Scott Carey wrote:
And there is an OS component to it too. You can actually get away with shared_buffers at 90% of RAM on Solaris. Linux will explode if you try that (unless recent kernels have fixed its shared memory accounting).
You can use much larger values for shared_buffers on Solaris with UFS as the filesystem than almost anywhere else, as you say. UFS defaults to caching an extremely tiny amount of memory by default. Getting PostgreSQL to buffer everything therefore leads to minimal double-caching and little write caching that creates checkpoint spikes, so 90% is not impossible there.
If you're using ZFS instead, that defaults to similar aggressive caching as Linux. You may even have to turn that down if you want the database to have a large amount of memory for its own use even with normal levels of sizing; just space for shared_buffers and work_mem can end up being too large of a pair of competitors for caching RAM. ZFS is not really not tuned all that differently from how Linux approaches caching in that regard.
-- Greg Smith 2ndQuadrant US greg@xxxxxxxxxxxxxxx Baltimore, MD PostgreSQL Training, Services, and 24x7 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
