On Thu, 26 Feb 2004, Dror Matalon wrote:

> Hi,
> We have postgres running on freebsd 4.9 with 2 Gigs of memory. As per
> repeated advice on the mailing lists we configured effective_cache_size
> = 25520 which you get by doing `sysctl -n vfs.hibufspace` / 8192
> Which results in using 200Megs for disk caching. 
> Is there a reason not to increase the hibufspace beyond the 200 megs and
> provide a bigger cache to postgres? I looked both on the postgres and
> freebsd mailing lists and couldn't find a good answer to this.

Actually, I think you're confusing effective_cache_size with 

effective_cache_size changes no cache settings for postgresql, it simply 
acts as a hint to the planner on about how much of the dataset your OS / 
Kernel / Disk cache can hold.

Making it bigger only tells the query planny it's more likely the data 
it's looking for will be in cache.

shared_buffers, OTOH, sets the amount of cache that postgresql uses.  It's 
generall considered that 256 Megs or 1/4 of memory, whichever is LESS, is 
a good setting for production database servers.

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