Contents
How to send a notification in PostgreSQL using PG _ notify?
To send a notification you can also use the function pg_notify(text, text). The function takes the channel name as the first argument and the payload as the second. The function is much easier to use than the NOTIFY command if you need to work with non-constant channel names and payloads. Configure and execute a listen/notify sequence from psql:
How to use PG _ notify function in Elixir?
In our procedure, we are calling the pg_notify function inside. accounts_changed is the name of the event to emit, and the contents will be a JSON object like here for example: returned as a text type for the function’s requirements.
How to register listener in PostgreSQL notification channel?
Registers a listener on the notification channel (if the current session is already registered as a listener for this notification channel, nothing is done). A session can be unregistered for a given notification channel with the UNLISTEN command.
How is notify guaranteed to listen on the same channel?
It is also guaranteed that messages from different transactions are delivered in the order in which the transactions committed. It is common for a client that executes NOTIFY to be listening on the same notification channel itself.
How to use notify to automatically refresh layers in QGIS?
This was developed by the wizards from Oslandia and is easily added to any existing table in your PostgreSQL database – including PostGIS tables. This feature was added in version 3.0 (see https://qgis.org/en/site/forusers/visualchangelog30/#feature-trigger-layer-refresh-or-layer-actions-from-postgresql-notify-signal ).
What can payload string be used for in PostgreSQL?
For example, a database designer could use several different channel names to signal different sorts of changes to a single table. Alternatively, the payload string could be used to differentiate various cases.
How big is the notify queue in PostgreSQL?
There is a queue that holds notifications that have been sent but not yet processed by all listening sessions. If this queue becomes full, transactions calling NOTIFY will fail at commit. The queue is quite large (8GB in a standard installation) and should be sufficiently sized for almost every use case.