XGROUP CREATE key group <id | $> [MKSTREAM]
Time complexity: O(1)
ACL categories: @write, @stream, @slow
Create a new consumer group for the specified stream. group is the name of the consumer group. key is the stream name.
A consumer group is a collection of consumers. Group is extreamly useful when it is required to distribute incoming stream entries to different consumers. Each group has its own pending entry list (PEL) where it stores the group received entries. Consumers only recieves entries that no other consumers already received from the group.
If a group already exists by the given name, XGROUP throws a -BUSYGROUP error.
The XGROUP command requires an <id> argument. It tells the command to set the last delivered entry of the newly created group to the specified ID. Entries with lower IDs than the last delivered entry do not belong to the group and hence consumers can't receive those entries.
If you want to set the last delivered entry to the latest stream entry and you don't want to mention the ID explicitly, you can use the special "$" character. When specified, it sets the last delivery entry to the latest entry.
By default, the XGROUP CREATE command expects that the target stream exists, and returns an error when it doesn't. If a stream does not exist, you can create it automatically with length of 0 by using the optional MKSTREAM subcommand as the last argument after the <id>:
XGROUP CREATE mystream mygroup $ MKSTREAM
Simple string reply: OK on success.