Hotspots v1.18.0: Compact Storage

Hotspots accumulates one snapshot per commit. Over time .hotspots/snapshots/ grows without bound — prune removes snapshots for commits that fell off your branch, but it doesn’t help with long-lived main branches. v1.18.0 fixes that with two compaction levels and a --dry-run mode.

hotspots compact --level 1

Level 1 converts intermediate snapshots to delta encoding. It keeps the oldest snapshot and the N most-recent snapshots as full representations; everything in between becomes a diff from its chronological predecessor.

hotspots compact --level 1
hotspots compact --level 1 --dry-run   # preview savings without touching files

Snapshots written before this version are loaded transparently — the delta reconstruction happens on read, so diff and trends work unchanged against compacted history.

Results on the hotspots repo itself (45 snapshots):

Stage	Storage	Files
Before	20 MB	45 (0 delta)
After level 1	2.5 MB	45 (43 delta, 2 full)

87% reduction. Delta encoding is effective because most commits change a small fraction of functions — full snapshots duplicate the unchanged majority every time.

hotspots compact --level 2

Level 2 goes further: it drops snapshots entirely where no function’s risk band changed since the last kept snapshot. Only the oldest and newest snapshots are always retained; everything in between is kept only if at least one function moved between Low, Moderate, High, or Critical.

hotspots compact --level 2
hotspots compact --level 2 --dry-run

When a delta snapshot’s base is dropped by level 2, it’s automatically promoted to a full snapshot so remaining chains stay intact.

The right-sizing caveat: level 2 is most effective on stable, mature codebases where risk bands rarely move. On an actively-developed repo like hotspots itself, bands change on nearly every commit, so level 2 yields modest additional savings after level 1. On a quiet maintenance repo it can drop 80%+ of remaining snapshots.

--dry-run before you commit

Both levels support --dry-run, which measures projected savings without modifying any file:

$ hotspots compact --level 1 --dry-run
Dry-run: would convert 43 snapshot(s) to delta encoding
Estimated storage reduction: 19.0 MB

$ hotspots compact --level 2 --dry-run
Dry-run: would drop 4 snapshot(s) with no band changes
Estimated storage reduction: 1.8 MB

Backwards compatibility

Snapshots written before v1.18.0 may be missing fields added in later releases — the compact implementation loads and reconstructs these snapshots, so any missing optional field needed a serde default to avoid a deserialization failure. This release adds #[serde(default)] to CallGraphMetrics::is_entrypoint, which was the only non-optional field without one. Older snapshot stores load cleanly.

Upgrading

# Homebrew
brew upgrade hotspots

# Cargo
cargo install hotspots-cli

# Install script
curl -fsSL https://raw.githubusercontent.com/Stephen-Collins-tech/hotspots/main/install.sh | sh

Full changelog and source: github.com/Stephen-Collins-tech/hotspots