Subject: PG 14 pg_basebackup accepts --compress=server-zst option

From: Ron Johnson <[email-masked]>
Date: Thu, 6 Jun 2024 21:54:20 -0400

https://www.postgresql.org/docs/14/app-pgbasebackup.html doesn't mention
"--compress=[{client|server}-]method".  That first appears in the v15 docs.

And yet pg_basebackup doesn't complain about an invalid option.
(Technically, this is a bug; I first noticed it a week after copying a
script from a PG 15 server to five PG 14 servers, and running it quite a
few times without fail.)

$ pg_basebackup \
>             --pgdata=$PGDATA \
>             --dbname=service=basebackup \
>             --verbose --progress \
>             --checkpoint=fast \
>             --write-recovery-conf \
>             --wal-method=stream \
>             --create-slot --slot=pgstandby1 \
>             --compress=server-zst ; echo $?
pg_basebackup: initiating base backup, waiting for checkpoint to complete
pg_basebackup: checkpoint completed
pg_basebackup: write-ahead log start point: 256/BC000028 on timeline 1
pg_basebackup: starting background WAL receiver
pg_basebackup: created replication slot "pgstandby1"
42567083/42567083 kB (100%), 1/1 tablespace
pg_basebackup: write-ahead log end point: 256/BC000138
pg_basebackup: waiting for background process to finish streaming ...
pg_basebackup: syncing data to disk ...
pg_basebackup: renaming backup_manifest.tmp to backup_manifest
pg_basebackup: base backup completed
0

---

From: Kashif Zeeshan <[email-masked]>
Date: Fri, 7 Jun 2024 09:27:07 +0500

Hi

> script from a PG 15 server to five PG 14 servers, and running it quite a
If the support is removed then it should be mentioned in the official
documentation.

Regards
Kashif Zeeshan
Bitnine Global

---

From: "David G. Johnston" <[email-masked]>
Date: Thu, 6 Jun 2024 21:32:09 -0700

>> script from a PG 15 server to five PG 14 servers, and running it quite a
Seems a bit suspect, but as your script doesn’t mention tar the option
itself is apparently ignored, I guess silently.  Assuming this isn’t an
actual regression in behavior in a patch-released older version I don’t see
us adding an error message at this point.

> If the support is removed then it should be mentioned in the official

Support wasn’t removed.  Re-read the email and check the version/times
being mentioned again.

David J.

---

From: Ron Johnson <[email-masked]>
Date: Fri, 7 Jun 2024 08:04:33 -0400

On Fri, Jun 7, 2024 at 12:32 AM David G. Johnston <
[email-masked]> wrote:

>>> https://www.postgresql.org/docs/14/app-pgbasebackup.html doesn't
>>> mention "--compress=[{client|server}-]method".  That first appears in the
>>> v15 docs.
>>>
> itself is apparently ignored, I guess silently.
>

Does this mean that "--compress=server-zst" is only relevant with
--format=tar?

> Assuming this isn’t an actual regression in behavior in a patch-released
> older version
>

My apologies for not mentioning the version: 14.12-1PGDG-rhel8.

> I don’t see us adding an error message at this point.
>

Me neither.  It just seemed odd.

---

From: Tom Lane <[email-masked]>
Date: Fri, 07 Jun 2024 11:33:08 -0400

> Me neither.  It just seemed odd.

v14 thinks the argument of --compress must be an integer, and doesn't
really bother with any syntax error checks:

            case 'Z':
                compresslevel = atoi(optarg);
                if (compresslevel < 0 || compresslevel > 9)
                {
                    pg_log_error("invalid compression level \"%s\"", optarg);
                    exit(1);
                }
                break;

In your example, atoi() will return zero and it will sail along with
no compression.  Releases 15 and up have more complex ideas of what
--compress can specify, and seem to syntax-check it much more
thoroughly.

This is a pretty common coding pattern, so I can't get excited
about changing it, especially not in long-stable branches.

			regards, tom lane