Session checkout

As noted in Blocking Sections for Operation Execution, implicit session checkout can be considered a blocking process for some drivers. Such drivers MUST apply the remaining timeoutMS value to this process when executing an operation. For explicit session checkout, drivers MUST apply the timeoutMS value of the MongoClient to the startSession call if set. Drivers MUST NOT allow users to override timeoutMS for startSession operations.

See timeoutMS cannot be overridden for startSession calls.

https://github.com/mongodb/specifications/blob/master/source/client-side-operations-timeout/client-side-operations-timeout.md#convenient-transactions-apiConvenient Transactions API

If timeoutMS is set, drivers MUST apply it to the entire withTransaction call. To propagate the timeout to the user-supplied callback, drivers MUST store the timeout as a field on the ClientSession object. This field SHOULD be private to ensure that a user can not modify it while a withTransaction call is in progress. Drivers that cannot make this field private MUST signal that the field should not be accessed or modified by users if there is an idiomatic way to do so in the language (e.g. underscore-prefixed variable names in Python) and MUST document that modification of the field can cause unintended correctness issues for applications. Drivers MUST document that the remaining timeout will not be applied to callback operations that do not use the ClientSession. Drivers MUST also document that overridding timeoutMS for operations executed using the explict session inside the provided callback will result in a client-side error, as defined in Validation and Overrides. If the callback returns an error and the transaction must be aborted, drivers MUST refresh the timeoutMS value for the abortTransaction operation.

If timeoutMS is not set, drivers MUST continue to exhibit the existing 120 second timeout behavior. Drivers MUST NOT change existing implementations to use timeoutMS=120000 for this case.

See withTransaction communicates timeoutMS via ClientSession and withTransaction refreshes the timeout for abortTransaction.