Re: Add LZ4 compression in pg_dump

On Sat, Dec 17, 2022 at 05:26:15PM -0600, Justin Pryzby wrote:
> 001: still refers to "gzip", which is correct for -Fp and -Fd but not
> for -Fc, for which it's more correct to say "zlib".

Or should we begin by changing all these existing "not built with zlib
support" error strings to the more generic "this build does not
support compression with %s" to reduce the number of messages to
translate? That would bring consistency with the other tools dealing
with compression.

> That affects the
> name of the function, structures, comments, etc. I'm not sure if it's
> an issue to re-use the basebackup compression routines here. Maybe we
> should accept "-Zn" for zlib output (-Fc), but reject "gzip:9", which
> I'm sure some will find confusing, as it does not output. Maybe 001
> should be split into a patch to re-use the existing "cfp" interface
> (which is a clear win), and 002 to re-use the basebackup interfaces for
> user input and constants, etc.
>
> 001 still doesn't compile on freebsd, and 002 doesn't compile on
> windows. Have you checked test results from cirrusci on your private
> github account ?

FYI, I have re-added an entry to the CF app to get some automated
coverage:
https://commitfest.postgresql.org/41/3571/

On MinGW, a complain about the open() callback, which I guess ought to
be avoided with a rename:
[00:16:37.254] compress_gzip.c:356:38: error: macro "open" passed 4 arguments, but takes just 3
[00:16:37.254] 356 | ret = CFH->open(fname, -1, mode, CFH);
[00:16:37.254] | ^
[00:16:37.254] In file included from ../../../src/include/c.h:1309,
[00:16:37.254] from ../../../src/include/postgres_fe.h:25,
[00:16:37.254] from compress_gzip.c:15:

On MSVC, some declaration conflicts, for a similar issue:
[00:12:31.966] ../src/bin/pg_dump/compress_io.c(193): error C2371: '_read': redefinition; different basic types
[00:12:31.966] C:\Program Files (x86)\Windows Kits\10\include\10.0.20348.0\ucrt\corecrt_io.h(252): note: see declaration of '_read'
[00:12:31.966] ../src/bin/pg_dump/compress_io.c(210): error C2371: '_write': redefinition; different basic types
[00:12:31.966] C:\Program Files (x86)\Windows Kits\10\include\10.0.20348.0\ucrt\corecrt_io.h(294): note: see declaration of '_write'

> 002 breaks "pg_dump -Fc -Z2" because (I think) AllocateCompressor()
> doesn't store the passed-in compression_spec.

Hmm. This looks like a gap in the existing tests that we'd better fix
first. This CI is green on Linux.

> 003 still uses <lz4.h> and not "lz4.h".

This should be <lz4.h>, not "lz4.h".
--
Michael