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The "NodeTool" page has been changed by JanneJalkanen: http://wiki.apache.org/cassandra/NodeTool?action=diff&rev1=21&rev2=22 Comment: setcompactionthroughput documented == Scrub == Cassandra v0.7.1 and v0.7.2 shipped with a bug that caused incorrect row-level bloom filters to be generated when compacting sstables generated with earlier versions. This would manifest in IOExceptions during column name-based queries. v0.7.3 provides "nodetool scrub" to rebuild sstables with correct bloom filters, with no data lost. (If your cluster was never on 0.7.0 or earlier, you don't have to worry about this.) Note that nodetool scrub will snapshot your data files before rebuilding, just in case. - == upgradesstables == + == Upgradesstables == While "scrub" does rebuild your sstables, it will also discard data it deems broken and create a snapshot, which you have to remove manually. If you just wish to rebuild your sstables without all that jazz, then use "nodetool upgradesstables". This is useful e.g. when you are upgrading your server, or changing compression options. upgradesstables is available from Cassandra 1.0.4 onwards. + + == Setcompactionthroughput == + + As of Cassandra 1.0, the amount of resources that compactions can use can be easily controlled using a single value: the compaction throughput, which is expressed in Megabytes/second. You can (and probably should) specify this in your cassandra.yaml file, but in some cases it can be very beneficial to change it live using the nodetool. + + For example, in [[http://www.slideshare.net/edwardcapriolo/m6d-cassandrapresentation|this presentation]] Edward Capriolo explains how their company throttles compaction during the day so that I/O is mostly reserved for serving requests, whereas during the night they allocate more capability for running compactions. This can be e.g. accomplished through a simple cron script: + + {{{ + # Script increases compaction throughput to 999 MB/s (i.e. nearly unlimited) for 00-06. + # + # turn into Mr.batch at night + 0 0 * * * root nodetool -h `hostname` setcompactionthroughput 999 + # turn back into Dr.Realtime for day + 0 6 * * * root nodetool -h `hostname` setcompactionthroughput 16 + }}} + + Setting the compaction throughput to zero disables compaction. This may be useful in some cases if you e.g. wish to avoid the compaction I/O during extremely busy periods. It is not a good idea to leave it on for a long period, since you will end up with a large number of very small sstables, which will start to slow down your reads. == Cfhistograms ==
