Message Replay / PubSub+ Cache Comparison
Message replay and PubSub+ Cache have similar purposes but there are a number of differences between them. Whether you choose message replay or PubSub+ Cache depends on your use cases.
The following table summarizes the differences.
| Attribute | Message Replay | PubSub+ Cache |
|---|---|---|
| Use Case |
Message Log Records all Guaranteed messages published to the Message VPN. Automatically trims oldest messages from log when the replays log exceeds 90% of its configured quota for |
Last Value Cache Typically keeps only the last message published on each topic. While PubSub+ Cache can be configured to keep more than one message per topic, it is a less common use case. |
| Message QoS |
Logs Guaranteed (or persistent) messages. Logs any messages that get promoted to Guaranteed messages. |
Intended for caching Direct (or non-persistent) messages. Connects to the event broker using Direct messaging. If any Guaranteed messages match PubSub+ Cache subscriptions, those messages are demoted to Direct when sent to PubSub+ Cache. |
|
Interactions With Client API |
All interactions with client APIs use Guaranteed messaging. |
All interactions with client APIs use Direct messaging. |
|
Topics Recorded |
Logs all Guaranteed messages published in the Message VPN by default. You can also configure message replay to log messages that match a set of wildcard subscriptions and filters. |
Administrator configures the wildcard topics that are to be stored in the cache. |
|
Message Delivery Order |
Replays messages in original published order. Publish order between topics is preserved. |
Cache requests are fulfilled topic-by-topic. Order is preserved within a topic (if depth is greater than 1), but original publishing order between topics is not preserved. |
| Replay Request Mechanism |
PubSub+ Messaging APIs Management interface |
PubSub+ Messaging APIs |
| Deployment Model | Integrated feature of the PubSub+ event broker. | Software application that runs on an external Linux server. |
| Message Storage | Uses the Guaranteed messaging infrastructure to persistently store messages. | Stores cached messages in RAM. |
| Redundancy Model | Leverages the event broker’s active-standby high-availability (HA) model. | Deploy multiple instances for N+1 redundancy. |
| Performance and Scaling |
Built for logging messages at Guaranteed messaging rates. Add more PubSub+ event brokers to horizontally scale Guaranteed messaging and message replay. |
Built for very high rate Direct messaging use-cases like market data distribution. Supports deploying multiple instances to horizontally scale. |
| Availability |
Integrated into the PubSub+ event broker; no extra license. |
Optional add-on product that requires purchased license. |