https://sunshowers.io/tags/vcs/Recent content in Vcs on sunshowersHugoen-us© Rain 2020-present. Licensed under <a rel="license" href="https://creativecommons.org/licenses/by-nc-sa/4.0">CC BY-NC-SA 4.0</a> unless marked otherwise. <!--# Theme based on Terminal by panr, and used under the MIT license: https://github.com/panr/hugo-theme-terminal -->Wed, 14 Oct 2026 00:00:00 +0000https://sunshowers.io/posts/anthropic-mononoke/Wed, 14 Oct 2026 00:00:00 +0000https://sunshowers.io/posts/anthropic-mononoke/<p><em>Discuss on <a href="https://news.ycombinator.com/item?id=50094694">Hacker News</a> or <a href="https://lobste.rs/s/plcgps/anthropic_s_scion_is_heavily_inspired_by">Lobsters</a>.</em></p> <p>Here is Anthropic <a href="https://www.anthropic.com/engineering/redesigning-source-control">describing</a> (<a href="https://ghostarchive.org/archive/hCFVA">archive link</a>) yesterday how their new version control system, Scion, uses a concept called &ldquo;derived data&rdquo; to make operations like blames more efficient:</p> <figure class="center" > <a href="../../images/scion-derived-data.png"> <img src="../../images/scion-derived-data.png" alt="A changeset records only what’s changed, so on its own, it can’t quickly answer questions like who last edited a line or which commits affected a file. To answer those, Scion builds additional data structures from the changesets, including dedicated structures for file blame and path history and skip lists for the commit graph. We call everything that isn’t directly part of the changeset “derived data,” and we compute it all through one generic mechanism. Each type of derived data is defined recursively, so its value for a changeset is computed from its values for that changeset’s parents. This mechanism has three benefits. First, we can easily add a new type of derived data when a new data structure would make some operation faster. Second, for each type, we can choose whether to compute it eagerly or defer the work, so we avoid materializing data we don’t need. And third, because the client never sees the internals of these data structures, we can optimize them without changing the client. We’ve added new types of derived data many times as the system has grown, such as new indices for performing copy detection or path-based file search." /> </a> <figcaption class="center" >How Anthropic describes Scion&rsquo;s derived data.</figcaption> </figure> <p>Here is me, back in 2022, describing in my Oxide candidate materials how the <a href="https://github.com/facebook/sapling/tree/main/eden/mononoke">Mononoke</a> source control server I helped build uses a concept called &ldquo;derived data&rdquo; to make operations like blames more efficient:</p>