Class ParallelCompositeReader

All Implemented Interfaces:
Closeable, AutoCloseable

public class ParallelCompositeReader extends BaseCompositeReader<LeafReader>
An CompositeReader which reads multiple, parallel indexes. Each index added must have the same number of documents, and exactly the same number of leaves (with equal maxDoc), but typically each contains different fields. Deletions are taken from the first reader. Each document contains the union of the fields of all documents with the same document number. When searching, matches for a query term are from the first index added that has the field.

This is useful, e.g., with collections that have large fields which change rarely and small fields that change more frequently. The smaller fields may be re-indexed in a new index and both indexes may be searched together.

Warning: It is up to you to make sure all indexes are created and modified the same way. For example, if you add documents to one index, you need to add the same documents in the same order to the other indexes. Failure to do so will result in undefined behavior. A good strategy to create suitable indexes with IndexWriter is to use LogDocMergePolicy, as this one does not reorder documents during merging (like TieredMergePolicy) and triggers merges by number of documents per segment. If you use different MergePolicys it might happen that the segment structure of your index is no longer predictable.

  • Constructor Details

    • ParallelCompositeReader

      public ParallelCompositeReader(CompositeReader... readers) throws IOException
      Create a ParallelCompositeReader based on the provided readers; auto-closes the given readers on IndexReader.close().
      Throws:
      IOException
    • ParallelCompositeReader

      public ParallelCompositeReader(boolean closeSubReaders, CompositeReader... readers) throws IOException
      Create a ParallelCompositeReader based on the provided readers.
      Throws:
      IOException
    • ParallelCompositeReader

      public ParallelCompositeReader(boolean closeSubReaders, CompositeReader[] readers, CompositeReader[] storedFieldReaders) throws IOException
      Expert: create a ParallelCompositeReader based on the provided readers and storedFieldReaders; when a document is loaded, only storedFieldsReaders will be used.
      Throws:
      IOException
  • Method Details

    • getReaderCacheHelper

      public IndexReader.CacheHelper getReaderCacheHelper()
      Description copied from class: IndexReader
      Optional method: Return a IndexReader.CacheHelper that can be used to cache based on the content of this reader. Two readers that have different data or different sets of deleted documents will be considered different.

      A return value of null indicates that this reader is not suited for caching, which is typically the case for short-lived wrappers that alter the content of the wrapped reader.

      Specified by:
      getReaderCacheHelper in class IndexReader
    • doClose

      protected void doClose() throws IOException
      Description copied from class: IndexReader
      Implements close.
      Specified by:
      doClose in class IndexReader
      Throws:
      IOException