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https://issues.apache.org/jira/browse/OPENNLP-421?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17799904#comment-17799904
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ASF GitHub Bot commented on OPENNLP-421:
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rzo1 opened a new pull request, #572:
URL: https://github.com/apache/opennlp/pull/572
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### Note:
This PR is a follow-up for OPENNLP-421 to remove unnecessary object creation
by removing `StringListWrapper` used in `Dictionary`.
The sole purpose of the `StringListWrapper` impl was to provide a way to
ignore cases for dictionary entries stored in a `StringList` by overriding the
related `hashCode()` and `equals(...)` method.
This PR delegates the behaviour to the actual `StringList` and adds methods
to "convert" the behaviour from a case-sensitive `StringList` to its
insensitive form.
By doing so, we can reduce the creation of objects for `contains(...)`,
`add(...)`, etc. operation. We only create new `StringLists` if their case does
not match the case of the dictionary.
> 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
> Assignee: Martin Wiesner
> Priority: Major
> Labels: performance
> Fix For: 2.3.2
>
> 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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