Developer tools · Crontab generator
Running a cron job every minute: when polling is wrong and what to use
· Why it matters
cron polling performance
Every-minute jobs are easy to write and expensive to live with. This post explains the costs, the cases where they are justified, and the alternatives from longer intervals to daemons and event triggers.
Every-minute syntax creates 1,440 calendar candidates on a complete 24-hour day
`* * * * *` expands to every minute from 0 through 59, every hour and every calendar date. On a complete twenty-four-hour day that produces 1,440 matching wall-clock minute labels. ToolAcre’s preset and tests establish the grammar, while its preview shows only the next five candidates to keep the interface readable.
The count describes opportunities, not successful actions. A nonexistent local minute during a forward zone transition can be omitted by this preview, and the browser never executes a task. Use the expression to reason about cadence, then measure actual runtime effects where the command and scheduler exist.
Runtime cost cannot be calculated from the expression alone
An expression contains no process startup time, connection count, log volume or resource usage. A one-line check and a large import can share the same five stars while imposing incomparable costs. The workbook’s list of overheads may be plausible, but ToolAcre cannot quantify them from schedule text.
Performance analysis therefore begins outside the generator: observe duration, CPU, I/O and downstream calls for the real action. Multiply carefully by candidate frequency only after measuring representative runs. The parser can tell you how many minute values match; it cannot tell you what each match costs.
Suitability depends on an external action and latency requirement
Whether every-minute polling is justified depends on the latency requirement and action design. ToolAcre does not know if the command is idempotent, whether an event source exists or what delay users can tolerate. It should not label the schedule inherently good or bad.
Translate the requirement into a maximum acceptable interval, then compare that with observed cost and failure handling. If five-minute latency is sufficient, `*/5 * * * *` reduces minute candidates to twelve per hour. If only one-minute latency works, retain the cadence and address execution concerns explicitly.
Minute offsets distribute fixed hourly work but do not randomize it
A fixed offset such as `7 * * * *` selects minute seven of every hour. It can separate that job from work pinned to minute zero, but it is deterministic rather than randomized. Multiple offsets can distribute known jobs across the hour when their exact wall minute is unimportant.
ToolAcre describes minute seven past every hour and previews corresponding dates. It does not inspect other schedules on the host, so it cannot prove that the chosen offset is quiet. Build an inventory before claiming load has been spread, and preserve the reason for the offset in documentation.
Workers and service timers are alternatives outside this repository
Long-running workers, event delivery and service-manager timers can replace polling in some systems. None is implemented by the Crontab generator, and their configuration cannot be inferred from `* * * * *`. The repository has no queue client or supervisor integration.
Choose alternatives from the target architecture’s evidence. A worker may remove repeated startup while introducing lifecycle and recovery requirements. An event path may reduce empty checks while adding delivery semantics. The generator remains useful for any residual periodic tasks, but it cannot adjudicate those tradeoffs.
Worked example: reduce candidate frequency and compare previews
Compare three expressions in the panel: every minute, `*/5 * * * *`, and `7 * * * *`. The first advances by one minute, the second selects 0, 5, 10 and subsequent multiples, and the third selects one minute position per hour. The descriptions expose each change without executing a poller.
Use those candidate lists to discuss latency in concrete terms. If a request arrives immediately after a five-minute candidate, the next opportunity is almost five minutes away. That simple bound is schedule evidence. Processing duration, queue delay and success remain additional measurements the browser cannot supply.
What this does not cover — sub-minute scheduling, which cron cannot express
Five-field cron cannot express seconds because this parser begins with minute. A six-field input is rejected rather than treated as higher frequency. Creating a shell loop to emulate sub-minute work is command behavior outside ToolAcre and is not recommended here without runtime-specific testing.
If the requirement is below one minute, select a scheduler or worker designed and documented for that resolution. Do not force an unsupported seconds value into the first field. The exact-five-fields error is a useful dialect guard that prevents a fast-looking expression from being silently misread.
Takeaway: choose the coarsest interval that meets the need — and the generator makes a */5 or */15 expression as easy as five stars
Choose the coarsest cadence that satisfies a measured need, but keep the decision separate from expression validity. ToolAcre can make minute, five-minute and offset schedules equally syntactically correct. Only operational evidence determines which one belongs in a system.
Use the generator to enumerate opportunities, then attach cost, latency and reliability measurements from the target. That combined record is more honest than declaring every-minute cron expensive in all cases or assuming a less frequent expression automatically fixes inefficient work.