| --- |
| 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. |
|
|
