Re: Do we need pre-allocate WAL files during end-of-recovery checkpoint?

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).