[ROOT] Optimizing performance in Windows

From: Ed Oltman (eoltman@imago.com)
Date: Sat Feb 23 2002 - 01:01:01 MET


Hello,

  I would like to know if anybody has any advice on performance optimizing
on Win2K - I am using qtRoot "version 3.02/06 25 January 2002".  My
application analyzed a root file which consists of a TNtuple.  The analysis
requires spinning though the TNtuple multiple times.  The TNtuple has 8-10
branches and can contain up to 10's of millions of entries.  Note: I have a
gigabyte of physical memory.  I have 2 questions: 

1. When I first spin through the ntuple, it takes a long time - I can see
that my root process is doing lots of I/O - fine.  when I do a .ls I see the
input ntuple "in memory" that is, it shows up on a line starting w/ OBJ:.
However my process memory is about the same size as it was before I read in
the TNtuple.  When I spin through the TNtuple subsequent times, it takes
just as long - I my process once again logs lots of I/O.  How can I read in
the ntuple in such a way that it lives in memory?

2.  At some point, I generate an output TNtuple.  When I do this, my root
process starts page faulting like crazy but eventually the process memory
size creeps up to the required size.  [Note: when I spin through the
TNtuple, its quite a bit faster!]  How can I configure root to use start out
with a larger allocated memory so that I don't need to page fault.

Thanks..

Ed Oltman






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