Re: Add LZ4 compression in pg_dump

On Fri, Feb 24, 2023 at 11:02:14PM -0600, Justin Pryzby wrote:
> I have some fixes (attached) and questions while polishing the patch for
> zstd compression. The fixes are small and could be integrated with the
> patch for zstd, but could be applied independently.

One more - WriteDataToArchiveGzip() says:

+ if (cs->compression_spec.level == 0)
+ pg_fatal("requested to compress the archive yet no level was specified");

That was added at e9960732a.

But if you specify gzip:0, the compression level is already enforced by
validate_compress_specification(), before hitting gzip.c:

| pg_dump: error: invalid compression specification: compression algorithm "gzip" expects a compression level between 1 and 9 (default at -1)

5e73a6048 intended that to work as before, and you *can* specify -Z0:

The change is backward-compatible, hence specifying only an integer
leads to no compression for a level of 0 and gzip compression when the
level is greater than 0.

$ time ./src/bin/pg_dump/pg_dump -h /tmp regression -t int8_tbl -Fp --compress 0 |file -
/dev/stdin: ASCII text

Right now, I think that pg_fatal in gzip.c is dead code - that was first
added in the patch version sent on 21 Dec 2022.

--
Justin