Subject: Large backup size of pg_dump

From: Ertan Küçükoglu <[email-masked]>
Date: Wed, 20 May 2026 10:17:57 +0300

Hello,

I am using PostgreSQL 18.4 x64 on Windows Server 2022. There is a very
small single database in the cluster.

There are hourly pg_dump backups scheduled and database backup size is
around 10GB.

command line is like below
pg_dump.exe -p 5432 -U dbuser --exclude-table=app -F p -b -c -f "hourly.bak"

When I check the cluster directory size it is 4.1 GB.

Database has one BLOB saved in a single record and it is 16MB in size and
that is in the "app" table which is excluded from the backup file.

I didn't understand about 2.5 times bigger backup sizes than the total
cluster size. I do not know what to check either. Is there a way for me to
make the hourly backup size smaller?

Thanks & Regards,
Ertan

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From: Priancka Chatz <[email-masked]>
Date: Wed, 20 May 2026 13:23:09 +0200

When you store large objects, the actual data resides on pg_largeobject
table (https://www.postgresql.org/docs/current/catalog-pg-largeobject.html).
So your "app" table might not be the only thing to exclude in your dump.

Regards,
Priyanka Chatterjee

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From: hubert depesz lubaczewski <[email-masked]>
Date: Wed, 20 May 2026 15:17:49 +0200

> There are hourly pg_dump backups scheduled and database backup size is

1. pg_dump is not the best choice for backups.
2. When using pg_dump, use at least -Fd, and -jX to make the dumps work
   in parallel
3. Check what is using the most space in dump, and compare it with db
4. What exactly do you mean by "BLOB"? What is the actual datatype of
   the field?
5. What is `\l+ your_db_name` output from psql?

> make the hourly backup size smaller?

Consider compressing it? Or use some backup tool that handles
incremental/differential backups, like, for example, backrest.

depesz

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From: Ron Johnson <[email-masked]>
Date: Wed, 20 May 2026 10:15:46 -0400

> pg_dump.exe -p 5432 -U dbuser --exclude-table=app -F p -b -c -f

1. Note that -Fp generates plain SQL files.
2. Where are you specifying the database name?  Or is everything going into
"postgres"?
3. No need to specify the default port 5432.

> that is in the "app" table which is excluded from the backup file.

Is 16MB *that* big?

> make the hourly backup size smaller?

Taking full backups every hour is suboptimal.

But if you *must*, then
pg_dump -Fp  --compress=zstd  $db > ${db}.sql.zst

-- 
Death to <Redacted>, and butter sauce.
Don't boil me, I'm still alive.
<Redacted> lobster!

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From: Adrian Klaver <[email-masked]>
Date: Wed, 20 May 2026 07:48:10 -0700

On 5/20/26 12:17 AM, Ertan Küçükoglu wrote:
> Database has one BLOB saved in a single record and it is 16MB in size 
> and that is in the "app" table which is excluded from the backup file.
> 
> cluster size. I do not know what to check either. Is there a way for me 
> to make the hourly backup size smaller?

Because you are using a plain text dump. The data is stored in an 
optimized binary form in the cluster files, when you ask for it to be 
plain text it 'expands' to be represented as text. Use something like 
this -Fc, which will compress the file produced. The handy part is that 
on restoring you can restore all or part of the file, with the caveat 
that for a partial restore it needs to make logical sense. In other 
words restoring a child table without it's parent will not work.

-- 
Adrian Klaver
[email-masked]