Configuring disk cache size on postgress

Dror Matalon dror at
Tue Mar 16 10:44:15 PST 2004

Hi Folks,

When configuring postgres, one of the variables to configure is
	Sets the optimizer's assumption about the effective size of the disk
	cache (that is, the portion of the kernel's disk cache that will be
	used for PostgreSQL data files). This is measured in disk pages, which
	are normally 8 kB each.

The conventional wisdom on the postgres list has been that for freebsd
you calculate this by doing `sysctl -n vfs.hibufspace` / 8192).

Now I'm running 4.9 with 2 Gig of ram and sysctl -n vfs.hibufspace
indicates usage of 200MB.

1. How much RAM is freebsd using for *disk* caching? Is it part of the
general VM or is it limited to the above 200MB? I read Matt Dillon's, but most of the
discussion there seems to be focused on caching programs and program

2. Can I tell, and if so how,  how much memory the OS is using for disk

3. What are the bufspace variables for?

This subject has been touched on before in
which point to a patch to increase the bufspace. 



Dror Matalon
Zapatec Inc 
1700 MLK Way
Berkeley, CA 94709

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