I've been on this list long enough to have a vast repository of
information about using a MultiSearcher versus an IndexSearcher that
works on a MultiReader. However, after looking through several hundred
list postings, I could not find what I was looking for. So if there is
a posting or thread (or website, for that matter) that answers all my
questions, please direct me there and, if so, I apologize in advance.
From what I have read, people seem to suggest using an IndexSearcher
initialized with a MultiReader over the use of a MultiSearcher. This
begs 2 questions:
1. Under what conditions is a MultiSearcher necessary/optimal?
2. Why doesn't the MultiReader implement the rather nice methods that
the MultiSearcher has (I'm thinking specifically of subSearcher(int) and
subDoc(int))?
Right now my application uses the MultiSearcher because I need to know
the original (single) index the document came from as well as the Lucene
document ID within that index (so I don't have to hold on to the entire
Lucene Document). I can calculate both if I get the size of all the
individual readers, and assume that the ID a MultiReader returns equals
the original IndexReader's given ID plus the size of every IndexReader
that precedes it (eg, if I have 3 indexes each of size 10, the Document
that the MultiReader gives an ID of 23 to will be the 3rd Document in
the 3rd IndexReader). This might be safe (and indeed might be exactly
what the MultiSearcher does), but I haven't dug into the Lucene code
much to find out.
Currently I'm leaning to switching to a MultiReader, as performance is
more important than having to write some extra code. I'm just a little
confused as to 1) why the MultiSearcher exists (as I can't seem to find
decent documentation) and 2) how safe my above algorithm is (or if I've
just completely missed existing functionality that does this).
Links to any detailed documentation would be greatly appreciated,
Kirk
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