buffer cache size

[michael luch]

I think that the buffer cache on my system is not growing sufficiently and 
wonder if I can I tune it.

Here's a snippet from the output of top on my system:

Mem: 646M Active, 2905M Inact, 174M Wired, 121M Cache, 112M Buf, 5460K Free
Swap: 512M Total, 192K Used, 512M Free

I have a MySQL db that's more than 1GB in size. When I do a SELECT, mysqld 
becomes about 25%busy (fair enough, it's waiting for disk). However, I was 
expecting to see the Buffer Cache size (that's the 121M Cache I think) grow, 
and expected to see subsequent SELECTs cause mysqld become CPU bound, as 
data from the database should now be in the buffer cache. However, this is 
not the case. I have 2GB of inactive memory, but a small buffer cache and a 
disk bound mysqld :(

Are there some tunables I should look at to allow the buffer cache to grow?
All the searches I did suggested that the vm system should look after this 
itself.

Thanks
M

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