Re: Enough RAM for entire Database.. cost aside, is this

Hi,

> That is certainly not correct. I don't have hard sources to back it up,
but if
> you open a file that you jus close it, linux does not go copying it from
it's
> cache to the process address space. It would rather juggle the page table
to mak
> e memory pages available to your process.

Phew. I wasn't sure about this. At least the CPUS can concentrate on all
that page swapping.

> - Postgresql or no postgresql, OS has to manage buffer cache. Why
duplicate the
> efforts which somebody is already better at? If OS improves, everybody
benefits.
> I can recall quite a few posts benefitting from moving to 2.6.x kernel
from 2.4.x.

I did read that the Linux kernel now tries something better than just LRU
for cache replacement. (Least Frequently Used? Or a combination - I can't
remember exactly).

That given, I understand the arguments you give when thinking about systems
where most of the database can't fit on the machine... and that is generally
the case now.

But when, as will become more and more common over the next 3 or 4 years,
the whole database *easily* fits into RAM on a dedicated DB machine, with
room for everything else to operate without swapping, then there is a real
opportunity to improve performance by simply getting the data into RAM in an
optimised indexed layout. There are some really interesting 64 bit linux
multi CPU server solutions coming out now, with huge addressing and RAM
potential.

>
> Well, best thing I can tell you is test yourself and find out the sweet
spot. It
> should be between 64-128MB by general wisdom. If you find otherwise, we
would be
> more than glad to hear.

Well I'll start with that, and see how it goes and let you know -it's a
while off.
>
> I read another thread where you posted your actual requirements etc. I
would be
> inclined to split it into multiple database servers with application
making
> decision how to consolidate data from various database servers. It might
take

Thanks for the suggestion - it's something to bear in mind and hope I don't
ever need to go down that road... :(

Regards,
Andy