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0 parents commit d56063b6c65b6b4807ee64fa05651cee629c3490 Alex Baranau committed Apr 19, 2011
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109 README
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+HBaseWD:
+---------
+http://github.com/sematext/HBaseWD
+
+April 2011
+
+Released under Apache License 2.0.
+
+Author:
+-------
+Alex Baranau
+
+Description:
+------------
+HBaseWD stands for Distributing (sequential) Writes. It was inspired by
+discussions on HBase mailing lists around the problem of choosing between:
+* writing records with sequential row keys (e.g. time-series data with row key
+ built based on ts)
+* using random unique IDs for records
+
+First approach makes possible to perform fast range scans with help of setting
+start/stop keys on Scanner, but creates single region server hot-spotting
+problem upon writing data (as row keys go in sequence all records end up
+written into a single region at a time).
+
+Second approach aims for fastest writing performance by distributing new
+records over random regions but makes not possible doing fast range scans
+against written data.
+
+The suggested approach stays in the middle of the two above and proved to
+perform well by distributing records over the cluster during writing data
+while allowing range scans over it. HBaseWD provides very simple API to
+work with which makes it perfect to use with existing code.
+
+Please refer to unit-tests for lib usage info as they aimed to act as example.
+
+Brief Usage Info (Examples):
+----------------------------
+
+Distributing records with sequential keys which are being written in up to
+Byte.MAX_VALUE buckets:
+
+ byte bucketsCount = (byte) 32; // distributing into 32 buckets
+ RowKeyDistributor keyDistributor =
+ new RowKeyDistributorByOneBytePrefix(bucketsCount);
+ for (int i = 0; i < 100; i++) {
+ Put put = new Put(keyDistributor.getDistributedKey(originalKey));
+ ... // add values
+ hTable.put(put);
+ }
+
+
+Performing a range scan over written data (internally <bucketsCount> scanners
+executed):
+
+ Scan scan = new Scan(startKey, stopKey);
+ ResultScanner rs = DistributedScanner.create(hTable, scan, keyDistributor);
+ for (Result current : rs) {
+ ...
+ }
+
+Performing mapreduce job over written data chunk specified by Scan:
+
+ Configuration conf = HBaseConfiguration.create();
+ Job job = new Job(conf, "testMapreduceJob");
+
+ Scan scan = new Scan(startKey, stopKey);
+
+ TableMapReduceUtil.initTableMapperJob("table", scan,
+ RowCounterMapper.class, ImmutableBytesWritable.class, Result.class, job);
+
+ // Substituting standard TableInputFormat which was set in
+ // TableMapReduceUtil.initTableMapperJob(...)
+ job.setInputFormatClass(WdTableInputFormat.class);
+ keyDistributor.addInfo(job.getConfiguration());
+
+
+Extending Row Keys Distributing Patterns:
+-----------------------------------------
+
+HBaseWD is designed to be flexible and to support custom row key distribution
+approaches. To define custom row key distributing logic just implement
+AbstractRowKeyDistributor abstract class which is really very simple:
+
+ public abstract class AbstractRowKeyDistributor implements Parametrizable {
+ public abstract byte[] getDistributedKey(byte[] originalKey);
+ public abstract byte[] getOriginalKey(byte[] adjustedKey);
+ public abstract byte[][] getAllDistributedKeys(byte[] originalKey);
+ ... // some utility methods
+ }
+
+
+Mailing List:
+-------------
+To participate more in the discussion, join the group at
+https://groups.google.com/group/hbasewd/
+
+Build Notes:
+------------
+Current pom configured to build against HBase 0.89.20100924.
+HBase jars are provided with sources, as only HBase trunk sources
+were mavenized and available in public repos.
+Tests take some time to execute (can be up to several minutes), to skip
+their execution use -Dmaven.skip.tests=true.
+
+HBase Version Compatibility:
+----------------------------
+Compatible with HBase 0.20.5 and higher.
+May be compatible with previous: tests needed (TODO)
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