On Sun, Jun 5, 2011 at 11:33 PM, Jason Rutherglen <jason.rutherg...@gmail.com> wrote: > Ok, the block index is only storing the first key of each block? > Hmm... I think we can store a pointer to an exact position in the > block, or at least allow that (for the FST implementation).
Are you sure that is a good idea? Surely the disk seeks would destroy you on index load? > > How efficient is the current seeking? > >> I have previously thought about prefix compression, it seemed doable, > > It does look like prefix compression should be doable. Eg, we'd seek > to a position based on the block index (from which we'd have the > entire key). From the seek'd to position, we could scan and load up > each subsequent prefix compressed key into a KeyValue, though right > the KV wouldn't be 'pointing' back to the internals of the block, it'd > be creating a whole new byte[] for each KV (which could have it's own > garbage related ramifications). > >> you'd need a compressing algorithm > > Lucene's terms dict is very simple. The next key has the position at > which the previous key differs. > > On Sat, Jun 4, 2011 at 3:35 PM, Ryan Rawson <ryano...@gmail.com> wrote: >> Also, dont break it :-) >> >> Part of the goal of HFile was to build something quick and reliable. >> It can be hard to know you have all the corner cases down and you >> won't find out in 6 months that every single piece of data you have >> put in HBase is corrupt. Keeping it simple is one strategy. >> >> I have previously thought about prefix compression, it seemed doable, >> you'd need a compressing algorithm, then in the Scanner you would >> expand KeyValues and callers would end up with copies, not views on, >> the original data. The JVM is fairly good about short lived objects >> (up to a certain allocation rate that is), and while the original goal >> was to reduce memory usage, it could make sense to take a higher short >> term allocation rate if the wins from prefix compression are there. >> >> Also note that in whole-system profiling, often repeated methods in >> KeyValue do pop up. The goal of KeyValue was to have a format that >> didnt require deserialization into larger data structures (hence the >> lack of vint), and would be simple and fast. Undoing that work should >> be accompanied with profiling evidence that new slowdowns were not >> introduced. >> >> -ryan >> >> On Sat, Jun 4, 2011 at 3:30 PM, Jason Rutherglen >> <jason.rutherg...@gmail.com> wrote: >>>> You'd have to change how the Scanner code works, etc. You'll find out. >>> >>> Nice! Sounds fun. >>> >>> On Sat, Jun 4, 2011 at 3:27 PM, Ryan Rawson <ryano...@gmail.com> wrote: >>>> What are the specs/goals of a pluggable block index? Right now the >>>> block index is fairly tied deep in how HFile works. You'd have to >>>> change how the Scanner code works, etc. You'll find out. >>>> >>>> >>>> >>>> On Sat, Jun 4, 2011 at 3:17 PM, Stack <saint....@gmail.com> wrote: >>>>> I do not know of one. FYI hfile is pretty standalone regards tests etc. >>>>> There is even a perf testing class for hfile >>>>> >>>>> >>>>> >>>>> On Jun 4, 2011, at 14:44, Jason Rutherglen <jason.rutherg...@gmail.com> >>>>> wrote: >>>>> >>>>>> I want to take a wh/hack at creating a pluggable block index, is there >>>>>> an open issue for this? I looked and couldn't find one. >>>>> >>>> >>> >> >
