On 3/18/11 11:15 AM, Jim Nasby wrote:
> To take the opposite approach... has anyone looked at having the OS just
> manage all caching for us? Something like MMAPed shared buffers? Even if we
> find the issue with large shared buffers, we still can't dedicate serious
> amounts of memory to them because of work_mem issues. Granted, that's
> something else on the TODO list, but it really seems like we're re-inventing
> the wheels that the OS has already created here...
As far as I know, no OS has a more sophisticated approach to eviction
than LRU. And clock-sweep is a significant improvement on performance
over LRU for frequently accessed database objects ... plus our
optimizations around not overwriting the whole cache for things like VACUUM.
2-level caches work well for a variety of applications.
Now, what would be *really* useful is some way to avoid all the data
copying we do between shared_buffers and the FS cache.
--
-- Josh Berkus
PostgreSQL Experts Inc.
http://www.pgexperts.com
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