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From "Andrzej Bialecki (JIRA)" <j...@apache.org>
Subject [jira] Commented: (NUTCH-339) Refactor nutch to allow fetcher improvements
Date Tue, 28 Nov 2006 16:16:24 GMT
    [ http://issues.apache.org/jira/browse/NUTCH-339?page=comments#action_12453989 ] 
            
Andrzej Bialecki  commented on NUTCH-339:
-----------------------------------------

Ah, we are getting somewhere ... fetchQueues.totalSize=0 means that all input entries from
the queues have been processed. You are running with 500 threads, out of which 296 threads
are still processing requests, and 204 threads are idle because they don't have anything more
to do (queues are empty).

Are you running in parsing mode? Could you please kill -SIGQUIT <pid> to produce a thread
dump and see why these threads are waiting? I bet they hang on regexes or pdf parsing, or
a DOMFragment bug ...

Before this happened, when spinWaiting was still close to 0, what was the maximum fetching
speed? Was it higher/lower/comparable to the regular fetcher? What about the CPU usage?

> Refactor nutch to allow fetcher improvements
> --------------------------------------------
>
>                 Key: NUTCH-339
>                 URL: http://issues.apache.org/jira/browse/NUTCH-339
>             Project: Nutch
>          Issue Type: Task
>          Components: fetcher
>    Affects Versions: 0.8
>         Environment: n/a
>            Reporter: Sami Siren
>         Assigned To: Andrzej Bialecki 
>             Fix For: 0.9.0
>
>         Attachments: patch.txt, patch2.txt, patch3.txt, patch4-fixed.txt, patch4-trunk.txt
>
>
> As I (and Stefan?) see it there are two major areas the current fetcher could be
> improved (as in speed)
> 1. Politeness code and how it is implemented is the biggest
> problem of current fetcher(together with robots.txt handling).
> With a simple code changes like replacing it with a PriorityQueue
> based solution showed very promising results in increased IO.
> 2. Changing fetcher to use non blocking io (this requires great amount
> of work as we need to implement the protocols from scratch again).
> I would like to start with working towards #1 by first refactoring
> the current code (plugins actually) in following way:
> 1. Move robots.txt handling away from (lib-http)plugin.
> Even if this is related only to http, leaving it to lib-http
> does not allow other kinds of scheduling strategies to be implemented
> (it is hardcoded to fetch robots.txt from the same thread when requesting
> a page from a site from witch it hasn't tried to load robots.txt)
> 2. Move code for politeness away from (lib-http)plugin
> It is really usable outside http and also the current design limits
> changing of the implementation (to queue based)
> Where to move these, well my suggestion is the nutch core, does anybody
> see problems with this?
> These code refactoring activities are to be done in a way that none
> of the current functionality is (at least deliberately) changed leaving
> current functionality as is thus leaving room and possibility to build
> the next generation fetcher(s) without destroying the old one at same time.

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