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

On Tue, Dec 7, 2021 at 12:09 PM Noah Misch <noah(at)leadboat(dot)com> wrote:
>
> 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.

Yeah. At times, end-of-recovery checkpoint itself will take a good
amount of time and adding to it the pre-allocation of WAL time doesn't
make sense.

> > 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).

I see.

Regards,
Bharath Rupireddy.