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From George Herlin <>
Subject Infinite loop bug in Nutch 0.9
Date Wed, 01 Apr 2009 10:25:57 GMT
Hello, there.

I believe I may have found a infinite loop in Nutch 0.9.

It happens when a site has a page that refers to itself through a

The code in, around line 200 - sorry, my Fetcher has been a
little modified, line numbers may vary a little - says, for that case:

output(url, new CrawlDatum(), null, null, CrawlDatum.STATUS_LINKED);

What that does is, inserts an extra (empty) crawl datum for the new url,
with a re-fetch interval of 0.0.

However, (see, particularly lines 144-145), the
non-refetch condition used seems to be last-fetch+refetch-interval>now ...
which is always false if refetch-interval==0.0!

Now, if there is a new link to the new url in that page, that crawl datum is
re-used, and the whole thing loops indefinitely.

I've fixed that for myself by changing the quoted line (twice) by:

output(url, new CrawlDatum(CrawlDatum.STATUS_LINKED, 30f), null, null,

and that works (btw the 30F should really be the value of
"db.default.fetch.interval", but I haven't the time right now to work out
the issues, but in reality the default constructor and the appropriate
updater method should, if I am right in analysing the algorithm always
enforce a positive refetch interval.

Of course, another method could be used to remove this self-reference, but
that couls be complicated, as that may happen through a loop (2 or more
pages etc..., you know what I mean).

Has that been fixed already, and by what method?

Best regards

George Herlin

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