Understanding Edge Function CPU limits

Last edited: 2/6/2026

Learn how Edge Functions manage CPU resources and what happens when limits are reached.

How isolates work

An isolate is like a worker that can handle multiple requests for a function. It works until a time limit of 400 seconds is reached. Edge Functions use isolates with soft and hard CPU limits.

Soft limit

When the isolate hits the soft limit, it retires. This means:

  • It won't take on any new requests
  • It will finish processing requests it's already working on
  • It keeps going until it hits the hard limit for CPU time or reaches the 400-second time limit, whichever comes first

Hard limit

If there are new requests after the soft limit is reached:

  • A new isolate is created to handle them
  • The original isolate continues until it hits the hard limit or the time limit
  • This ensures existing requests are completed while new ones are managed by a fresh isolate

Current limits

  • Wall clock time limit: 400 seconds total duration
  • CPU execution time: 200 milliseconds of active computing

What happens when limits are exceeded

When your function exceeds CPU limits, you may see:

  • 546 error responses
  • Function termination with CPUTime shutdown reason
  • Degraded performance as new isolates spin up

Optimizing CPU usage

Profile your code

Identify CPU-intensive sections in your function:

  • Complex calculations
  • Data processing loops
  • Encryption operations

Optimize algorithms

  • Use more efficient data structures
  • Cache computed results
  • Reduce algorithmic complexity

Offload heavy work

  • Move intensive processing to background jobs
  • Use external services for heavy computations
  • Break large tasks into smaller functions

Additional resources