Re: TTree memory usage

Hi Phil,

Which version of ROOT are you using? With which version of ROOT was the file written?

Philippe.

On 8/10/11 12:20 PM, Philip Rodrigues wrote:
> Hi roottalk,
> I'm trying to understand the memory usage of a simple macro that loops over a
> TTree, calling GetEntry() (and essentially nothing else).
>
> The pattern I see is shown in this plot of memory use (as reported by
> gSystem->GetProcInfo()) as a function of entry in the tree:
>
> http://www.pas.rochester.edu/~prodrigues/memusage.png
>
> Red is "resident" memory usage, and blue is "virtual". The thing I'm
> interested in is the pattern of flat memory usage for a number of entries,
> followed by a quick increase, over the course of a few entries, that is not
> reclaimed afterwards (eg, at around 1400).
>
> I tried fiddling around with TTree:SetMaxVirtualSize and TTree:SetMaxCacheSize
> (as you might guess from the title in the plot), but the pattern I describe
> still occurs, just with slightly different sizes of jumps.
>
> Can anyone explain what causes this pattern, or suggest ways of investigating
> it?
>
> Thanks,
> Phil
>
> PS Some other information that might be relevant:
>
> The input tree has a single branch containing and (large and complex) event
> class. The typical uncompressed size of an entry (as reported by
> TTree::GetEntry()) is 1-3 MB, although there are occasional large entries
> (such as one of 300MB at around 1100 that causes the spike in memory that can
> be seen there).
>
> The spiky, messy memory usage at the start appears to be the region which has
> 1 entry per TBasket on disk. This region *does* change when I change
> TTree::SetMaxVirtualSize. For entry numbers>100, there are typically ~5
> entries per TBasket. I suspect that the memory jumps have something to do with
> switching TBaskets, but I don't really have a firm idea what's going on.
>
Received on Wed Aug 10 2011 - 20:08:58 CEST