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https://issues.apache.org/jira/browse/ACCUMULO-4145?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15146994#comment-15146994
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ASF GitHub Bot commented on ACCUMULO-4145:
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Github user ctubbsii commented on the pull request:
https://github.com/apache/accumulo/pull/70#issuecomment-184089574
For reference, String.intern() should not be used for Java 1.6 runtime, as
that could grow the PermGen space significantly. It could possibly replace the
WeakHashMap in 1.7, because intern storage has been moved to the main Java
heap. It might not actually be needed at all, since we've effectively
eliminated all the extra objects and copies that were left around with Text.
And, in Java 1.8 update 30, the G1 GC has a String dedupe feature which may
eliminate the extra copies without needing to intern.
> Eliminate constant unnecessary Text wrapping of immutable tableIDs
> ------------------------------------------------------------------
>
> Key: ACCUMULO-4145
> URL: https://issues.apache.org/jira/browse/ACCUMULO-4145
> Project: Accumulo
> Issue Type: Improvement
> Reporter: Christopher Tubbs
> Assignee: Christopher Tubbs
> Labels: tedious
> Fix For: 1.8.0
>
>
> I started looking at ACCUMULO-4138 to see how KeyExtent is used to do
> overlaps, and I noticed a *lot* of {{new KeyExtent(new Text(String), ...)}}
> calls, where that first parameter is the Text version of tableId.
> It appears, we even do this practice so much, that KeyExtent has a built-in
> WeakReference caching of these tableIds, so the Java GC we can dedupe them
> and avoid creating too many.
> The thing is... a lot of this attempt to optimize appears to be the result of
> unnecessarily wrapping all these immutable String tableIDs with a Text
> object, yet it doesn't really seem to buy us anything. In most of our API and
> a lot of internal utilities, these are already Strings with references
> elsewhere in the code... so even if we dedupe the Text objects, we're not
> doing anything about these Strings. Worse, we're actually doing some
> protective copying here and there as we pass around these Text objects, using
> TextUtil, etc. This is completely unnecessary, because they were immutable
> before we copied them and wrapped them.
> In some cases, we actually call toString on the text objects to pass them
> around, and they get flip-flopped a few times between String and Text,
> depending on what the internal API accepts.
> At best, using the Text object helps us serialize KeyExtent... but that's
> questionably beneficial since DataOutput can already serialize with:
> {{out.writeUTF(String)}}, so that's not actually that helpful.
> The only other benefit I could possibly see is with compareTo for
> lexicographical comparison, but I have a hard time believing Text can compare
> faster than {{java.lang.String}}, and there shouldn't be any difference in
> the results of the comparison between the UTF-8 encoding of Text and the
> modified UTF encoding which is native to Java Strings, certainly not for the
> base-36 characters and fixed constants (for special tables) we use in
> tableIDs.
> We should just completely strip out all the Text versions of tableId,
> wherever possible. I've already done this as an exercise in the 1.6 branch,
> but it might be potentially risky as these are put in Java maps which don't
> have strict type checking ({{map.get(Object)}}, for instance) and are
> sometimes compared with {{.equals(Object)}}. For what it's worth, the only
> public API this really touches is {{o.a.a.core.data.KeyExtent}}, which was
> only inadvertently in the public API and has since been moved (IIRC). We can
> preserve the old methods for compatibility, if necessary (deprecated, of
> course).
> Also, getting rid of these Text objects, and just sticking with the immutable
> String objects, we'll be able to take advantage of future JVM improvements
> for String deduplication, like
> http://java-performance.info/java-string-deduplication/
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