WL#396: Enhance client protocol to allow notifications.
Currently all information client gets from server is initiated by client. So if client would need to wait for some event it will have to poll server in a loop which produces extra load and requires special programming techniques to work. So it would be good to add to client server protocol notifications of a different sort - so client would register it is waiting some event and it will get notofication from server as soon as it happens. Also some events may be sent as notifications to all of the clients, for example if server will go down shortly. This for example may be used to get rid of special application server for some if interactive applications. Let's say application is displaying the list of records to the client and would like to have it actual - so if some records arrive they are added to the list automatically as well as removed if they are deleted. Currently you will have to use application server to maintain such list or poll MySQL server in a loop which would require extra connection and produce overhead. There are two options for implementing this - blocking. Then you are waiting for event by issuing LISTEN
query which will complete as soon as event happens and non blocking. Then client just register function which should be called in case event happens, and client may be informed about this event in any time (similar to signals). Events may be raised internally by some of system operations, or executed by other/users/triggers/stored procedures by getting use of special statement. Ie NOTIFY
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