Plugin repository cache can lead to memory leak
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Key: NUTCH-356
URL: http://issues.apache.org/jira/browse/NUTCH-356
Project: Nutch
Issue Type: Bug
Affects Versions: 0.8
Reporter: Enrico Triolo
Attachments: NutchTest.java, patch.txt
While I was trying to solve a problem I reported a while ago (see Nutch-314), I
found out that actually the problem was related to the plugin cache used in
class PluginRepository.java.
As I said in Nutch-314, I think I somehow 'force' the way nutch is meant to
work, since I need to frequently submit new urls and append their contents to
the index; I don't (and I can't) have an urls.txt file with all urls I'm going
to fetch, but I recreate it each time a new url is submitted.
Thus, I think in the majority of times you won't have problems using nutch
as-is, since the problem I found occours only if nutch is used in a way similar
to the one I use.
To simplify your test I'm attaching a class that performs something similar to
what I need. It fetches and index some sample urls; to avoid webmasters
complaints I left the sample urls list empty, so you should modify the source
code and add some urls.
Then you only have to run it and watch your memory consumption with top. In my
experience I get an OutOfMemoryException after a couple of minutes, but it
clearly depends on your heap settings and on the plugins you are using (I'm
using
'protocol-file|protocol-http|parse-(rss|html|msword|pdf|text)|language-identifier|index-(basic|more)|query-(basic|more|site|url)|urlfilter-regex|summary-basic|scoring-opic').
The problem is bound to the PluginRepository 'singleton' instance, since it
never get released. It seems that some class maintains a reference to it and
this class is never released since it is cached somewhere in the configuration.
So I modified the PluginRepository's 'get' method so that it never uses the
cache and always returns a new instance (you can find the patch in attachment).
This way the memory consumption is always stable and I get no OOM anymore.
Clearly this is not the solution, since I guess there are many performance
issues involved, but for the moment it works.
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