Crates / memmap2
Rust crate · real downloads · data Oct 24, 2026
memmap2 downloads, and should you depend on it?
Cross-platform Rust API for memory-mapped file IO crates.io · docs · repository
Owned on crates.io by tbu-, RazrFalcon, de-vri-es, allan2 · alternatives · is it still maintained?
Widely used and steady.
memmap2: 2,487 crates depend on it; downloads jump on release days (1.9x the baseline).
How this verdict is decided (4 rules)
- Usage: crates.io reverse dependencies (crates that list it as a dependency): 10,000+ = foundational, 1,000+ = widely used, 100+ = established, under 100 = few direct dependents.
- Direction: the median quiet day in the last 30 days of the window against the first 30, read against the median tracked crate (the whole field moved +39% from late summer to October, so a raw trend says nothing). 10%+ ahead of the field = gaining; 10%+ behind = losing ground; otherwise steady. Steady with no release in 2+ years = quiet for years.
- Release spikes: the median release-window day against the quiet-day baseline: under 1.15x = no spike, 1.15x to 1.3x = small bumps, 1.3x or more = jumps on release days.
- Release recency: days since the newest version that was not yanked, from crates.io publish times.
release window (release day + next day)quiet dayquiet-day median · download the 89 days as CSV
The numbers in one paragraphmemmap2 got 97,546,018 crates.io downloads from Jul 27, 2026 to Oct 23, 2026. 4% of them landed within 2 days of one of its 1 release. On the other 87 quiet days it got a median of 1,039,105 a day, about 7,273,735 a week. Capping release days at that baseline leaves 95,744,646 release-adjusted downloads for the window.
What this means if you're choosing a dependency
- Well trodden. 2,487 crates depend on it, so common problems tend to have public answers and breaking changes get noticed fast.
- Actively released. 0.9.12 shipped 3 days ago (Oct 21, 2026).
- Still pre-1.0 (0.9.12). Under Cargo's semver rules a 0.x minor bump may break you, so pin the minor version (
memmap2 = "0.9") and read the changelog on upgrades. - Fit check: license MIT OR Apache-2.0, edition 2021, needs Rust 1.65 or newer (from the latest version's manifest).
- Compare it by the baseline, not the raw count. 4% of its 97,546,018 downloads in the window landed within 2 days of a release; the steady number is 1,039,105 a day.
Alternatives that do a similar job
Crates that share its crates.io category or keywords, most similar first. Each line is the crate's own description, then how it compares on the same data.
Its place in the dependency graph
Built on memmap2
2 of the 1000 crates we track depend on it directly (biggest first).
memmap2 builds on
Tracked crates its latest version (0.9.12) depends on (optional ones marked).
What the chart says
- Weekend quiet days ran at 61% of weekday quiet days (715,993 vs 1,181,718). A dip that deep is the signature of work-week CI pipelines and developers building on weekdays.
- Biggest day: 1,994,442 on Oct 22, 2026, inside a release window.
Every number
| All-time downloads | 391,355,448 (rank #343 on crates.io by all-time downloads) |
| Downloads in the window | 97,546,018 (Jul 27, 2026 to Oct 23, 2026, 89 days) |
| Within 2 days of a release | 3,879,582 (4.0%) |
| Quiet-day median (baseline) | 1,039,105 a day; weekdays 1,181,718, weekends 715,993 |
| Release-adjusted downloads | 95,744,646 (release-window days capped at the baseline) |
| Baseline rank | #369 of the 1000 crates we track |
| Quiet-day trend | +45% raw, +5% against the median tracked crate (+39%) |
| Releases in the window | 1 |
| Versions published, ever | 37 |
| Latest version | 0.9.12, published Oct 21, 2026 (license MIT OR Apache-2.0, edition 2021, MSRV 1.65) |
| First published | Jan 18, 2020 |
| Reverse dependencies | 2,487 |
Releases in the window
Each one opens a 2-day release window on the chart.
| Version | Published | Downloads that version got (lifetime) |
|---|---|---|
| 0.9.12 | Oct 21, 2026 | 328,626 |
How we compute this
crates.io counts every download, including CI runners, mirrors and bots that fetch each new version, so raw counts run high (why, in The Manual). We split the last 89 days into release windows (the day a version of memmap2 was published, plus the next day) and quiet days, and use the median quiet day as the baseline: an upper bound on steady use, never a head count. The method and data come from our study of 90 days of crates.io data from 69 crates, featured in This Week in Rust #674; check any crate live with the real-downloads checker.
Badge for your README
Maintainers can show the baseline in a README. It is optional, updates when we refresh the data, and links back here. Preview, then copy:
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Categories
Sources
- Daily downloads: crates.io API, /crates/memmap2/downloads (last 90 days, all versions), fetched Oct 24, 2026.
- Versions and publish times: crates.io API, /crates/memmap2/versions, same fetch.
- Reverse dependencies: crates.io reverse dependencies, same fetch. Dependency edges between tracked crates: each crate's default version, crates.io API.
- Fetched politely (one request every 2 seconds, identified User-Agent) per the crates.io data access policy. Data is crates.io's; the release-window split, baseline and verdict rules are ours, CC BY 4.0.
Up next
Next by real downloads: The next crate down the real-downloads ranking: 1,036,052 a day. Widely used and gaining.hkdfRust crate. HMAC-based Extract-and-Expand Key Derivation Function (HKDF). Real use: 1M downloads a day on quiet days; 1,202 crates depend on it.Read it next →Also worth your time