How deeply does Akka in Action, Second Edition cover consistent hashing?

Explains deterministic key-based routing and shows Akka configuration, while treating detailed router steps as internal.

Consistent hashing

As explained in Akka in Action, Second Edition

Consistent hashing is a hashing algorithm that assigns keys to a changing set of nodes while minimizing key reassignment when nodes are added or removed.

Consistent hashing assigns related messages to the same routee, preserving message affinity as routees join or leave. In a worker pipeline, it lets obfuscation and enrichment results reach the same aggregator instead of being merged incorrectly. section 6.3.4

A consistent-hashing router follows this path:

Convert each message into a string key. section 6.3.4
Hash the key and use the result to select a routee deterministically. section 6.3.4 section 6.5
Use the same mapping for corresponding worker outputs, so the aggregator receives both pieces of one original message. section 6.3.4

Routing enrichment results to the matching aggregator

Define the aggregator key as the message id, then configure a group router with consistent hashing: Routers.group(Aggregator.serviceKey).withConsistentHashingRouting(10, Aggregator.mapping). The enricher sends Aggregator.Enriched(id, content + ":metadata"), allowing matching results to reach the same aggregator.

How Akka in Action, Second Edition covers it

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Also explained in

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Elixir in Action, Third EditionConsistent hashing is a key-to-node mapping technique that limits remapping when nodes are added to or removed from a distributed system.

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Related concepts

distributed cachingused by · Distributed caching is a technique for storing reusable data in a cache shared across multiple networked processes, servers, or nodes.
hash functionuses · A hash function deterministically maps input data to a value in a bounded output range, commonly for indexing, lookup, comparison, or integrity checking.
dataset splitused by · A dataset split is the division of a dataset into distinct subsets assigned different purposes, such as training, validation, or testing.
routingaddresses · Routing is the selection of a path, destination, or processing component to direct an item, request, or flow toward an intended endpoint.

This explainer was generated by Manning's knowledge graph from the text of Akka in Action, Second Edition. The section links point to the parts of the book it draws on.