> ## Documentation Index
> Fetch the complete documentation index at: https://docs.sqd.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# clickhouseTarget

> ClickHouse target for Pipes SDK

See the [ClickHouse guide](../../../guides/basic-development/targets/clickhouse) for usage examples, table design, and setup instructions.

```ts theme={"system"}
import { clickhouseTarget } from '@subsquid/pipes/targets/clickhouse'
```

## `clickhouseTarget`

```ts theme={"system"}
clickhouseTarget<T>({
  client: ClickHouseClient,
  onStart?: (ctx: { store: ClickhouseStore; logger: Logger }) => unknown | Promise<unknown>,
  onData: (ctx: { store: ClickhouseStore; data: T; ctx: Ctx }) => unknown | Promise<unknown>,
  onRollback?: (ctx: {
    type: 'offset_check' | 'blockchain_fork'
    store: ClickhouseStore
    safeCursor: BlockCursor
    /** @deprecated Use `safeCursor` instead. */
    cursor: BlockCursor
  }) => unknown | Promise<unknown>,
  settings?: Settings,
})
```

| Parameter    | Required | Description                                                                  |
| ------------ | -------- | ---------------------------------------------------------------------------- |
| `client`     | Yes      | Client from `@clickhouse/client`.                                            |
| `onStart`    | No       | Runs once before processing starts. Use for table creation or other setup.   |
| `onData`     | Yes      | Called for each batch.                                                       |
| `onRollback` | No       | Called on startup (`'offset_check'`) and on each fork (`'blockchain_fork'`). |
| `settings`   | No       | Configuration for the internal cursor state table. See `Settings` below.     |

**`Settings`:**

| Field      | Default                      | Description                                             |
| ---------- | ---------------------------- | ------------------------------------------------------- |
| `database` | Client's configured database | ClickHouse database for the state table.                |
| `table`    | `'sync'`                     | Name of the state table.                                |
| `id`       | `'stream'`                   | Stream identifier within the state table.               |
| `maxRows`  | `10000`                      | Maximum rows retained per stream id in the state table. |

## `ClickhouseStore` methods

| Method                                                  | Description                                                                                                                               |
| ------------------------------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------- |
| `store.insert(params)`                                  | Queues an insert. Non-blocking — returns a `Promise` but need not be awaited inside `onData`; inserts are flushed when the target closes. |
| `store.query(params)`                                   | Passthrough to `client.query()`.                                                                                                          |
| `store.command(params)`                                 | Passthrough to `client.command()`.                                                                                                        |
| `store.removeAllRows({ tables, where, params? })`       | Cancels rows matching `where` by re-inserting them with `sign = -1`. Requires `CollapsingMergeTree`.                                      |
| `store.removeAllRowsByQuery({ table, query, params? })` | Like `removeAllRows`, but uses a custom `SELECT` to identify the rows to cancel.                                                          |
| `store.executeFiles(dir)`                               | Executes all `.sql` files found in `dir`.                                                                                                 |