---
license: cc0-1.0
pretty_name: Internet Archive census (April 2016) — per-file md5+sha1
tags:
- file-hashes
configs:
- config_name: data
  data_files: data/census-*.parquet
- config_name: maps
  data_files: maps/md5.parquet
---

# Internet Archive census (April 2016) — per-file md5+sha1

The April 2016 [Internet Archive census](https://archive.org/details/ia_census_201604)
recorded md5 and sha1 for **every file of every public IA item** —
the only bulk file-hash inventory of the Archive ever published (the
census was not repeated; nothing uploaded after 2016-04-11 appears
here). This dataset is those two dumps joined — they are line-aligned
outputs of one item walk — into single witness rows co-observing both
digests, republished as page-indexed parquet for point lookups over
HTTP range reads.

Every row's claim URL exists by construction:
`https://archive.org/download/<identifier>/<filename>`
(filenames are stored percent-encoded, exactly as the census dumps
spell them — use them verbatim in URLs). Items can go dark after the
fact, so a claim is "this item *held* these bytes in April 2016", and
some URLs now 403.

Both digests are weak (md5, sha1): rows are corroboration and
crosswalk evidence, never byte-identity proof. Downstream tools
should render matches as "consistent with", not "is".
[hashdex](https://github.com/davidar/hashdex) does exactly that —
its scan reports census matches in a separate "consistent (sha1)"
tier.

**150,129,712 rows** across ~14.9M items; **129,730,596 distinct
sha1s** (equal to the md5→sha1 pair count: no sha1 in the corpus is
claimed by two md5s). Items' own `_meta.xml`/`_files.xml`/`.torrent`
sidecars (39.1M) are dropped as per-item plumbing; 496 rows with
malformed hash fields skipped.

## Layout

- `data/census-{0..f}.parquet` — sha1, md5, identifier, filename;
  **sorted by sha1**, sharded by its first nibble (~580 MB each).
- `maps/md5.parquet` — md5 → sha1, **sorted by md5** (5.4 GB).
- `ia-census.sha1.bloom` — DCSO membership filter over the distinct
  sha1s (p = 10⁻⁴, 311 MiB, UPPERCASE-hex keys); `hdx filters fetch
  ia-census` installs it so scans can route matching files here.

All parquet carries page indexes (zstd, no dictionaries, 128 KiB
pages): a point lookup over HTTP range reads fetches a few tens of
KB.

## Rebuild

`ia_census_parquet.py` in this repo streams the two census dumps
(11.3 GB, from the IA item above), zip-joins them with per-line
alignment checks, sorts one output file per sha1 nibble (DuckDB,
memory-bounded), and transcodes with page indexes in per-file
subprocesses (verified: sortedness, offset indexes, counts). The
bloom is built by hdx from the distinct sha1 column:

```
hdx filters build ia-census sha1 sha1_keys.txt
```

The source census is frozen — a rebuild is deterministic.

Census data by the Internet Archive and the 2016 census effort,
generously public; this compilation CC0.