Niels de Carpentier <niels <at> decarpentier.com> writes: > > I'd like to see how they do that. The fact is you are still going to get > > random > > seeks since you have to binary search the blocks in an entire row since > > there is > > no way you can read a several thousand block row into memory to search it, > > so > > once your rows get pretty big you are doing just as much if not more > > random io > > as a btree. > > Why? The rows are sequential on disk, so you're never doing more random > seeks than the number of rows as long as you can search faster than the > disk can provide data. If they indeed can limit the number of searches per > row to a constant, it shouldn't be an issue at all. > > > I don't buy that its better in the insert case either for similar reasons, > > you > > are talking about having to rewrite entire rows to maintain the sequential > > nature of everything, so if you end up adding a giant row you have to go > > and > > write the whole thing out again, so you are talking about a lot more IO > > than > > with b-trees, albeit sequential. So maybe it's a win since it's > > sequential but > > I wonder at what tree size that benefit no longer exists. > > The worst case might be bad, but on average it should be good. I don't > doubt it is always better on rotating disks, probably not on ssd's. > > > > Of course all this analysis is based on a power point presentation and > > there may > > be some detail I'm missing, but that's mostly my point, claiming that > > b-trees > > are now obsolete because we can maybe do inserts faster is just idiotic. > > It's a presentation from a company, so lots of marketing. Of course it > doesn't make btrees obsolete, it's optimized for specific cases. Like they > say they reduce random seeks at the cost of disk bandwidth and cpu usage. > It depends on the use case if that is useful or not. Probably not for > btrfs, since the future will be ssd's, and meta data will generally be > cached. > > Niels >
I'm reviving a very old thread from here: http://thread.gmane.org/gmane.comp.file-systems.btrfs/16484 I found a bunch of more recent info from the company doing most of the work behind fractal tree FS that I'd love to hear your thoughts on. https://www.youtube.com/watch?v=c-n2LGPpQEw http://www.tokutek.com/2013/02/mongodb-fractal-tree-indexes-high-compression https://www.usenix.org/conference/hotstorage12/tokufs-streaming-file-system Does this address earlier concerns at all? I just hope their work will be released as unpatented GPL-compatible free software. -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
