[NUTCH-570] Improvement of URL Ordering in Generator.java

• Type: Improvement
• Status: Closed
• Priority: Minor
• Resolution: Won't Fix
• Component/s: generator
• Patch Info: Patch Available
• Assignee: Otis Gospodnetic
• Reporter: Ned Rockson
• Created: 26/Oct/07 00:00
• Updated: 01/Apr/11 15:07
• Resolved: 12/Apr/10 17:23

Description

[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.

Issue Links

• is related to: NUTCH-776 Configurable queue depth