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MCPg - Production-grade PostgreSQL MCP Server

MCPg - Production-grade PostgreSQL MCP Server

by devopam
OverviewSchemaSourceRelated ServersDiscussionsAdmin
Python
Hybrid

Read PG stat lock

read_pg_stat_lock
Read-only

Read per-lock-type acquire, wait, and wait-time counters from PostgreSQL 19's pg_stat_lock view to diagnose lock contention and track activity since the last statistics reset.

Instructions

Return every row from PG 19's pg_stat_lock view (per-lock-type acquire / wait / wait-time counters since the most recent pg_stat_reset). Empty list on PG < 19 or when the view isn't present. Returns a list of objects with lock_type (relation / page / tuple / xid / virtualxid / advisory / ...), acquires, waits, and wait_time_us.

Example: read_pg_stat_lock()

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": "read_pg_stat_lock"
  }
}

Input Schema

NameRequiredDescriptionDefault
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, so safety is covered; the description goes further by disclosing the version-gated failure mode ('empty list on PG < 19 or when the view isn't present') and the reset-relative window of the counters. That is exactly the kind of context annotations cannot express. It stops short of noting privilege requirements or whether the counters are cluster-wide or per-database.

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?

Two compact sentences plus a trivial example. Purpose is front-loaded, the version caveat and return shape follow, and every clause carries information an agent needs. No filler.

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?

For a single-optional-param read tool with full annotation coverage and an output schema, this is nearly complete: it covers scope, version fallback, and counter semantics. Minor gap is scope granularity (whether results are per-database or server-wide) given the `database` parameter, but that is small.

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 100%, and the sole `database` parameter is fully documented in the schema including the configured-id restriction. The description adds nothing about that parameter, so the baseline 3 applies.

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 ('Return every row from PG 19's pg_stat_lock view') and pins down the data model: per-lock-type acquire/wait/wait-time counters. That counter-based, cumulative semantics implicitly separates it from the current-lock listing siblings (list_locks, find_blocking_chains), though it never names them explicitly.

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?

Usage is implied rather than prescribed: the 'since the most recent pg_stat_reset' phrasing tells an agent this is for cumulative lock statistics, not live contention. There is no explicit when-to-use vs. when-not, and no alternative named for troubleshooting active blocking, which is what list_locks and find_blocking_chains exist for.

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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