Re: measuring shared memory usage on Windows

>     > So: has anybody a hint how I can check how much shared_memory
>     > is really used by PostgreSQL on Windows, to fine tune
> this parameter?
>     >
>     > I learned the hard way that just rising it can lead to a hard
>     > performance loss :)
>
>     Not really sure :) We're talking about anonymous mapped
> memory, and I
>     don't think perfmon lets you look at that.
>
>
> thanks for the clarification. However,
>
> "anonymous mapped memory"  site:microsoft.com
>
> turns out 0 (zero) results. And even splitting it up there
> seems to be nearly no information ... is the same thing by
> any chance also known by different names?

Hmm. Yeah, most likely :) I may have grabbed that name from something
else. THe documentation for the call is on
http://windowssdk.msdn.microsoft.com/en-us/library/ms685007(VS.80).aspx,
we specifu INVALID_HANDLE_VALUE for hFile, which means:

If hFile is INVALID_HANDLE_VALUE, the calling process must also specify
a mapping object size in the dwMaximumSizeHigh and dwMaximumSizeLow
parameters. In this scenario, CreateFileMapping creates a file mapping
object of a specified size that the operating system paging file backs,
instead of by a named file in the file system.



> > However, there is no limit to it as there often is on Unix
> - you can
> > map up to whatever the virtual RAM size is (2Gb/3Gb
> dependingo n what
> > boot flag you use, IIRC). You can monitor it as a part of the total
> > memory useage on the server, but there's no way to
> automatically show the difference between them.
>
> So the "performance shock" with high shared memory gets
> obvious: memory mapped files get swapped to disk. I assume
> that swapping is nearly transparent for the application,
> leading to a nice trashing ...

Yes :-)
There is a performance manager counter for pages swapped out to disk. If
that one goes above very low numbers, you're in trouble...

//Magnus