RFR: 8342040: Further improve entry lookup performance for multi-release JARs [v2]

[Claes Redestad]

On Thu, 17 Oct 2024 08:40:05 GMT, Eirik Bjørsnøs <eirbjo at openjdk.org> wrote:

>> I guess performance leans on there being only one or a small number of versions per entry. Which I think is a fair assumption. Still would be good to have a stress test with many entries having many versions and make sure we don't regress such cases too much, no?
>
>> I guess performance leans on there being only one or a small number of versions per entry. 
> 
> I checked Spring Petclinic:
> 
> * 109 JAR dependencies
> * 15 are multi-release enabled.
> * The 15 MR-JARs have 9347 entries, of which 21 are versioned
> * 9 of 15 MR JARs use the feature exclusively to hide `module-info.class` from Java 8.
> * 3 of the 6 remaining JAR files version a single class file
> * The remaining JARs mostly version on the 9 release.
> * The maximum number of versioned entries in a file is 5.
> * Zero entries have more than a single version.
> 
>> Which I think is a fair assumption. Still would be good to have a stress test with many entries having many versions and make sure we don't regress such cases too much, no?
> 
> Such a test would be somewhat speculative. If I add 5 versions of each entry in `ZipFileOpen`, then yes, this PR sees a regression over mainline:
> 
> Baseline:
> 
> Benchmark                     (size)  Mode  Cnt       Score       Error  Units
> ZipFileOpen.openCloseZipFile    1024  avgt   15  718234.380 ? 29454.645  ns/op
> 
> 
> PR:
> 
> Benchmark                     (size)  Mode  Cnt        Score       Error  Units
> ZipFileOpen.openCloseZipFile    1024  avgt   15  1284944.601 ? 74919.522  ns/op
> 
> 
> While `JarFileGetEntry` improves over baseline:
> 
> Baseline:
> 
> Benchmark                              (mr)  (size)  Mode  Cnt    Score   Error  Units
> JarFileGetEntry.getEntryHit           false    1024  avgt   15   68.984 ? 2.791  ns/op
> JarFileGetEntry.getEntryHit            true    1024  avgt   15  324.763 ? 9.690  ns/op
> JarFileGetEntry.getEntryHitUncached   false    1024  avgt   15   95.884 ? 1.404  ns/op
> JarFileGetEntry.getEntryHitUncached    true    1024  avgt   15  333.491 ? 3.576  ns/op
> JarFileGetEntry.getEntryMiss          false    1024  avgt   15   37.358 ? 2.215  ns/op
> JarFileGetEntry.getEntryMiss           true    1024  avgt   15  650.467 ? 5.116  ns/op
> JarFileGetEntry.getEntryMissUncached  false    1024  avgt   15   61.059 ? 0.382  ns/op
> JarFileGetEntry.getEntryMissUncached   true    1024  avgt   15  678.457 ? 4.390  ns/op
> 
> 
> PR:
> 
> 
> Benchmark                              (mr)  (size)  Mode  Cnt    Score    Error  Units
> JarFileGetEntry.getEntryHit           false    1024  avgt   15   61.333 ?  3.665  ns/op
> JarFileGetEntry.getEntryHit            true    1024  avgt   15  153.987 ?  8.889  ns/op
> JarFileGetEntry.getEntryHitUncached   false    1024  avgt   15   90.008 ?  4.158  ns/op
> JarFileGetEntry.getEntryHitUncached    true    1024  avgt   15  168.831 ?  1.676  ns/o...

I poked around with an alternative approach that uses `java.util.BitSet`. This also allows us to use the map we build up as-is, avoids sorting et.c. Performance on `JarFileGetEntry` (#21489 version) is the same in my testing, but performance on `ZipFileOpen` with your 5 versions of each entry stress test should be much improved (might beat the baseline). Can you share your local changes to that micro in a gist or e-mail so I can verify?

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/21489#discussion_r1805524895