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HBase, mail # user - Task tracker timeout with filtered table scan


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Task tracker timeout with filtered table scan
Bryan Keller 2012-05-31, 16:27
I have a large table that I am running a map reduce job on. The job scans for a particular column value in the table using a TableInputFormat with a filter on the scan. This value only matches a few rows, so most of the rows are filtered out.

The problem is that the TableInputFormat  will not report status back to the task tracker until the regionserver sends back a row matching the filter. If there are only few matching rows, and the table is very large, it can take a while for a row to come back from the regionserver. This can result in a task tracker timeout. The problem is exacerbated with large region file sizes.

I can sort of work around this by increasing the mapred.task.timeout property, but that doesn't seem very optimal. The other solution would be to not use a filter, and to filter out rows in the map reduce job, which would increase I/O. Any other solutions? It seems the TableInputFormat shouldn't wait for the regionserver to report back status to the task tracker.