Lambda manages your function's asynchronous event queue and attempts to retry on errors. If the function returns an error, by default Lambda attempts to run it two more times, with a one-minute wait between the first two attempts, and two minutes between the second and third attempts.

Function errors include errors returned by the function's code and errors returned by the function's runtime, such as timeouts.

If the function doesn't have enough concurrency available to process all events, additional requests are throttled. For throttling errors (429) and system errors (500-series),
Lambda returns the event to the queue and attempts to run the function again for up to 6 hours by default. The retry interval increases exponentially from
1 second after the first attempt to a maximum of 5 minutes. If the queue contains many entries,
 Lambda increases the retry interval and reduces the rate at which it reads events from the queue.