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From: Andrew <[email protected]>
To: Laurenz Albe <[email protected]>
Cc: Greg Sabino Mullane <[email protected]>
Cc: Colin 't Hart <[email protected]>
Cc: PostgreSQL General <[email protected]>
Subject: Re: wal segment size
Date: Fri, 19 Dec 2025 09:26:17 +0100
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>

As an oracle dba new to Postgres, I’m used to the concept of context switches and latch issues with regards to transaction log switches. Does Postgres have a similar mechanism with latching etc when it switches to a new wal segment that is alleviated when increasing the size of the wal segments?

Regards
Andrew
Sent from my iPhone

> On 17 Dec 2025, at 18:58, Laurenz Albe <[email protected]> wrote:
> 
> On Wed, 2025-12-17 at 12:21 -0500, Greg Sabino Mullane wrote:
>>> On Wed, Dec 17, 2025 at 11:10 AM Colin 't Hart <[email protected]> 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.
>> 
>> Switch to archive-async = on. When doing that, the typical time drops to 10ms or less.
>> Also use a compress-type of lz4 or zst, which perform way better than the default gz.
>> If you are encrypting, that's a bottleneck you just have to deal with, no shortcuts there. :)
> 
> I second that.  Asynchronous archiving in pgBackRest tends to work around the problem.
> 
>> tl;dr try other things before messing with the WAL size. The current size can work very
>> well even on very large and very, very busy systems.
> 
> On the other hand, 16MB on a very busy system is somewhat ridiculous.
> A somewhat bigger segment size may be appropriate.
> 
> Yours,
> Laurenz Albe
> 
> 

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