Zone Events Serialization
Currently, there are multiple event sources (the event scheduler, knotc commands) and there is no control of parallel operations performed on one zone at the time (except for RCU).
Current Problems
The current implementation of parallel operations causes following issues:
- Only the last-finished event has a real impact on the zone.
- An operation is confirmed as successful and other last-finishing operation will revert its effect later.
- Unnecessarily complicated RCU locking.
- Wasting memory, CPU, and blocking XFR (worker) threads.
Proposed Solution
Proposed by:
All operations working with one zone will be serialized. The serialization will be realized by adding a queue to each zone. An event will be put in the queue when it occurs (by the event scheduler, knotc response processing, DDNS response processing). The worker threads (formely XFR threads) will be picking the events from the queues in a way, that only one operation will be performed with each zone.
Resolved Problems
All described problems of current solution will be resolved.
New Problems
Some operations have to be performed immediately, because a response must be sent to the requestor. Some of these operations are blocked naturally (e.g., processing zone transfer and DDNS request), some need a special processing (e.g., processing zone reload and DDNS request). A possible solution of a special processing means refusing the upcoming events temporarily, if the zone event queue is non-empty (probably an acceptable solution, still better than current solution).