On Wednesday 2025-08-27 00:54, Adrian Klaver wrote:
Date: Wed, 27 Aug 2025 00:54:52
From: Adrian Klaver <adrian.klaver@xxxxxxxxxxx>
To: Dimitrios Apostolou <jimis@xxxxxxx>, pgsql-general@xxxxxxxxxxxxxxxxxxxx
Subject: Re: In-order pg_dump (or in-order COPY TO)
On 8/26/25 12:43, Dimitrios Apostolou wrote:
Hello list,
I am storing dumps of a database (pg_dump custom format) in a de-
duplicating backup server. Each dump is many terabytes in size, so
deduplication is very important. And de-duplication itself is based on
rolling checksums which is pretty flexible, it can compensate for blocks
moving by some offset.
Unfortunately after I did pg_restore to a new server, I notice that the
dumps from the new server are not being de-duplicated, all blocks are
considered new.
What are the pg_dump/pg_restore commands?
What are the Postgres versions involved?
Are they community versions of Postgres or something else?
What is the depduplication program?
Dump is from PostgreSQL 16, it's pg_dump writing to stdout:
pg_dump -v --format=custom --compress=none --no-toast-compression --serializable-deferrable db_name | borg create ...
As you can see the backup (and deduplicating) program is borgbackup.
Restore is in PostgreSQL 17:
I first create the empty tables by running the DDL commands in version
control to setup the database. And then I do pg_restore --data-only:
pg_restore -vvvv -j 8 -U db_owner -d db_name --schema=public --section=data dump_file
Worth noting is that the above pg_restore goes through the WAL, i.e. all
writes are done by walwriter, not the backend directly.
Postgres is standard open source running on own server. It has a couple
of custom patches that shouldn't matter in this codepath.
Thanks in advance,
Dimitris
