Michael McCandless wrote:
Supriya Kumar Shyamal wrote:
If I am not mistaken the process of locking the Index by different
objects like IndexReader or Indexwriter, theoratically only one
Thread can access the index at a time.
Actually, only one writer can write to the index at once. Multiple
readers can read from the index.
On top of that, multiple threads may share one writer and one reader.
Ie, these classes are thread safe.
When we do search on the index it creates a commit lock so the other
thread does not modify the index, so other thread waits until the
previosu therads release the lock, is it right?
So in this case I should say index accessed one by one not parallel?
The commit lock is only held while a reader is loading the index and
while a writer is "committing" its changes to the index. These times
should be brief. Whereas, the write lock is held for the entire time
that a writer is open.
But IndexSearcher open index using INdexReader right?
Its just my speculation, please don't get me wrong.
Because I try to share the same index by 6 instances and since the
lock for 5 instances are disabled and only once instance can modify
the index, at this case I achive the parallel read of the index. Only
disadvantage is that when the index modified then I get
FileNotFoundException, ao I do some kind of respawn the search again.
You should not have to disable locking to do this sharing; in fact,
disabling locking will lead to the "FileNotFoundException" on
instantiating a reader when a writer is committing.
If I implement the lock mechanism in the DB using the custom locking
then I am afraid the index performance will be reduced but the only
advantage is that I can avoid FNFE.
There are also open issues at least over NFS eg:
http://issues.apache.org/jira/browse/LUCENE-673
Whereby even with proper (native) locking it's still possible to
hit exceptions due to caching in the NFS client. Are you using NFS?
Yes I am using NFS and for sharing I use the READ-ONLY FS mount so that
the search instance cannot do any modification by mistake , otherwise it
can corrupt the index.
Mike
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