[jira] Commented: (NUTCH-356) Plugin repository cache can lead to memory leak

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[jira] Commented: (NUTCH-356) Plugin repository cache can lead to memory leak

Sebastian Nagel (Jira)

    [ https://issues.apache.org/jira/browse/NUTCH-356?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12540866 ]

Doğacan Güney commented on NUTCH-356:


Thanks for testing the patch. I am happy to hear that it solves out of memory problem. However, this is a complex patch and I would like to get an approval from other reviewers before I commit it. Also, it has been a while since I wrote the patch so I don't remember it quite well right now :). I am going to "re-review" my patch and assuming others are OK with it (last time, Enzo and others suggested another approach), commit it .

> Plugin repository cache can lead to memory leak
> -----------------------------------------------
>                 Key: NUTCH-356
>                 URL: https://issues.apache.org/jira/browse/NUTCH-356
>             Project: Nutch
>          Issue Type: Bug
>    Affects Versions: 0.8
>            Reporter: Enrico Triolo
>         Attachments: cache_classes.patch, 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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