On Thu, Sep 5, 2013 at 12:48:54PM -0400, Tom Lane wrote: > Magnus Hagander <mag...@hagander.net> writes: > > On Thu, Sep 5, 2013 at 3:01 AM, Bruce Momjian <br...@momjian.us> wrote: > >> I have developed the attached patch which implements an auto-tuned > >> effective_cache_size which is 4x the size of shared buffers. I had to > >> set effective_cache_size to its old 128MB default so the EXPLAIN > >> regression tests would pass unchanged. > > > That's not really autotuning though. ISTM that making the *default* 4 > > x shared_buffers might make perfect sense, but do we really need to > > hijack the value of "-1" for that? That might be useful for some time > > when we have actual autotuning, that somehow inspects the system and > > tunes it from there. > > Well, the real problem with this patch is that it documents what the > auto-tuning algorithm is; without that commitment, just saying "-1 means > autotune" might be fine.
OK, but I did this based on wal_buffers, which has a -1 default, calls it auto-tuning, and explains how the default is computed. > Did you consider the alternative of just tweaking initdb to insert a > default for effective_cache_size that's 4x whatever it picks for > shared_buffers? That would probably be about 3 lines of code, and it > wouldn't nail down any particular server-side behavior. The problem there is that many users are told to tune shared_buffers, but don't touch effective cache size. Having initdb set the effective_cache_size value would not help there. Again, this is all based on the auto-tuning of wal_buffers. -- Bruce Momjian <br...@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com + It's impossible for everything to be true. + -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers