Definition
A retry queue is a durable store of operations that have failed temporarily and need to be re-attempted. The typical pattern: when an operation fails, instead of losing the data, the system writes it to a queue with metadata about the failure. A separate worker periodically pulls from the queue and retries, usually with exponential backoff (wait 1 second, then 2, then 4, then 8) and a maximum retry count to avoid loops.
Good retry queues are idempotent-safe: retrying the same operation twice does not produce duplicate results. They are also observable - you can see queue depth, age of the oldest entry, and failure reasons. And they have a dead-letter tier: operations that fail all retries get surfaced to humans rather than silently dropped.
How SheetLinkWP relates to Retry Queue
SheetLink Forms includes a built-in retry queue for webhook deliveries. If a form submission cannot reach your Apps Script endpoint or Apps Script returns a transient error, the submission lands in the retry queue. The plugin's WP-Cron job retries up to 5 times with exponential backoff (1m, 5m, 15m, 1h, 6h). Successful retries write to the sheet and clear from the queue. Final failures are surfaced in SheetLink > Tools > Retry Queue with the error message, so you can diagnose and manually re-push.