Re: Question about wal_compression and what to expect

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Yes, my question was essentially do I need to separately compress WAL files for storage/archiving even with wal_compression set. So, I think you've answered my question.


On June 20, 2023, "Wetmore, Matthew (CTR)" <matthew.wetmore@xxxxxxxxxxxxxxxxxxx> wrote:

From my understanding,


Wal_compression will compress full page writes in the wal file.  The size of your wal is configurable.


So for your 16MB wal, it’s already compressed into the wal, and your wal_size won’t change.  (just more data can fit into your 16MB)


As far as archiving, I create a dir, then tar.gz the dir for storage. (if that was your question)




From: Sean O'Grady <sean@xxxxxxxxxxx>
Sent: Tuesday, June 20, 2023 11:19 AM
To: pgsql-admin@xxxxxxxxxxxxxxxxxxxx
Subject: [EXTERNAL] Question about wal_compression and what to expect



I've enabled wal_compression however I do not see any change in the 16MB size for each WAL file. Through all my googling and searching the mailing lists, I could not find a description if a change *should* be expected even though many of the articles I've read indicate compression can save disk space. 

I am currently thinking that the records in the WAL file are compressed for the purpose of writing less data to disk, but that the file is still padded to 16MB. If so, does that mean to realize a space savings for archiving that my archive_command should compress the file (gzip, bz2, etc)?

Sean O'Grady

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