Hi, Could I please get a review of this OpenJDK 8u only fix? JDKs 11+ don't seems to have this issue as with the TLS 1.3 feature (JDK-8196584) SessionId.hashCode() got changed to use Arrays.hashCode() already.
webrev: http://cr.openjdk.java.net/~sgehwolf/webrevs/JDK-8203190/01/webrev/ Bug: https://bugs.openjdk.java.net/browse/JDK-8203190 The rationale for the fix are these assumptions: a) elements in trees on hash collision of LinkedHashMap used internally by the MemoryCache class become prohibitively large for many SessionId entries in the cache, b) moderate speed of the new hashCode() impl will not have a detrimental effect on performance overall. Comparison of performance of hashCode impls[1]: Benchmark Mode Cnt Score Error Units SessionIDBench.newHashCode thrpt 100 43649538.284 ± 678702.696 ops/s SessionIDBench.oldHashCode thrpt 100 94068843.923 ± 1379930.266 ops/s Collision testing[2] showed that indeed, the current hashCode() implementation of SessionId produces more collissions and, thus, produce more elements in trees for collision resolution in the underlying LinkedHashMap. The default cache expiry is 24 hours per entry and this can result in millions of entries in the cache in some circumstances[3]. Before: ################################################## Collision test for 100 sessions: ------------------------------------------------ Total number of collisions: 4 Max length of collision list over all buckets: 2 Collision test for 20480 sessions: ------------------------------------------------ Total number of collisions: 18311 Max length of collision list over all buckets: 30 Collision test for 10000000 sessions: ------------------------------------------------ Total number of collisions: 9996395 Max length of collision list over all buckets: 9709 ################################################## After: ################################################## Collision test for 100 sessions: ------------------------------------------------ Total number of collisions: 0 Collision test for 20480 sessions: ------------------------------------------------ Total number of collisions: 0 Collision test for 10000000 sessions: ------------------------------------------------ Total number of collisions: 11530 Max length of collision list over all buckets: 2 ################################################## Testing: Above testing, and make test. No new failures. Thoughts? Thanks, Severin [1] http://cr.openjdk.java.net/~sgehwolf/webrevs/JDK-8203190/SessionIDBench.java [2] http://cr.openjdk.java.net/~sgehwolf/webrevs/JDK-8203190/SessionIdCollissionTest.java [3] https://bugs.openjdk.java.net/browse/JDK-8210985
