On Tue, Sep 10, 2013 at 11:39 AM, Jeff Janes <jeff.ja...@gmail.com> wrote: > On Mon, Sep 9, 2013 at 6:29 PM, Bruce Momjian <br...@momjian.us> wrote: >> On Thu, Sep 5, 2013 at 09:02:27PM -0700, Josh Berkus wrote: >>> On 09/05/2013 03:30 PM, Merlin Moncure wrote: >>> >>> >> Standard advice we've given in the past is 25% shared buffers, 75% >>> >> effective_cache_size. Which would make EFS *3X* shared_buffers, not 4X. >>> >> Maybe we're changing the conventional calculation, but I thought I'd >>> >> point that out. >>> > >>> > This was debated upthread. >>> >>> Actually, no, it wasn't. Tom threw out a suggestion that we use 4X for >>> historical reasons. That's all, there was no discussion. >>> >>> So, my point stands: our historical advice has been to set EFS to 75% of >>> RAM. Maybe we're changing that advice, but if so, let's change it. >>> Otherwise 3X makes more sense. >> >> So, what do we want the effective_cache_size default to be? 3x or 4x? >> We clearly state: >> >> If you have a dedicated database server with 1GB or more of RAM, >> a reasonable starting value for shared_buffers is 25% of the >> memory in your system. There are some workloads where even >> >> If we make the default 4x, that means that people using the above >> suggestion would be setting their effective_cache_size to 100% of RAM? >> If we go with 4x, which I believe was the majority opinion, what shall >> we answer to someone who asks about this contradiction? > > I vote for 3x. The past defaults had a different ratio, but we are > changing things to make them better, not to leave them the same. We > should change it be consistent with the advice we have long given. > Sure, 3 is not a power of 2, but I usually root for the underdog.
I vote 4x on the basis that for this setting (unlike almost all the other memory settings) the ramifications for setting it too high generally aren't too bad. Also, the o/s and temporary memory usage as a share of total physical memory has been declining over time (meaning, that if you have a 256gb memory server and follow the advice to set to 64gb, your memory for caching is approximately 64gb). merlin -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers