Package org.apache.hadoop.hbase.mapreduce

Class TableSnapshotInputFormat

java.lang.Object
org.apache.hadoop.mapreduce.InputFormat<ImmutableBytesWritable,Result>
org.apache.hadoop.hbase.mapreduce.TableSnapshotInputFormat
Direct Known Subclasses:
MultiTableSnapshotInputFormat
@Public public class TableSnapshotInputFormat extends org.apache.hadoop.mapreduce.InputFormat<ImmutableBytesWritable,Result>
TableSnapshotInputFormat allows a MapReduce job to run over a table snapshot. The job bypasses HBase servers, and directly accesses the underlying files (hfile, recovered edits, wals, etc) directly to provide maximum performance. The snapshot is not required to be restored to the live cluster or cloned. This also allows to run the mapreduce job from an online or offline hbase cluster. The snapshot files can be exported by using the ExportSnapshot tool, to a pure-hdfs cluster, and this InputFormat can be used to run the mapreduce job directly over the snapshot files. The snapshot should not be deleted while there are jobs reading from snapshot files.

Usage is similar to TableInputFormat, and TableMapReduceUtil.initTableSnapshotMapperJob(String, Scan, Class, Class, Class, Job, boolean, Path) can be used to configure the job. 

 {
   @code
   Job job = new Job(conf);
   Scan scan = new Scan();
   TableMapReduceUtil.initTableSnapshotMapperJob(snapshotName, scan, MyTableMapper.class,
     MyMapKeyOutput.class, MyMapOutputValueWritable.class, job, true);
 }

Internally, this input format restores the snapshot into the given tmp directory. By default, and similar to TableInputFormat an InputSplit is created per region, but optionally you can run N mapper tasks per every region, in which case the region key range will be split to N sub-ranges and an InputSplit will be created per sub-range. The region is opened for reading from each RecordReader. An internal RegionScanner is used to execute the CellScanner obtained from the user.

HBase owns all the data and snapshot files on the filesystem. Only the 'hbase' user can read from snapshot files and data files. To read from snapshot files directly from the file system, the user who is running the MR job must have sufficient permissions to access snapshot and reference files. This means that to run mapreduce over snapshot files, the MR job has to be run as the HBase user or the user must have group or other privileges in the filesystem (See HBASE-8369). Note that, given other users access to read from snapshot/data files will completely circumvent the access control enforced by HBase.

See Also:

  • Constructor Details

  • Method Details

    • createRecordReader

      public org.apache.hadoop.mapreduce.RecordReader<ImmutableBytesWritable,Result> createRecordReader(org.apache.hadoop.mapreduce.InputSplit split, org.apache.hadoop.mapreduce.TaskAttemptContext context) throws IOException
      Specified by:
      createRecordReader in class org.apache.hadoop.mapreduce.InputFormat<ImmutableBytesWritable,Result>
      Throws:
      IOException

    • getSplits

      public List<org.apache.hadoop.mapreduce.InputSplit> getSplits(org.apache.hadoop.mapreduce.JobContext job) throws IOException, InterruptedException
      Specified by:
      getSplits in class org.apache.hadoop.mapreduce.InputFormat<ImmutableBytesWritable,Result>
      Throws:
      IOException
      InterruptedException

    • setInput

      public static void setInput(org.apache.hadoop.mapreduce.Job job, String snapshotName, org.apache.hadoop.fs.Path restoreDir) throws IOException
      Configures the job to use TableSnapshotInputFormat to read from a snapshot.
      Parameters:
      job - the job to configure
      snapshotName - the name of the snapshot to read from
      restoreDir - a temporary directory to restore the snapshot into. Current user should have write permissions to this directory, and this should not be a subdirectory of rootdir. After the job is finished, restoreDir can be deleted.
      Throws:
      IOException - if an error occurs

    • setInput

      public static void setInput(org.apache.hadoop.mapreduce.Job job, String snapshotName, org.apache.hadoop.fs.Path restoreDir, RegionSplitter.SplitAlgorithm splitAlgo, int numSplitsPerRegion) throws IOException
      Configures the job to use TableSnapshotInputFormat to read from a snapshot.
      Parameters:
      job - the job to configure
      snapshotName - the name of the snapshot to read from
      restoreDir - a temporary directory to restore the snapshot into. Current user should have write permissions to this directory, and this should not be a subdirectory of rootdir. After the job is finished, restoreDir can be deleted.
      splitAlgo - split algorithm to generate splits from region
      numSplitsPerRegion - how many input splits to generate per one region
      Throws:
      IOException - if an error occurs

    • cleanRestoreDir

      public static void cleanRestoreDir(org.apache.hadoop.mapreduce.Job job, String snapshotName) throws IOException
      clean restore directory after snapshot scan job
      Parameters:
      job - the snapshot scan job
      snapshotName - the name of the snapshot to read from
      Throws:
      IOException - if an error occurs