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From "Jim (JIRA)" <>
Subject [jira] Created: (NUTCH-551) performance for generate is often really bad
Date Fri, 07 Sep 2007 23:43:31 GMT
performance for generate is often really bad

                 Key: NUTCH-551
             Project: Nutch
          Issue Type: Bug
          Components: generator
    Affects Versions: 0.9.0
         Environment: Ubuntu, Core duo 2.4GhZ, 1 gig ram, 750GB hard drive.
 The ethernet connection has a dedicated 1gb connection to the web, so certainly that isn't
a problem.
I have tested on nutch 0.9 and the newest daily build from 2007-08-28.

            Reporter: Jim

        Generate often takes many hours to finish (6+), where I would expect it to be done
in minutes.

        This behavior has been observed for topN of small (~100) and large (~1000000) values.
 Other configuration values are -1 false

        I added debug code to Generator-> to see when map is called and returns,
and observed interesting behavior, described here:

        1. Most of the time, when generate is run urls are processed in chunky batches, usually
about 40 at a time, followed by a 1 second delay.  I timed the delay, and it really is a 1
second delay (ie- 30 batches was 30 seconds.)  When this happens it takes hours to complete.

        2. Sometimes (randomly as far as I can tell) when I run nutch, the urls are processed
without delays.  It is an all or nothing event, either I run and all urls process quickly
without delay (in minutes), or more likely I get the chunky processing with many 1 second
delays and the program takes hours to end.  The one exception is....

        3. When the processing runs quickly I've seen the main thread end (I have some profiling
going, so I know when a thread ends), and then more likely than not a second thread begins
where the first starts, chunky like usual.  Although I sometimes can get fast processing in
one thread, it is almost impossible for me te get it in all threads and therefore general
processing is very slow (hours).

        4. I tried to put in more debug code to find the line where the delays occured, but
the last line printed to the log at a delay seemed random, leading me to believe that the
log is not being flushed uniformly.  The timestamps in the log always indicate that the delay
is wither right before or after the first log item in the map function.

        5. The profiler I used seemed to imply that about 100% of the time was spent in javallang.Thread.sleep.
 I am not completely familiar with the profiler I used so I am not completely sure I inturpreted
this correctly.

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