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Client connection reuse and server-side query cancellation #152

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84700dd
add client conn reuse and server-side query cancellation
joe-clickhouse Mar 25, 2026
8634304
linting
joe-clickhouse Mar 26, 2026
8ead304
Merge remote-tracking branch 'origin/main' into joe/client-reuse-impr…
joe-clickhouse Apr 21, 2026
23673e7
harden client reuse and query cancellation
joe-clickhouse Apr 22, 2026
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11 changes: 11 additions & 0 deletions CHANGELOG.md
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Expand Up @@ -4,6 +4,17 @@ All notable changes to this project will be documented in this file.

## Unreleased

### Added
- Client connection reuse across tool calls via a config-keyed cache, eliminating per-call connection overhead. ([#152](https://github.com/ClickHouse/mcp-clickhouse/pull/152))
- Server-side query cancellation: timed-out queries now issue `KILL QUERY` on the ClickHouse server instead of leaving zombie workers consuming threads and server resources. ([#152](https://github.com/ClickHouse/mcp-clickhouse/pull/152))
- `CLICKHOUSE_MCP_MAX_WORKERS` environment variable to configure the query worker thread pool size (default: `10`). ([#152](https://github.com/ClickHouse/mcp-clickhouse/pull/152))

### Changed
- `CLICKHOUSE_SEND_RECEIVE_TIMEOUT` is now auto-capped to `CLICKHOUSE_MCP_QUERY_TIMEOUT + 5` unless explicitly set, so HTTP reads unblock shortly after an MCP timeout fires. ([#152](https://github.com/ClickHouse/mcp-clickhouse/pull/152))

### Fixed
- Session config overrides from PR #115 are now resolved on the request thread where the FastMCP context is available, so overrides are correctly applied to queries dispatched to the worker pool. ([#152](https://github.com/ClickHouse/mcp-clickhouse/pull/152))

## 0.3.0 - 2026-04-14

### Added
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13 changes: 9 additions & 4 deletions README.md
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Expand Up @@ -496,9 +496,9 @@ The following environment variables are used to configure the ClickHouse and chD
* `CLICKHOUSE_CONNECT_TIMEOUT`: Connection timeout in seconds
* Default: `"30"`
* Increase this value if you experience connection timeouts
* `CLICKHOUSE_SEND_RECEIVE_TIMEOUT`: Send/receive timeout in seconds
* Default: `"300"`
* Increase this value for long-running queries
* `CLICKHOUSE_SEND_RECEIVE_TIMEOUT`: Send/receive timeout in seconds for the underlying HTTP connection
* Default: automatically set to `CLICKHOUSE_MCP_QUERY_TIMEOUT + 5` so worker threads unblock shortly after a query timeout
* If explicitly set, the value is used as-is (e.g. `"300"` for long-running queries)
* `CLICKHOUSE_DATABASE`: Default database to use
* Default: None (uses server default)
* Set this to automatically connect to a specific database
Expand All @@ -512,9 +512,14 @@ The following environment variables are used to configure the ClickHouse and chD
* `CLICKHOUSE_MCP_BIND_PORT`: Port to bind the MCP server to when using HTTP or SSE transport
* Default: `"8000"`
* Only used when transport is `"http"` or `"sse"`
* `CLICKHOUSE_MCP_QUERY_TIMEOUT`: Timeout in seconds for SELECT tools
* `CLICKHOUSE_MCP_QUERY_TIMEOUT`: Timeout in seconds for query tool calls
* Default: `"30"`
* Increase this if you see `Query timed out after ...` errors for heavy queries
* When a query times out, the server issues a `KILL QUERY` on the ClickHouse server to cancel it
* Unless `CLICKHOUSE_SEND_RECEIVE_TIMEOUT` is explicitly set, the HTTP read timeout is automatically aligned to this value plus a small buffer, so worker threads unblock shortly after a timeout
* `CLICKHOUSE_MCP_MAX_WORKERS`: Maximum number of concurrent query worker threads
* Default: `"10"`
* Increase if your workload requires many concurrent tool calls
* `CLICKHOUSE_MCP_AUTH_TOKEN`: Authentication token for HTTP/SSE transports
* Default: None
* **Required** when using HTTP or SSE transport (unless `CLICKHOUSE_MCP_AUTH_DISABLED=true`)
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9 changes: 9 additions & 0 deletions mcp_clickhouse/mcp_env.py
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Expand Up @@ -300,6 +300,7 @@ class MCPServerConfig:
CLICKHOUSE_MCP_BIND_HOST: Bind host for HTTP/SSE (default: 127.0.0.1)
CLICKHOUSE_MCP_BIND_PORT: Bind port for HTTP/SSE (default: 8000)
CLICKHOUSE_MCP_QUERY_TIMEOUT: SELECT tool timeout in seconds (default: 30)
CLICKHOUSE_MCP_MAX_WORKERS: Maximum thread pool workers for query execution (default: 10)
CLICKHOUSE_MCP_AUTH_TOKEN: Authentication token for HTTP/SSE transports (required
unless CLICKHOUSE_MCP_AUTH_DISABLED=true)
CLICKHOUSE_MCP_AUTH_DISABLED: Disable authentication (default: false, use
Expand All @@ -326,6 +327,14 @@ def bind_port(self) -> int:
def query_timeout(self) -> int:
return int(os.getenv("CLICKHOUSE_MCP_QUERY_TIMEOUT", "30"))

@property
def max_workers(self) -> int:
"""Maximum thread pool workers for query execution.

Default: 10
"""
return int(os.getenv("CLICKHOUSE_MCP_MAX_WORKERS", "10"))

@property
def auth_token(self) -> Optional[str]:
"""Get the authentication token for HTTP/SSE transports."""
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