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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