Yonik Seeley wrote:
I think it's quite feasible, but, it'd still have a "reopen" cost
in that
any buffered delete by term or query would have to be
"materialiazed" into
docIDs on reopen. Though, if this somehow turns out to be a
problem, in the
future we could do this materializing immediately, instead of
buffering, if
we already have a reader open.
Right... it seems like re-using readers internally is something we
could already be doing in IndexWriter.
True.
Flushing is somewhat tricky because any open RAM readers would then
have to
cutover to the newly flushed segment once the flush completes, so
that the
RAM buffer can be recycled for the next segment.
Re-use of a RAM buffer doesn't seem like such a big deal.
But, how would you maintain a static view of an index...?
IndexReader r1 = indexWriter.getCurrentIndex()
indexWriter.addDocument(...)
IndexReader r2 = indexWriter.getCurrentIndex()
I assume r1 will have a view of the index before the document was
added, and r2 after?
Right, getCurrentIndex would return a MultiReader that includes
SegmentReader for each segment in the index, plus a "RAMReader" that
searches the RAM buffer. That RAMReader is a tiny shell class that
would basically just record the max docID it's allowed to go up to
(the docID as of when it was opened), and stop enumerating docIDs (eg
in the TermDocs) when it hits a docID beyond that limit.
For reading stored fields and term vectors, which are now flushed
immediately to disk, we need to somehow get an IndexInput from the
IndexOutputs that IndexWriter holds open on these files. Or, maybe,
just open new IndexInputs?
Another thing that will help is if users could get their hands on the
sub-readers of a multi-segment reader. Right now that is hidden in
MultiSegmentReader and makes updating anything incrementally
difficult.
Besides what's handled by MultiSegmentReader.reopen already, what else
do you need to incrementally update?
Mike
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