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Free Space Map

Category: Dev Tools  ·  Sub-category: tools-misc  ·  Last updated:
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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).
Security AStatic scan found no risk patternsHow grading works ›

From the source SKILL.md

The Free Space Map tracks approximate free space per page in a relation, so INSERT and other appenders can find a target page without scanning. It's a fork of the relation (like the visibility map — a separate file at <relfilenumber>_fsm), organized as a tree over the heap's page numbers.

What this skill does

Free Space Map is a community-contributed Claude Code skill in the tools-misc sub-category. It ships as a SKILL.md file that Claude Code auto-discovers under ~/.claude/skills/free-space-map/ and loads when your prompt matches the skill's trigger.

Who uses this skill

The Free Space Map Claude Code skill is built for developers, power users, and teams automating repetitive workflows and improving developer experience. It's part of ClaudSkills (also referred to as Claude Skills or Claude Code Skills) — the open community-curated registry of 213,000+ SKILL.md files for Anthropic's Claude Code agent and the wider Claude ecosystem (Claude API, Claude Agent SDK).

How to install

Free

Manual install (2 steps)

mkdir -p ~/.claude/skills/free-space-map
curl -L https://claudskills.com/skills/free-space-map/SKILL.md \
  -o ~/.claude/skills/free-space-map/SKILL.md

Or just download SKILL.md directly and drop it into ~/.claude/skills/free-space-map/. Claude Code auto-discovers it on next session.

Skills live at ~/.claude/skills/free-space-map/SKILL.md on macOS/Linux, or %USERPROFILE%\.claude\skills\free-space-map\SKILL.md on Windows. See the full install guide for step-by-step instructions.

Telegram

📱 Install from your phone or desktop Telegram

Open @claudskills_bot on Telegram, tap Open Desktop App, and the desktop app installs this skill for you. Or share the bot link with a colleague — they get the same one-tap install. Learn more →

Pro

One-click install via the desktop app

The ClaudSkills desktop app installs any skill directly into ~/.claude/skills/ with one click — no terminal required. Pro starts at $9/mo or $149 lifetime.

Pro

For the full experience including quality scoring and one-click install features for each skill — upgrade to Pro.

See pricing → Download desktop app

Frequently asked questions

How do I install the Free Space Map Claude Code skill?
Install via the ClaudSkills desktop app (one click) or copy SKILL.md from the source repository to ~/.claude/skills/free-space-map/SKILL.md and restart Claude Code. Both flows are detailed at claudskills.com/install/.
What does the Free Space Map skill do?
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).
Is this skill free to install?
Yes. ClaudSkills is an open registry — every skill keeps its source repository's license, and manual install via copy is free. ClaudSkills Pro ($9/mo, $79/yr, or $149 one-time) adds one-click install via the desktop app and a multi-signal Quality Score.
When should I use the Free Space Map skill?
Use Free Space Map when your Claude Code task falls under the Dev Tools category — specifically in the tools misc area. Claude Code auto-discovers installed skills and invokes the right one based on the task description, so you can also ask Claude directly (e.g. "use Free Space Map" or describe the task and let Claude pick). Browse related skills at /category/tools/.
What is a Claude Code skill and how does the Free Space Map skill fit in?
A Claude Code skill is a SKILL.md file that lives under ~/.claude/skills/<name>/ and tells the Claude Code CLI agent how to perform a specific task (instructions, prompts, allowed tools). Skills are auto-discovered at session start. Free Space Map is one of 67,000+ skills indexed in the open ClaudSkills catalog, classified under the Dev Tools category. Learn more at /learn/what-is-a-claude-skill/.

Attribution & license

Cite this skill

If you reference this skill in a blog post, paper, or documentation, you can cite it as:

APA
matejformanek. (2026). Free Space Map [Claude Code skill]. ClaudSkills. https://claudskills.com/skills/free-space-map/
BibTeX
@misc{free-space-map-2026,
  author    = {matejformanek},
  title     = {Free Space Map [Claude Code skill]},
  year      = {2026},
  publisher = {ClaudSkills},
  url       = {https://claudskills.com/skills/free-space-map/}
}

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Security scan

Grade A · scanned 2026-11-01 — free static scan against the OWASP Agentic Skills Top 10.

No risk patterns were found in any of the ten OWASP-aligned categories. How grading works ›

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[![Security: A](https://img.shields.io/badge/Security-A-2e7d32)](https://claudskills.com/skills/free-space-map/#security)

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