ZFS ARC actually works the same way, i.e. the records would remain compressed in memory. When running PostgreSQL, I would probably go with `primarycache=all` f

ZFS ARC actually works the same way, i.e. the records would remain compressed in memory. When running PostgreSQL, I would probably go with `primarycache=all` for the data dir, a largish ARC cache, and a smallish shared buffers, to take advantage of the filesystem compression. When running MySQL, I would probably go with `primarycache=metadata` for the data dir, a smallish ARC cache, and a largish buffer pool, to still benefit (slightly) from the filesystem compression.