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Planner Cost Model

Category: Engineering  ·  Sub-category: backend  ·  Last updated:
PostgreSQL's cost model — how the planner estimates query cost to pick among candidate plans. Covers `src/backend/optimizer/path/costsize.c` (the cost functions: `cost_seqscan`, `cost_index`, `cost_bitmap_heap_scan`, `cost_nestloop`, `cost_mergejoin`, `cost_hashjoin`, `cost_sort`, `cost_hashagg`, `cost_windowagg`, etc.) plus the cost GUCs (`seq_page_cost`, `random_page_cost`, `cpu_tuple_cost`, `cpu_index_tuple_cost`, `cpu_operator_cost`, `parallel_setup_cost`, `parallel_tuple_cost`, `jit_*_cost`). Loads when the user asks about cost estimation, why a plan differs from expected, how to tune cost GUCs, what units the numbers are in, or when to touch a specific `cost_*` function. Skip when the ask is about selectivity estimation (that's `clauselist_selectivity` and extended-stats territory) or about the actual EXPLAIN output rendering.
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From the source SKILL.md

The planner generates many candidate Paths for a query. Each Path has a cost — a numeric estimate of how expensive it is to execute. The planner picks the cheapest.

What this skill does

Planner Cost Model is a community-contributed Claude Code skill in the backend sub-category. It ships as a SKILL.md file that Claude Code auto-discovers under ~/.claude/skills/planner-cost-model/ and loads when your prompt matches the skill's trigger.

Who uses this skill

The Planner Cost Model Claude Code skill is built for software engineers, backend developers, full-stack teams, and technical leads building and maintaining production systems. It's part of ClaudSkills (also referred to as Claude Skills or Claude Code Skills) — the open community-curated registry of 158,000+ 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/planner-cost-model
curl -L https://claudskills.com/skills/planner-cost-model/SKILL.md \
  -o ~/.claude/skills/planner-cost-model/SKILL.md

Or just download SKILL.md directly and drop it into ~/.claude/skills/planner-cost-model/. Claude Code auto-discovers it on next session.

Skills live at ~/.claude/skills/planner-cost-model/SKILL.md on macOS/Linux, or %USERPROFILE%\.claude\skills\planner-cost-model\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 Planner Cost Model Claude Code skill?
Install via the ClaudSkills desktop app (one click) or copy SKILL.md from the source repository to ~/.claude/skills/planner-cost-model/SKILL.md and restart Claude Code. Both flows are detailed at claudskills.com/install/.
What does the Planner Cost Model skill do?
PostgreSQL's cost model — how the planner estimates query cost to pick among candidate plans. Covers `src/backend/optimizer/path/costsize.c` (the cost functions: `cost_seqscan`, `cost_index`, `cost_bitmap_heap_scan`, `cost_nestloop`, `cost_mergejoin`, `cost_hashjoin`, `cost_sort`, `cost_hashagg`, `cost_windowagg`, etc.) plus the cost GUCs (`seq_page_cost`, `random_page_cost`, `cpu_tuple_cost`, `cpu_index_tuple_cost`, `cpu_operator_cost`, `parallel_setup_cost`, `parallel_tuple_cost`, `jit_*_cost`). Loads when the user asks about cost estimation, why a plan differs from expected, how to tune cost GUCs, what units the numbers are in, or when to touch a specific `cost_*` function. Skip when the ask is about selectivity estimation (that's `clauselist_selectivity` and extended-stats territory) or about the actual EXPLAIN output rendering.
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 Planner Cost Model skill?
Use Planner Cost Model when your Claude Code task falls under the Engineering category — specifically in the backend 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 Planner Cost Model" or describe the task and let Claude pick). Browse related skills at /category/engineering/.
What is a Claude Code skill and how does the Planner Cost Model 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. Planner Cost Model is one of 67,000+ skills indexed in the open ClaudSkills catalog, classified under the Engineering 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). Planner Cost Model [Claude Code skill]. ClaudSkills. https://claudskills.com/skills/planner-cost-model/
BibTeX
@misc{planner-cost-model-2026,
  author    = {matejformanek},
  title     = {Planner Cost Model [Claude Code skill]},
  year      = {2026},
  publisher = {ClaudSkills},
  url       = {https://claudskills.com/skills/planner-cost-model/}
}

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Browse all Engineering skills → Top 100 skills
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