CopyC#

n

CopyC#

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.

NOTE: You should not try using sub-readers returned by this method to make any changes (setNorm, deleteDocument, etc.). While this might succeed for one composite reader (like MultiReader), it will most likely lead to index corruption for other readers (like DirectoryReader obtained through {@link #open}. Use the parent reader directly.

If this reader is based on a Directory (ie, was created by calling {@link #Open}, or {@link #Reopen} on a reader based on a Directory), then this method returns the version recorded in the commit that the reader opened. This version is advanced every time {@link IndexWriter#Commit} is called.

If instead this reader is a near real-time reader (ie, obtained by a call to {@link IndexWriter#GetReader}, or by calling {@link #Reopen} on a near real-time reader), then this method returns the version of the last commit done by the writer. Note that even as further changes are made with the writer, the version will not changed until a commit is completed. Thus, you should not rely on this method to determine when a near real-time reader should be opened. Use {@link #IsCurrent} instead.

If this reader is based on a Directory (ie, was created by calling {@link #open}, or {@link #reopen} on a reader based on a Directory), then this method checks if any further commits (see {@link IndexWriter#commit} have occurred in that directory).

If instead this reader is a near real-time reader (ie, obtained by a call to {@link IndexWriter#getReader}, or by calling {@link #reopen} on a near real-time reader), then this method checks if either a new commmit has occurred, or any new uncommitted changes have taken place via the writer. Note that even if the writer has only performed merging, this method will still return false.

In any event, if this returns false, you should call {@link #reopen} to get a new reader that sees the changes.

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.

CopyC#

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.