Hi Harsh, You are right, Our Hadoop version is "0.20.2-cdh3u1" which is lack of HDFS-2379.
As you suggest i have doubled the DN heap size, Now i will monitor the Block scanning speed. The 2nd idea is good, but I can not merge the small files(~1 MB) since its all in hive table partitions. -Selva On Wed, May 1, 2013 at 2:25 PM, Harsh J <[email protected]> wrote: > Hi, > > Neither block reports nor block scanning should affect general DN I/O, > although the former may affect DN liveliness in older versions, if > they lack HDFS-2379 in them. Brahma is partially right in having > mentioned the block reports, hence. > > Your solution, if the # of blocks per DN is too high (counts available > on Live Nodes page in NN UI), say > 1m or so blocks, is to simply > raise the DN heap by another GB to fix issues immediately, and then > start working on merging small files together for more efficient > processing and reducing overall block count to lower memory pressure > at the DNs. > > > > On Wed, May 1, 2013 at 12:02 PM, selva <[email protected]> wrote: > > 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 > >> > Transient scan errors : 0 > >> > Current scan rate limit KBps : 3205 > >> > Progress this period : 101% > >> > Time left in cur period : 86.02% > >> > > >> > Thanks > >> > Selva > >> > > >> > > >> > -----Original Message----- > >> > From "S, Manoj" <[email protected]> > >> > Subject RE: High IO Usage in Datanodes due to Replication > >> > Date Mon, 29 Apr 2013 06:41:31 GMT > >> > Adding to Harsh's comments: > >> > > >> > You can also tweak a few OS level parameters to improve the I/O > >> > performance. > >> > 1) Mount the filesystem with "noatime" option. > >> > 2) Check if changing the IO scheduling the algorithm will improve the > >> > cluster's performance. > >> > (Check this file /sys/block/<device_name>/queue/scheduler) > >> > 3) If there are lots of I/O requests and your cluster hangs because of > >> > that, > >> > you can increase > >> > the queue length by increasing the value in > >> > /sys/block/<device_name>/queue/nr_requests. > >> > > >> > -----Original Message----- > >> > From: Harsh J [mailto:[email protected]] > >> > Sent: Sunday, April 28, 2013 12:03 AM > >> > To: <[email protected]> > >> > Subject: Re: High IO Usage in Datanodes due to Replication > >> > > >> > They seem to be transferring blocks between one another. This may most > >> > likely be due to under-replication > >> > and the NN UI will have numbers on work left to perform. The inter-DN > >> > transfer is controlled > >> > by the balancing bandwidth though, so you can lower that down if you > >> > want > >> > to, to cripple it > >> > - but you'll lose out on time for a perfectly replicated state again. > >> > > >> > On Sat, Apr 27, 2013 at 11:33 PM, selva <[email protected]> wrote: > >> >> Hi All, > >> >> > >> >> I have lost amazon instances of my hadoop cluster. But i had all the > >> >> data in aws EBS volumes. So i launched new instances and attached > >> >> volumes. > >> >> > >> >> But all of the datanode logs keep on print the below lines it cauased > >> >> to high IO rate. Due to IO usage i am not able to run any jobs. > >> >> > >> >> Can anyone help me to understand what it is doing? Thanks in advance. > >> >> > >> >> 2013-04-27 17:51:40,197 INFO > >> >> org.apache.hadoop.hdfs.server.datanode.DataNode: > >> >> DatanodeRegistration(10.157.10.242:10013, > >> >> storageID=DS-407656544-10.28.217.27-10013-1353165843727, > >> >> infoPort=15075, > >> >> ipcPort=10014) Starting thread to transfer block > >> >> blk_2440813767266473910_11564425 to 10.168.18.178:10013 > >> >> 2013-04-27 17:51:40,230 INFO > >> >> org.apache.hadoop.hdfs.server.datanode.DataNode: > >> >> DatanodeRegistration(10.157.10.242:10013, > >> >> storageID=DS-407656544-10.28.217.27-10013-1353165843727, > >> >> infoPort=15075, ipcPort=10014):Transmitted block > >> >> blk_2440813767266473910_11564425 to > >> >> /10.168.18.178:10013 > >> >> 2013-04-27 17:51:40,433 INFO > >> >> org.apache.hadoop.hdfs.server.datanode.DataNode: Receiving block > >> >> blk_2442656050740605335_10906493 src: /10.171.11.11:60744 dest: > >> >> /10.157.10.242:10013 > >> >> 2013-04-27 17:51:40,450 INFO > >> >> org.apache.hadoop.hdfs.server.datanode.DataNode: Received block > >> >> blk_2442656050740605335_10906493 src: /10.171.11.11:60744 dest: > >> >> /10.157.10.242:10013 of size 25431 > >> >> > >> >> Thanks > >> >> Selva > >> >> > >> >> > >> >> > >> >> > >> >> > >> >> > >> > > >> > > >> > > >> > -- > >> > Harsh J > >> > > >> > >> > >> > >> -- > >> Harsh J > > > > > > > > > > -- > > -- selva > > > > > > > > > > > > > > > > > > -- > Harsh J > -- -- selva
