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https://issues.apache.org/jira/browse/OPENNLP-421?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17797377#comment-17797377
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ASF GitHub Bot commented on OPENNLP-421:
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kinow commented on PR #568:
URL: https://github.com/apache/opennlp/pull/568#issuecomment-1858767471
> I think, we c/should consider using a `ConcurrentHashMap`-based
deduplicator approach to replace "intern()" calls, as investigated and
explained by Shipilev in his blog post here:
>
> https://shipilev.net/jvm/anatomy-quarks/10-string-intern/
>
> The removal of the String deduplication, as found in the code segments of
this PR, could otherwise lead to more required RAM at runtime - as @kinow
already expressed.
>
> Wdyt? @jzonthemtn @rzo1
>
> (A) Removal (PR as is now), or (B) Replacement with concurrent-capable
custom deduplicator?
(B) looks interesting, +1 for trying that out, and for @rzo1 suggestion to
add that on top of this one.
>`CHMInterner`
First time I've seen an intern made in the code (intentionally like that).
Sounds like a good idea! You do the intern without using the heap. Not sure if
it will perform as fast as String.intern, but I think it might work! Thanks
@mawiesne
> 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: Richard Zowalla
> 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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