Free Space Map | Agent Skills Atlas

About this skill

PostgreSQL's Free Space Map (FSM) — the tree-of-pages that tracks per-heap-page free space so INSERT / COPY / heapmultiinsert can find a page with room without scanning the whole relation. Covers src/backend/storage/freespace/ (freespace.c + fsmpage.c + indexfsm.c), the tree layout (leaf-page nodes + 2 upper levels), category encoding (bucketed free-byte counts), the FSM lock discipline, VACUUM's post-scan FreeSpaceMapVacuum, and index FSM's simpler use case. Skip when the ask is about visibility map (VM — sibling but different subsystem) or about pgfreespacemap contrib module (that's the SQL introspection wrapper).

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Automated security scan: Partial

Only SKILL.md was scanned. Supporting files and scripts were not checked. No safety grade has been assigned.

0 potential findings · Scanned 11/4/2026 · Scanner 0.2.1

Content SHA-256: 4d3aede718ae45afdf85c7f117dc5647faf0adfc513a470750e8b81f53f49607

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Original listing metadata

Original name

free-space-map

Original description

PostgreSQL's Free Space Map (FSM) — the tree-of-pages that tracks per-heap-page free space so `INSERT` / `COPY` / `heap_multi_insert` can find a page with room without scanning the whole relation. Covers `src/backend/storage/freespace/` (`freespace.c` + `fsmpage.c` + `indexfsm.c`), the tree layout (leaf-page nodes + 2 upper levels), category encoding (bucketed free-byte counts), the FSM lock discipline, VACUUM's post-scan `FreeSpaceMapVacuum`, and index FSM's simpler use case. Skip when the ask is about visibility map (VM — sibling but different subsystem) or about `pg_freespacemap` contrib module (that's the SQL introspection wrapper).

About this listing

Category: Developer tools
Reported license: PostgreSQL
Listing language (estimated): English
Review status: Not individually reviewed
Agent compatibility: Atlas installation supports Claude Code, Codex, and Cursor. Skill-specific dependencies and features are checked during setup.