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https://issues.apache.org/jira/browse/LUCENE-7966?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16308486#comment-16308486
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Uwe Schindler edited comment on LUCENE-7966 at 1/2/18 6:46 PM:
---------------------------------------------------------------
Sorry for silence on this. I wanted to improve the patch tomorrow.
[~mikemccand]:
bq. I retested w/ Uwe's patch:
By reading the Java mailing lists, I have an idea what could cause Mike's
differences: Are you sure that you used the same garbage collector in Java 8
and Java 9? By default Java 9 uses G1GC, which Java 8 uses the good old
ParallelGC by default. On the mailinglist jdk-dev there was a discussion that
suddenly computing-intensive stuff was significantly slower with Java 9. The
reason was the Garbage Collector! So be sure to use the same one (give it
explicit on command line). G1GC adds additional barriers and because of them
the number of free CPU registers is lowered by 1. This causes some algorithms
to behave worse as missing CPU registers don't allow to do everything in the
CPU ([~dweiss] has seen a sigicficant slowdown for some of his code). More than
10% slowdown is possible! This also affects code that has no garbage collection
and barriers because of G1. It's just limited resources causing this.
Interestingly the person complaining was talking about LZ4 compression:
http://openjdk.5641.n7.nabble.com/Reduced-performance-in-Java-9-0-1-vs-8u152-td322825.html
Could you compare Java 8 and Java 9 with same garbage collector? (a) G1GC on
both and (b) ParallelGC and/or CMS ?
Uwe
was (Author: thetaphi):
Sorry for silence on this. I wanted to improve the patch tomorrow.
[~mikemccand]:
bq. I retested w/ Uwe's patch:
By reading the Java mailing lists, I have an idea what could cause Mike's
differences: Are you sure that you used the same garbage collector in Java 8
and Java 9? By default Java 9 uses G1GC, which Java 8 uses the good old
ParallelGC by default. On the mailinglist jdk-dev there was a discussion that
suddenly computing-intensive stuff was significantly slower with Java 9. The
reason was the Garbage Collector! So be sure to use the same one (give it
explicit on command line). G1GC adds additional barriers and because of them
the number of free CPU registers is lowered by 1. This causes some algorithms
to behave worse as missing CPU registers don't allow to do everything in the
CPU ([~dweiss] has seen a sigicficant slowdown for some of his code). More than
10% slowdown is possible! This also affects code that has no garbage collection
and barriers because of G1. It's just limited resources causing this.
Could you compare Java 8 and Java 9 with same garbage collector? (a) G1GC on
both and (b) ParallelGC and/or CMS ?
Uwe
> 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: core/other, general/build
> Reporter: Robert Muir
> Labels: Java9
> Attachments: LUCENE-7966.patch, LUCENE-7966.patch, LUCENE-7966.patch,
> 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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