Outbound Message clarification

Question

We are building an outbound message listener that expects large volumes and near real-time performance.

As we are working through our low-level design, we have two questions that are not crystal clear from the documentation.

Question 1. What is the amount of time before the first "retry" occurs.

The documentation ( https://developer.salesforce.com/docs/atlas.en-us.api.meta/api/sforce_api_om_outboundmessaging_notifications.htm ) says "If a message cannot be delivered, the interval between retries increases exponentially, up to a maximum of two hours between retries." So I understand the upper bound of that retry interval, but what is the minimum? Meaning, we are planning on processing the message before sending the acknowledgement back to Salesforce, and I want to ensure that SLA for processing is less than the amount of time that will take place before the first retry occurs. Obviously, if processing time than the length of time before the first retry attempt occurs, then I have a problem as all records would be processed twice.

question #2: How long does outbound messaging “wait” as it bundles records / notifications before it sends a single message? Is it all qualifying records within one second? Two seconds? The millisecond level?

Answer 1

1. There's no documented minimum, and its subject to change, but its in the order of 2-5 seconds [depending on various things such as the performance of your endpoint]. However your latter comment highlights an issue, OM is at least once delivery, even if you ack the response that might not make it back to salesforce, and the messages will get delivered again, this is a very real condition your listener should handle [by tracking the recently processed notification Ids, and dropping already successfully processed messages].

2. Highly variable, depends on both the performance characteristics of your endpoint, and server load, can be anywhere from 100ms to minutes.

I think in general these are good ballpark numbers to know, but your design shouldn't be particularly dependent on them.