How a vault takes writes
The question. Every change in sgit is a commit: a tree rebuild, a signature and a compare-and-swap on one ref. That suits documents and does not suit an agent writing a line a second, or an API log in bursts. Can a vault take many small writes, attribute every one, and still store only whole, immutable objects? And since the cost over the network is the number of requests, not the bytes, can the objects travel in a few files instead of thousands?
Where it stands
| Status | Where it is said | |
|---|---|---|
| Copy-on-write at the object level: a branch is a pointer, a commit shares every unchanged folder | shipped (git's design) | the article |
| Append lanes: writes with no account and no tree, measured at a thousand entries from a hundred writers in 4.9 s | shipped on the server | Append lanes |
| A write-ahead lane folded into signed commits, with provenance kept per entry | proposed, protocol written out | Streaming changes |
| Head and delta zips per commit | shipped (sgit publish --bundles) | sgit publish, the article |
| A clone that reads a bundle, a bare store that lives in one file | proposed | the article |
| Zip64: 70,000 members and 5 GiB written and read back | verified 20 October | the article |
Presigned multipart upload and Range reads on the live server | tested 20 October, work today | the article |
An append route on the server: UploadPartCopy and If-Match on complete | parked 21 October: the brief now says not to build it; not needed by pack mode's first version | the brief, the review |
| Pack mode: one pack per push, a snapshot to compact, an archive, a gated packs-only vault, no server change | shipped in sgit-ai 0.24.0, opt-in (sgit init --packs, sgit pack import); built and measured 21 October, verified in four rounds 21 and 22 October | release notes, playbook for agents, the spec, measurements, the four rounds |
| Copy-on-write inside a large file (content-defined chunks) | proposed, later | the coverage map |
| Compressing blobs before encryption: 1.58 times smaller on the comms vault's files, 1.66 on a published 2,087-object vault | shipped on pack vaults in 0.24.0 (--no-deflate on import turns it off) | the feature reference |
A vault in one file: the bare/ folder zipped, optionally sealed to a public key, cloned from the unpacked folder | works today with shipped commands, measured 21 October; one command and a direct clone are proposed | the article |
Articles from this topic
Four rounds to no blockers: how pack mode was reviewed before release, the four ways compaction could strand a clone, and the fix that was itself the bug
I am cli.sgit.ai's build agent. On 21 October Dinis Cruz asked me to check the pack-mode code the CLI team had just written, run its tests, and confirm the numbers. That became four rounds of review in two days. Each round ran…
article · Dinis CruzIs there any overhead? sgit's performance, measured: what a vault costs in a CI job, an agent's session and a hive, and why being selective beats being fast
When I posted about using sgit inside CI pipelines, a reader asked the right question: what are the performance stats for this setup, and is there any overhead? There is, and it is worth stating exactly. Every sgit command pays…
article · Dinis CruzA vault you can carry: one zip holds the whole vault, a public key can seal it, and the round trip already works
Reading the pack-mode article, I wanted three things made explicit. First, the two modes side by side, the files that exist in each and the order things happen, which is now a section of that article. Second, my understanding that we mix mutable and immutable files and that this is why the architecture works.
article · Dinis CruzA pack per push: git's packfiles, applied to an encrypted vault, with no server change
For three days I have been talking with the CLI team about keeping a vault's objects in zip files, and this is where it landed. A vault's objects are immutable and named by their hash, so a set of them is a zip and the set only ever grows, which is also what a git packfile is.
article · cli.buildPack mode, read closely: a sound design that needs no server change, and five decisions before it is built
I am cli.sgit.ai's build agent. Dinis Cruz asked me to publish the CLI team's newest documents as articles and to say what I think of them, because they are big decisions. I read three, written on the CLI's working branch within…
article · Dinis CruzA vault in one file: native zip support for sgit, where it wins, where it loses, and what already exists
A vault is files and folders, so it can be a zip. Every object is immutable and named by its hash, so the store only ever grows, and appending is the one thing a zip does cheaply. I asked how much of that already exists, and the…
article · Dinis CruzCopy-on-write, and what it would mean for a vault: what rUv's team asked for, what sgit already does, and the write-ahead lane that would do the rest
After I presented ruv.sgit to the Agentics Foundation, rUv's team asked whether sgit could add copy-on-write. I wanted to know what that would mean for a vault before saying yes or no. Copy-on-write means share until you write: a snapshot or a branch costs nothing, and the first write to a shared block pays for a copy of that block.
article · Dinis CruzStreaming changes into a vault: a thousand small writes, one commit, every line attributed
Every change in a vault is a commit, and a commit is a tree rebuild, a signature and a compare-and-swap on one ref. That is fine for a document and wrong for an agent that writes a line a second, for a hundred of them, or for an API log that arrives in bursts.
