coldkeep

module
v0.6.0 Latest Latest
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 Go to latest Published: Mar 22, 2026 License: Apache-2.0

README

coldkeep

CI Go Version License Status Release

Status: Experimental research project.
Not production-ready. Do not use for real or sensitive data.
On-disk format and APIs may change before v1.0.

coldkeep is a content-addressed storage engine for cold data.

It splits files into content-defined chunks, deduplicates them using SHA-256, and stores them in append-only container files with database-backed metadata.

coldkeep guarantees deterministic, byte-identical restore of stored data, validated by end-to-end hashing and resilient across garbage collection and restart/recovery.

The system prioritizes correctness, determinism, and recoverability over performance or feature completeness.

What it does (today)

  • Store files or folders by splitting them into content-defined chunks.
  • Deduplicate chunks using SHA-256 (content-addressed storage).
  • Pack chunks into container files up to a configurable maximum size.
  • Restore files by reconstructing them from stored chunks.
  • Guarantee byte-identical restore outputs (verified by SHA-256).
  • Use an append-only container model for deterministic and safe writes.
  • Remove logical files (decrementing chunk reference counts).
  • Run garbage collection to remove unreferenced chunks safely.
  • Recover from interrupted operations on startup.
  • Provide storage statistics and container health information.
  • Perform multi-level integrity verification (metadata, container structure, and full data integrity).

Verification

coldkeep provides a multi-level integrity verification system to ensure consistency and detect corruption across metadata and stored data.

Levels

  • Standard

    • Validates metadata integrity
    • Checks reference counts, chunk ordering, and orphan records

  • Full

    • Includes all standard checks
    • Verifies container files exist and match recorded sizes
    • Validates container hashes and chunk-to-container consistency

  • Deep

    • Includes all full checks
    • Reads container data and recomputes chunk hashes
    • Detects physical data corruption at the byte level
Usage

Verify the entire system:

coldkeep verify system --level standard
coldkeep verify system --level full
coldkeep verify system --level deep

Verify a specific file:

coldkeep verify file <file_id> --level standard
coldkeep verify file <file_id> --level full
coldkeep verify file <file_id> --level deep
Notes

Deep verification performs full reads of container files and may be slow.
Recommended for periodic integrity audits rather than frequent execution.

Deterministic restore guarantees (v0.5)

Coldkeep v0.5 guarantees deterministic restore at the logical file level.

Current integration coverage validates:

  • deterministic stored logical files under deduplication
  • byte-identical restore outputs verified by SHA-256
  • consistent restore behavior after GC and restart/recovery
  • deterministic results across representative and edge-case datasets

This guarantee applies to logical files and dataset-level workflows.

Coldkeep does not yet define a first-class contract for restoring full directory trees with exact original layout. Current tests restore logical files individually rather than reconstructing folder structure.

Design sketch

Core tables:

  • logical_file
    User-visible file entry (name, size, file_hash).

  • chunk
    Content-addressed chunk (chunk_hash, size, ref_count, container_id, offset).

  • file_chunk
    Ordered mapping between logical files and chunks.

  • container
    Physical container file storing chunk data.

Containers are stored on disk under:

storage/containers/

Containers follow an append-only write model.

Lifecycle states:

  • logical_file: PROCESSING → COMPLETED → ABORTED
  • chunk: PROCESSING → COMPLETED → ABORTED

These states allow coldkeep to detect interrupted operations and recover safely on startup.

Project structure

coldkeep/
│
├─ cmd/
│   └─ coldkeep/          # CLI entrypoint
│
├─ internal/
│   ├─ chunk/             # chunking logic
│   ├─ container/         # container format + management
│   ├─ db/                # database helpers
│   ├─ listing/           # file listing operations
│   ├─ maintenance/       # gc, stats, verify_command
│   ├─ recovery/          # system recovery logic
│   ├─ storage/           # store / restore / remove pipeline
│   ├─ utils_env/         # env helpers
│   ├─ utils_print/       # print helpers
│   └─ verify/            # verification logic
│
├─ tests/                 # integration tests
├─ scripts/               # smoke / development scripts
├─ db/                    # database schema
│
├─ docker-compose.yml
├─ go.mod
└─ README.md

Quickstart

A small samples/ folder is included for testing.

