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Documentation Index

Fetch the complete documentation index at: https://beta.docs.sqd.dev/llms.txt

Use this file to discover all available pages before exploring further.

Install the ClickHouse Node.js client: 
npm install @clickhouse/client
At a glance, the pipeline looks like this:

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Table design

Use CollapsingMergeTree with a sign Int8 DEFAULT 1 column. This engine enables efficient fork rollbacks: to cancel rows, the target re-inserts them with sign = -1 and ClickHouse merges the pair during background processing. Design notes:
  • Apply DoubleDelta + ZSTD codecs to monotonically increasing columns such as block numbers and timestamps.
  • Use LowCardinality for columns with low cardinality like addresses to reduce storage and speed up filtering.
  • Store 256-bit integers as UInt256; serialize JavaScript BigInt values to strings before insertion.
Create the table in onStart using store.command(): 
onStart: async ({ store }) => {
  await store.command({ query: `CREATE TABLE IF NOT EXISTS transfers ( ... )` })
}

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onData

Call store.insert() to queue an insert. The call is non-blocking — inserts fire concurrently and are fully flushed when the target closes:

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onRollback

Implement onRollback to handle blockchain forks. It is invoked in two situations:
  • type: 'offset_check' — on startup, when a saved cursor is found, to discard writes from a previous crashed or partial run
  • type: 'blockchain_fork' — when the stream detects a chain reorganisation
Use store.removeAllRows() to cancel rows past the safe point. For CollapsingMergeTree tables this re-inserts matching rows with sign = -1:

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Complete example

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Docker setup

docker-compose.yml
services:
  clickhouse:
    image: clickhouse/clickhouse-server:latest
    ports:
      - "8123:8123"
      - "9000:9000"
    environment:
      CLICKHOUSE_DB: default
      CLICKHOUSE_USER: default
      CLICKHOUSE_PASSWORD: default
    volumes:
      - clickhouse-data:/var/lib/clickhouse

volumes:
  clickhouse-data:

docker compose up -d
See the clickhouseTarget reference for the full API.