Re: Configuring postmaster to use all available memory

> I have noticed that postmaster usually doesn't take up that much
> memory. I'm glad it is coded for efficiency, but, I have it running on
> a dedicated machine which does absolutely nothing more than allow me to
> log in via ssh and run postmaster. I want postmaster to consume
> basically all available RAM, so any query which is a read (not an
> updating query) shouldn't have to touch disk at all. Is there a way to
> do this? I looked at the -B option, and set it as -B 1024 but it didn't
> seem to do much. Should I crank it further up, or are there other
> things to do?

Sure, there's a way to keep it from touching disk. There are two
ways, actually. One is to allocate a huge amount of memory for your
shared buffers. Another is to simply let your kernel cache the entire
data directory.

In my case, because I trust my machine, I've turned off fsync() in PG,
so that even updates don't need to hit the disk, at least not until the
kernel gets bored and decides to flush things out. Also, -B 1024 isn't a
whole lot - it's 1,000 8K blocks, so you're allocating about 8 megabytes.
A decent place to start is about a quarter of your RAM, so if you have two
gigs, about 512 megs of shared buffers would be good - so you'd use -B
65536 . You may have to fiddle with your OS to be able to allocate such a
large shared memory segment.

You can also increase the amount of memory used for sorting by using
the "-S" parameter. Be aware that multiple sorts can occur for each
backend, amplifying the amount of memory that is used. In other words, if
you put "-S 98304", you'll use 96 megs for a single sort operation.
There can be a good deal of sorts in a single query, each taking up to 96
megs - and multiple backends executing similar queries at the same time.

steve