User Guide

Everything you need to install, configure, and build with Montycat — from getting started to governance, advanced operations, and security.

Subscriptions

Subscription overview

Montycat provides a native subscription mechanism that allows clients to receive real-time notifications about changes in keyspaces.
Subscriptions can be set up for both in-memory and persistent keyspaces.
When a record is inserted, updated, or deleted, all clients subscribed to that keyspace are notified with the details of the change.

Create a subscription

To create a subscription, clients need to send a subscription request to Montycat, specifying the keyspace or even particular key they want to subscribe.

Subscriptions are not persistent. They will be lost if the client disconnects. Clients can re-subscribe to the same keyspace or key after reconnecting.
Note: Subscriptions can be created only for existing persistent keyspaces.

from keyspaces import Employees #keyspaces.py

def callback_on_data(data):
    print("Received data:", data)

sub_task, stop_event = await Employees.subscribe(callback=callback_on_data)

# {"status": True, "message": "Subscription started", "payload": null, "error": null}

# on every insert/update in the keyspace: {
#   "status": True,
#   "message": "Key inserted/updated",
#   "payload": {
#     "__key__": "128222336824100726154851618391811195396",
#     "__value__": {"username": "Name", "location": "Location", "age": 21}
#   },
#   "error": null
# }

# on every removal in the keyspace: {
#   "status": True,
#   "message": "Key removed",
#   "payload": {
#     "__key__": "128222336824100726154851618391811195396",
#   },
#   "error": null
# }

Subscribe on a specific key

Clients can subscribe to a specific key within a keyspace by sending a subscription request to Montycat, specifying the key they want to monitor.

from keyspaces import Employees #keyspaces.py

async def callback_on_data(data):
    print("Received data:", data)

subscription, stop_event = await Employees.subscribe(
    key="128222336824100726154851618391811195396",
    callback=callback_on_data
)

Cancel a subscription

Clients can cancel their subscriptions at any time by sending a cancellation request.

from keyspaces import Employees #keyspaces.py
import asyncio

def callback(response):
    print(f"Received data: {response}")

async def subscription():
    sub_task, stop_event = await Employees.subscribe(callback=callback)
    await asyncio.sleep(100)
    stop_event.set() # stops the subscription after 100 seconds

Allow / restrict subscriptions

Subscriptions can be governed engine-wide. Use these switches to allow or restrict clients from opening subscriptions to the database — for example to shed load or lock down a node.

# Engine-wide switch: allow clients to open subscriptions to this database.
await connection.allow_subscriptions()

# {"status": True, "payload": None, "error": None}

# Restrict subscriptions engine-wide (existing and new subscription attempts):
await connection.restrict_subscriptions()