🐳 Local development (With Docker)

Start services:

docker compose up -d --build

Store a sample file:

docker compose run --rm -v "$PWD/samples:/samples" app store /samples/hello.txt

Store the sample folder:

docker compose run --rm -v "$PWD/samples:/samples" app store-folder /samples

List stored files:

docker compose run --rm app list

Restore a file:

docker compose run --rm app restore 1 _out.bin

Show stats:

docker compose run --rm app stats

Run garbage collection:

docker compose run --rm app gc

💻 Local development (without Docker)

Start Postgres (example):

docker compose up -d postgres

Build the CLI:

go build -o coldkeep ./cmd/coldkeep

Store the sample folder:

./coldkeep store-folder samples

List stored files:

./coldkeep list

Restore a file:

./coldkeep restore 1 restored.bin

Show stats:

./coldkeep stats

Run GC:

./coldkeep gc

Configuration

Database configuration is read from environment variables
(see docker-compose.yml for defaults).

Storage is written to:

./storage/

During development you can safely delete this directory.

Additional environment variables used in development:

  • COLDKEEP_STORAGE_DIR
  • COLDKEEP_SAMPLES_DIR

Known limitations

Crash recovery

coldkeep includes a crash recovery model based on lifecycle states.

Operations use explicit states (PROCESSING, COMPLETED, ABORTED) to detect and handle interrupted operations safely.

On startup the system:

  • marks stale PROCESSING rows as ABORTED
  • prevents incomplete chunks from being reused
  • allows safe retries of interrupted operations

This model ensures that partially written data does not corrupt the logical state of the system.

In v0.6, the append-only container model further simplifies recovery by eliminating in-place mutations of container data.

However, the system is still experimental and full transactional guarantees across filesystem and database layers are not yet complete.

Use only with disposable test data.

Container compression

Whole-container compression has been removed in v0.6.

Future versions may introduce block-level compression.

Concurrency & integrity

Concurrency support has been significantly improved in v0.6, including locking and retry mechanisms.

However, it is still evolving and not yet optimized for extreme parallel workloads.

Security

See SECURITY.md.

This is an experimental research project

Do not use for real or sensitive data

Development

Build

go build -o coldkeep ./cmd/coldkeep

Tests

Run all tests:

go test ./...

Integration tests live under:

tests/

and require a running PostgreSQL instance.

Smoke test

scripts/smoke.sh runs a full end-to-end workflow : using the samples/ directory.

store → stats → list → restore → dedup check.

Local
docker compose up -d postgres
go build -o coldkeep ./cmd/coldkeep
bash scripts/smoke.sh
Docker
docker compose up -d postgres

docker compose run --rm \
  -e COLDKEEP_SAMPLES_DIR=/samples \
  -e COLDKEEP_STORAGE_DIR=/tmp/coldkeep-storage \
  -v "$PWD/samples:/samples" \
  --entrypoint bash \
  app scripts/smoke.sh

Roadmap

Coldkeep follows a risk-reduction approach, where each release removes a class of failure until the system becomes fully trustworthy.

  • v0.2 — Crash Consistency Foundation
    Eliminate DB ↔ filesystem divergence and ensure safe recovery after crashes.

  • v0.3 — Safe Garbage Collection
    Guarantee that GC cannot remove referenced data.

  • v0.4 — Integrity & Verification Layer
    Enable full-system verification and corruption detection.

  • v0.5 — Deterministic Restore Guarantees
    Ensure byte-identical, reproducible restore across GC and restart.

  • v0.6 — Storage Model Evolution
    Introduce an append-only container model, remove legacy compression, and improve concurrency coordination as a foundation for future block abstraction and encryption.

  • v0.7 — Block Abstraction & Encryption Foundations
    Introduce block-level structure to enable partial reads, compression, and encryption in a controlled and extensible way.

  • v0.8 — Simulation & CLI Stabilization
    Add simulation capabilities for storage planning and define a stable command-line interface.

  • v0.9 — Internal Hardening
    Improve reliability, simplify internals, and finalize implementation details.

  • v1.0 — Storage Engine Stable
    Coldkeep becomes a trustworthy storage engine for real cold backups.

Contributing

Contributions and discussion are welcome.

See CONTRIBUTING.md.

License

Apache-2.0. See LICENSE

Directories

Path Synopsis
cmd
coldkeep command
internal
chunk
container
db
listing
maintenance
recovery
storage
utils_env
utils_hash
utils_print
verify

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