io.debezium.connector.mongodb.Replicator class doesn't use batch size to limit memory allocation of MongoDB cursor:
MongoDB server chooses an appropriate batch size if the size isn't specified.
I propose to add the following option:
|documents.fetch.size||0||Positive integer value that specifies the maximum number of documents that should be read in one go from each collection while taking a snapshot. The connector will read the collection contents in multiple batches of this size. Default to 0, which indicates that the server chooses an appropriate fetch size.|