IssueTracker

Request that Cloud Tasks queues can be configured with a "concurrency key" and "concurrency limit per key" (in addition to the existing overall concurrency limit).

Consider a queue that performs an operation on a user, and that we can operate on many users at once, but we want to limit to one operation at a time per user.

An example queue configuration may look like this:

• maxConcurrentDispatches: 1000
• concurrencyKey: "userId"
• maxConcurrentDispatchesPerKey: 1

Where the queue would dispatch up to 1000 tasks at a time, but only one task at a time for tasks that have the same userId metadata value.

Alternatives are:

• Create a unique queue for every user (doesn't scale well for thousands or millions of users?)
• Limit overall concurrency for all users to 1 (won't scale)
• Don't limit concurrency per user, and wrangle with database contention