I tried running my test with 0.94.4, unfortunately performance was about the same. I'm planning on profiling the regionserver and trying some other things tonight and tomorrow and will report back.
On May 1, 2013, at 8:00 AM, Bryan Keller <brya...@gmail.com> wrote: > Yes I would like to try this, if you can point me to the pom.xml patch that > would save me some time. > > On Tuesday, April 30, 2013, lars hofhansl wrote: > If you can, try 0.94.4+; it should significantly reduce the amount of bytes > copied around in RAM during scanning, especially if you have wide rows and/or > large key portions. That in turns makes scans scale better across cores, > since RAM is shared resource between cores (much like disk). > > > It's not hard to build the latest HBase against Cloudera's version of Hadoop. > I can send along a simple patch to pom.xml to do that. > > -- Lars > > > > ________________________________ > From: Bryan Keller <brya...@gmail.com> > To: user@hbase.apache.org > Sent: Tuesday, April 30, 2013 11:02 PM > Subject: Re: Poor HBase map-reduce scan performance > > > The table has hashed keys so rows are evenly distributed amongst the > regionservers, and load on each regionserver is pretty much the same. I also > have per-table balancing turned on. I get mostly data local mappers with only > a few rack local (maybe 10 of the 250 mappers). > > Currently the table is a wide table schema, with lists of data structures > stored as columns with column prefixes grouping the data structures (e.g. > 1_name, 1_address, 1_city, 2_name, 2_address, 2_city). I was thinking of > moving those data structures to protobuf which would cut down on the number > of columns. The downside is I can't filter on one value with that, but it is > a tradeoff I would make for performance. I was also considering restructuring > the table into a tall table. > > Something interesting is that my old regionserver machines had five 15k SCSI > drives instead of 2 SSDs, and performance was about the same. Also, my old > network was 1gbit, now it is 10gbit. So neither network nor disk I/O appear > to be the bottleneck. The CPU is rather high for the regionserver so it seems > like the best candidate to investigate. I will try profiling it tomorrow and > will report back. I may revisit compression on vs off since that is adding > load to the CPU. > > I'll also come up with a sample program that generates data similar to my > table. > > > On Apr 30, 2013, at 10:01 PM, lars hofhansl <la...@apache.org> wrote: > > > Your average row is 35k so scanner caching would not make a huge > > difference, although I would have expected some improvements by setting it > > to 10 or 50 since you have a wide 10ge pipe. > > > > I assume your table is split sufficiently to touch all RegionServer... Do > > you see the same load/IO on all region servers? > > > > A bunch of scan improvements went into HBase since 0.94.2. > > I blogged about some of these changes here: > > http://hadoop-hbase.blogspot.com/2012/12/hbase-profiling.html > > > > In your case - since you have many columns, each of which carry the rowkey > > - you might benefit a lot from HBASE-7279. > > > > In the end HBase *is* slower than straight HDFS for full scans. How could > > it not be? > > So I would start by looking at HDFS first. Make sure Nagle's is disbaled in > > both HBase and HDFS. > > > > And lastly SSDs are somewhat new territory for HBase. Maybe Andy Purtell is > > listening, I think he did some tests with HBase on SSDs. > > With rotating media you typically see an improvement with compression. With > > SSDs the added CPU needed for decompression might outweigh the benefits. > > > > At the risk of starting a larger discussion here, I would posit that > > HBase's LSM based design, which trades random IO with sequential IO, might > > be a bit more questionable on SSDs. > > > > If you can, it would be nice to run a profiler against one of the > > RegionServers (or maybe do it with the single RS setup) and see where it is > > bottlenecked. > > (And if you send me a sample program to generate some data - not 700g, > > though :) - I'll try to do a bit of profiling during the next days as my > > day job permits, but I do not have any machines with SSDs). > > > > -- Lars > > > > > > > > > > ________________________________ > > From: Bryan Keller <brya...@gmail.com> > > To: user@hbase.apache.org > > Sent: Tuesday, April 30, 2013 9:31 PM > > Subject: Re: Poor HBase map-reduce scan performance > > > > > > Yes, I have tried various settings for setCaching() and I have > > setCacheBlocks(false) > > > > On Apr 30, 2013, at 9:17 PM, Ted Yu <yuzhih...@gmail.com> wrote: > > > >> From http://hbase.apache.org/book.html#mapreduce.example : > >> > >> scan.setCaching(500); // 1 is the default in Scan, which will > >> be bad for MapReduce jobs > >> scan.setCacheBlocks(false); // don't set to true for MR jobs > >> > >> I guess you have used the above setting. > >> > >> 0.94.x releases are compatible. Have you considered upgrading to, say > >> 0.94.7 which was recently released ? > >> > >> Cheers > >> > >> On Tue, Apr 30, 2013 at 9:01 PM, Bryan Keller <bryanck@gm
