This commit moves the code in charge of deparsing the method and detail
strings fed later to parse_compress_specification() to a common routine,
where the backward-compatible case of only an integer being found (N
= 0 => "none", N > 1 => gzip at level N) is handled.
Note that this has a side-effect for pg_basebackup, as we now attempt to
detect "server-" and "client-" before checking for the integer-only
pre-14 grammar, where values like server-N and client-N (without the
follow-up detail string) are now valid rather than failing because of an
unsupported method name. Past grammars are still handled the same way,
but these flavors are now authorized, and would now switch to consider N
= 0 as no compression and N > 1 as gzip with the compression level used
as N, with the caller still controlling if the compression method should
be done server-side, client-side or is unspecified. The documentation
of pg_basebackup is updated to reflect that.
This benefits other code paths that would like to rely on the same logic
as pg_basebackup and pg_receivewal with option values used for
compression specifications, one area discussed lately being pg_dump.
Author: Georgios Kokolatos, Michael Paquier
Discussion: https://postgr.es/m/O4mutIrCES8ZhlXJiMvzsivT7ztAMja2lkdL1LJx6O5f22I2W8PBIeLKz7mDLwxHoibcnRAYJXm1pH4tyUNC4a8eDzLn22a6Pb1S74Niexg=@pm.me
PG_COMPRESSION_OPTION_LEVEL is removed from the compression
specification logic, and instead the compression level is always
assigned with each library's default if nothing is directly given. This
centralizes the checks on the compression methods supported by a given
build, and always assigns a default compression level when parsing a
compression specification. This results in complaining at an earlier
stage than previously if a build supports a compression method or not,
aka when parsing a specification in the backend or the frontend, and not
when processing it. zstd, lz4 and zlib are able to handle in their
respective routines setting up the compression level the case of a
default value, hence the backend or frontend code (pg_receivewal or
pg_basebackup) has now no need to know what the default compression
level should be if nothing is specified: the logic is now done so as the
specification parsing assigns it. It can also be enforced by passing
down a "level" set to the default value, that the backend will accept
(the replication protocol is for example able to handle a command like
BASE_BACKUP (COMPRESSION_DETAIL 'gzip:level=-1')).
This code simplification fixes an issue with pg_basebackup --gzip
introduced by ffd5365, where the tarball of the streamed WAL segments
would be created as of pg_wal.tar.gz with uncompressed contents, while
the intention is to compress the segments with gzip at a default level.
The origin of the confusion comes from the handling of the default
compression level of gzip (-1 or Z_DEFAULT_COMPRESSION) and the value of
0 was getting assigned, which is what walmethods.c would consider
as equivalent to no compression when streaming WAL segments with its tar
methods. Assigning always the compression level removes the confusion
of some code paths considering a value of 0 set in a specification as
either no compression or a default compression level.
Note that 010_pg_basebackup.pl has to be adjusted to skip a few tests
where the shape of the compression detail string for client and
server-side compression was checked using gzip. This is a result of the
code simplification, as gzip specifications cannot be used if a build
does not support it.
Reported-by: Tom Lane
Reviewed-by: Tom Lane
Discussion: https://postgr.es/m/1400032.1662217889@sss.pgh.pa.us
Backpatch-through: 15
Compression option handling (level, algorithm or even workers) can be
used across several parts of the system and not only base backups.
Structures, objects and routines are renamed in consequence, to remove
the concept of base backups from this part of the code making this
change straight-forward.
pg_receivewal, that has gained support for LZ4 since babbbb5, will make
use of this infrastructure for its set of compression options, bringing
more consistency with pg_basebackup. This cleanup needs to be done
before releasing a beta of 15. pg_dump is a potential future target, as
well, and adding more compression options to it may happen in 16~.
Author: Michael Paquier
Reviewed-by: Robert Haas, Georgios Kokolatos
Discussion: https://postgr.es/m/YlPQGNAAa04raObK@paquier.xyz
