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DiceDB

Reactive Hello, World!

DiceDB is a truly reactive database allows you to create query subscriptions on the database and get notified whenever the data changes, thus eradicating the need to poll the database for changes. This is a simple Hello, World! example to get a taste of reactivity.

But, before we start, make sure you have

  1. a running instance of DiceDB
  2. installed DiceDB CLI

Starting DiceDB

Start the DiceDB server with the two flags --enable-multithreading and --enable-watch to enable multi-threading and watch mode, respectively. Your command would look something like this

Terminal window
docker run -p 7379:7379 dicedb/dicedb --enable-multithreading --enable-watch

Also, connect to the database using the CLI as mentioned in the above installation steps or the previous hello world example.

Storing Data: The SET Command

Let’s store <k1, v1> in DiceDB. We’ll use the SET command, which is responsible for storing a string value under a specified key.

Terminal window
dicedb> SET k1 v1
OK

Watch k1 in two terminal sessions

Now, open two terminal sessions, connect both with the same DiceDB server using the DiceDB CLI and watch the changes on the key k1 in both the sessions.

Terminal window
dicedb> GET.WATCH k1

In return you will get fingerprint and initial data which you can ignore for now.

At this step you have total 3 terminal sessions,

  1. one where you fired the SET k1 v1 command
  2. two where you fired the GET.WATCH k1 command

Update the value of k1

Now, go back to the first terminal session and update the value of k1 to v2 using the SET command.

Terminal window
dicedb> set k1 v2
OK

Now, you will see the changes in the other two terminal sessions where you have watched the key k1 and you will get the updated value v2 in both the sessions.

This is the reactivity in action. You can create multiple subscriptions on the database and get notified whenever the data changes. CDC (Change Data Capture) notifies the subscribers about the changes in the database and sends an event with the delta, but but DiceDB evaluates the query/command and sends the updated result set to the subscribers.

This can be used to build real-time applications like leaderboards, monitoring, alerting, instant recommendations, etc.

WATCH commands

We are in process of implementing the .WATCH commands for all query commands in DiceDB, but today we support GET.WATCH and ZRANGE.WATCH, you can read more about them in the commands documentation.

With subsequent releases, we will keep shipping .WATCH commands for all the query commands in DiceDB.