Re: Fixes for compression options of pg_receivewal and refactoring of backup_compression.{c,h}

On Tue, Apr 12, 2022 at 06:22:48PM +0900, Michael Paquier wrote:
> On Mon, Apr 11, 2022 at 12:46:02PM +0000, gkokolatos@pm.me wrote:
>> It looks good. If you choose to discard the comment regarding the use of
>> 'method' over 'algorithm' from above, can you please use the full word in the
>> variable, e.g. 'wal_compress_algorithm' instead of 'wal_compress_algo'. I can
>> not really explain it, the later reads a bit rude. Then again that may be just
>> me.
> 
> Thanks.  I have been able to do an extra pass on 0001 and 0002, fixing
> those naming inconsistencies with "algo" vs "algorithm" that you and
> Robert have reported, and applied them.  For 0003, I'll look at it
> later.  Attached is a rebase with improvements about the variable
> names.

This has been done with the proper renames.  With that in place, I see
no reason now to not be able to set the compression level as it is
possible to pass it down with the options available.  This requires
only a couple of lines, as of the attached.  LZ4 has a dummy structure
called LZ4F_INIT_PREFERENCES to initialize LZ4F_preferences_t, that
holds the compression level before passing it down to
LZ4F_compressBegin(), but that's available only in v1.8.3.  Using it
risks lowering down the minimal version of LZ4 we are able to use now,
but replacing that with a set of memset()s is also a way to set up
things as per its documentation.

Thoughts?
--
Michael