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Re: wal segment size - Mailing list pgsql-general

From Ron Johnson
Subject Re: wal segment size
Date
Msg-id CANzqJaAXOGvS3sEN1o0xAkA1Ud0JmzBEuPSJiF0gOkVBgKFYog@mail.gmail.com
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In response to Re: wal segment size  ("Colin 't Hart" <colinthart@gmail.com>)
List pgsql-general
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Adding this to ~/.ssh/config will almost totally eliminate the cost of ssh authentication:

Host *
    ControlMaster auto
    #ControlPath /run/user/%i/%L_%r_at_%n:%p
    ControlPath ~/.ssh/%L_%r_at_%n:%p
    ControlPersist 5m

Pointing ControlPath to /run/user/%i is even faster, but it doesn't always exist if you sudo into the postgres service account.

On Wed, Dec 17, 2025 at 11:10 AM Colin 't Hart <colinthart@gmail.com> wrote:
Thanks Laurenz, that confirms what I was assuming. Archiving is via pgbackrest to a backup server, over SSH. Approx 750ms to archive each segment is crazy -- I'll check compression parameters too.

Any reason not to bump it up to 1GB? Or is that overkill?

/Colin

On Wed, 17 Dec 2025 at 16:25, Laurenz Albe <laurenz.albe@cybertec.at> wrote:
On Wed, 2025-12-17 at 16:13 +0100, Colin 't Hart wrote:
> I see very little advice on tuning WAL segment size.
>
> One of my clients has a few datawarehouses at around 8 - 16 TB
>
> On one of the nodes there are approx 15000 WAL segments of 16MB each, totalling
> approx 230GB. The archiver is archiving approx one per second, so approx 4 hours to clear.
>
> Would we gain anything by bumping the WAL segment size?

Very likely yes, if the problem is the overhead of starting the archive_command.

Another thing that can slow down archiving is if you compress these segments
too aggressively.

Yours,
Laurenz Albe


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