Bruce Cran írta:
Wojciech Puchar wrote:
> Laszlo wrote:
Hi All,
Is there a way (sysctl?) to tell FreeBSD (6.2 RELEASE) how many
memory can it use for caching file data from disk?
It might be that FreeBSD will use all available RAM, and reduce the
cache
it already does
It may seem strange since it's generally accepted that you can never
have enough disk cache, but FreeBSD apparently doesn't actually use
all the free memory for caching. By default it uses up to 256MB for
buffering/caching and there's no way it can use all available memory
on i386 in machines with more than 1GB installed since the
buffer/cache is allocated from KVM and the default maximum is 1GB.
You can increase the amount of memory used, but it might not help -
there's a thread on performance@ from 2004 which describes how it all
works; see
http://lists.freebsd.org/pipermail/freebsd-performance/2004-April/000785.html
The information there is quite old now though so I don't know if
things are done differently in 6.x.
OK, and how about amd64 arch? The reason I ask this is that we have a
big postresql database (over 3GB) and PostgreSQL rely on the OS for
caching files in memory. This database is mostly read-only, so it would
be nice to use all free memory for caching. Especially that this machine
is the database server, it does nothing else. Now, it is an i386 but we
are about to migrate to AMD X2, then we can put in 8GB of memory. But
only if the OS can use if for caching. Otherwise it would be useless.
Thank you for the link. That thread is quite old - things might have
changed.
Thanks,
Laszlo
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