Connection pool becomes exhausted after query timeouts with token-bound DB config

[SinMayFly]

Bug Description

When running doris-mcp-server in Docker with HTTP transport and token authentication enabled, the MCP server works initially but becomes unusable after running for some time.

After several query timeouts, later tool calls start failing with:

Failed to acquire connection from token pool:
Failed to get connection for authenticated token. This is a security measure to prevent using default high-privilege credentials. Error:

The server process itself is still alive and /health may still respond, but MCP tool calls cannot reliably acquire Doris connections anymore.

Environment

• Deployment: Docker image
• Transport: Streamable HTTP
• Auth: token auth enabled
• Database: Apache Doris
• Token-bound database config: enabled
• Server version: v0.6.x based on the current Docker image/release

Observed Logs

The sequence observed in production logs is:

Query execution failed: Query timeout after 30 seconds
Session mcp_session: Failed to acquire connection from token pool:
Session mcp_session: Token pool error:
Query execution failed for session mcp_session: Failed to get connection for authenticated token. This is a security measure to prevent using default high-privilege credentials. Error:

This pattern repeats after the first few timeouts. There are also frequent MCP ping requests:

Processing request of type PingRequest
Database configuration validated successfully for token ... (source: token-bound)

Expected Behavior

A query timeout should not corrupt, occupy, or exhaust the token-specific connection pool. Later requests should still be able to acquire healthy connections.

Suspected Cause

DorisQueryExecutor._execute_query_internal() wraps the whole DB execution with asyncio.wait_for().

When a timeout occurs, the coroutine is cancelled, but the underlying MySQL/Doris query may still be running or the aiomysql connection may be left in an unsafe state.

DorisConnectionManager.execute_query() then releases the same connection back to the token pool in finally, which may return a cancelled, busy, or broken connection to the pool. Over time this appears to exhaust or poison the token pool.

Relevant code areas:

• doris_mcp_server/utils/query_executor.py
  • asyncio.wait_for(self.connection_manager.execute_query(...), timeout=...)
• doris_mcp_server/utils/db.py
  • execute_query(...)
  • release_connection_for_token(...)

Suggested Fix

1. When query execution is cancelled or times out, close/discard the underlying DB connection instead of releasing it back to the pool.
2. Improve acquire timeout logging by including exception type, since asyncio.TimeoutError string is empty.
3. Avoid validating token-bound database connectivity on every MCP ping request. Add a short TTL cache for token DB config validation.
4. Consider reducing or sanitizing request header logs, especially Authorization.

Additional Compatibility Issue

In the same environment, resource metadata queries may fail with:

Unknown column 'table_comment' in 'table list'

The query against information_schema.tables.table_comment may not be compatible with all Doris versions/configurations. A fallback or compatible metadata query would help.