Anatomy of a Throttler, part 1

A database throttler is a service or component that regulates incoming requests to prevent system overload. It focuses on throttling non-time critical operations such as ETLs, data imports, and mass purges of data. The choice of metrics for determining the health of a database varies depending on factors like scope of queries, hot spots or cold spots in affected data, and state of the page cache. Replication lag is a popular metric used to push back against long running jobs. Other common metrics include threads_running, transaction queue latency, queue delay, load average, and pool usage. A throttler should be able to push back based on a combination of these metrics rather than just one. The granularity of the metrics collected by the throttler can significantly affect its performance and efficiency.