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MCPg - Production-grade PostgreSQL MCP Server

MCPg - Production-grade PostgreSQL MCP Server

by devopam
OverviewSchemaSourceRelated ServersDiscussionsAdmin
Python
Hybrid

List prewarmed relations

list_prewarmed_relations
Read-only

Reports shared-buffer residency per relation, ranked by cached blocks, so you can identify prewarmed tables and dirty pages.

Instructions

Report current shared-buffer residency per relation, ranked by blocks-cached descending. Requires the pg_buffercache extension; returns an empty list when it's missing. Returns a list of objects with schema, table, blocks_cached (8 KiB pages currently in shared buffers), total_blocks (the relation's on-disk size in the same unit), pct_cached (the residency ratio rounded to 2 decimals), and dirty_blocks (pages with pending writes).

Example: list_prewarmed_relations(schema='public', limit=50)

Tool call template

This tool declares no required parameters. Add optional parameters from the input schema as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {},
    "name": "list_prewarmed_relations"
  }
}

Input Schema

NameRequiredDescriptionDefault
limitNo
schemaNo
databaseNoOptional: a database id from list_databases, to target a configured secondary (read-only) database; omit for the primary. Database names that are not configured ids are rejected.

Output Schema

NameRequiredDescriptionDefault
resultYes

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed1 schema field changedv0.8.4
    • changedInput schema / properties / database / description
      Previous value: -"Optional: target a configured secondary (read-only) database by name; omit for the primary. Call list_databases to see the configured ids."New value: +"Optional: a database id from list_databases, to target a configured secondary (read-only) database; omit for the primary. Database names that are not configured ids are rejected."
  2. First observedv0.6.8

TDQS

A3.8/5.0
Behavior4/5

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

Annotations already declare readOnlyHint=true and openWorldHint=false, and the description adds real value on top: the pg_buffercache dependency, graceful degradation to an empty list, the sort order, and the unit (8 KiB pages) for the block counts. It does not mention cost on large catalogs, but nothing required is missing or contradicted.

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

Conciseness5/5

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

Three tightly packed sentences plus a one-line example, front-loaded with the core action and sort order. Every sentence adds new information — dependency, degradation behavior, field semantics — with no restatement of the name.

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

Completeness4/5

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

An output schema exists, so enumerating return fields is a bonus rather than a necessity, and the description covers the extension requirement and failure mode that the schema cannot express. The remaining gap is the unspecified `limit` semantics, which matters for a tool with a default of 100 rows.

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

Parameters3/5

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

Schema description coverage is only 33% (only `database` is documented), so the description must compensate for `limit` and `schema`. It does so partially: the example shows `schema='public'` and `limit=50`, implying filtering and top-N truncation, but it never states that `limit` caps row count or that `schema` is an exact-match filter.

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

Purpose4/5

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

States a specific verb and resource (report shared-buffer residency per relation) plus a defined ordering (blocks-cached descending), which lets an agent distinguish it from a plain buffer-cache dump. It never names the closely related siblings (read_pg_buffercache_relations, read_pg_buffercache_summary, recommend_prewarm_targets), so the differentiation is implied rather than explicit.

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

Usage Guidelines3/5

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

The extension prerequisite and the empty-list-when-missing behavior give useful preconditions for calling it. However there is no explicit when-to-use guidance against the many sibling cache/prewarm tools, so the agent must infer that this is for per-relation residency rather than summary or recommendation workflows.

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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