Engine guides
ClickHouse.
Query ClickHouse over HTTP(S) with a read-only grid, mutation warnings and a plan view.
Connecting#
Choose ClickHouse or paste a clickhouse:// URL. Plasma speaks HTTP: the default port is 8123, the default user and database are default, and the TLS selector is labelled HTTPS. SSH tunnels work. ClickHouse is stateless over HTTP, so a lost connection shows up as the next request failing rather than as a dropped session.
What works#
| Feature | ClickHouse |
|---|---|
| SQL editor, results, history, snippets, notebooks, codegen | Yes |
| Grid editing | No. Results are read-only; change data with SQL. |
| Structure tab | Viewer |
| EXPLAIN | Plain EXPLAIN (no ANALYZE) |
| ER diagram | No. ClickHouse has no foreign keys; its "primary key" is a sorting key. |
| Safe Run, Health, Import, Roles, Schema diff | Not available |
Mutations are asynchronous#
ALTER TABLE … UPDATE, ALTER TABLE … DELETE, DELETE FROM and UPDATE … SET do not change the data inside the statement. ClickHouse queues a background job that rewrites data parts; it cannot be rolled back and may take a long time on a large table. Before running one, Plasma shows Run an asynchronous mutation? with that explanation, and the statement returns before the change is complete. Check progress in system.mutations.
Behaviour to know#
- Read-only uses ClickHouse’s own
readonly=1setting, which the server refuses to lift. AI and MCP queries always use a separate client in that mode, even on a connection that is not read-only. - Cancel aborts the HTTP request and sends
KILL QUERYfor it. - Values. Arrays arrive as JSON arrays. A
Stringcolumn is not binary-safe through the JSON output Plasma reads.