Improvement of URL Ordering in Generator.java
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Key: NUTCH-570
URL: https://issues.apache.org/jira/browse/NUTCH-570
Project: Nutch
Issue Type: Improvement
Components: generator
Reporter: Ned Rockson
Priority: Minor
[Copied directly from my email to nutch-dev list]
Recently I switched to Fetcher2 over Fetcher for larger whole web fetches
(50-100M at a time). I found that the URLs generated are not optimal because
they are simply randomized by a hash comparator. In one crawl on 24 machines
it took about 3 days to crawl 30M URLs. In comparison with old benchmarks I
had set with regular Fetcher.java this was at least 3 fold more time.
Anyway, I realized that the best situation for ordering can be approached by
randomization, but in order to get optimal ordering, urls from the same host
should be as far apart in the list as possible. So I wrote a series of 2
map/reduces to optimize the ordering and for a list of 25M documents it takes
about 10 minutes on our cluster. Right now I have it in its own class, but I
figured it can go in Generator.java and just add a flag in nutch-default.xml
determining if the user wants to use it.
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