isolated-execution.md

Isolated Execution

Sometimes you want to run your commands on an exclusive connection. There are a few reasons to do this:

• You're using transactions and need to WATCH a key or keys for changes.
• You want to run a blocking command that will take over the connection, such as BLPOP or BLMOVE.
• You're using the MONITOR command which also takes over a connection.

Below are several examples of how to use isolated execution.

NOTE: Behind the scenes we're using generic-pool to provide a pool of connections that can be isolated. Go there to learn more.

The Simple Scenario

This just isolates execution on a single connection. Do what you want with that connection:

await client.executeIsolated(async isolatedClient => {
    await isolatedClient.set('key', 'value');
    await isolatedClient.get('key');
});

Transactions

Things get a little more complex with transactions. Here we are .watch()ing some keys. If the keys change during the transaction, a WatchError is thrown when .exec() is called:

try {
    await client.executeIsolated(async isolatedClient => {
        await isolatedClient.watch('key');

        const multi = isolatedClient.multi()
            .ping()
            .get('key');

        if (Math.random() > 0.5) {
            await isolatedClient.watch('another-key');
            multi.set('another-key', await isolatedClient.get('another-key') / 2);
        }

        return multi.exec();
    });
} catch (err) {
    if (err instanceof WatchError) {
        // the transaction aborted
    }
}

Blocking Commands

For blocking commands, you can execute a tidy little one-liner:

await client.executeIsolated(isolatedClient => isolatedClient.blPop('key'));

Or, you can just run the command directly, and provide the isolated option:

await client.blPop(
    commandOptions({ isolated: true }),
    'key'
);