Reference
Engine Modes & States
Background, Balanced, and Throughput — understanding concurrency and execution flow.
Alchemist uses Modes to dictate performance limits and States to control execution flow.
Engine Modes (Concurrency)
Modes define the maximum number of concurrent jobs the engine will attempt to run.
| Mode | Concurrent Jobs | Ideal For |
|---|---|---|
| Background | 1 | Server in active use by other applications. |
| Balanced | floor(cpu_count / 2) (min 1, max 4) | Default. Shared server usage. |
| Throughput | floor(cpu_count / 2) (min 1, no cap) | Dedicated server; clearing a large backlog. |
Manual override
You can override the computed limit in Settings → Runtime. A “Manual” badge will appear in the engine status. Switching modes clears manual overrides.
Engine States (Execution)
States determine whether the engine is actively processing the queue.
| State | Behavior |
|---|---|
| Running | Engine is active. Jobs start up to the current mode’s limit. |
| Paused | No new jobs start. Active jobs continue until they finish. |
| Draining | Engine is stopping. Active jobs finish, but no new jobs start. |
| Scheduler Paused | Engine is temporarily paused by a configured Schedule Window. |
Changing Engine Behavior
Engine behavior can be adjusted in real-time via the Runtime dashboard or the API. Changes take effect immediately without cancelling in-progress jobs.
Authoritative source
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