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From "Dave Latham (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HBASE-8778) Region assigments scan table directory making them slow for huge tables
Date Thu, 20 Jun 2013 23:37:20 GMT
Dave Latham created HBASE-8778:
----------------------------------

             Summary: Region assigments scan table directory making them slow for huge tables
                 Key: HBASE-8778
                 URL: https://issues.apache.org/jira/browse/HBASE-8778
             Project: HBase
          Issue Type: Improvement
            Reporter: Dave Latham
         Attachments: HBASE-8778-0.94.5.patch

On a table with 130k regions it takes about 3 seconds for a region server to open a region
once it has been assigned.

Watching the threads for a region server running 0.94.5 that is opening many such regions
shows the thread opening the reigon in code like this:
{noformat}
"PRI IPC Server handler 4 on 60020" daemon prio=10 tid=0x00002aaac07e9000 nid=0x6566 runnable
[0x000000004c46d000]
   java.lang.Thread.State: RUNNABLE
        at java.lang.String.indexOf(String.java:1521)
        at java.net.URI$Parser.scan(URI.java:2912)
        at java.net.URI$Parser.parse(URI.java:3004)
        at java.net.URI.<init>(URI.java:736)
        at org.apache.hadoop.fs.Path.initialize(Path.java:145)
        at org.apache.hadoop.fs.Path.<init>(Path.java:126)
        at org.apache.hadoop.fs.Path.<init>(Path.java:50)
        at org.apache.hadoop.hdfs.protocol.HdfsFileStatus.getFullPath(HdfsFileStatus.java:215)
        at org.apache.hadoop.hdfs.DistributedFileSystem.makeQualified(DistributedFileSystem.java:252)
        at org.apache.hadoop.hdfs.DistributedFileSystem.listStatus(DistributedFileSystem.java:311)
        at org.apache.hadoop.fs.FilterFileSystem.listStatus(FilterFileSystem.java:159)
        at org.apache.hadoop.fs.FileSystem.listStatus(FileSystem.java:842)
        at org.apache.hadoop.fs.FileSystem.listStatus(FileSystem.java:867)
        at org.apache.hadoop.hbase.util.FSUtils.listStatus(FSUtils.java:1168)
        at org.apache.hadoop.hbase.util.FSTableDescriptors.getTableInfoPath(FSTableDescriptors.java:269)
        at org.apache.hadoop.hbase.util.FSTableDescriptors.getTableInfoPath(FSTableDescriptors.java:255)
        at org.apache.hadoop.hbase.util.FSTableDescriptors.getTableInfoModtime(FSTableDescriptors.java:368)
        at org.apache.hadoop.hbase.util.FSTableDescriptors.get(FSTableDescriptors.java:155)
        at org.apache.hadoop.hbase.util.FSTableDescriptors.get(FSTableDescriptors.java:126)
        at org.apache.hadoop.hbase.regionserver.HRegionServer.openRegion(HRegionServer.java:2834)
        at org.apache.hadoop.hbase.regionserver.HRegionServer.openRegion(HRegionServer.java:2807)
        at sun.reflect.GeneratedMethodAccessor64.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:597)
        at org.apache.hadoop.hbase.ipc.WritableRpcEngine$Server.call(WritableRpcEngine.java:320)
        at org.apache.hadoop.hbase.ipc.HBaseServer$Handler.run(HBaseServer.java:1426)
{noformat}

To open the region, the region server first loads the latest HTableDescriptor.  Since HBASE-4553
HTableDescriptor's are stored in the file system at "/hbase/<tableDir>/.tableinfo.<sequenceNum>".
 The file with the largest sequenceNum is the current descriptor.  This is done so that the
current descirptor is updated atomically.  However, since the filename is not known in advance
FSTableDescriptors it has to do a FileSystem.listStatus operation which has to list all files
in the directory to find it.  The directory also contains all the region directories, so in
our case it has to load 130k FileStatus objects.  Even using a globStatus matching function
still transfers all the objects to the client before performing the pattern matching.  Furthermore
HDFS uses a default of transferring 1000 directory entries in each RPC call, so it requires
130 roundtrips to the namenode to fetch all the directory entries.

Consequently, to reassign all the regions of a table (or a constant fraction thereof) requires
time proportional to the square of the number of regions.

In our case, if a region server fails with 200 such regions, it takes 10+ minutes for them
all to be reassigned, after the zk expiration and log splitting.


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