Re: Add LZ4 compression in pg_dump

[ blast-from-the-past department ]

Michael Paquier <michael@paquier.xyz> writes:
> At the end I am finishing with the attached.  I also saw an overlap
> with the addition of --jobs for the directory format vs not using the
> option, so I have removed the case where --jobs was not used in the
> directory format.

(This patch became commit 98fe74218.)

I am wondering if you remember why this bit:

+        # Give coverage for manually compressed blob.toc files during
+        # restore.
+        compress_cmd => {
+            program => $ENV{'GZIP_PROGRAM'},
+            args    => [ '-f', "$tempdir/compression_gzip_dir/blobs.toc", ],
+        },

was set up to manually compress blobs.toc but not the main TOC in the
toc.dat file.  It turns out that Gzip_read is broken for the case
of a zero-length read request [1], but we never reach that case
unless toc.dat is compressed.  We don't cover the getc_func member
of the compression stream API, either.

I thought for a bit about proposing that we compress toc.dat but not
blobs.toc, but that loses coverage in another way: the gets_func API
turns out to be used only while reading blobs.toc.  So we need to
compress both files manually if we want full coverage.

I think this change won't lose coverage, because there are other tests
in 002_pg_dump.pl that exercise directory format without extra
compression of anything.

Thoughts?

            regards, tom lane

[1] https://www.postgresql.org/message-id/3686.1760232320%40sss.pgh.pa.us