Expert: returns a readonly reader, covering all committed as well as
un-committed changes to the index. This provides "near real-time"
searching, in that changes made during an IndexWriter session can be
quickly made available for searching without closing the writer nor
calling {@link #commit}.
Note that this is functionally equivalent to calling {#commit} and then
using {@link IndexReader#open} to open a new reader. But the turarnound
time of this method should be faster since it avoids the potentially
costly {@link #commit}.
You must close the {@link IndexReader} returned by this method once you are done using it.
It's
near real-time because there is no hard
guarantee on how quickly you can get a new reader after
making changes with IndexWriter. You'll have to
experiment in your situation to determine if it's
faster enough. As this is a new and experimental
feature, please report back on your findings so we can
learn, improve and iterate.
The resulting reader suppports {@link
IndexReader#reopen}, but that call will simply forward
back to this method (though this may change in the
future).
The very first time this method is called, this
writer instance will make every effort to pool the
readers that it opens for doing merges, applying
deletes, etc. This means additional resources (RAM,
file descriptors, CPU time) will be consumed.
For lower latency on reopening a reader, you should call {@link #setMergedSegmentWarmer}
to call {@link #setMergedSegmentWarmer} to
pre-warm a newly merged segment before it's committed
to the index. This is important for minimizing index-to-search
delay after a large merge.
If an addIndexes* call is running in another thread,
then this reader will only search those segments from
the foreign index that have been successfully copied
over, so far
.
NOTE: Once the writer is closed, any
outstanding readers may continue to be used. However,
if you attempt to reopen any of those readers, you'll
hit an {@link AlreadyClosedException}.
NOTE: This API is experimental and might
change in incompatible ways in the next release.
Syntax