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https://issues.apache.org/jira/browse/HBASE-8778?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13693060#comment-13693060
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Dave Latham commented on HBASE-8778:
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{quote}Yes, currently NN does a binary search for this, but I am not sure we
should rely on that. Having 100K entries in a single directory does not seem
right. {quote}
I can't image HDFS would revert looking up an inode to linear or anything
slower than log time. That would be a major regression. Still, if you think
having all the region directories in the same table directory is just not
right, let's open another issue and discuss the merits there. For this one, do
you propose waiting for that change and in that case leaving the descriptor
files to sit in the top level table dir alongside the first level of region
subdirectories? Even with a hierarchy it would seem to be that descriptor
files would be better off in their own table metadata directory.
> 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, 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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