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https://issues.apache.org/jira/browse/KAFKA-3499?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15235799#comment-15235799
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Michael Noll commented on KAFKA-3499:
-------------------------------------
FWIW, we ran into the same problem when handling byte[] in Twitter Algebird.
Back then I introduced a custom
[Bytes|https://github.com/twitter/algebird/blob/develop/algebird-core/src/main/scala/com/twitter/algebird/Bytes.scala]
wrapper for byte arrays ([original
PR|https://github.com/twitter/algebird/pull/399/files]), which happens to use
java.nio.ByteBuffer. The Bytes.scala code might be a good starting point; it
includes a sane implementations of hashCode, ordering/compare, equals, etc.
> 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: Sub-task
> Components: streams
> Reporter: josh gruenberg
> Labels: user-experience
> 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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