Clickhouse

Clickhouse sink connector

Key Features​

• exactly-once

• cdc

The Clickhouse sink plug-in can achieve accuracy once by implementing idempotent writing, and needs to cooperate with aggregatingmergetree and other engines that support deduplication.

Description​

Used to write data to Clickhouse.

Data Type Mapping​

Nexus Data Type	Clickhouse Data Type
STRING	String / Int128 / UInt128 / Int256 / UInt256 / Point / Ring / Polygon MultiPolygon
INT	Int8 / UInt8 / Int16 / UInt16 / Int32
BIGINT	UInt64 / Int64 / IntervalYear / IntervalQuarter / IntervalMonth / IntervalWeek / IntervalDay / IntervalHour / IntervalMinute / IntervalSecond
DOUBLE	Float64
DECIMAL	Decimal
FLOAT	Float32
DATE	Date
TIME	DateTime
ARRAY	Array
MAP	Map

Sink Options​

Name	Type	Required	Default	Description
host	String	Yes	-	ClickHouse cluster address, the format is host:port , allowing multiple hosts to be specified. Such as "host1:8123,host2:8123".
database	String	Yes	-	The ClickHouse database.
table	String	Yes	-	The table name.
username	String	Yes	-	ClickHouse user username.
password	String	Yes	-	ClickHouse user password.
clickhouse.config	Map	No		In addition to the above mandatory parameters that must be specified by clickhouse-jdbc , users can also specify multiple optional parameters, which cover all the parameters provided by clickhouse-jdbc.
bulk_size	String	No	20000	The number of rows written through Clickhouse-jdbc each time, the default is 20000.
split_mode	String	No	false	This mode only support clickhouse table which engine is 'Distributed'.And internal_replication option-should be true.They will split distributed table data in Nexus and perform write directly on each shard. The shard weight define is clickhouse will counted.
sharding_key	String	No	-	When use split_mode, which node to send data to is a problem, the default is random selection, but the 'sharding_key' parameter can be used to specify the field for the sharding algorithm. This option only worked when 'split_mode' is true.
primary_key	String	No	-	Mark the primary key column from clickhouse table, and based on primary key execute INSERT/UPDATE/DELETE to clickhouse table.
support_upsert	Boolean	No	false	Support upsert row by query primary key.
allow_experimental_lightweight_delete	Boolean	No	false	Allow experimental lightweight delete based on *MergeTree table engine.
common-options		No	-	Sink plugin common parameters, please refer to Sink Common Options for details.

How to Create a Clickhouse Data Synchronization Jobs​

The following example demonstrates how to create a data synchronization job that writes randomly generated data to a Clickhouse database:

# Set the basic configuration of the task to be performed
env {
  parallelism = 1
  job.mode = "BATCH"
  checkpoint.interval  = 1000
}

source {
  FakeSource {
      row.num = 2
      bigint.min = 0
      bigint.max = 10000000
      split.num = 1
      split.read-interval = 300
      schema {
        fields {
          c_bigint = bigint
        }
      }
    }
}

sink {
  Clickhouse {
    host = "127.0.0.1:9092"
    database = "default"
    table = "test"
    username = "xxxxx"
    password = "xxxxx"
  }
}

Tips​

1.The table to be written to needs to be created in advance before synchronization. 2.When sink is writing to the ClickHouse table, you don't need to set its schema because the connector will query ClickHouse for the current table's schema information before writing.

Clickhouse Sink Config​

sink {
  Clickhouse {
    host = "localhost:8123"
    database = "default"
    table = "fake_all"
    username = "xxxxx"
    password = "xxxxx"
    clickhouse.config = {
      max_rows_to_read = "100"
      read_overflow_mode = "throw"
    }
  }
}

Split Mode​

sink {
  Clickhouse {
    host = "localhost:8123"
    database = "default"
    table = "fake_all"
    username = "xxxxx"
    password = "xxxxx"
    
    # split mode options
    split_mode = true
    sharding_key = "age"
  }
}

CDC(Change data capture) Sink​

sink {
  Clickhouse {
    host = "localhost:8123"
    database = "default"
    table = "fake_all"
    username = "xxxxx"
    password = "xxxxx"
    
    # cdc options
    primary_key = "id"
    support_upsert = true
  }
}

CDC(Change data capture) for *MergeTree engine​

sink {
  Clickhouse {
    host = "localhost:8123"
    database = "default"
    table = "fake_all"
    username = "xxxxx"
    password = "xxxxx"
    
    # cdc options
    primary_key = "id"
    support_upsert = true
    allow_experimental_lightweight_delete = true
  }
}