On 07/17/2018 09:12 PM, Peter Eisentraut wrote: > On 17.07.18 00:04, Jerry Jelinek wrote: >> There have been quite a few comments since last week, so at this point I >> am uncertain how to proceed with this change. I don't think I saw >> anything concrete in the recent emails that I can act upon. > > The outcome of this could be multiple orthogonal patches that affect the > WAL file allocation behavior somehow. I think your original idea of > skipping recycling on a COW file system is sound. But I would rather > frame the option as "preallocating files is obviously useless on a COW > file system" rather than "this will make things mysteriously faster with > uncertain trade-offs". >
Makes sense, I guess. But I think many claims made in this thread are mostly just assumptions at this point, based on our beliefs how CoW or non-CoW filesystems work. The results from ZFS (showing positive impact) are an exception, but that's about it. I'm sure those claims are based on real-world experience and are likely true, but it'd be good to have data from a wider range of filesystems / configurations etc. so that we can give better recommendations to users, for example. That's something I can help with, assuming we agree on what tests we want to do. I'd say the usual batter of write-only pgbench tests with different scales (fits into s_b, fits into RAM, larger then RAM) on common Linux filesystems (ext4, xfs, btrfs) and zfsonlinux, and different types of storage would be enough. I don't have any freebsd box available, unfortunately. regards -- Tomas Vondra http://www.2ndQuadrant.com PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
