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From Apache Wiki <>
Subject [Cassandra Wiki] Update of "LargeDataSetConsiderations" by PeterSchuller
Date Sat, 18 Dec 2010 17:03:51 GMT
Dear Wiki user,

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The "LargeDataSetConsiderations" page has been changed by PeterSchuller.


   * As your data set becomes larger and larger (assuming significantly larger than memory),
you become more and more dependent on caching to elide I/O operations. As you plan and test
your capacity, keep in mind that:
    * The cassandra row cache is in the JVM heap and unaffected (remains warm) by compactions
and repair operations. This is a plus, but the down-side is that the row cache is not very
memory efficient compared to the operating system page cache.
    * The key cache is affected by compaction and repair.
-    * Soon no longer true as of: TODO: insert jira ticket link
+    * Soon no longer true as of: [[|CASSANDRA-1878]]
    * The operating system's page cache is affected by compaction and repair operations. If
you are relying on the page cache to keep the active set in memory, you may see significant
degradation on performance as a result of compaction and repair operations.
     * Potential future improvements: [[|CASSANDRA-1470]],
   * If you have column families with more than 143 million row keys in them, bloom filter
false positive rates are likely to go up because of implementation concerns that limit the
maximum size of a bloom filter. See [[ArchitectureInternals]] for information on how bloom
filters are used. The negative effects of hitting this limit is that reads will start taking
additional seeks to disk as the row count increases. Note that the effect you are seeing at
any given moment will depend on when compaction was last run, because the bloom filter limit
is per-sstable. It is an issue for column families because after a major compaction, the entire
column family will be in a single sstable.

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