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From "Karthick Sankarachary (JIRA)" <j...@apache.org>
Subject [jira] Created: (LUCENE-2429) A Rotating Split Policy For Managing Bounded Indices
Date Sun, 02 May 2010 16:10:57 GMT
A Rotating Split Policy For Managing Bounded Indices
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                 Key: LUCENE-2429
                 URL: https://issues.apache.org/jira/browse/LUCENE-2429
             Project: Lucene - Java
          Issue Type: New Feature
          Components: contrib/*, Index
    Affects Versions: 3.0.1
            Reporter: Karthick Sankarachary


(Please note that the feature described in LUCENE-2425 is required reading for this issue.)

A rotating split policy maintains a bounded set of sub-indices underneath the split index's
directory. The motivation for such a policy is to be able to control the size of the index
in a user-defined manner. It comes in handy in scenarios where (a) documents are added at
a higher-than-normal rate, and (b) documents older than a certain cut-off date needn't be
searchable. As a matter of fact, this policy is applicable to most real-time streams, given
that they tend to satisfy both of the above properties.

In short, when the number of sub-indices hits the maximum allowed number (@see {@link ROTATING_POLICY_MAXIMUM_SUB_INDICES}),
then this policy effectively forces the last sub-index out of the split index. A sub-index
is deemed to be the last one if it is considered to be lesser (according to #getDirectoryComparator)
than every other sub-index.

The exact point in time at which rotation occurs is determined by the split rule(s) in effect
for this policy. For example, one may apply a scheduled split rule (see LUCENE-2427) if one
wishes the split to occur at fixed intervals. For finer control over the periodicity of the
interval, a cron split rule (see LUCENE-2428) may be employed.
  
To illustrate the behavior of the rotation policy policy, consider a split rule that triggers
a split on the hour every hour. Furthermore, let's assume that the maximum number of sub-indices
allowed is 7. In this case, the rotation policy will have no more than 8 hours worth of data
(1 hour in the super-index and each of the 7 sub-indices).

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