Hi Michel Yes, that is exactly what I do in step 2. I am aware of the reason for the scanner timeout exceptions. It is the time between two consecutive invocations of the next call on a specific scanner object. I increased the scanner timeout to 10 min on the region server and still I keep seeing the timeouts. So I reduced my scanner cache to 128.
Full table scan takes 130 seconds and there are 2.2 million rows in the table as of now. Each row is around 2 KB in size. I measured time for the full table scan by issuing `count` command from the hbase shell. I kind of understood the fix that you are specifying, but do I need to change the table structure to fix this problem? All I do is a n^2 operation and even that fails with 10 different types of exceptions. It is mildly annoying that I need to know all the low level storage details of HBase to do such a simple operation. And this is happening for just 14 parallel scanners. I am wondering what would happen when there are thousands of parallel scanners. Please let me know if there is any configuration param change which would fix this issue. Thanks a lot Narendra On Thu, Apr 19, 2012 at 4:40 PM, Michel Segel <michael_se...@hotmail.com>wrote: > So in your step 2 you have the following: > FOREACH row IN TABLE alpha: > SELECT something > FROM TABLE alpha > WHERE alpha.url = row.url > > Right? > And you are wondering why you are getting timeouts? > ... > ... > And how long does it take to do a full table scan? ;-) > (there's more, but that's the first thing you should see...) > > Try creating a second table where you invert the URL and key pair such > that for each URL, you have a set of your alpha table's keys? > > Then you have the following... > FOREACH row IN TABLE alpha: > FETCH key-set FROM beta > WHERE beta.rowkey = alpha.url > > Note I use FETCH to signify that you should get a single row in response. > > Does this make sense? > ( your second table is actually and index of the URL column in your first > table) > > HTH > > Sent from a remote device. Please excuse any typos... > > Mike Segel > > On Apr 19, 2012, at 5:43 AM, Narendra yadala <narendra.yad...@gmail.com> > wrote: > > > I have an issue with my HBase cluster. We have a 4 node HBase/Hadoop > (4*32 > > GB RAM and 4*6 TB disk space) cluster. We are using Cloudera distribution > > for maintaining our cluster. I have a single tweets table in which we > store > > the tweets, one tweet per row (it has millions of rows currently). > > > > Now I try to run a Java batch (not a map reduce) which does the > following : > > > > 1. Open a scanner over the tweet table and read the tweets one after > > another. I set scanner caching to 128 rows as higher scanner caching is > > leading to ScannerTimeoutExceptions. I scan over the first 10k rows > only. > > 2. For each tweet, extract URLs (linkcolfamily:urlvalue) that are there > > in that tweet and open another scanner over the tweets table to see who > > else shared that link. This involves getting rows having that URL from > the > > entire table (not first 10k rows). > > 3. Do similar stuff as in step 2 for hashtags > > (hashtagcolfamily:hashtagvalue). > > 4. Do steps 1-3 in parallel for approximately 7-8 threads. This number > > can be higher (thousands also) later. > > > > > > When I run this batch I got the GC issue which is specified here > > > http://www.cloudera.com/blog/2011/02/avoiding-full-gcs-in-hbase-with-memstore-local-allocation-buffers-part-1/ > > Then I tried to turn on the MSLAB feature and changed the GC settings by > > specifying -XX:+UseParNewGC and -XX:+UseConcMarkSweepGC JVM flags. > > Even after doing this, I am running into all kinds of IOExceptions > > and SocketTimeoutExceptions. > > > > This Java batch opens approximately 7*2 (14) scanners open at a point in > > time and still I am running into all kinds of troubles. I am wondering > > whether I can have thousands of parallel scanners with HBase when I need > to > > scale. > > > > It would be great to know whether I can open thousands/millions of > scanners > > in parallel with HBase efficiently. > > > > Thanks > > Narendra >
