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  1. doc: Improve description of wal_compression

  1. Possible inaccurate description of wal_compression in docs

    Jingtang Zhang <mrdrivingduck@gmail.com> — 2025-08-10T10:53:19Z

    Hi hackers~

I find the specification of wal_compression in our docs a little bit confusing
for it 'compress full page images when FPW is on or during a base backup',
which was true before v17. Since v17, we will also use full page images for
creating index or table rewrites through bulk write, so it is inaccurate.

Should we change the doc a little bit: 'compress full page images written
to WAL, **like** when FPW is on, or during a base backup', if we may use
FPI in other places in the future?

--
Regards, Jingtang

  2. Re: Possible inaccurate description of wal_compression in docs

    Xuneng Zhou <xunengzhou@gmail.com> — 2025-08-11T15:41:23Z

    Hi,

On Sun, Aug 10, 2025 at 6:53 PM Jingtang Zhang <mrdrivingduck@gmail.com> wrote:
>
> Hi hackers~
>
> I find the specification of wal_compression in our docs a little bit confusing
> for it 'compress full page images when FPW is on or during a base backup',
> which was true before v17. Since v17, we will also use full page images for
> creating index or table rewrites through bulk write, so it is inaccurate.
>
> Should we change the doc a little bit: 'compress full page images written
> to WAL, **like** when FPW is on, or during a base backup', if we may use
> FPI in other places in the future?
>

+1 for the update.

Best,
Xuneng

  3. Re: Possible inaccurate description of wal_compression in docs

    x4mmm@yandex-team.ru — 2025-08-11T15:59:55Z

    
> On 10 Aug 2025, at 13:53, Jingtang Zhang <mrdrivingduck@gmail.com> wrote:
> 
> Hi hackers~
> 
> I find the specification of wal_compression in our docs a little bit confusing
> for it 'compress full page images when FPW is on or during a base backup',
> which was true before v17. Since v17, we will also use full page images for
> creating index or table rewrites through bulk write, so it is inaccurate.
> 
> Should we change the doc a little bit: 'compress full page images written
> to WAL, **like** when FPW is on, or during a base backup', if we may use
> FPI in other places in the future?

FPWs are used here and there in a lot of places, like "FPI for hint". And indexes are build using FPI for many years, it did not start with 17...
This list is not exhaustive in any case, so I agree that formulation should not be very strict.

Best regards, Andrey Borodin.

  4. Re: Possible inaccurate description of wal_compression in docs

    Jingtang Zhang <mrdrivingduck@gmail.com> — 2025-08-11T17:05:26Z

    Hi~

> FPWs are used here and there in a lot of places, like "FPI for hint". And indexes are build using FPI for many years, it did not start with 17...

Yeah, my fault. Creating index prior to v17 was also using log_newpages.

—
Regards, Jingtang

  5. Re: Possible inaccurate description of wal_compression in docs

    Michael Paquier <michael@paquier.xyz> — 2025-08-12T04:41:40Z

    On Mon, Aug 11, 2025 at 06:59:55PM +0300, Andrey Borodin wrote:
> FPWs are used here and there in a lot of places, like "FPI for
> hint". And indexes are build using FPI for many years, it did not
> start with 17... 
> This list is not exhaustive in any case, so I agree that formulation
> should not be very strict. 

Perhaps, yes, the formulation used in this paragraph could be a bit
more evasive.  What we do not want is to keep a wording that would
require more maintenance each time the internals of the backend are
changed, so adding an extra "like" may be OK.

Do any of you have a specific wording in mind?
--
Michael

  6. Re: Possible inaccurate description of wal_compression in docs

    Xuneng Zhou <xunengzhou@gmail.com> — 2025-08-13T05:33:26Z

    Hi,

On Tue, Aug 12, 2025 at 12:41 PM Michael Paquier <michael@paquier.xyz>
wrote:

> On Mon, Aug 11, 2025 at 06:59:55PM +0300, Andrey Borodin wrote:
> > FPWs are used here and there in a lot of places, like "FPI for
> > hint". And indexes are build using FPI for many years, it did not
> > start with 17...
> > This list is not exhaustive in any case, so I agree that formulation
> > should not be very strict.
>
> Perhaps, yes, the formulation used in this paragraph could be a bit
> more evasive.  What we do not want is to keep a wording that would
> require more maintenance each time the internals of the backend are
> changed, so adding an extra "like" may be OK.
>
> Do any of you have a specific wording in mind?
>
>
"Like" LGMT.

Best,
Xuneng

  7. Re: Possible inaccurate description of wal_compression in docs

    Jingtang Zhang <mrdrivingduck@gmail.com> — 2025-08-13T15:22:34Z

    > Do any of you have a specific wording in mind?

'Like when FPW is on …' would be okay, or '(e.g., when FPW is on …)'
would be formal?

--
Regards, Jingtang

  8. Re: Possible inaccurate description of wal_compression in docs

    Xuneng Zhou <xunengzhou@gmail.com> — 2025-08-20T01:01:12Z

    Hi,

On Wed, Aug 13, 2025 at 11:22 PM Jingtang Zhang <mrdrivingduck@gmail.com> wrote:
>
> > Do any of you have a specific wording in mind?
>
> 'Like when FPW is on …' would be okay, or '(e.g., when FPW is on …)'
> would be formal?
>

+1 for e.g.

Best,
Xuneng

  9. Re: Possible inaccurate description of wal_compression in docs

    Michael Paquier <michael@paquier.xyz> — 2025-08-21T04:28:28Z

    On Wed, Aug 20, 2025 at 09:01:12AM +0800, Xuneng Zhou wrote:
> +1 for e.g.

e.g. feels more elegant, so I have reused your suggestion, and applied
the result down to v13.
--
Michael