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From Shai Erera <ser...@gmail.com>
Subject Re: Improving TimeLimitedCollector
Date Sat, 27 Jun 2009 10:37:27 GMT
I like the overall approach. However it's very local to an IndexReader.
I.e., if someone wanted to limit other operations (say indexing), or does
not use an IndexReader (for a Scorer impl maybe), one cannot reuse it.

What if we factor out the timeout logic to a Timeout class (I think it can
be a static class, with the way you implemented it) and use it in
TimeLimitingIndexReader? That class can offer a method check() which will do
the internal logic (the 'if' check and throw exception). It will be similar
to the current ensureOpen() followed by an operation.

It might be considered more expensive since it won't check a boolean, but
instead call a check() method, but it will be more reusable. Also,
ensureOpen today is also a method call, so I don't think Timeout.check() is
that bad. We can even later create a TimeLimitingIndexWriter and document
Timeout class for other usage by external code.

Aside, how about using a PQ for the threads' times, or a TreeMap. That will
save looping over the collection to find the next candidate. Just an
implementation detail though.

Shai

On Sat, Jun 27, 2009 at 3:31 AM, Mark Harwood <markharw00d@yahoo.co.uk>wrote:

> Going back to my post re TimeLimitedIndexReaders - here's an incomplete but
> functional prototype:
> http://www.inperspective.com/lucene/TimeLimitedIndexReader.java
> http://www.inperspective.com/lucene/TestTimeLimitedIndexReader.java
>
>
> The principle is that all reader accesses check a volatile variable
> indicating something may have timed out (no need to check thread locals
> etc.) If and only if a time out has been noted threadlocals are checked to
> see which thread should throw a timeout exception.
>
> All time-limited use of reader must be wrapped in try...finally calls to
> indicate the start and stop of a timed set of activities. A background
> thread maintains the next anticipated timeout deadline and simply waits
> until this is reached or the list of planned activities changes with new
> deadlines.
>
>
> Performance seems reasonable on my Wikipedia index:
>
> //some tests for heavy use of termenum/term docs
> Read term docs for 200000 terms  in 4755 ms using no timeout limit (warm
> up)
> Read term docs for 200000 terms  in 4320 ms using no timeout limit (warm
> up)
> Read term docs for 200000 terms  in 4320 ms using no timeout limit
> Read term docs for 200000 terms  in 4388 ms using  reader with time-limited
> access
>
> //Example query with heavy use of termEnum/termDocs
> +text:f* +text:a* +text:b* no time limit matched 1090041 docs in 2000 ms
> +text:f* +text:a* +text:b* time limited collector matched 1090041 docs in
> 1963 ms
> +text:f* +text:a* +text:b* time limited reader matched 1090041 docs in 2121
> ms
>
> //Example fuzzy match burning CPU reading TermEnum
> text:accomodation~0.5 no time limit matched 192084 docs in 6428 ms
> text:accomodation~0.5 time limited collector matched 192084 docs in 5923
> ms
> text:accomodation~0.5 time limited reader matched 192084 docs in 5945 ms
>
>
> The reader approach to limiting time is slower but has these advantages :
>
> 1) Multiple reader activities can be time-limited rather than just single
> searches
> 2) No code changes required to scorers/queries/filters etc
> 3) Tasks that spend plenty of  time burning CPU before collection happens
> can be killed earlier
>
> I'm sure there's some thread safety issues to work through in my code and
> not all reader classes are wrapped (e.g. TermPositions) but the basics are
> there and seem to be functioning
>
> Thoughts?
>

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