change notify timeout Performance issue

Peter Polkinghorne Peter.Polkinghorne at brunel.ac.uk
Tue Feb 8 15:05:24 GMT 2000


I have just been upgrading my Samba servers from 1.9.18p10 to 2.0.6

So far as I can tell users have been happy (or at least not noticed!).

Our clients are almost exclusively NT 4.0 (most at SP5).
Our servers are Suns running Solaris 2.5.1 and 7.

On upgrading 2 of our busier servers (for admin - home directories and NT
binaries), I observed a considerable increase in server load.

Home server CPU usage went from 50% with 15% wait IO to 80% with 15% wait IO,
Application server CPU went from 10% with 5% wait IO to 60% with 5% wait IO.

The configuration did not change much between versions of Samba and by using
truss (system call tracer) it was clear that directory stating was taking
place every 60 seconds.  This was confirmed by:

a) increase change notify timeout from 60 to 120 and then 240 and observing
decreased load, despite reasonably constant number of connections.
(to 45% with 30% wait IO for home server, and 45% with 5% wait IO for
application server).

b) Turning up logging on selected Samba processes.

There may of course be other load factors involved in the transition.


Now as far as I can tell, I cannot turn off the change_notify function,
is this correct?

Will bad things happen if I raise the timeout value to say 10 minutes?

Is there any prospect of Kernel support for this feature (ie kernel notifies
process of changed directory)?

Other there any other obvious performance gotchas going from 1.9.18p10 to
2.0.X?

Thanks,
-- 
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| Peter Polkinghorne, Computer Centre, Brunel University, Uxbridge, UB8 3PH,|
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