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From "Otis Gospodnetic (JIRA)" <>
Subject [jira] Resolved: (NUTCH-570) Improvement of URL Ordering in
Date Mon, 12 Apr 2010 17:23:53 GMT


Otis Gospodnetic resolved NUTCH-570.

    Resolution: Won't Fix

> Improvement of URL Ordering in
> ---------------------------------------------
>                 Key: NUTCH-570
>                 URL:
>             Project: Nutch
>          Issue Type: Improvement
>          Components: generator
>            Reporter: Ned Rockson
>            Assignee: Otis Gospodnetic
>            Priority: Minor
>         Attachments: GeneratorDiff.out, GeneratorDiff_v1.out
> [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 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 and just add a flag in nutch-default.xml
determining if the user wants to use it.

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