| From: | Michael Paquier <michael(at)paquier(dot)xyz> |
|---|---|
| To: | Bharath Rupireddy <bharath(dot)rupireddyforpostgres(at)gmail(dot)com> |
| Cc: | Nathan Bossart <nathandbossart(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: Simplify standby state machine a bit in WaitForWALToBecomeAvailable() |
| Date: | 2023-03-06 07:56:35 |
| Message-ID: | ZAWcs2oy7MkU5bPC@paquier.xyz |
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| Lists: | pgsql-hackers |
On Sat, Mar 04, 2023 at 09:47:05AM +0530, Bharath Rupireddy wrote:
> Okay, here's a patch attached.
Thanks.
+ * When source == XLOG_FROM_ANY, this function first searches for the segment
+ * with a TLI in archive first, if not found, it searches in pg_wal. This way,
+ * if there is a WAL segment with same passed-in segno but different TLI
+ * present in both the archive and pg_wal, it prefers the one with higher TLI.
+ * The reason for this is that if for example we try to do archive recovery to
+ * timeline 2, which branched off timeline 1, but the WAL for timeline 2 is not
+ * archived yet, we would replay past the timeline switch point on timeline 1
+ * using the archived WAL segment, before even looking timeline 2's WAL
+ * segments in pg_wal.
This is pretty much what the commit has mentioned. The first half
provides enough details, IMO.
--
Michael
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