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Posted to issues@opennlp.apache.org by "Joern Kottmann (JIRA)" <ji...@apache.org> on 2013/09/16 12:35:53 UTC
[jira] [Commented] (OPENNLP-421) Large dictionaries cause JVM
OutOfMemoryError: PermGen due to String interning
[ https://issues.apache.org/jira/browse/OPENNLP-421?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13768218#comment-13768218 ]
Joern Kottmann commented on OPENNLP-421:
----------------------------------------
A bit late, yes it would be appreciated to enhance this code. Please send a proposal to the dev mailing list.
> Large dictionaries cause JVM OutOfMemoryError: PermGen due to String interning
> ------------------------------------------------------------------------------
>
> Key: OPENNLP-421
> URL: https://issues.apache.org/jira/browse/OPENNLP-421
> Project: OpenNLP
> Issue Type: Bug
> Components: Name Finder
> Affects Versions: tools-1.5.2-incubating
> Environment: RedHat 5, JDK 1.6.0_29
> Reporter: Jay Hacker
> Priority: Minor
> Labels: performance
> Original Estimate: 168h
> Remaining Estimate: 168h
>
> The current implementation of StringList:
> https://svn.apache.org/viewvc/incubator/opennlp/branches/opennlp-1.5.2-incubating/opennlp-tools/src/main/java/opennlp/tools/util/StringList.java?view=markup
> calls intern() on every String. Presumably this is an attempt to reduce memory usage for duplicate tokens. Interned Strings are stored in the JVM's permanent generation, which has a small fixed size (seems to be about 83 MB on modern 64-bit JVMs: [http://www.oracle.com/technetwork/java/javase/tech/vmoptions-jsp-140102.html]). Once this fills up, the JVM crashes with an OutOfMemoryError: PermGen space.
> The size of the PermGen can be increased with the -XX:MaxPermSize= option to the JVM. However, this option is non-standard and not well known, and it would be nice if OpenNLP worked out of the box without deep JVM tuning.
> This immediate problem could be fixed by simply not interning Strings. Looking at the Dictionary and DictionaryNameFinder code as a whole, however, there is a huge amount of room for performance improvement. Currently, DictionaryNameFinder.find works something like this:
> for every token in every tokenlist in the dictionary:
> copy it into a "meta dictionary" of single tokens
> for every possible subsequence of tokens in the sentence: // of which there are O(N^2)
> copy the sequence into a new array
> if the last token is in the "meta dictionary":
> make a StringList from the tokens
> look it up in the dictionary
> Dictionary itself is very heavyweight: it's a Set<StringListWrapper>, which wraps StringList, which wraps Array<String>. Every entry in the dictionary requires at least four allocated objects (in addition to the Strings): Array, StringList, StringListWrapper, and HashMap.Entry. Even contains and remove allocate new objects!
> From this comment in DictionaryNameFinder:
> // TODO: improve performance here
> It seems like improvements would be welcome. :) Removing some of the object overhead would more than make up for interning strings. Should I create a new Jira ticket to propose a more efficient design?
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