[ 
http://issues.apache.org/jira/browse/NUTCH-272?page=comments#action_12412642 ] 

Matt Kangas commented on NUTCH-272:
-----------------------------------

Ok, I just re-read Generator.java ( 
http://svn.apache.org/viewvc/lucene/nutch/trunk/src/java/org/apache/nutch/crawl/Generator.java?view=markup
 )

 * Selector.map() keeps values where crawlDatum.getFetchTime() <= curTime

 * Selector.reduce() collects until "limit" is reached, optionally skipping the 
url if "hostCount.get() > maxPerHost"

So it caps _URLs/host going in this fetchlist_. Not total URLs/host. That's 
what I thought, and is insufficent for the reasons stated above. (Will 
incrementally fetch everything.)

If the cap is 50k and a host has 70k active URLs in the crawldb, what Generate 
needs to say is "Here are the first 50k URLs added for this site, and I see 
only 3 are scheduled. We'll put 3 in this fetchlist."

Generate can only enforce a limit if it knows which 50k were _first_ added to 
the db, and _never_ fetch
any of the latter 20k.

Hmm... it seems straightforward to modify Generate.java to count total 
URLs/host during map(), regardless of fetchTime. But I don't see what action we 
could take besides halting all fetches for the site. We'd have to traverse 
crawldb in order of record-creation time to be able to see which were the first 
N added to the crawldb. (i think the crawldb is sorted by url, not ctime)

> Max. pages to crawl/fetch per site (emergency limit)
> ----------------------------------------------------
>
>          Key: NUTCH-272
>          URL: http://issues.apache.org/jira/browse/NUTCH-272
>      Project: Nutch
>         Type: Improvement

>     Reporter: Stefan Neufeind

>
> If I'm right, there is no way in place right now for setting an "emergency 
> limit" to fetch a certain max. number of pages per site. Is there an "easy" 
> way to implement such a limit, maybe as a plugin?

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