cancelQuery · Postgresql MCP: Risk & Policy

WHAT IT DOES

What cancelQuery does on Postgresql

AI agents invoke cancelQuery to trigger actions in Postgresql. What it does depends on the arguments the agent supplies, and its effects often reach beyond the immediate call — builds kicked off, notifications sent, workflows started.

WHY IT NEEDS A POLICY

Why cancelQuery needs a policy

Canceling a query sends an interrupt signal to a running database process, which is an external operation with side effects (stopping execution). It is not purely destructive (data is not deleted) nor a read operation. It falls under Execute as it triggers an external operation (SIGINT/pg_cancel_backend) that affects a running process.

From the tool's definition Cancel a running query by its process ID (PID)... This sends a cancel signal — the query may take a moment to actually stop.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

cancelQuery Rate-limited

cancelQuery stays usable, but rate-capped — a runaway agent can't fire it dozens of times a minute. Everything else on the server is denied unless you say otherwise.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "cancelQuery": {
      "limits": [
        {
          "counter": "cancelquery_rate",
          "window": "minute",
          "max": 10,
          "scope": "grant"
        }
      ]
    }
  }
}

RATE-LIMIT THIS TOOL →

Instant setup, no code required.

PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches Postgresql, so you can run agents against it safely.

FAQ

Questions about cancelQuery

What does the cancelQuery tool do? +

Cancel a running query by its process ID (PID). Use getActiveQueries first to find the PID. This sends a cancel signal — the query may take a moment to actually stop. Does NOT terminate the connection. It is categorised as a Execute tool in the Postgresql MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on cancelQuery? +

Register the Postgresql MCP server in PolicyLayer and add a rule for cancelQuery: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches Postgresql. Nothing to install.

What risk level is cancelQuery? +

cancelQuery is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.

Can I rate-limit cancelQuery? +

Yes. Add a rate_limit block to the cancelQuery rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.

How do I block cancelQuery completely? +

Set action: deny in the PolicyLayer policy for cancelQuery. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.

What MCP server provides cancelQuery? +

cancelQuery is provided by the Postgresql MCP server (vnikhilbuddhavarapu/postgresql-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.