Istvan Toth created HBASE-26398:
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Summary: CellCounter fails for large tables filling up local disk
Key: HBASE-26398
URL: https://issues.apache.org/jira/browse/HBASE-26398
Project: HBase
Issue Type: Bug
Components: mapreduce
Affects Versions: 3.0.0-alpha-2
Reporter: Istvan Toth
Assignee: Istvan Toth
CellCounter dumps all cell coordinates into its output, which can become huge.
The spill can fill the local disk on the reducer.
CellCounter hardcodes *mapreduce.job.reduces* to *1*, so it is not possible to
use multiple reducers to get around this.
Fixing this is easy, by not hardcoding *mapreduce.job.reduces*, it still
defaults to 1, but can be overriden by the user.
CellCounter also generates two extra records with constant keys for each cell,
which have to be processed by the reducer.
Even with multiple reducers, these (1/3 of the totcal records) will got the
same reducer, which can also fill up the disk.
This can be fixed by adding a Combiner to the Mapper, which sums the counter
records, thereby reducing the Mapper output records to 1/3 of their previous
amount.
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