jason rutherglen wrote:
I was thinking you implied that you knew of someone who had customized their own, but it was a closed source solution. And if so then you would know how that project faired.
I don't recall the details, but I know folks have discussed this
previously, and probably even posted patches, but I don't think any of
the patches was ready to commit.
Wouldn't there also need to be a hack on the IndexWriter to keep track of new
I think the 'public static IndexReader.reopen(IndexReader old)' method I
proposed can easily compare the current list of segments for the
directory of old to those that old already has open, and determine which
can be reused and which new segments must be opened. Deletions would be
a little tricky to track. If a segment has had deletions, then a new
SegmentReader could be cloned from the old, sharing everything but the
deletions, which could be re-read from disk. This would invalidate
cached filters for segments that had deletions.
You could even try to figure out what documents have been deleted, then
update filters incrementally. That would be fastest, but more complicated.
----- Original Message ----
From: Doug Cutting <cutting@xxxxxxxxxx>
Sent: Wednesday, April 26, 2006 11:27:44 AM
Subject: Re: GData, updateable IndexSearcher
jason rutherglen wrote:
Interesting, does this mean there is a plan for incrementally updateable
IndexSearchers to become part of Lucene?
In general, there is no plan for Lucene. If someone implements a
generally useful, efficient, feature in a back-compatible, easy to use,
manner, and submits it as a patch, then it becomes a part of Lucene.
That's the way Lucene changes. Since we don't pay anyone, we can't make
plans and assign tasks. So if you're particularly interested in this
feature, you might search the archives to find past efforts, or simply
try to implement it yourself.
I think a good approach would be to create a new IndexSearcher instance
based on an existing one, that shares IndexReaders. Similarly, one
should be able to create a new IndexReader based on an existing one.
This would be a MultiReader that shares many of the same SegmentReaders.
Things get a little tricky after this.
Lucene caches filters based on the IndexReader. So filters would need
to be re-created. Ideally these could be incrementally re-created, but
that might be difficult. What might be simpler would be to use a
MultiSearcher constructed with an IndexSearcher per SegmentReader,
avoiding the use of MultiReader. Then the caches would still work.
This would require making a few things public that are not at present.
Perhaps adding a 'MultiReader.getSubReaders()' method, combined with an
'static IndexReader.reopen(IndexReader)' method. The latter would
return a new MultiReader that shared SegmentReaders with the old
version. Then one could use getSubReaders() on the new multi reader to
extract the current set to use when constructing a MultiSearcher.
Another tricky bit is figuring out when to close readers.
Does this make sense? This discussion should probably move to the
Are there any negatives to updateable IndexSearchers?
Not if implemented well!
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