I have done some tests using pgbench-tools with different configurations on our new server with 768G RAM and it seems for our purpose 32G shared_buffers would give the best results.
Regards Johann On 17 November 2014 at 07:17, Stuart Bishop <stu...@stuartbishop.net> wrote: > On 15 November 2014 06:00, Mark Kirkwood <mark.kirkw...@catalyst.net.nz> > wrote: > > > It is probably time to revisit this 8GB limit with some benchmarking. We > > don't really have a hard and fast rule that is known to be correct, and > that > > makes Alexey's job really difficult. Informally folk (including myself at > > times) have suggested: > > > > min(ram/4, 8GB) > > > > as the 'rule of thumb' for setting shared_buffers. However I was recently > > It would be nice to have more benchmarking and improve the rule of > thumb. I do, however, believe this is orthogonal to fixing pgtune > which I think should be using the current rule of thumb (which is > overwhelmingly min(ram/4, 8GB) as you suggest). > > > > > benchmarking a machine with a lot of ram (1TB) and entirely SSD storage > [1], > > and that seemed quite happy with 50GB of shared buffers (better > performance > > than with 8GB). Now shared_buffers was not the variable we were > > concentrating on so I didn't get too carried away and try much bigger > than > > about 100GB - but this seems like a good thing to come out with some > numbers > > for i.e pgbench read write and read only tps vs shared_buffers 1 -> 100 > GB > > in size. > > I've always thought the shared_buffers setting would need to factor in > things like CPU speed and memory access, since the rational for the > 8GB cap has always been the cost to scan the data structures. And the > kernel would factor in too, since the PG specific algorithms are in > competition with the generic OS algorithms. And size of the hot set, > since this gets pinned in shared_buffers. Urgh, so many variables. > > -- > Stuart Bishop <stu...@stuartbishop.net> > http://www.stuartbishop.net/ > > > -- > Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-performance > -- Because experiencing your loyal love is better than life itself, my lips will praise you. (Psalm 63:3)
