How deeply does Akka in Action, Second Edition cover hash function?

Explains key extraction, hashing, virtual-node selection, and routee selection, while leaving Akka internals invisible to normal users.

Hash function

As explained in Akka in Action, Second Edition

A hashing algorithm is an algorithm that deterministically maps input data to hash values.

A hash function turns a message key into a hash code that helps a consistent-hashing router select a virtual node and its routee. Similar messages therefore follow the same routing path when they share a key. section 6.3.4 section 6.3.4

Consistent-hashing routing proceeds through these steps:

Extract a stable String key from the message, such as its ID, using a message-specific mapping function. section 6.3.4
Create a hash code from that key and use it to select a virtual node. section 6.3.4
Send the message to the routee responsible for that virtual node; virtual nodes improve distribution and support route changes. section 6.3.4

Routing messages by ID

Define mapping(command) = command.id, then configure an Akka group router with consistent hashing. Messages carrying the same ID produce the same hash and reach the same routee.

How Akka in Action, Second Edition covers it

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Related concepts

hash valueproduces · A hash value is a deterministic, typically fixed-size value produced by applying a hash function to input data, often for lookup, comparison, identification, or integrity checking.
SHA-256includes · SHA-256 is a standardized cryptographic hash function in the SHA-2 family that maps arbitrary input data to a fixed-length 256-bit digest.
cryptographic hashproduces · A cryptographic hash is a fixed-length digest computed from input data by a deterministic function designed to resist preimage, second-preimage, and collision attacks.
bloom filterused by · A Bloom filter is a space-efficient probabilistic data structure for testing set membership that permits false positives but not false negatives.
SHA-2includes · SHA-2 is a standardized family of cryptographic hash algorithms that produces fixed-length digests, including SHA-224, SHA-256, SHA-384, and SHA-512.
HMACused by · HMAC is a keyed message authentication code constructed from a cryptographic hash function and a secret key to authenticate data and verify its integrity.

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