PG postmaster size

[Anon]

When php opens a connection to postgres the backend postmaster in almost 6000K is size. Is this the typical size? If not where can this size be reduced> It maxes out my memory under heavy loads.
Thanks

[[deleted]]

... and heavy load means...

how much memory does your machine have, and how many processes are started?

Shouldn't you be either buying more memory or trying to cut down the number of connections that are made?

[Anon]

I am buying more memory, but I am just wondering if 6 megs is a typical backend postmaster size. And if it is not what factors comtribute to its size :-)

[smarlowe]

Use top to look at it while beating up the database with a tool like pgbench (in the contrib directory of the postresql tar ball)

You see that while the postmasters may show 6 Megs in size, the majority of that is "shared" memory. This means that each postmaster is sharing a portion of the 6 megs you see it using with all the other postmasters.

This means that while the first postmaster weighs in at 6 meg, each one after that is really only the difference between that 6 megs and the amount of shared memory each has (typically around 1 meg or so less than the whole.)

On my machine, my postmasters look something like this:

Size: 4492
Shared: 3764
Delta: ~730
All numbers in kilobytes.

So, each new backend only costs me about 730k.

I can prove it by running pgbench with 50 threads. On my box, with no other loads. While the 50 backends are beating away on my box, I show 1.7 Meg free, right after they finish, I show 42 meg free, which, comes out to about 730k*50+5 Megs...