relation is created or destroyed within
a certain range of WAL records, or otherwise the shortest length to
which the relation was truncated during that range of WAL records, or
otherwise InvalidBlockNumber. In addition, it stores a list of blocks
which have been modified during that range of WAL records, but
excluding blocks which were removed by truncation after they were
modified and never subsequently modified again.
In other words, it tells us which blocks need to copied in case of an
incremental backup covering that range of WAL records. But this
doesn't yet add the capability to actually perform an incremental
backup; the next patch will do that.
A new parameter summarize_wal enables or disables this new background
process. The background process also automatically deletes summary
files that are older than wal_summarize_keep_time, if that parameter
has a non-zero value and the summarizer is configured to run.
Patch by me, with some design help from Dilip Kumar and Andres Freund.
Reviewed by Matthias van de Meent, Dilip Kumar, Jakub Wartak, Peter
Eisentraut, and Álvaro Herrera.
Discussion: http://postgr.es/m/CA+TgmoYOYZfMCyOXFyC-P+-mdrZqm5pP2N7S-r0z3_402h9rsA@mail.gmail.com
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