Acme Engineering

Acme Engineering
Engineering

How offline sync works in Acme 4.0

CRDTs, a write-ahead log and a lot of patience.

Sophie Tan
8 min read
A desk with a keyboard, a tablet and a notebook
The first sketch of the sync pipeline, March 2026.
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Sync is the feature nobody notices until it fails. Our goal for 4.0 was simple to state and hard to build: never lose a keystroke, online or off.

Why CRDTs

A conflict-free replicated data type lets two devices edit the same document without a server deciding who wins. Every operation commutes - merging becomes a set union.

The best sync is the one you forget is there.

Hannah Lee, Design
Written by

Sophie Tan

Staff engineer, Sync team

Sophie leads the sync team at Acme. Before that she built storage engines at two databases you have heard of. She writes about distributed systems, testing, and calm engineering.

Contributors

  • Sophie TanStaff engineer
  • Hannah LeeDesign lead
  • AH
    Aron HombergCEO

With help from Hannah Lee and Aron Homberg