Construct a FilterIndexReader based on the specified base reader. Directory locking for delete, undeleteAll, and setNorm operations is left to the base reader.

Note that base reader is closed if this FilterIndexReader is closed.

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n

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Document

NOTE: for performance reasons, this method does not check if the requested document is deleted, and therefore asking for a deleted document may yield unspecified results. Usually this is not required, however you can call {@link #IsDeleted(int)} with the requested document ID to verify the document is not deleted.

WARNING: this API is new and experimental and may suddenly change.

For IndexReader implementations that use TermInfosReader to read terms, this returns the current indexDivisor as specified when the reader was opened.

Opening an IndexReader is an expensive operation. This method can be used to refresh an existing IndexReader to reduce these costs. This method tries to only load segments that have changed or were created after the IndexReader was (re)opened.

If the index has not changed since this instance was (re)opened, then this call is a NOOP and returns this instance. Otherwise, a new instance is returned. The old instance is not closed and remains usable.

If the reader is reopened, even though they share resources internally, it's safe to make changes (deletions, norms) with the new reader. All shared mutable state obeys "copy on write" semantics to ensure the changes are not seen by other readers.

You can determine whether a reader was actually reopened by comparing the old instance with the instance returned by this method:

            IndexReader reader = ... 
            ...
            IndexReader newReader = r.reopen();
            if (newReader != reader) {
            ...     // reader was reopened
            reader.close(); 
            }
            reader = newReader;
            ...
            

NOTE: If this reader is a near real-time reader (obtained from {@link IndexWriter#GetReader()}, reopen() will simply call writer.getReader() again for you, though this may change in the future.

For IndexReader implementations that use TermInfosReader to read terms, this sets the indexDivisor to subsample the number of indexed terms loaded into memory. This has the same effect as {@link IndexWriter#setTermIndexInterval} except that setting must be done at indexing time while this setting can be set per reader. When set to N, then one in every N*termIndexInterval terms in the index is loaded into memory. By setting this to a value > 1 you can reduce memory usage, at the expense of higher latency when loading a TermInfo. The default value is 1.

NOTE: you must call this before the term index is loaded. If the index is already loaded, an IllegalStateException is thrown.

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term

Term    =>    <docNum, freq, <pos₁, pos₂, ... pos_freq-1> >^*

This positional information facilitates phrase and proximity searching.

The enumeration is ordered by document number. Each document number is greater than all that precede it in the enumeration.