A Cron Split Rule For Sub-Dividing Indices At Variable Intervals [LUCENE-2428]

(Please note that the feature described in #3499 is required reading for this issue.)

Herein, we define a cron split rule that causes a split to occur in the split index to which it applies, at variable time periods, as specified by the given cron trigger. In essence, this allows the arrangement of sub-indices in a split index to be re-organized at variable-rate intervals.

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Migrated from [LUCENE-2428](https://issues.apache.org/jira/browse/LUCENE-2428) by Karthick Sankarachary
Attachments: [LUCENE-2428.patch](https://apache.github.io/lucene-jira-archive/attachments/LUCENE-2428/LUCENE-2428.patch)

Start by reading issue #3499, which this issue identifies as required background, then review the migrated LUCENE-2428 description and attached patch. The completed work should provide a cron-driven split rule that reorganizes sub-indices at variable time intervals.

Written by the indexing model from the issue text.