Question: What determines the throughput of Redis Pub/Sub?

Answer

Redis Pub/Sub is a feature offered by Redis that allows clients to subscribe to channels and receive messages published to these channels. When it comes to throughput, a variety of factors come into play.

1. Network bandwidth: The maximum amount of data that can be transmitted over your network connection in a given amount of time can limit the throughput of Redis Pub/Sub.

2. Message size: Larger messages take more time to transmit than smaller ones which can impact the rate at which they are passed through the system.

3. System resources: How powerful your server is (CPU, memory, disk I/O) can affect how efficiently Redis processes incoming requests and thus impact the throughput of Pub/Sub.

4. Number of subscribers: More subscribers translate into more messages being delivered and therefore more processing power and network bandwidth is needed.

5. Number of publishers: More publishers mean more messages are being sent into the system which can increase the demand on the server resources.

To measure the rate of message transmission, you can use the redis-benchmark command-line tool provided with Redis.

Here's a sample usage for testing pub/sub performance:

redis-benchmark -t pubsub -n 1000000 -q

This will test publishing and subscribing to messages 1,000,000 times. The -q option means "quiet" - only display the query/sec values.

Understanding these factors can help you optimize Redis Pub/Sub throughput. You may need to partition your messages across multiple channels, use smaller message sizes, or scale your server resources depending on what is limiting your throughput.