Bug - crawl job hangs

[danizen]

In https://github.com/Norconex/collector-http/issues/477, I diagnosed a serial problem where my crawling job experienced a Fatal OutOfMemoryError, and then later an attempt to stop the collector failed, because the JVM to be stopped would not exit.

It seems likely that the crawler job entered a terminal state, but the code was waiting for it to stop logically, except that it had failed or something instead.

The exception that produced this state was:

FATAL [JobSuite] Fatal error occured in job: monitor_lessdepth_crawler
INFO  [JobSuite] Running monitor_lessdepth_crawler: END (Tue Feb 06 17:13:41 EST 2018)
Exception in thread "monitor_lessdepth_crawler" java.lang.OutOfMemoryError: Java heap space
        at java.util.Arrays.copyOf(Arrays.java:3236)
        at java.lang.StringCoding.safeTrim(StringCoding.java:79)
        at java.lang.StringCoding.encode(StringCoding.java:365)
        at java.lang.String.getBytes(String.java:941)
        at org.apache.http.entity.StringEntity.<init>(StringEntity.java:70)
        at com.norconex.committer.elasticsearch.ElasticsearchCommitter.commitBatch(ElasticsearchCommitter.java:589)
        at com.norconex.committer.core.AbstractBatchCommitter.commitAndCleanBatch(AbstractBatchCommitter.java:179)
        at com.norconex.committer.core.AbstractBatchCommitter.commitComplete(AbstractBatchCommitter.java:159)
        at com.norconex.committer.core.AbstractFileQueueCommitter.commit(AbstractFileQueueCommitter.java:233)
        at com.norconex.committer.elasticsearch.ElasticsearchCommitter.commit(ElasticsearchCommitter.java:537)
        at com.norconex.collector.core.crawler.AbstractCrawler.execute(AbstractCrawler.java:274)
        at com.norconex.collector.core.crawler.AbstractCrawler.doExecute(AbstractCrawler.java:228)
        at com.norconex.collector.core.crawler.AbstractCrawler.resumeExecution(AbstractCrawler.java:190)
        at com.norconex.jef4.job.AbstractResumableJob.execute(AbstractResumableJob.java:51)
        at com.norconex.jef4.suite.JobSuite.runJob(JobSuite.java:355)
        at com.norconex.jef4.job.group.AsyncJobGroup.runJob(AsyncJobGroup.java:119)
        at com.norconex.jef4.job.group.AsyncJobGroup.access$000(AsyncJobGroup.java:44)
        at com.norconex.jef4.job.group.AsyncJobGroup$1.run(AsyncJobGroup.java:86)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
        at java.lang.Thread.run(Thread.java:748)

For me, reducing the size of the elasticsearch commitSize resolved the problem, but still worth preventing job crawl hangs.

[essiembre]

Often OOM exceptions can't be recovered from and as such cannot be handled reliably. The JVM application state is already compromised the moment you get this and killing/restarting with more memory is usually the best approach.

Still, if you want to prevent hangs, the best options likely is to use that JVM trick with a kill command or equivalent (from Oracle JVM documentation):

-XX:OnOutOfMemoryError="<cmd args>; <cmd args>"

As of Java 8u92, you can also use those JVM argument (described here):

-XX:ExitOnOutOfMemoryError
-XX:CrashOnOutOfMemoryError 

The next major release will require Java 8 so the launch scripts shipped with the collector may be modified to include one of the Java 8 arguments.

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.