What is Concurrency Policy?
A rule that defines behavior when a new job run is triggered while a previous run is still active.
Definition
A concurrency policy governs what happens when a cron job's next scheduled execution arrives while a previous execution is still running. Common policies include: Allow (run both simultaneously), Forbid/Skip (skip the new run), and Replace (cancel the running job and start the new one). The right policy depends on whether the job is safe to run in parallel.
Simple Analogy
Like a policy for a single-occupancy bathroom — if someone is inside, do you wait in line (queue), walk away and come back later (skip), or knock and ask them to hurry up (replace)?
Why It Matters
Without a concurrency policy, overlapping executions can cause data corruption, resource exhaustion, or duplicate processing. A payment processing job running in parallel with itself could charge customers twice. CronJobPro's concurrency controls ensure predictable behavior when execution times exceed schedule intervals.
How to Verify
Check your job's concurrency settings in CronJobPro. Review execution history for overlapping time ranges that indicate concurrent runs. In Kubernetes, check the CronJob's concurrencyPolicy field. Test by temporarily making a job slow and observing the next scheduled run's behavior.
Common Mistakes
Leaving the default "Allow" policy for jobs that are not safe to run concurrently. Setting "Forbid" on jobs with unpredictable duration, causing missed runs. Not realizing that "Replace" cancels the running job, which may leave work half-done.
Best Practices
Default to "Forbid/Skip" for most jobs — it is the safest option. Only use "Allow" for jobs proven safe to run in parallel. Use "Replace" only for jobs where the latest data supersedes any in-progress work. Monitor skipped runs to detect if your job consistently takes too long.
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What is Concurrency Policy?
A concurrency policy governs what happens when a cron job's next scheduled execution arrives while a previous execution is still running. Common policies include: Allow (run both simultaneously), Forbid/Skip (skip the new run), and Replace (cancel the running job and start the new one). The right policy depends on whether the job is safe to run in parallel.
Why does Concurrency Policy matter for cron jobs?
Without a concurrency policy, overlapping executions can cause data corruption, resource exhaustion, or duplicate processing. A payment processing job running in parallel with itself could charge customers twice. CronJobPro's concurrency controls ensure predictable behavior when execution times exceed schedule intervals.
What are best practices for Concurrency Policy?
Default to "Forbid/Skip" for most jobs — it is the safest option. Only use "Allow" for jobs proven safe to run in parallel. Use "Replace" only for jobs where the latest data supersedes any in-progress work. Monitor skipped runs to detect if your job consistently takes too long.
Related Terms
Schedule Overlap
When a new job execution starts before the previous one has finished running.
Execution Duration
The measured wall-clock time from when a job starts running to when it finishes.
Distributed Lock
A coordination mechanism ensuring only one instance of a job runs across multiple servers.
Job
A discrete unit of work — typically an HTTP request or script — that a scheduler runs.