---
license: mit
language:
- en
pretty_name: key-order
size_categories:
- n<1K
tags:
- postgres
- database
- benchmark
- uuid
- btree
configs:
- config_name: measurements
  data_files:
  - split: train
    path: out/measurements-pass*.jsonl
- config_name: reads
  data_files:
  - split: train
    path: out/reads-pass*.jsonl
- config_name: measurements_docker
  data_files:
  - split: train
    path: out-docker/measurements-pass*.jsonl
---

# key-order

Author: Dmitriy Semenkevich (dimhold)

This dataset is an independent replication of the cost of a random UUID primary key against ordered keys on Postgres: 3 key strategies (random uuid, uuid v7, bigint TSID) inserted into identical tables, with every batch timing and buffer counter.

Headline, from the repository: after three million rows the index on random keys has 49.8% leaf fragmentation and 66.7% leaf density, while the index on time ordered keys has 0% fragmentation and 90% density, on identical data. Reads cost the same: a point lookup answered in 236 us cold on both indexes.

This is a mirror. The canonical home is the Zenodo record and the GitHub repository; criteria, limitations and full tables live there.

- Paper: https://dimhold.by/papers/key-order/
- Code and full write up: https://github.com/dimhold/key-order
- DOI: https://doi.org/10.5281/zenodo.22128828

## Files

| path | what it is |
|---|---|
| `out/measurements-pass*.jsonl` | insert passes: per strategy sizes, `pgstatindex`, batch timings, settings |
| `out/reads-pass*.jsonl` | cold and warm point lookups with buffer counters |
| `out-docker/measurements-pass*.jsonl` | the same insert passes in Docker |

Files ending in `.jsonl` here are `.ndjson` in the GitHub repository, renamed so the viewer reads them; the content is unchanged.

## How it was produced

Keys are generated deterministically ahead of time into a source table identical for every strategy, `fsync` stays on and the strategy order alternates between passes. The disproof threshold was fixed before counting (`CRITERIA.md` in the repository). No model was involved. The scripts that turn these files into every number are in the GitHub repository.

## Licence

MIT, the licence of the repository, covering code and data.

## Citation

```bibtex
@misc{semenkevich2026keyorder,
  author = {Semenkevich, Dmitriy},
  title  = {key-order: what a random primary key costs on Postgres, an independent replication},
  year   = {2026},
  doi    = {10.5281/zenodo.22128828},
  url    = {https://doi.org/10.5281/zenodo.22128828}
}
```