Outbox Optimization: Deduplication and Display of Latest Object State

[Jiwoon-Kim]

I might not fully understand how the outbox and inbox mechanisms work, but if the inbox simply replaces the entire object instead of performing partial updates, wouldn’t it be sufficient for the outbox to only retain Update activities rather than both Create and Update?

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Bloated Outbox: The Outbox contains redundant history, increasing the payload size and the number of items clients need to process.

Since WordPress already has a built-in revision system, I believe implementing Partial Updates would be relatively easy.

However, one thing I found curious is that when inspecting the outbox, I noticed both Create and Update activities being published.
Is this really necessary?
It feels somewhat like exposing the internal revision history rather than just reflecting the current state of the object.

Originally posted by @Jiwoon-Kim in #2308 (comment)

[obenland]

It feels somewhat like exposing the internal revision history

That's exactly how the Outbox works.

[Jiwoon-Kim]

@obenland That seems a bit odd.
The problem is that each Activity in the Outbox actually contains the object’s full content.
So when a post is frequently edited, the Outbox becomes filled with repeated Update activities referencing the same object.

One more thing — since Create, Update, and Delete activities all refer to the same object:
when a Delete activity is sent, do the previous Create and Update entries still remain in the Outbox?
If so, that would mean the record isn’t really deleted — it just becomes an immutable log of revisions, not an actual removal.

[Jiwoon-Kim]

The Inbox reflects only the final state of an object, which means that ActivityPub operations are idempotent — each update replaces the previous one, rather than creating a new revision.
ActivityPub doesn’t expose a version history; it only communicates that an update occurred.

So my question is:
If that’s the case, should the Outbox really keep every historical version of a post?
Because at the moment, the Outbox stores each Create and Update activity containing the full object content.
This effectively duplicates the same object many times and behaves more like a revision log than a feed of current activities.

Wouldn’t it make more sense for the Outbox to reference only the latest version of each object, aligning its behavior with the Inbox’s idempotent state model?

[pfefferle]

The Inbox reflects only the final state of an object, which means that ActivityPub operations are idempotent — each update replaces the previous one, rather than creating a new revision. ActivityPub doesn’t expose a version history; it only communicates that an update occurred.

The inbox works the same way as the outbox and stores every change on a remote object (Creates, Updates, Deletes, Follows, ...).

[pfefferle]

But sure, we can have a better mechanism to remove items. But it is not as easy as you describe it in your comment. Some Activity have an Undo options, so we have to get sure that we do not break this functionality!