Re: root file size?

Rene Brun (Rene.Brun@cern.ch)
Mon, 19 Apr 1999 14:28:46 +0000

Hi Olivier,
We recommend compression level 1. Higher compression levels take far
more time to compress and the additional gain is often negligible.
When you do not use compression, the file size should be dependent on
the specified buffer size because the final (may be nearly empty) buffer
is written to the file. This effect should be visible only with very
small files
when the total size of the branch buffers is about the same size than
the
file itself.

Rene Brun

Olivier Meplan wrote:
>
> Hello Rooters!
>
> I have questions about root file size... I save a Tree in a file (with
> 1 branch)
> and I want to make this file as small as possible...
> Fisrtly, I was thinking that in the SetCompressionLevel(J) function, for
> bigger J, the filesize should be smaller. But It don't seem to be... Is
> it normal or am I doing something wrong?
> Secondly, I have remarked that the file size is very dependent to the
> Branch buffersize; but I don't know how: If for a given number of
> entries I find "the best" buffer size, for a different number of entries
> the "best" buffer size is also different. Why ?
> Thank you for your answer,
>
> Olivier Meplan