David Smiley created LUCENE-6031:
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Summary: TokenSources
Key: LUCENE-6031
URL: https://issues.apache.org/jira/browse/LUCENE-6031
Project: Lucene - Core
Issue Type: Improvement
Components: core/termvectors
Reporter: David Smiley
Assignee: David Smiley
Fix For: 5.0
TokenSources.java, in the highlight module, is a facade that returns a
TokenStream for a field by either un-inverting & converting the TermVector
Terms, or by text re-analysis if TermVectors are unavailable or don't have the
right options. TokenSources is used by the default highlighter, which is the
most accurate highlighter we've got. When documents are large (say hundreds of
kilobytes on up), I found that most of the highlighter's activity was up-front
spent un-inverting & converting the term vector to a TokenStream, not on the
actual/real highlighting that follows. Much of that time was on a huge sort of
hundreds of thousands of Tokens. Time was also spent doing lots of String
conversion and char copying, and it used a lot of memory, too.
In this patch, I overhauled TokenStreamFromTermPositionVector.java, and I
removed similar logic in TokenSources that was used in circumstances when
positions weren't available but offsets were. This class can un-invert term
vectors that have positions *and/or* offsets (at least one). It doesn't sort.
It places Tokens _directly_ into an array of tokens directly indexed by
position. When positions aren't available, the startOffset/8 is a substitute.
I've got a more light-weight Token inner class used in place of the former and
deprecated Token that ultimately forms a linked-list when the process is done.
There is no string conversion; character copying is minimized. The Token array
is GC'ed after initialization, it's only needed during construction.
Misc:
* It implements reset() efficiently so it need not be wrapped in
CachingTokenFilter (I'll supply a patch later on this).
* It only fetches payloads if you ask for them by adding the attribute (the
default highlighter won't add the attribute).
* It exposes the underlying TermVector terms via a getter too, which is needed
by another patch to follow later.
A key assumption is that the position increment gap or first position isn't
gigantic, as that will create wasted space and the linked-list formation
ultimately has to visit all the slots. We also assume that there aren't a ton
of tokens at the same position, since inserting new tokens in sorted order is
O(N^2) where 'N' is the average co-occurring token length.
My performance testing using Lucene's benchmark module on a megabyte document
showed >5x speedup, in conjunction with some other patches to be posted
separately. This patch made the most difference.
As an aside, our JIRA "Components" ought to be updated to reflect our Lucene
modules. There should be a component for highlighting, and not for term
vectors.
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