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From "Dave Latham (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-8778) Region assigments scan table directory making them slow for huge tables
Date Sat, 20 Jul 2013 15:02:51 GMT

    [ https://issues.apache.org/jira/browse/HBASE-8778?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13714448#comment-13714448

Dave Latham commented on HBASE-8778:

{quote}There is already some migration and re-shuffling going on for hdfs directories, so
please take a look at HBASE-8015 to see whether you can piggy back on that. {quote}

Thanks, [~enis], for the tip.  I read through the latest patch there and looked at the code
up on GitHub.  It looks to me like it should be fairly easy to combine the updates.  HBASE-8015
moves the tabledir and uses a new FullyQualifiedTableName.  The same changes can be done to
the updated FSTableDescriptors to use FullyQualifiedTableName and call FSUtil as this patch
doesn't care where the tabledir is as long as it can get to it.
> 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
>            Assignee: Dave Latham
>             Fix For: 0.98.0, 0.95.2, 0.94.11
>         Attachments: HBASE-8778-0.94.5.patch, HBASE-8778-0.94.5-v2.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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