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https://issues.apache.org/jira/browse/LUCENE-7966?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16162696#comment-16162696
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Uwe Schindler commented on LUCENE-7966:
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bq. As for performance I wonder what the actual gain will be - I bet you a beer
the performance will be within the noise levels on larger tasks.
Of course, we have to test this how much it gains! We should compare:
- Java 8 without and with patch
- Java 9 without and with patch
But the main reason is to make our code "safer". We omitted bounds checks at
many places, because the overhead was immense (e.g. BytesRef,
ByteBufferIndexInput,...) and sometimes not even added asserts. If we make that
code safer, it will not be slower in Java 9. So we can say: We still work with
Java 8, but you should really use Java 9 for optimal performance.
Robert just started with the important stuff, but there is room for
improvements.
> build mr-jar and use some java 9 methods if available
> -----------------------------------------------------
>
> Key: LUCENE-7966
> URL: https://issues.apache.org/jira/browse/LUCENE-7966
> Project: Lucene - Core
> Issue Type: Improvement
> Components: general/build
> Reporter: Robert Muir
> Attachments: LUCENE-7966.patch, LUCENE-7966.patch
>
>
> See background: http://openjdk.java.net/jeps/238
> It would be nice to use some of the newer array methods and range checking
> methods in java 9 for example, without waiting for lucene 10 or something. If
> we build an MR-jar, we can start migrating our code to use java 9 methods
> right now, it will use optimized methods from java 9 when thats available,
> otherwise fall back to java 8 code.
> This patch adds:
> {code}
> Objects.checkIndex(int,int)
> Objects.checkFromToIndex(int,int,int)
> Objects.checkFromIndexSize(int,int,int)
> Arrays.mismatch(byte[],int,int,byte[],int,int)
> Arrays.compareUnsigned(byte[],int,int,byte[],int,int)
> Arrays.equal(byte[],int,int,byte[],int,int)
> // did not add char/int/long/short/etc but of course its possible if needed
> {code}
> It sets these up in {{org.apache.lucene.future}} as 1-1 mappings to java
> methods. This way, we can simply directly replace call sites with java 9
> methods when java 9 is a minimum. Simple 1-1 mappings mean also that we only
> have to worry about testing that our java 8 fallback methods work.
> I found that many of the current byte array methods today are willy-nilly and
> very lenient for example, passing invalid offsets at times and relying on
> compare methods not throwing exceptions, etc. I fixed all the instances in
> core/codecs but have not looked at the problems with AnalyzingSuggester. Also
> SimpleText still uses a silly method in ArrayUtil in similar crazy way, have
> not removed that one yet.
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