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From Apache Wiki <wikidi...@apache.org>
Subject [Cassandra Wiki] Trivial Update of "SecondaryIndexes" by JimAncona
Date Thu, 07 Jun 2012 21:57:10 GMT
Dear Wiki user,

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The "SecondaryIndexes" page has been changed by JimAncona:
http://wiki.apache.org/cassandra/SecondaryIndexes?action=diff&rev1=3&rev2=4

     A: Inequalities on secondary indices are always done in memory, so without at least one
EQ on another secondary index you will be loading every row in the database, which with a
massive database isn't a good idea. So by requiring at least one EQ on an index, you hopefully
limit the set of rows that need to be read into memory to a manageable size. Although obviously
you can still get into trouble with that as well.  
  
   * Q: How does choice of Consistency Level affect cluster availability when using secondary
indexes?
-    A: Because secondary indexes are distributed, you must have CL level nodes available
for all token ranges in the cluster in order to complete a query. For example, with RF = 3,
when two out of three consecutive nodes in the ring are unavailable, all secondary index queries
at CL = QUORUM will fail, however secondary index queries at CL = ONE will succeed. This is
true regardless of cluster size.
+    A: Because secondary indexes are distributed, you must have CL level nodes available
for '''all''' token ranges in the cluster in order to complete a query. For example, with
RF = 3, when two out of three consecutive nodes in the ring are unavailable, '''all''' secondary
index queries at CL = QUORUM will fail, however secondary index queries at CL = ONE will succeed.
This is true regardless of cluster size.
  

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