clickhouse-js-node-coding/reference/client-configuration.md

Client Configuration

Applies to: all versions, with these notable additions:

• pathname config option: client >= 1.0.0.
• clickhouse_setting_* / ch_* URL parameters: client >= 1.0.0.
• keep_alive.idle_socket_ttl (Node-only): client >= 0.3.0.

Answer checklist

When answering configuration questions, include the relevant points:

• Show createClient from @clickhouse/client with explicit fields when the user is writing code; this is easier to read and review than encoding everything into a URL string.
• When mentioning the URL form for environment variables / DSNs: show a Bash export with the literal URL value, and createClient({ url: process.env.CLICKHOUSE_URL }) in the Node code. Never construct a URL in application code — no string concatenation, no template literals, no query-string builders.
• If URL parameters and object fields both set the same option, URL parameters override the rest of the configuration object.
• If clickhouse_settings appear on createClient, explain that they are defaults for every request and can be overridden on individual query(), insert(), command(), or exec() calls.
• Remind long-running services to close the client during graceful shutdown.
• The application field sets the name that appears in system.query_log. Do not mention any specific HTTP header name — the client handles header mapping internally and the header names are an implementation detail.

Minimal client

import { createClient } from "@clickhouse/client";

const client = createClient({
  url: process.env.CLICKHOUSE_URL, // defaults to 'http://localhost:8123'
  username: process.env.CLICKHOUSE_USER, // defaults to 'default'
  password: process.env.CLICKHOUSE_PASSWORD, // defaults to ''
  database: "analytics", // defaults to 'default'
});
// ... your queries ...
await client.close();

url accepts a string or a URL object. The accepted string format is:

http[s]://[username:password@]hostname:port[/database][?param1=value1&param2=value2]

Configuration via URL

Prefer explicit object fields in application code. Use the URL form when the application receives one connection string from an environment variable, secret manager, or config file. The URL value belongs in the environment, not in the source code — show it as a shell export and read it in Node:

# In your shell environment / deployment config (e.g. .env, Kubernetes secret):
export CLICKHOUSE_URL='https://bob:[email protected]:8124/analytics'

// In your Node.js code — no URL construction needed:
const client = createClient({ url: process.env.CLICKHOUSE_URL });

Per-client vs per-request clickhouse_settings ⭐

Always mention this when discussing clickhouse_settings: settings set on createClient are defaults; any individual call can override them.

Settings on createClient apply to every request. Settings on a single operation (query, insert, command, exec) override the client defaults for that call only.

const client = createClient({
  clickhouse_settings: {
    output_format_json_quote_64bit_integers: 0, // applied to every request
  },
});

const rows = await client.query({
  query: "SELECT number FROM system.numbers LIMIT 2",
  format: "JSONEachRow",
  clickhouse_settings: {
    output_format_json_quote_64bit_integers: 1, // overrides client default for this call
  },
});

default_format for exec()

client.exec() runs an arbitrary statement and returns a stream. If your query has no trailing FORMAT … clause, set default_format so the server knows what to send back, then wrap the response in a ResultSet:

import { createClient, ResultSet } from "@clickhouse/client";

const client = createClient();
const format = "JSONCompactEachRowWithNamesAndTypes";
const { stream, query_id } = await client.exec({
  query: "SELECT database, name, engine FROM system.tables LIMIT 5",
  clickhouse_settings: { default_format: format },
});
const rs = new ResultSet(stream, format, query_id);
console.log(await rs.json());
await client.close();

For ordinary SELECTs prefer client.query({ format }) — default_format is only needed for raw exec().

Common pitfalls

• Don't put a path in url and expect it to be the database name when you're behind a proxy. Use pathname for the proxy path and database for the DB. (Symptom: "wrong database selected.") See the troubleshooting skill for diagnosis.
• Don't create a client per request. createClient opens a connection pool; share one client across requests and close() on shutdown.
• max_open_connections must be >= 1 when set explicitly.