 | | | locking problems | locking problems 2004-10-08 - By Doug Cutting
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Aad Nales wrote:
> 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; or
So 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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