On 2020-09-24 5:00 p.m., Fujii Masao wrote:
On 2020/09/25 8:15, David Zhang wrote:
Hi,
My understanding is that the "archiver" won't even start if
"archive_mode = on" has been set on a "replica". Therefore, either
(XLogArchiveMode == ARCHIVE_MODE_ALWAYS) or (XLogArchiveMode !=
ARCHIVE_MODE_OFF) will produce the same result.
Yes, the archiver isn't invoked in the standby when archive_mode=on.
But, with the original patch, walreceiver creates .ready archive
status file
even when archive_mode=on and no archiver is running. This causes
the history file to be archived after the standby is promoted and
the archiver is invoked.
With my patch, walreceiver creates .ready archive status for the
history file
only when archive_mode=always, like it does for the streamed WAL files.
This is the difference between those two patches. To prevent the streamed
timeline history file from being archived, IMO we should use the
condition
archive_mode==always in the walreceiver.
+1
Please see how the "archiver" is started in
src/backend/postmaster/postmaster.c
5227 /*
5228 * Start the archiver if we're responsible for
(re-)archiving received
5229 * files.
5230 */
5231 Assert(PgArchPID == 0);
5232 if (XLogArchivingAlways())
5233 PgArchPID = pgarch_start();
I did run the nice script "double_switchover.sh" using either
"always" or "on" on patch v1 and v2. They all generate the same
results below. In other words, whether history file
(00000003.history) is archived or not depends on "archive_mode"
settings.
echo "archive_mode = always" >> ${PGDATA_NODE2}/postgresql.auto.conf
$ ls -l archive
-rw------- 1 david david 16777216 Sep 24 14:40 000000010000000000000002
... ...
-rw------- 1 david david 16777216 Sep 24 14:40 00000002000000000000000A
-rw------- 1 david david 41 Sep 24 14:40 00000002.history
-rw------- 1 david david 83 Sep 24 14:40 00000003.history
echo "archive_mode = on" >> ${PGDATA_NODE2}/postgresql.auto.conf
$ ls -l archive
-rw------- 1 david david 16777216 Sep 24 14:47 000000010000000000000002
... ...
-rw------- 1 david david 16777216 Sep 24 14:47 00000002000000000000000A
-rw------- 1 david david 41 Sep 24 14:47 00000002.history
Personally, I prefer patch v2 since it allies to the statement here,
https://www.postgresql.org/docs/13/warm-standby.html#CONTINUOUS-ARCHIVING-IN-STANDBY
"If archive_mode is set to on, the archiver is not enabled during
recovery or standby mode. If the standby server is promoted, it will
start archiving after the promotion, but will not archive any WAL it
did not generate itself."
By the way, I think the last part of the sentence should be changed
to something like below:
"but will not archive any WAL, which was not generated by itself."
I'm not sure if this change is an improvement or not. But if we apply
the patch I proposed, maybe we should mention also history file here.
For example, "but will not archive any WAL or timeline history files
that it did not generate itself".
make sense for me
Regards,
--
David
Software Engineer
Highgo Software Inc. (Canada)
www.highgo.ca
