Re: tuning for AIX 5L with large memory

Clinging to sanity, fbsd(at)drivefaster(dot)net (Dan Harris) mumbled into her beard:
> I will soon have at my disposal a new IBM pSeries server. The main
> mission for this box will be to serve several pg databases. I have
> ordered 8GB of RAM and want to learn the best way to tune pg and AIX
> for this configuration. Specifically, I am curious about shared
> memory limitations. I've had to tune the shmmax on linux machines
> before but I'm new to AIX and not sure if this is even required on
> that platform? Google has not been much help for specifics here.
>
> Hoping someone else here has a similar platform and can offer some advice..

We have a couple of these at work; they're nice and fast, although the
process of compiling things, well, "makes me feel a little unclean."

One of our sysadmins did all the "configuring OS stuff" part; I don't
recall offhand if there was a need to twiddle something in order to
get it to have great gobs of shared memory.

A quick Google on this gives me the impression that AIX supports, out
of the box, multiple GB of shared memory without special kernel
configuration. A DB/2 configuration guide tells users of Solaris and
HP/UX that they need to set shmmax in sundry config files and reboot.
No such instruction for AIX.

If it needs configuring, it's probably somewhere in SMIT. And you can
always try starting up an instance to see how big it'll let you make
shared memory.

The usual rule of thumb has been that having substantially more than
10000 blocks worth of shared memory is unworthwhile. I don't think
anyone has done a detailed study on AIX to see if bigger numbers play
well or not. I would think that having more than about 1 to 1.5GB of
shared memory in use for buffer cache would start playing badly, but I
have no numbers.
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