ocas/.cards/garbage-collection.md

title, aliases, tags, related

title	aliases	tags	related
Garbage Collection	GC 垃圾回收	concept api	Variable Schema Store

Garbage Collection

OCAS uses mark-and-sweep garbage collection to reclaim storage from nodes that are no longer referenced.

Algorithm

1. Roots — all Variable values are roots
2. Mark — from each root, recursively walk() the DAG via Schema edges, marking every reachable node and its schema
3. Schema chain preservation — walk each reachable node's type chain upward to preserve the meta-schema hierarchy
4. Bootstrap preservation — self-referencing nodes (where type === hash) are always kept alive
5. Sweep — delete all unmarked nodes

ocas gc
# → { total, reachable, collected, scanned }

Key Properties

• Global — GC operates on the entire Store, not scoped to any variable prefix. Cross-reference between variables is valid and expected
• Schema-aware — the type (schema) of every reachable node is also marked as reachable, preventing orphaned schemas
• Safe — bootstrap nodes (the self-referencing meta-schema) are unconditionally preserved, so GC can never break the store's foundation
• Deterministic — same store state always produces the same GC result

What Stays Alive

A node survives GC if any of the following is true:

• A Variable points to it directly
• It is reachable via ocas_ref edges from a variable's value
• It is the schema (type) of any reachable node
• It is a self-referencing Bootstrap node