thrashing; ratio virtual/real

[mdet]

Hi,
I'm looking for information regarding thrashing.
I know what thrashing is and I know how to find out whether a system is trashing or not. What I need is some statement or procedure to calculate thrashing in advance.
In other words:
Provided the mere number of running processes isn't a problem (i.e. is not high) then how much memory might these processes consume until the system starts to thrash.
I guess there only will be a rough "rule of thumb" for that but maybe there are admins who experienced thrashing and do remember the circumstances.
We're running an application server whose resident memory part is constantly growing and I'm asked to give a tip how long the system will be still working.
Don't ask me whether this is correct IT-Management.
We're running Solaris 8

Any idea is well appreciated.

 

[Annihilannic]

Thrashing occurs when the page scanner starts running to start stealing pages to add to the free list (as you probably know). The scanner doesn't start working until the amount of free memory drops below lotsfree, which by default is 1/64th of your main memory. That's probably the best figure to estimate on?

Annihilannic.

 

[mdet]

Hi Annihilannic,
thanks for the tip. I know that Solaris' memory management changed with version 8. No more silly questions "who eats my memory?". Although I'm not sure that the page scanners activity is a proper indicator of thrashing.

Well I take this... (no complains)

 

[Annihilannic]

The changes in Solaris 8 mean that it reuses pages freed from the filesystem buffer cache more intelligently and is less likely to steal memory from application processes that need it. The page scanner will still run when memory gets very low and thrashing may still occur, but hopefully with less impact to your application.

Annihilannic.