From: | Noah Misch <noah(at)leadboat(dot)com> |
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To: | Bharath Rupireddy <bharath(dot)rupireddyforpostgres(at)gmail(dot)com> |
Cc: | PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
Subject: | Re: Do we need pre-allocate WAL files during end-of-recovery checkpoint? |
Date: | 2021-12-07 06:39:04 |
Message-ID: | 20211207063904.GA2039126@rfd.leadboat.com |
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Lists: | pgsql-hackers |
On Mon, Dec 06, 2021 at 06:21:40PM +0530, Bharath Rupireddy wrote:
> The function PreallocXlogFiles doesn't get called during
> end-of-recovery checkpoint in CreateCheckPoint, see [1]. The server
> becomes operational after the end-of-recovery checkpoint and may need
> WAL files.
PreallocXlogFiles() is never a necessity; it's just an attempted optimization.
I expect preallocation at end-of-recovery would do more harm than good,
because the system would accept no writes at all while waiting for it.
> However, I'm not sure how beneficial it is going to be if
> the WAL is pre-allocated (as PreallocXlogFiles just allocates only 1
> extra WAL file).
Yeah, PreallocXlogFiles() feels like a relict from the same era that gave us
checkpoint_segments=3. It was more useful before commit 63653f7 (2002).
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