Bitbucket's adaptive throttling sub-system is a system protection mechanism that uses a ticketing system whereby "heavyweight" Git hosting operations (such as clone/fetch) are throttled. That is, when the system is too busy to handle a Git hosting operation immediately it will queue the request, then after 5 minutes if that request didn’t make it to the front of the queue and get executed, it will be rejected.

The data that is included in this dynamic throttling includes:

• Number of CPU cores
• %CPU usage
• Total system memory
• Various constraints that can be tuned

One of the more commonly used tunables used is `throttle.resource.scm-hosting.adaptive.limit.max`. This this sets the upper limit on the number of SCM hosting operations, meaning clones and fetches over HTTP or SSH, which may be running concurrently.

A common reason for doing this is if a system has insufficient memory relative to the size of the largest repositories. For such a system, if tuning is not carried out it is possible for the Git processes Bitbucket forks to exhaust system memory.

A useful improvement to adaptive throttling would be to account for RAM in a dynamic manner, potentially taking into account:

• Available RAM at the time the ticket is granted; not just total ram calculated when Bitbucket starts; and/or
• Average or maximum RAM usage of forked Git processes for each ticket granted

This doesn't eliminate the chance of an out-of-memory situation, because Bitbucket can't predict exactly how much memory a Git process may consume, but may reduce the chance of an out-of-memory condition occurring in a system that is not appropriately configured.