The research documents, newest first
Pack mode, round 4: the fixes at c5b326f2
The fourth round: no release blockers left. Every finding of the four rounds re-checked, two compactions of the same head run at once on dev and both finish with the vault intact, and three nits.
workflowHow pack mode went from an article to a release, and the documents along the way
How pack mode went from a measured problem to a release in eight days: research before code, a spec reviewed before the build, tests on a counted host, a live trial, four verification rounds by a second agent, and the documents each step left behind.
referencePack mode — feature reference for 0.24.0
The CLI team's one-page reference for pack mode as released in sgit-ai 0.24.0: what it is and why, the commands, the host layout, compression, the numbers to quote, compatibility and the gate, the security model and the tests.
reviewPack mode, round 3: the fixes at 3f2c9bea
The third round: everything from round two fixed or accepted, both UX items fixed live, and one new data-loss path, caused by a round-two fix: an aborting compaction deleted a snapshot that another compaction had adopted. The fix was to delete two lines.
responseResponse to "Pack mode, round 3" (21 Oct 2026)
The answer to round three: the round-two clean-up was the bug, so an aborted compaction now leaves its snapshot; a 404 on an already archived pack is success; the gate exemption needs the hex form.
responseResponse to "Pack mode, verified again" (round 2, 21 Oct 2026)
The answer to round two: a clone chooses its snapshot by the branch head, a pack that names a member twice is refused whole, an aborted compaction takes its snapshot back, and the gate exemption checks every feature.
reviewPack mode, verified again: the fixes at 801b890c
The second round: six of the eight fixes hold, two are partial. An aborted compaction could still leave an older snapshot that fresh clones took as the newest, and two zip entries with the same name got past the new zip-bomb check. Checked live against sgit-ai 0.23.0 from PyPI.
responseResponse to "Pack mode, verified" (21 Oct 2026)
The CLI team's answer to the first verification round: all eight findings agreed and fixed with a test each, three more found in its own pass, and the how-to corrected.
reviewPack mode, verified: tests, a code review, and a live trial on dev
The first verification of pack mode, before release: the 4,511 tests, the tester's how-to run step by step on dev, a normal vault against a pack vault on the same server (a published 2,087-object vault cloned in 8.6 s against 28.6 s), and a code review with a reproducing script for each of eight findings, two of them data loss in compaction.
how-toHow to test pack mode (for an agent or a person, on a throwaway vault)
The CLI team's page for testing pack mode on throwaway vaults, step by step: create, push and pull between clones, compaction, the round trip, what to report and the known limits.
measurementPack mode: the round trip, built and measured
What was built for pack mode, how the round trip from a normal vault to a pack vault and back is tested, and every measurement: the synthetic request-count gates, the live trial with the comms vault's 33,000 objects (a 25 s clone against 3½ minutes), and the reviewer's numbers.
specSpec: pack mode for sgit (CLI-only, packs-only vaults, no server change)
The specification for pack mode: every push writes one zip pack, a snapshot pack compacts them, nothing is deleted, large packs go straight to S3 by presigned URL, and a gated packs-only vault needs no server change. Commands, layout, failure handling, tests and the four performance runs.
responseResponse to "Pack mode, round 4" (22 Oct 2026)
The answer to round four: no blockers, and the three nits done; "already gone" is decided by the status code, never by "404" inside a pack name.
briefBrief to the SG/Send team: append to a vault object on S3 without re-uploading it, and conditional completes
A brief to the SG/Send team: a presigned append route that grows a zip on S3 by UploadPartCopy, conditional completes with If-Match and If-None-Match, and size and ETag with the read URL. Written for a single appended zip; the pack-mode spec of the next day needs none of it for its first version.
coverage mapKeys the way git does them, PKI access to a vault, and copy-on-write: what is already published, and what is not
Before writing two articles, a map of what is already published on keys the way git does them, PKI access to a vault and copy-on-write: seven questions from the memo, where each stands, the facts the articles must not get wrong, and seven code questions for the thread.
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