Oliver: Thanks for digging. Please file Jira's for these issues.
On Feb 15, 2012, at 1:53 AM, "Oliver Meyn (GBIF)" <om...@gbif.org> wrote: > On 2012-02-15, at 9:09 AM, Oliver Meyn (GBIF) wrote: > >> On 2012-02-15, at 7:32 AM, Stack wrote: >> >>> On Tue, Feb 14, 2012 at 8:14 AM, Stack <st...@duboce.net> wrote: >>>>> 2) With that same randomWrite command line above, I would expect a >>>>> resulting table with 10 * (1024 * 1024) rows (so 10485700 = roughly 10M >>>>> rows). Instead what I'm seeing is that the randomWrite job reports >>>>> writing that many rows (exactly) but running rowcounter against the table >>>>> reveals only 6549899 rows. A second attempt to build the table produces >>>>> slightly different results (e.g. 6627689). I see a similar discrepancy >>>>> when using 50 instead of 10 clients (~35% smaller than expected). Key >>>>> collision could explain it, but it seems pretty unlikely (given I only >>>>> need e.g. 10M keys from a potential 2B). >>>>> >>>> >>> >>> I just tried it here and got similar result. I wonder if its the >>> randomWrite? What if you do sequentialWrite, do you get our 10M? >> >> Thanks for checking into this stack - when using sequentialWrite I get the >> expected 10485700 rows. I'll hack around a bit on the PE to count the >> number of collisions, and try to think of a reasonable solution. > > So hacking around reveals that key collision is indeed the problem. I > thought the modulo part of the getRandomRow method was suspect but while > removing it improved the behaviour (I got ~8M rows instead of ~6.6M) it > didn't fix it completely. Since that's really what UUIDs are for I gave that > a shot (i.e UUID.randomUUID()) and sure enough now I get the full 10M rows. > Those are 16-byte keys now though, instead of the 10-byte that the integers > produced. But because we're testing scan performance I think using a > sequentially written table would probably be cheating and so will stick with > randomWrite with slightly bigger keys. That means it's a little harder to > compare to the results that other people get, but at least I know my internal > tests are apples to apples. > > Oh and I removed the outer 10x loop and that produced the desired number of > mappers (ie what I passed in on the commandline) but made no difference in > the key generation/collision story. > > Should I file bugs for these 2 issues? > > Thanks, > Oliver >
