Configuring compaction

Steps for configuring compaction. The compaction process merges keys, combines columns, evicts tombstones, consolidates SSTables, and creates a new index in the merged SSTable.

As discussed earlier, the compaction process merges keys, combines columns, evicts tombstones, consolidates SSTables, and creates a new index in the merged SSTable.

In the cassandra.yaml file, you configure these global compaction parameters:

The compaction_throughput_mb_per_sec parameter is designed for use with large partitions because compaction is throttled to the specified total throughput across the entire system.

Cassandra provides a start-up option for testing compaction strategies without affecting the production workload.

Using CQL, you configure a compaction strategy:

SizeTieredCompactionStrategy (STCS)
DateTieredCompactionStrategy (DTCS)
LeveledCompactionStrategy (LCS)

Note: When using DTCS disabling read repair is recommended. Use full repair as necessary.

To configure the compaction strategy property and CQL compaction subproperties, such as the maximum number of SSTables to compact and minimum SSTable size, use CREATE TABLE or ALTER TABLE.

Procedure

Update a table to set the compaction strategy using the ALTER TABLE statement.
```
ALTER TABLE users WITH
  compaction = { 'class' :  'LeveledCompactionStrategy'  }
```
Change the compaction strategy property to SizeTieredCompactionStrategy and specify the minimum number of SSTables to trigger a compaction using the CQL min_threshold attribute.
```
ALTER TABLE users
  WITH compaction =
  {'class' : 'SizeTieredCompactionStrategy', 'min_threshold' : 6 }
```

Results

You can monitor the results of your configuration using compaction metrics, see Compaction metrics.