Home | About | Sematext search-lucene.com search-hadoop.com
NEW: Monitor These Apps!
elasticsearch, apache solr, apache hbase, hadoop, redis, casssandra, amazon cloudwatch, mysql, memcached, apache kafka, apache zookeeper, apache storm, ubuntu, centOS, red hat, debian, puppet labs, java, senseiDB
 Search Hadoop and all its subprojects:

Switch to Threaded View
MapReduce >> mail # user >> Re: High IO Usage in Datanodes due to Replication


Copy link to this message
-
Re: High IO Usage in Datanodes due to Replication
Thanks a lot Harsh. Your input is really valuable for me.

As you mentioned above, we have overload of many small files in our
cluster.

Also when i load data huge data to hive tables, It throws an exception like
"replicated to to 0 nodes instead of 1". When i google it i found one of
the reason matches my case  "Data Node is Busy with block report and block
scanning" @ http://bit.ly/ZToyNi

Is increasing the Block scanning and scanning all inefficient small files
will fix my problem ?

Thanks
Selva
On Wed, May 1, 2013 at 11:37 AM, Harsh J <[EMAIL PROTECTED]> wrote:

> The block scanner is a simple, independent operation of the DN that
> runs periodically and does work in small phases, to ensure that no
> blocks exist that aren't matching their checksums (its an automatic
> data validator) - such that it may report corrupt/rotting blocks and
> keep the cluster healthy.
>
> Its runtime shouldn't cause any issues, unless your DN has a lot of
> blocks (more than normal due to overload of small, inefficient files)
> but too little heap size to perform retention plus block scanning.
>
> > 1. Is data node will not allow to write the data during
> DataBlockScanning process ?
>
> No such thing. As I said, its independent and mostly lock free. Writes
> or reads are not hampered.
>
> > 2. Is data node will come normal only when "Not yet verified" come to
> zero in data node blockScannerReport ?
>
> Yes, but note that this runs over and over again (once every 3 weeks IIRC).
>
> On Wed, May 1, 2013 at 11:33 AM, selva <[EMAIL PROTECTED]> wrote:
> > Thanks Harsh & Manoj for the inputs.
> >
> > Now i found that the data node is busy with block scanning. I have TBs
> data
> > attached with each data node. So its taking days to complete the data
> block
> > scanning. I have two questions.
> >
> > 1. Is data node will not allow to write the data during DataBlockScanning
> > process ?
> >
> > 2. Is data node will come normal only when "Not yet verified" come to
> zero
> > in data node blockScannerReport ?
> >
> > # Data node logs
> >
> > 2013-05-01 05:53:50,639 INFO
> > org.apache.hadoop.hdfs.server.datanode.DataBlockScanner: Verification
> > succeeded for blk_-7605405041820244736_20626608
> > 2013-05-01 05:53:50,664 INFO
> > org.apache.hadoop.hdfs.server.datanode.DataBlockScanner: Verification
> > succeeded for blk_-1425088964531225881_20391711
> > 2013-05-01 05:53:50,692 INFO
> > org.apache.hadoop.hdfs.server.datanode.DataBlockScanner: Verification
> > succeeded for blk_2259194263704433881_10277076
> > 2013-05-01 05:53:50,740 INFO
> > org.apache.hadoop.hdfs.server.datanode.DataBlockScanner: Verification
> > succeeded for blk_2653195657740262633_18315696
> > 2013-05-01 05:53:50,818 INFO
> > org.apache.hadoop.hdfs.server.datanode.DataBlockScanner: Verification
> > succeeded for blk_-5124560783595402637_20821252
> > 2013-05-01 05:53:50,866 INFO
> > org.apache.hadoop.hdfs.server.datanode.DataBlockScanner: Verification
> > succeeded for blk_6596021414426970798_19649117
> > 2013-05-01 05:53:50,931 INFO
> > org.apache.hadoop.hdfs.server.datanode.DataBlockScanner: Verification
> > succeeded for blk_7026400040099637841_20741138
> > 2013-05-01 05:53:50,992 INFO
> > org.apache.hadoop.hdfs.server.datanode.DataBlockScanner: Verification
> > succeeded for blk_8535358360851622516_20694185
> > 2013-05-01 05:53:51,057 INFO
> > org.apache.hadoop.hdfs.server.datanode.DataBlockScanner: Verification
> > succeeded for blk_7959856580255809601_20559830
> >
> > # One of my Data node block scanning report
> >
> > http://<datanode-host>:15075/blockScannerReport
> >
> > Total Blocks                 : 2037907
> > Verified in last hour        :   4819
> > Verified in last day         : 107355
> > Verified in last week        : 686873
> > Verified in last four weeks  : 1589964
> > Verified in SCAN_PERIOD      : 1474221
> > Not yet verified             : 447943
> > Verified since restart       : 318433
> > Scans since restart          : 318058
> > Scan errors since restart    :      0

NEW: Monitor These Apps!
elasticsearch, apache solr, apache hbase, hadoop, redis, casssandra, amazon cloudwatch, mysql, memcached, apache kafka, apache zookeeper, apache storm, ubuntu, centOS, red hat, debian, puppet labs, java, senseiDB