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https://issues.apache.org/jira/browse/KAFKA-3499?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15224928#comment-15224928
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Tommy Becker commented on KAFKA-3499:
-------------------------------------
This was/is a problem in Samza as well. Though many classes may have this
problem, byte[] seems particularly common in this scenario. It's hard to
imagine a situation where byte array keys are ever going to be what you want in
a cache.
https://issues.apache.org/jira/browse/SAMZA-505
> byte[] should not be used as Map key nor Set member
> ---------------------------------------------------
>
> Key: KAFKA-3499
> URL: https://issues.apache.org/jira/browse/KAFKA-3499
> Project: Kafka
> Issue Type: Bug
> Components: kafka streams
> Reporter: josh gruenberg
> Fix For: 0.10.0.0
>
>
> On the JVM, Array.equals and Array.hashCode do not incorporate array
> contents; they inherit Object.equals/hashCode. This implies that Collections
> that rely upon equals/hashCode (eg, HashMap/HashSet and variants) treat two
> arrays with equal contents as distinct elements.
> Many of the Kafka Streams internal classes currently use generic HashMaps and
> Sets to manage caches and invalidation status. For example,
> RocksDBStore.cacheDirtyKeys is a HashSet<K>. Then, in RocksDBWindowStore, the
> Elements are constructed as RocksDBStore<byte[], byte[]>.
> Similarly, the MemoryLRUCache<K, RocksDBCacheEntry> internally holds a
> LinkedHashMap<K,V> map, and a HashSet<K> keys, and these end up holding
> byte[] keys. Finally, user-code may attempt to use any of these provided
> types with byte[], with undesirable results.
> Keys that are byte-arrays should be wrapped in a type that incorporates the
> content in their computation of equals/hashCode. java.nio.ByteBuffer is one
> such type that could be used, but a purpose-built immutable class would
> likely be a better solution.
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