One small correction here: NRT reopen is much cheaper than IW.commit /
IR.reopen, for getting indexed changes visible to your reader, since
it doesn't invoke fsync and doesn't have to write deleted docs to the
directory only to then load them again in the reader.

But, it's still fairly costly, so you shouldn't, say, reopen your NRT
reader for every query, if you have a high query rate; it's better to
rate limit the reopens.

Mike McCandless


On Wed, Jul 20, 2011 at 6:02 PM, Simon Willnauer
On Wed, Jul 20, 2011 at 11:50 PM, Saurabh Gokhale
Hi All,

I am using Lucene 3.1 in the project.

*Background for the question:*
I am working on the application which starts with 2 threads, one performs
indexing activity and other performs searching activity (I create searcher
object from reader object). Both these threads run periodically and index or
search new documents if they are available.
My searcher searches a string in the lucene index using a BooleanQuery with
SHOULD clause.

My problem is as follows:

As I see there are 2 ways to create indexReader (to create searcher)
A. indexWriter.getReader() --> to get near real time searching
B. Using directly the index directory path like indexReader =
IndexReader.open(NIOFSDirectory.open(new File(DIR_PATH)), true)

Now when the application starts, since there is no index created yet if I
use option "B" to create indexReader, I fail with IndexNotFoundException.
If I create IndexReader using option "A", I dont fail with exception but do
not get any result for my input which is ok since I dont have searchable
index yet.

My problem is, with option "A" of creating reader object, even after
indexing say 1000 documents and I still dont match any result. (The index
does have matching results. I can say that for sure because if I stop my
application, change the code to create reader using option B and then search
the same string on the newly created index of 1000 documents, I get lot of

I am missing something due to which I am not getting any match for option A?
What am I doing wrong?
hi there,

the answer is yes, you are missing something :). When you open the
reader from your writer via IW#getReader() you get a "current view" of
your index (same is true when opening from directory). To refresh this
view you need to call IndexReader#reopen() in order to seen any
updates. For the NRT reader (created via IW#getReader()) this will be
an uncommitted view giving you access to documetns not yet committed.
If you are opened from a Directory you see all the already committed

you should use the reopen like this:
IndexReader reader = ...
IndexReader newReader = r.reopen();
if (newReader != reader) {
// reader was reopened
reader = newReader;

please be careful with reopening the reader, this operation can be
costly if you are useing NRT readers. You should maybe do this
periodically or if you don't have any freshness constraints simply use
a reader opened from a directoy and reopen after commit.



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