I was wondering on pg_lesslog integration on our architecture based on wal shipping using pg_standby (thanks Simon) as recovery tool. The main target is to reduce wal files accumulation on "master" host (thus consumming disk space) in case of slave unavailability. As far as I've read the source of pg_stanby, WAL size is checked in CustomizableNextWALFileReady function, allowing customization of file size check. Actually, the "legacy" way WAL is checked, is "if file size is normal WAL file size then we've got a supposed-good WAL". Thus, we cannot use compressed log files out of "pg_lesslog", we need to "decompress" it before processing, including a "pre-processing" stage and/or command.
There are three ways to do such : - first, we could write a script on master to compress, rsync then decompress (on slave) file, but the idea to call a remote processing on slave seems to be quite hazardous to me (in some way it may lead to strange situations) - second, we could rsync compressed log to a directory, use a local "daemon" on slave to watch a directory and decompress files to final place (pg_standby WAL source directory) - third, we could add some functionnalities to pg_standby allowing to pre-process WAL file (thus customizing CustomizableNextWALFileReady function?), this might be usefull for other issues or use cases than pg_lesslog but it applies quite good to it :)