This is a followup issue for the following Elasticsearch issue: https://github.com/elasticsearch/elasticsearch/pull/6714
Basically the problem is the following:
- Elasticsearch has a pool of Analyzers that are used for analysis in several indexes
- Each index uses a different PerFieldAnalyzerWrapper
PerFieldAnalyzerWrapper uses PER_FIELD_REUSE_STRATEGY. Because of this it caches the tokenstreams for every field. If there are many fields, this are a lot. In addition, the underlying analyzers may also cache tokenstreams and other PerFieldAnalyzerWrappers do the same, although the delegate Analyzer can always return the same components.
We should add similar code to Elasticsearch's directly to Lucene: If the delegating Analyzer just delegates per Field or just wraps CharFilters around the Reader, there is no need to cache the TokenStreamComponents a second time in the delegating Analyzers. This is only needed, if the delegating Analyzers adds additional TokenFilters (like ShingleAnalyzerWrapper).
We should name this new class DelegatingAnalyzerWrapper extends AnalyzerWrapper. The wrapComponents method must be final, because we are not allowed to add additional TokenFilters, but unlike ES, we don't need to disallow wrapping with CharFilters.
Internally this class uses a private ReuseStrategy that just delegates to the underlying analyzer. It does not matter here if the strategy of the delegate is global or per field, this is private to the delegate.