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Re: Does pg_dump custom format only compress the table data? - Mailing list pgsql-admin

From Ron Johnson
Subject Re: Does pg_dump custom format only compress the table data?
Date
Msg-id CANzqJaAh+mPakfiEB2=GiNioMYRPef0eO7ex04-mmDLvoDPX0g@mail.gmail.com
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In response to Re: Does pg_dump custom format only compress the table data?  (Laurenz Albe <laurenz.albe@cybertec.at>)
Responses Re: Does pg_dump custom format only compress the table data?
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On Tue, Feb 3, 2026 at 7:48 AM Laurenz Albe <laurenz.albe@cybertec.at> wrote:
On Tue, 2026-02-03 at 08:51 +0100, Holger Jakobs wrote:
> Am 03.02.26 um 07:06 schrieb Laurenz Albe:
> > On Mon, 2026-02-02 at 10:55 -0500, Ron Johnson wrote:
> > > Out of curiosity, I opened that dump file in vim, and saw not only DDL strings but cleartext table data.
> > >
> > > Why isn't it compressed?
> > Are your DDL statement large enough that you would expect that compressing
> > them would offer any real advantage?
>
> That wasn't the question. It was about why table DATA aren't compressed,
> but in clear text.

Ah, I see.

By default, you wouldn't see any table data, because they get compressed.

If a custom format dump is not compressed, the reason could be:

- PostgreSQL was built without support for compression (--without-zlib)

- pg_dump was called with --compress=0

I always install RPMs from postgresql.org, and in this case specified --compress=zstd:long.

$ psql -V
psql (PostgreSQL) 17.7

dba=# insert into do_not_delete (node_name) values ('foo');
INSERT 0 1
dba=# insert into do_not_delete (node_name) values ('bar');
INSERT 0 1
dba=# insert into do_not_delete (node_name) values ('blarge');
INSERT 0 1
dba=#

$ pg_dump -V
pg_dump (PostgreSQL) 17.7

db=dba
$ pg_dump -Fc --compress=zstd:long -v -d${db} -f ${db}.dump  2> ${db}.log
$ dir ${db}.dump
-rw-r--r-- 1 postgres postgres 2205102870 2026-02-03 11:07:34 dba.dump

$ strings ${db}.dump | grep -E 'foo|bar|blarge'
foo     \N
bar     \N
blarge  \N
\Afoo
barYD
[snip]


--
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Don't boil me, I'm still alive.
<Redacted> lobster!

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