A Caching Split Policy For Real-Time Index Caching
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Key: LUCENE-2432
URL: https://issues.apache.org/jira/browse/LUCENE-2432
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.)
he caching split policy builds on the real-time split policy, providing a
caching mechanism that serves to buffer writes to the split index.
As one might expect, this policy delays writes to the index, holding them in
the RAM-based splits (created by the real-time policy) instead. When a flush is
forced (typically through a commit, but in general, through a split rule), then
all un-flushed changes (splits) are written to the super-directory.
There are a couple of reasons why one may wish to use the caching split policy
opposed to a RAMDirectory. The latter is primarily used to "load a disk-based
index into memory", and suffers from a limitation: "the resulting RAMDirectory
instance is fully independent from the original Directory (it is a complete
copy). Any subsequent changes to the original Directory will not be visible
in the RAMDirectory instance". Furthermore, the RAMDirectory gives little
control over when changes are flushed to the disk. The caching split policy
attempts to address those limitations by allowing (a) changes to the original
directory (which we refer to as the super-directory) are in fact visible to the
reader and (b) the user to define exactly when to flush writes to the
underlying directory.
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