Re: Add LZ4 compression in pg_dump

Hello,
23.02.2023 23:24, Tomas Vondra wrote:
> On 2/23/23 16:26, Tomas Vondra wrote:
>> Thanks for v30 with the updated commit messages. I've pushed 0001 after
>> fixing a comment typo and removing (I think) an unnecessary change in an
>> error message.
>>
>> I'll give the buildfarm a bit of time before pushing 0002 and 0003.
>>
> I've now pushed 0002 and 0003, after minor tweaks (a couple typos etc.),
> and marked the CF entry as committed. Thanks for the patch!
>
> I wonder how difficult would it be to add the zstd compression, so that
> we don't have the annoying "unsupported" cases.

With the patch 0003 committed, a single warning -Wtype-limits appeared in the
master branch:
$ CPPFLAGS="-Og -Wtype-limits" ./configure --with-lz4 -q && make -s -j8
compress_lz4.c: In function ‘LZ4File_gets’:
compress_lz4.c:492:19: warning: comparison of unsigned expression in ‘< 0’ is
always false [-Wtype-limits]
  492 |         if (dsize < 0)
      |
(I wonder, is it accidental that there no other places that triggers
the warning, or some buildfarm animals had this check enabled before?)

It is not a false positive as can be proved by the 002_pg_dump.pl modified as
follows:
-                       program => $ENV{'LZ4'},
+                       program => 'mv',
                        args    => [
-                               '-z', '-f', '--rm',
"$tempdir/compression_lz4_dir/blobs.toc",
"$tempdir/compression_lz4_dir/blobs.toc.lz4",
                        ],
                },
A diagnostic logging added shows:
LZ4File_gets() after LZ4File_read_internal; dsize: 18446744073709551615

and pg_restore fails with:
error: invalid line in large object TOC file
".../src/bin/pg_dump/tmp_check/tmp_test_22ri/compression_lz4_dir/blobs.toc": "????"

Best regards,
Alexander