[dtcristo]

Hey, David here.

Below is my AI-assisted implementation of basic coalescing described in #834.

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What

Adds coalesce key: to Active Job classes. Jobs enqueued with the same key share one pending job. The first creates it, and later ones, including scheduled ones, are discarded into it until a worker claims it. A job enqueued during the run then queues the next pending job. coalesce_status (:created or :discarded) and provider_job_id tell the caller what happened.

It adds a solid_queue_coalesce_keys table, with bin/rails solid_queue:update for existing installations.

Why

See #834, which is the place to discuss the design. This PR is a minimal version to make that discussion concrete. It shows the approach, and leaves out edge cases a real implementation would need.

How

• ActiveJob::Coalescing sits next to ActiveJob::ConcurrencyControls. It adds coalesce and builds keys the way concurrency_key does, scoped to the class and batch.
• Job.enqueue sends coalesced jobs to SolidQueue::Job::Coalescing, the way Job::ConcurrencyControls pairs with its Active Job counterpart. In one transaction, it inserts the key's row unless it exists, locks it, and either creates the job and records it on the row, or discards the call into the job already there. Calls with the same key wait on that lock. Database errors raise EnqueueError, as for other jobs. Job.enqueue_all handles coalesced jobs one at a time, in key order.
• ReadyExecution.claim locks the keys of the jobs it claims in key order, the same order as bulk enqueue, and deletes them in the claim's transaction. A pending job that's deleted takes its key with it, through the foreign key.
• Retries aren't coalesced, because they continue work that already started.

Left out on purpose: deadlock retries on MySQL, instrumentation, and keeping the key for a claimed job that's released back to the queue. An app transaction that coalesces several keys in arbitrary order can also deadlock with a claim.

🤖 Written by @dtcristo's agent (Claude Opus 5.5, GPT-6.1 Sol)