Re: TTree memory usage

From: Philip Rodrigues <p.rodrigues1_at_physics.ox.ac.uk>
Date: Fri, 12 Aug 2011 15:18:16 -0400


Hi Philippe,

Thanks for the explanations - that makes sense. Do I understand right that this means that in v5.28, the memory use of the process is going to be roughly the uncompressed size of the largest basket read so far? That would explain the memory use pattern in my plot.

> > I tried fiddling around with TTree:SetMaxVirtualSize
>
> Increasing this value would allow the TTree to hold to more than one basket
> at a time hence increase memory consumption and possibly improving random
> access within the TTree. Decreasing its value would not reduce the actual
> usage below one basket per (used) branch.

Ah, I see - that does explain what I saw. If I'm understanding the contents of TBranch::GetBasketEntry() correctly, each basket in my input files contains a handful of events (is this a possible configuration? My understanding of how branches, baskets and entries relate is a little fuzzy), so the only way to reduce the peak memory usage would be to reduce the number of entries per basket. Is it possible to do this?

(I guess a better solution to all of these problems is to reduce the size of the events [especially the few very large ones], which is something we're working on, but now I'm curious about how things work, hence the questions).

Thanks,
Phil Received on Fri Aug 12 2011 - 21:18:24 CEST

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