Josh Berkus wrote:
We talked about bumping it to 512kB or 1MB for 9.1. Did that get in? Do I need to write that patch?
If it defaulted to 3% of shared_buffers, min 64K & max 16MB for the auto setting, it would for the most part become an autotuned parameter. That would make it 0.75 to 1MB at the standard anemic Linux default kernel parameters. Maybe more than some would like, but dropping shared_buffers from 24MB to 23MB to keep this from being ridiculously undersized is probably a win. That percentage would reach 16MB by the time shared_buffers was increased to 533MB, which also seems about right to me. On a really bad setup (brief pause to flip off Apple) with only 4MB to work with total, you'd end up with wal_buffers between 64 and 128K, so very close to the status quo.
Code that up, and we could probably even remove the parameter as a tunable altogether. Very few would see a downside relative to any sensible configuration under the current situation, and many people would notice better automagic performance with one less parameter to tweak. Given the recent investigations about the serious downsides of tiny wal_buffers values on new Linux kernels when using open_datasync, a touch more aggression about this setting seems particularly appropriate to consider now. That's been swapped out as the default, but it's still possible people will switch to it.
-- Greg Smith 2ndQuadrant US greg@xxxxxxxxxxxxxxx Baltimore, MD PostgreSQL Training, Services and Support www.2ndQuadrant.us "PostgreSQL 9.0 High Performance": http://www.2ndQuadrant.com/books -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
