Hi Richard,
In Root version 2.21/07 made available yesterday, we introduce some
improvements in the I/O subsystem, in the Read part in particular.
On the Alice data, we have gained more than a factor 2 in the read time.
It would be nice if you could run a test with this new version and let
me
know the results. Note that increasing the branch buffer size also helps
in the Read performance.

Rene Brun


Richard Dubois wrote:
> 
>  The new Root Event classes are in place and I have done similar
> benchmarking to my January tests. See
> 
> http://www.slac.stanford.edu/cgi-bin/lwgate/LCD-DEV/archives/lcd-dev.199901/date/article-21.html
> 
>  Recall that the mods were to replace all TMaps with TObjArrays, replace
> cross-subsystem pointers with indices, and to write out separate
> branches per subsystem.
> 
> Doing the same tests as before on 5 Gev single pions and on a 500 GeV ZZ
> PYBMS file, I am seeing approximately a factor of 2 increase in speed in
> reading back the data. (Note: I have done these new tests on my work PC
> which is nominally the same as my one at home, including the JAZ disk. I
> should repeat it there for the comparison with January's results.) Full
> simulation ZZ events now take 0.3 s/event instead of 0.6 previously.
> 
>  Root reports back 2.4 MB/s in the reading back the ZZ file, a factor of
> 3 more than previously.
> 
>  The other benefit we expected from the change was from having separate
> branches. When I just read in the tracker+VXD hits & MC truth, the read
> goes 20x faster (ie it pops through the file in 1/20th the time).
> 
>  The vast majority (90%) of the data is in the calorimeters and that
> takes all the time. The structures are a little more complex, so I
> expect we're seeing some effect of unpacking the structures: for the
> calorimetry the throughput is reported as 2.43 MB/s, while for
> MC+tracking it reports 3.6 MB/s (but only reading 1/10th the data
> volume).
> 
>  So, bottom line is that the revamp gained us a factor of 2 overall and
> a factor of 20 for just reading tracking data. Worth it! I'll check that
> the numbers hold up at home...
> 
> Richard
> --
> Richard Dubois
> SLD, Stanford Linear Accelerator Center
> [log in to unmask]
> http://www.slac.stanford.edu/~richard/
> 650-926-3824
> 650-926-2923 (FAX)