1. can I have one or multiple searchers open when I open a writer? 2. can I have one or multiple readers open when I open a writer?
Yes, with one caveat: if you've called the IndexReader methods delete(), undelete() or setNorm() then you may not open an IndexWriter until you've closed that IndexReader instance.
In general, only a single object may modify an index at once, but many may access it simultaneously in a read-only manner, including while it is modified. Indexes are modified by either an IndexWriter or by the IndexReader methods delete(), undelete() and setNorm().
Typically an application which modifies and searches simultaneously should keep the following open:
1. A single IndexReader instance used for all searches, perhaps opened via an IndexSearcher. Periodically, as the index changes, this is discarded, and replaced with a new instance.
2. Either:
a. An IndexReader to delete documents.
b. An IndexWriter to add documents; orSo an updating thread might open (2a), delete old documents, close it, then open (2b) add new documents, perhaps optimize, then close. At this point, when the index has been updated (1) can be discarded and replaced with a new instance. Typically the old instance of (1) is not explicitly closed, rather the garbage collector closes it when the last thread searching it completes.
Doug
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