This new component will be built on top of the current collection critical section and will be used to prevent DDL(drop, rename, shard, etc...) operations to be executed concurrently on the same collection, when running in a sharded cluster.

Each DDL operation needs to enter the DDL critical section before to start and will release it on its cleanup. If a DDL operation tries to enter a critical section already occupied by another DDL operation, an exception will be thrown and will be propagated to the router.

This component will be exposed by the CollectionShardingRuntime and will expose two main functions:

• Enter DDL critical section (may throw exception)
• Exit DDL critical section