[jira] [Created] (HBASE-8778) Region assigments scan table directory making them slow for huge tables

["Dave Latham (JIRA)" <ji...@apache.org>]

Dave Latham created HBASE-8778:
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             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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