On Thu, May 19, 2011 at 20:43, Michael McCandless <luc...@mikemccandless.com> wrote: > On Thu, May 19, 2011 at 12:35 PM, Jason Rutherglen > <jason.rutherg...@gmail.com> wrote: >>> And I do agree there are times when mmap is appropriate, eg if query >>> latency is unimportant to you, but it's not a panacea and it comes >>> with serious downsides >> >> Do we have a benchmark of ByteBuffer vs. byte[]'s in RAM? > > I don't know of a straight up comparison... I did compare MMapDir vs RAMDir variant a couple of years ago. Searches slowed down a teeny-weeny little bit. GC times went down noticeably. For me it was a big win.
Whatever Mike might say, mmap is great for latency-conscious applications : ) If someone tries to create artificial benchmark for byte[] VS ByteBuffer, I'd recommend going through Lucene's abstraction layer. If you simply read/write in a loop, JIT will optimize away boundary checks for byte[] in some cases. This didn't ever happen to *Buffer family for me. >> There's also RAM based SSDs whose performance could be comparable with >> well, RAM. > > True, though it's through layers of abstraction designed originally > for serving files off of spinning magnets :) > >> Also, with our heap based field caches, the first sorted >> search requires that they be loaded into RAM. Then we don't unload >> them until the reader is closed? With MMap the unloading would happen >> automatically? > > True, but really if the app knows it won't need that FC entry for a > long time (ie, long enough to make it worth unloading/reloading) then > it should really unload it. MMap would still have to write all those > pages to disk... > > DocValues actually makes this a lot cheaper because loading DocValues > is much (like ~100 X from Simon's testing) faster than populating > FieldCache since FieldCache must do all the uninverting. > > Mike > > --------------------------------------------------------------------- > To unsubscribe, e-mail: dev-unsubscr...@lucene.apache.org > For additional commands, e-mail: dev-h...@lucene.apache.org > > -- Kirill Zakharenko/Кирилл Захаренко E-Mail/Jabber: ear...@gmail.com Phone: +7 (495) 683-567-4 ICQ: 104465785 --------------------------------------------------------------------- To unsubscribe, e-mail: dev-unsubscr...@lucene.apache.org For additional commands, e-mail: dev-h...@lucene.apache.org
