Max Payload Size in Axon Server

Axon Server
1

We are using Axon Server version 2025.0.1.
From the interface, I filtered events with this query to see their size:

select (length(payloadData) as length, payloadType, formatDate(timestamp, "yyyy/MM/dd HH:mm") as time)
| payloadType contains "X"

However, for the same event type, I sometimes see different sizes.

Is there a way to get the event with the largest payload size?

2

There is no ascending or descending operation in Axon Sever’s query language I am afraid. Hence, your easiest way forward would be to perform a simple “greater than {some-value}” task step by step, until you’ve found the largest.

By the way, do note that the length operation returns the number of characters the payloadData contains! Hence, it is not the stored size, strictly speaking. Although you might already know, I figured it would be important to stress this point regardless.

3

Thanks, @Steven_van_Beelen
Is there a way to retrieve the stored size of the event?

4

Sure thing, @Aymen_Kanzari!

Sadly, there is not such a feature.

For Axon Server, the stored size can differ slightly, depending on the amount of events in a transaction. Is it just one event? Then the event is paired with its own transaction headers. Are you publishing several events in one go, they get lumped together in one transaction, thus with one set of headers.

Anyhow, long story short, it’s not functionality that currently exists. So, let me ask you a follow-up: What do you need the stored size of a specific event for?

5

To follow up on my original intent:
We are exploring the performance impact of event size in our Axon-based system (using Axon Server version 2025.0.1).

So here’s the core question:
Is there any performance recommendation or practical limit on the number of characters in an event?
For example, will an event with a payload of ~199,999 characters perform significantly worse (in terms of publishing, storing, and replaying) compared to one with ~1,500 characters?

I know Axon Server stores events efficiently, but I wonder if very large events (even just textual data) could negatively impact:

Event store write/read throughput
Event processor handling time
Replay performance

Are there any known thresholds, or best practices around event size we should follow?