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commitTransaction¶New in version 4.0.版本4.0中的新功能。
Saves the changes made by the operations in the multi-document transaction and ends the transaction.
To run the commitTransaction, the command must be run against the admin database and run within a Session. Rather than run the commitTransaction command directly, most users should use the driver method or the mongo shell Session.commitTransaction() helper.
The command has the following syntax:语法如下所示：
When committing the transaction, the session uses the write concern specified at the transaction start. See Session.startTransaction().
If you commit using "w: 1" write concern, your transaction can be rolled back if there is a failover..
When a transaction commits, all data changes made in the transaction are saved and visible outside the transaction. That is, a transaction will not commit some of its changes while rolling back others.
Until a transaction commits, the data changes made in the transaction are not visible outside the transaction.
However, when a transaction writes to multiple shards, not all outside read operations need to wait for the result of the committed transaction to be visible across the shards. For example, if a transaction is committed and write 1 is visible on shard A but write 2 is not yet visible on shard B, an outside read at read concern "local" can read the results of write 1 without seeing write 2.