Re: Does pg_dump custom format only compress the table data?

On Tue, Feb 3, 2026 at 7:48 AM Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)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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