# Reclaim

How the vacuum finds versions nobody can reach and gives their space back, without ever deleting something still referenced.

The vacuum deletes by reachability, never by age. One command reports, one command sweeps, and policy blockers are checked before any deletion. A later I/O error can leave a partial sweep.

## The problem

An append-only store that never reclaims grows with every write, including every rewrite of the same record. Reclaim is what makes append-only affordable.

## Reachability, not age

The vacuum walks from every durable pin: the branch heads, the retained snapshots, and any reference directory you name. Everything it reaches is kept. Everything else is the deletion set.

## Two commands

`stats` reports. It enumerates the store strictly, walks reachability, and tells you what is live and what is reclaimable. It deletes nothing.

`vacuum --dry-run` runs the whole pass and reports the deletion set without removing anything. `vacuum --sweep` removes exactly that set. Any policy blocker refuses before deletion. A failure during unlinking is reported with the progress reached.

**Terminal**

```bash
haematite vacuum /var/lib/haematite/ward --dry-run
```


> Pins outside the store
> If another process keeps snapshots or references outside the data directory, name them on the command line. A pin the vacuum cannot see is a pin it cannot honour.


The step-by-step is in [Storage and vacuum](/haematite/operations/storage-and-vacuum/).