On Fri, May 6, 2011 at 5:31 PM, Greg Smith <g...@2ndquadrant.com> wrote: > On 05/05/2011 05:06 AM, Mitsuru IWASAKI wrote: >> >> In summary, PgFincore's target is File System Buffer Cache, Buffer >> Cache Hibernation's target is DB Buffer Cache(shared buffers). >> > > Right. The thing to realize is that shared_buffers is becoming a smaller > fraction of the total RAM used by the database every year. On Windows it's > been stuck at useful settings being less than 512MB for a while now. And on > UNIX systems, around 8GB seems to be effective upper limit. Best case, > shared_buffers is only going to be around 25% of total RAM; worst-case, > approximately, you might have Windows server with 64GB of RAM where > shared_buffers is less than 1% of total RAM. > > There's nothing wrong with the general idea you're suggesting. It's just > only targeting a small (and shrinking) subset of the real problem here. > Rebuilding cache state starts with shared_buffers, but that's not enough of > the problem to be an effective tweak on many systems. > > I think that all the complexity with CRCs etc. is unlikely to lead anywhere > too, and those two issues are not completely unrelated. The simplest, > safest thing here is the right way to approach this, not the most > complicated one, and a simpler format might add some flexibility here to > reload more cache state too. The bottleneck on reloading the cache state is > reading everything from disk. Trying to micro-optimize any other part of > that is moving in the wrong direction to me. I doubt you'll ever measure a > useful benefit that overcomes the expense of maintaining the code. And you > seem to be moving to where someone can't restore cache state when they > change shared_buffers. A simpler implementation might still work in that > situation; reload until you run out of buffers if shared_buffers shrinks, > reload until you're done with the original size.
Yeah, I'm pretty well convinced this whole approach is a dead end. Priming the OS buffer cache seems way more useful. I also think saving the blocks to be read rather than the actual blocks makes a lot more sense. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
