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IBM WebSphere eXtreme Scale 6 by Anthony Chaves

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Hash map refresher (or crash course)

Locks on objects need to be stored somewhere accessible to different threads. Much like how objects are stored in buckets in the BackingMap, locks are also stored in buckets. This brings us to the numberOfBuckets and numberOfLockBuckets settings on a BackingMap. These settings are implementation details of a BackingMap, but it's important to know these details in order to assign optimum settings for concurrency and performance. BackingMaps use a hash table data structure to store objects.

Let's review a basic implementation of the hash map data structure so we know what the number of buckets means. Hash maps store objects in buckets. A bucket is a place for a value object keyed with a key object. A good key ...

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