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

[Eirik Bjørsnøs]

On Tue, 15 Oct 2024 16:08:32 GMT, Claes Redestad <redestad at openjdk.org> wrote:

> 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/op
JarFileGetEntry.getEntryMiss          false    1024  avgt   15   34.525 ?  1.878  ns/op
JarFileGetEntry.getEntryMiss           true    1024  avgt   15   61.036 ?  2.568  ns/op
JarFileGetEntry.getEntryMissUncached  false    1024  avgt   15   75.246 ? 20.375  ns/op
JarFileGetEntry.getEntryMissUncached   true    1024  avgt   15   81.484 ?  1.981  ns/op


Future work could probably improve this situation by shifting version resolution to `initCEN` time. That way, only the single version relevant to the `JarFile` `featureVersion` would need to be considered. That's not so easy to do currently, since this happens in `JarFile`s super constructor. But with flexible constructor bodies, we may be able to do something. But not for this PR.

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

PR Review Comment: https://git.openjdk.org/jdk/pull/21489#discussion_r1804355452