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Chapter 7. Index Optimization

From time to time, the Lucene index needs to be optimized. The process is essentially a defragmentation. Until an optimization is triggered Lucene only marks deleted documents as such, no physical deletions are applied. During the optimization process the deletions will be applied which also effects the number of files in the Lucene Directory.
Optimizing the Lucene index speeds up searches but has no effect on the indexation (update) performance. During an optimization, searches can be performed, but will most likely be slowed down. All index updates will be stopped. It is recommended to schedule optimization:
  • on an idle system or when the searches are less frequent
  • after a lot of index modifications

7.1. Automatic optimization
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Hibernate Search can automatically optimize an index after:
  • a certain amount of operations (insertion, deletion)
  • or a certain amount of transactions
The configuration for automatic index optimization can be defined on a global level or per index:

Example 7.1. Defining automatic optimization parameters

hibernate.search.default.optimizer.operation_limit.max = 1000
hibernate.search.default.optimizer.transaction_limit.max = 100
hibernate.search.Animal.optimizer.transaction_limit.max = 50
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An optimization will be triggered to the Animal index as soon as either:
  • the number of additions and deletions reaches 1000
  • the number of transactions reaches 50 (hibernate.search.Animal.optimizer.transaction_limit.max having priority over hibernate.search.default.optimizer.transaction_limit.max)
If none of these parameters are defined, no optimization is processed automatically.
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