* Russ Cox <[EMAIL PROTECTED]> wrote: > > VAC eg. is good for archiving, but it's tree-based structure > > is probably not optimal for streaming (on large files, a lot > > of blocks IMHO have to be loaded before getting the first > > payload block can be reached). > > A typical venti tree has a branching factor of 409 (8192/20).
I gues, 8k is vac's index block size ? So, maybe it could even be improved (for my case) by increasing it to the 56k venti limit ? > For a 1GB file, that means you have to load two extra blocks to find > the first one, and 322 interior blocks to find all 131,072 data blocks. > Is improving that 0.2% really your justification for a less capable > data structure? Well, I'll have to think about this. My primary goal is to make the sequential read as fast as possible. There won't be any non-sequential access. > Venti's performance is dominated much more by fragmentation > in where the blocks are laid out in the arena logs (that causes seeks) > than anything in higher level data structures. There is a paper about > this in the upcoming Usenix. See http://swtch.com/~rsc/papers/ > for a link to PDF and HTML. (Because the paper is targeted at a > non-Plan 9 audience, "Venti" in that paper refers to venti as described > in the original paper. The current venti sources implement all the > improvements described as "Foundation" in the paper.) thx, I'll have a look at this (as soon as time allows ;-o). cu -- ---------------------------------------------------------------------- Enrico Weigelt, metux IT service -- http://www.metux.de/ cellphone: +49 174 7066481 email: [EMAIL PROTECTED] skype: nekrad666 ---------------------------------------------------------------------- Embedded-Linux / Portierung / Opensource-QM / Verteilte Systeme ----------------------------------------------------------------------
