RE: hadd: "too many open files"

There is no need to open all files to merge it.

For example STAR experiment uses the MergeHistogramFile.C attached.

( it can be found on afs

/afs/rhic.bnl.gov/star/packages/DEV/StRoot/macros/analysis/MergeHistogra mFile.C )

The script opens the input files one by one. Been compiled with ACliC it works much faster than the regular 'hadd"

.

Best regards , Valeri Fine

Brookhaven National Laboratory

Upton, NY 11973

Phone +1-631-344-7806  

From: owner-roottalk_at_root.cern.ch [mailto:owner-roottalk_at_root.cern.ch] On Behalf Of Noel Dawe
Sent: Saturday, August 06, 2011 6:19 AM
To: roottalk_at_cern.ch
Subject: [ROOT] hadd: "too many open files"  

I don't know why hadd needs to open all the files at the same time but probably a better way to write this tool would be to never open more than two files at once: copy the first file to the destination and keep it open, then pop off the next file, open it, merge it into the first, close it, then pop off the next file and open it, etc...

Noel