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MCPg - Production-grade PostgreSQL MCP Server

Recommend index drops

recommend_index_drops
Read-only

Identifies large, unused or rarely used indexes and generates DROP INDEX CONCURRENTLY statements to reduce storage and write overhead.

Instructions

Sibling of recommend_indexes for indexes to remove. Walks pg_stat_user_indexes + pg_stat_user_tables for existing indexes that look like pure cost — large on disk but never (or barely) scanned. Three reason codes, descending strength: never_used (no recorded idx_scans since the last stats reset — candidate for drop, but verify before removal), scan_no_fetch (planner picks it but it returns no rows — usually existence-check pattern), rarely_used (scan rate below low_scan_ratio of the table's total scan activity). Primary-key / unique / exclusion-constraint indexes are excluded (dropping those would be a schema change, not a performance win); indexes below min_index_size_bytes are skipped too. Returns a ready-to-run DROP INDEX CONCURRENTLY statement per candidate. Read-only advisor — execution is on the operator.

Example: recommend_index_drops(schema='public', min_index_size_bytes=1000000, low_scan_ratio=0.01)

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
schemaNo
databaseNoOptional: target a configured secondary (read-only) database by name; omit for the primary. Call list_databases to see the configured ids.
low_scan_ratioNo
min_index_size_bytesNo

Output Schema

TableJSON Schema
NameRequiredDescriptionDefault
resultYes
Behavior5/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Describes internal logic: walks `pg_stat_user_indexes` and `pg_stat_user_tables`, uses three reason codes. States it is read-only. Does not contradict annotations (readOnlyHint=true).

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Detailed with example, but slightly lengthy. Every sentence adds value. Good structure: purpose, logic, exclusions, return, example.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given output schema exists, description covers the tool's purpose, behavior, and return type adequately. Provides enough information for an AI agent to understand and use the tool correctly.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Adds meaning to `low_scan_ratio` and `min_index_size_bytes` in context, with an example usage. However, the `schema` parameter is not described, and schema coverage is low (25%). Overall helpful but not exhaustive.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states it is a sibling of `recommend_indexes` for index removal, explaining it walks system catalogs to find large, rarely-scanned indexes. This distinguishes it from the sibling by focusing on drops.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Provides clear context for when to use: to identify drop candidates. Exclusions are listed (PK/unique, small indexes). Read-only nature noted. Could be more explicit about when not to use, but the reason codes guide the user.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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