Description
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/
Attachments
Issue Links
- breaks
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ACCUMULO-4371 WALSunnyDayIT.test consistently failing, comparing String and Text
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- Resolved
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