![]() ![]() ![]() This requirement rules out eventually consistent solutions and means that Netflix engineers want linearizable consistency at the queue level. It is important since work that tends to happen in Cosmos is resource-intensive and can fan out to thousands of actions, and one of the goals was to reduce resource waste. When worker_2 issues a dequeue call, they lease msg_2 instead of msg_1, even though msg_1 has a higher priorityĪnother requirement is that a message can only be assigned to one worker at any given time. Therefore, if the "project"-based exclusive queue in our example has two messages with the key-value pair "project=foo" in it, and one of them is already leased out to a worker, the other one is not dequeueable. The contract for exclusive queues is that at any point in time, there can be only up to one consumer per exclusivity value. In this example, we call "foo", the value that corresponds to the exclusivity key, the message's exclusivity value. For instance, a message with "project=foo" will be accepted into the queue a message without the project key will not be. All messages posted to that queue must carry this key in their metadata. When an exclusive queue is created, it is associated with a user-defined exclusivity key - for example, "project". Kostas Christidis, a software engineer at Netflix, explains how Exclusive Queues work: Timestone introduces the concept of "Exclusive Queues" to support this notion. This requirement means that Timestone should not release some messages for processing until previous items belonging to the same work set are completed first. ![]() One of these requirements is the ability to mark some work items as non-parallelizable without requiring any locking or coordination on the consumer side. Engineers state that they built Timestone since they could not find an off-the-shelf solution that met all of its requirements. Netflix built the queuing system using open-source components such as Redis, Apache Kafka, Apache Flink and Elasticsearch. Netflix recently published how it built Timestone, a custom high-throughput, low-latency priority queueing system. ![]()
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