Re: Different compression methods for FPI

Hi,

I have a small question for those involved:

Context: I'm trying to get the smallest BKPIMAGE size possible
regardless of CPU cost, which means I'm trying multiple compressions
to get the smallest data possible with the options available. This
means ignoring the wal_compression GUC in XLogCompressBackupBlock and
brute-forcing the smallest compression available, potentially layering
compression methods, and returning the bimg_info compression flags
that will be stored in XLogCompressBackupBlock and used to decompress
the block's data.

Is there a prescribed order of compression algorithms to apply when
(de)compressing full page images in WAL, when the bimg_info has more
than one BKPIMAGE_COMPRESS_*-flags set? That is, when I want to check
the compression of the block image with both ZSTD and LZ4, which order
is the ordering indicated by bimg_info = (COMPRESS_LZ4 |
COMPRESS_ZSTD)?

Kind regards,

Matthias van de Meent