mapreduce - Write to multiple tables in HBASE

Question

I have a situation here where I need to write to two of the hbase tables say table1,table 2. Whenever a write happens on table 1, I need to do some operation on table 2 say increment a counter in table 2 (like triggering). For this purpose I need to access (write) to two tables in the same task of a map-reduce program. I heard that it can be done using MultiTableOutputFormat. But I could not find any good example explaining in detail. Could some one please answer whether is it possible to do so. If so how can/should I do it. Thanks in advance.

Please provide me an answer that should not include co-processors.

Answer 1

To write into more than one table in map-reduce job, you have to specify that in job configuration. You are right this can be done using MultiTableOutputFormat. Normally for a single table you use like:

TableMapReduceUtil.initTableReducerJob("tableName", MyReducer.class, job);

Instead of this write:

job.setOutputFormatClass(MultiTableOutputFormat.class);
job.setMapperClass(MyMapper.class);
job.setReducerClass(MyReducer.class);
job.setNumReduceTasks(2);
TableMapReduceUtil.addDependencyJars(job);
TableMapReduceUtil.addDependencyJars(job.getConfiguration());

Now at the time of writing data in table write as:

context.write(new ImmutableBytesWritable(Bytes.toBytes("tableName1")),put1);
context.write(new ImmutableBytesWritable(Bytes.toBytes("tableName2")),put2);