Hi Matt,
The behaviour you describe is normal. See URL:
http://root.cern.ch/root/html225/TTree.html#TTree:AutoSave
The default value for AutoSave is to save a copy of the Tree header
as soon as you have written 100 Mbytes (uncompressed) to the file.
When AutoSave is called, a new key is created with the current header.
If the creation of the key is successful, the previous key is deleted.
At the end of the job, when you do tree.Write, a new key is
always created, keeping the previous cycle of the same key, if any.
You can use the option kOverwrite when calling the final tree.Write
if you want to keep one single key.
The Autosave facility has been introduced against possible job crashes.
You can always recover data up to the last AutoSave.
In case you loop yourself on the list of TKeys in a directory,
you have to take into account teh fact that one key may have more than
one cycle.
Rene Brun
Matthew D. Langston wrote:
>
> The problem concerns ROOT 2.25.03 under RedHat Linux 6.1 Intel, and is
> reproducible.
>
> I have come across an anomaly with TFile's containing large TTrees (where
> "large" means each TTree is anywhere from a few hundred MB to 1 GB
> uncompressed, and the total size of the TFile is about 1 GB compressed).
> The problem is that the ROOT I/O seems to be creating erroneous TKey cycles
> in the TFile. Are my TFiles being created corrupt? Or, are these extra
> TKey cycles just an artifact of the TTree creation and filling process? If
> so, do I need to "purge" (ala VMS) these erroneous cycles? If so, how?
>
> I have attached to this e-mail (in the file called TTree_Print.txt) the
> output of calling TTree::Print just after I write each of six TTrees to a
> TFile, where each TTree is written to a separate TDirectory within the
> TFile. As you can see by looking at this attached file, there are six
> sections of output from TTree::Print for each of the six TTrees that I
> created and filled.
>
> However, when I later look at this TFile with TBrowser, or by simply
> iterating through each TKey in the TFile and printing out the name and cycle
> number of the TTrees that I find, I see several cycles for each TTree. I
> have attached this output in the second file included with this email (this
> file is called TFile_contents.txt).
>
> For example, the first TTree that I create has 72019 entries according to
> TTree::Print just after filling and writing the TTree. However, when I
> later reopen the TFile and iterate over it, I find two TTrees with cycle
> numbers 1 and 2, each with 67509 entries and 72019 entries, respectively.
>
> Finally, I have attached a table (in the file TKey_cycle_anomaly.txt) of the
> output for the TFile that shows the cycle numbers, the number of entries in
> each TTree, and the difference in the number of entries between the "good"
> cycle and the "erroneous" cycle. Note that one of the TTrees, the one in
> the TDirectory named "year_1995", didn't have one of the erroneous TKey
> cycles created (i.e. this particular TTree is fine). It would appear that
> this "erroneous TKey cycle effect" is triggered after a certain number of
> bytes is written to the TFile.
>
> So, based on this data, I would claim that ROOT created these additional
> TTree cycles when it shouldn't have:
>
> year_1993/SelectedWABEvents;1
>
> year_1994/SelectedWABEvents;1
>
> year_1996/SelectedWABEvents;2
>
> year_1997/SelectedWABEvents;5
>
> year_1998/SelectedWABEvents;10
>
> Would anyone be able to comment on this? This is such a dramatic effect
> that I would assume that other collaborations which create large TTrees and
> TFiles would have seen this too. Is there a workaround for this?
>
> Regards, Matt
>
> --
> Matthew D. Langston
> SLD, Stanford Linear Accelerator Center
> langston@SLAC.Stanford.EDU
>
> --------------------------------------------------------------------------------
>
> Name: TTree_Print.txt
> TTree_Print.txt Type: Plain Text (text/plain)
> Encoding: 7BIT
>
> Name: TFile_contents.txt
> TFile_contents.txt Type: Plain Text (text/plain)
> Encoding: 7BIT
>
> Name: TKey_cycle_anomaly.txt
> TKey_cycle_anomaly.txt Type: Plain Text (text/plain)
> Encoding: 7BIT
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