Configuring Lucene

Elements of the API require access to various Lucene components, such as IndexWriter, TaxonomyWriter, SearcherTaxonomyManager, FacetsConfig, etc. These are configured as usual for the application and encapsulated in a LuceneBackend instance.

Official documentation on the relationship and interactions between IndexSearcher and IndexWriter instances appears to be very difficult to source. Advice resulting from various internet searches appears to be subjective and also very possibly out of date.

What becomes clear is that there is no “one size fits all solution” to the problem of making data searchable
and a solution which may be appropriate for one application may not be a good fit for another.

The lowest common denominator for this problem is that:

• An application needs to manage the resources used to read and write data.
• Read and write operations require some level of coordination in order to achieve expected behaviour

The API abstracts these concerns behind the LuceneBackend in order that application logic might be agnostic to the implementation.

Resource management

A LuceneBackend provides an application with access to these resources via AutoCloseable Lease objects, which can be used in a try-with-resources construct to automatically close a resource or release it back to a managed pool such as SearcherTaxonomyManager.

Commit and refresh phases

In addition to resource management, AutoCloseable#close() provides a convenient hook into the workflow for performing commit or refresh operations.

The default implementation provided by the core module implements this approach. It makes the assumption that when an IndexWriter is done with and AutoCloseable#close() is called, the application will most likely want to start reading data from the index. In order for this to be possible, Lucene requires:

• IndexWriter changes are commited
• TaxonomyWriter changes are commited
• SearcherTaxonomyManager is refreshed

This functionality may or may not be considered too presumptive of the API, but it is required by Lucene in order to search the updated index. Utilising AutoCloseable#close() negates the need for applications to implement such boilerplate.

Leased components

Two types of leases are provided by the LuceneBackend:

• SearchComponents are components relevant to read operations.
• UpdateComponents are components required to update the index.

The default implementation makes use of Lucene ReferenceManager types. The API wraps interactions with the reference manager’s acquire(), release() and maybeRefresh() in AutoCloseable leases.

---

Next: Domain Operations