Faster RegexNormalize with more features
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Key: NUTCH-410
URL: http://issues.apache.org/jira/browse/NUTCH-410
Project: Nutch
Issue Type: Improvement
Components: fetcher
Affects Versions: 0.8
Environment: Tested on MacOS X 10.4.7/10.4.8
Reporter: Doug Cook
Priority: Minor
The patch associated with this is backwards-compatible and has several
improvements over the stock 0.8 RegexURLNormalizer:
1) About a 34% performance improvement, from only executing the superclass
(BasicURLNormalizer) once in most cases, instead of twice as the stock version
did.
2) Support for expensive host-specific normalizations with good performance.
Each <regex> block optionally takes a list of hosts to which to apply the
associated regex. If supplied, the regex will only be applied to these hosts.
This should have scalable performance; the comparison is O(1) regardless of the
number of hosts. The format is:
<regex>
<host>www.host1.com</host>
<host>host2.site2.com</host>
<pattern> my pattern here </pattern>
<substitution> my substitution here </substitution>
</regex>
3) Support for decoding URLs with escaped character encodings (e.g. %20,
etc.). This is useful, for example, to decode "jump redirects" which have the
target URL encoded within the source, as on Yahoo. I tried to create an
extensible notion of "options," the first of which is "unescape." The unescape
function is applied *after* the substitution and *only* if the substitution
pattern matches. A simple pattern to unescape Yahoo directory redirects would
be something like:
<regex>
<pattern>^http://[a-z\.]*\.yahoo\.com/.*/\*+(http[^&]+)</pattern>
<substitution>$1</substitution>
<options>unescape</options>
</regex>
4) Added the notion of iterating the pattern chain. This is useful when the
result of a normalization can itself be normalized. While some of this can be
handled in the stock version by repeating patterns, or by careful ordering of
patterns, the notion of iterating is cleaner and more powerful. The chain is
defined to iterate only when the previous iteration changes the input, up to a
configurable maxium number of iterations. The config parameter to change is:
urlnormalizer.regex.maxiterations, which defaults to 1 (previous behavior). The
change is performance-neutral when disabled, and has a relatively small
performance cost when enabled.
Pardon any potentially unconventional Java on my part. I've got lots of C/C++
search engine experience, but Nutch is my first large Java app. I welcome any
feedback, and hope this is useful.
Doug
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