Cassandra

Source Cassandra #

The extracted replicant-cli will be referred to as the $REPLICANT_HOME directory.

CDC Prerequisites #

Arcion Replicant supports two mechanisms for accessing the Cassandra CDC log files. The working method depends on whether the CDC log files are accessible locally to the Replicant.

  1. If Replicant is running on the same node as the source Cassandra server or the Cassandra CDC log files are accessible to Replicant using NFS mount, then you must configure the access-method as LOCAL and provide the locations of cdc-log-dir and cdc-raw-dir in the connection configuration file (explained in step I).

    cdc-log-config:
      access-method: LOCAL
      cdc-log-dir: '/var/lib/cassandra/commitlog'
      cdc-raw-dir: '/var/lib/cassandra/cdc_raw'
    
  2. If Replicant is running on a different node than the source Cassandra server and the Cassandra CDC logs are not accessible to Replicant using NFS mount, then you must configure the access-method as SFTP, provide the locations of cdc-log-dir and cdc-raw-dir, and setup the SFTP coniguration in the connection configuration file (explained in step I).

    cdc-log-config:
      access-method: SFTP
      cdc-log-dir: '/var/lib/cassandra/commitlog'
      cdc-raw-dir: '/var/lib/cassandra/cdc_raw'
      sftp-config:
        username: 'cassandra'
        password: 'cassandra'
        port: 22
    

Steps to enable CDC Replication

  1. Enable the CDC logging for the desired tables by setting the cdc property of table to true when creating or altering the table:

    CREATE TABLE foo (a int, b text, PRIMARY KEY(a)) WITH cdc=true;
    OR
    ALTER TABLE foo WITH cdc=true;
    
  2. When Replicant is configured to use the SFTP access-method, the SFTP server should be running on the machine running the Cassandra node. If SFTP server is not present on the machine, it can be installed with the following commands:

    sudo apt-get update
    sudo apt-get install openssh-server
    /etc/init.d/ssh start
    

I. Set up Connection Configuration #

  1. From $REPLICANT_HOME navigate to the connection configuration file:

    vi conf/conn/cassadra.yaml
    
  2. Make the necessary changes as follows:

    type: CASSANDRA
    
    cassandra-nodes:
      node1:
        host: 172.17.0.2
        port: 9042
        cdc-log-config:
          access-method: SFTP  # access-method can be LOCAL, SFTP
          cdc-log-dir: '/var/lib/cassandra/commitlog' # Enter the path of the directory containing Cassandra commit log
          cdc-raw-dir: '/var/lib/cassandra/cdc_raw' # Enter the path of the directory containing Cassandra CDC log
    
          #Only specify the following configurations if your access method is SFTP
          sftp-config:
            username: 'cassandra'
            password: 'cassandra'
            port: 22
    
      #If you are using multiple nodes, specify them in this section using the format above
    
    csv-load-connection:
      storage-location: /path/to/extracted/csvs
      access-method: LOCAL # access-method can be LOCAL, SFTP
      max-connections: 30
      sftp-config:
        username: 'cassandra' # if access-method is SFTP, provide sftp-username to log on to host using SFTP
        password: 'cassandra' # if access-method is SFTP, provide sftp-password to log on to host using SFTP
        port: 22 # if access-method is SFTP, provide port on which SFTP service is running
    
    username: 'cassandra'
    password: 'cassandra'
    
    read-consistency-level: LOCAL_QUORUM  #Enter one of the allowed values: ANY, ONE, TWO, THREE, QUORUM, ALL, LOCAL_QUORUM, EACH_QUORUM, SERIAL, LOCAL_SERIAL, LOCAL_ONE
    
    auth-type: "PlainTextAuthProvider" #Enter one of the allowed values: DsePlainTextAuthProvider, PlainTextAuthProvider
    
    max-connections: 30 #Maximum number of connections Replicant can open in Cassandra    
    

II. Setup Filter Configuration #

  1. From $REPLICANT_HOME navigate to the filter configuration file:

    vi filter/cassandra_filter.yaml
    
  2. In accordance to you replication needs, specify the data which is to be replicated. Use the format of the example explained below:

    allow:
      #In this example, data of object type Table in the schema tpch will be replicated
      schema: "tpch"
      types: [TABLE]
    
      #From schema tpch, only the lineitem, ng_test, and usertable tables will be replicated.
      #Note: Unless specified, all tables in the catalog will be replicated
      allow:
        lineitem:
        #Within lineitem, only the item_one and item_two columns will be replicated
        allow: ["item_one, item_two"]
    
        ORDERS:  
          #Within ORDERS, only the test_one and test_two columns will be replicated as long as they meet the condition "o_orderkey < 5000"
          allow: ["test_one", "test_two"]
          conditions: "o_orderkey <5000"
    
        usertable: #All columns in the table usertable will be replicated without any predicates
    

    The following is a template of the format you must follow:

    allow:
      schema: <your_schema_name>
      types: <your_object_type>
    
    
      allow:        
        your_table_name_1:  
           allow: ["your_column_name"]
           conditions: "your_condition"
    
        your_table_name_2:
    
        your_table_name_3:
          allow: ["your_column_name"]
          conditions: "your_condition"         
    

For a detailed explanation of configuration parameters in the filter file, read: Filter Reference

III. Set up Extractor Configuration #

For real-time replication, you must create a heartbeat table in the source Casandra.

  1. Create a heartbeat table in the catalog you are going to replicate with the following DDL:

    CREATE TABLE "<user_keyspace>"."replicate_io_cdc_heartbeat"("timestamp" BIGINT, PRIMARY KEY("timestamp"));
    
  2. Grant INSERT, UPDATE, and DELETE privileges to the user configured for replication.

  3. From $REPLICANT_HOME navigate to the extractor configuration file:

    vi conf/src/cassandra.yaml
    
  4. If required, make the necessary changes as follows:

    snapshot:
       extraction-method: CSVLOAD #Allowed values are QUERY, CSVLOAD
       native-extract-options:
         control-chars:
           delimiter: ','
           quote: '"'
           escape: "\u0000"
           null-string: "NULL"
           line-end: "\n"
    
    realtime:
      heartbeat:
        enable: true
        table-name [20.09.14.3]: replicate_io_cdc_heartbeat #Heartbeat table name if changed
        column-name [20.10.07.9]: timestamp #Heartbeat table column name if changed
    

Limitations #

The following limitations will apply when replicating from Casandra as a source:

  1. Replication of counter tables is not supported.
  2. Changes resulted from any of these features are ignored:
    • TTL on collection-type columns
    • Range deletes
    • Static columns
    • Triggers
    • Secondary indices
    • Light-weight transactions
  3. Unsupported Datatypes:
    • map
    • set

Note: The operation(Insert/Update/Delete) count during real-time replication will be displayed on the dashboard as (number of operations)*(number of replication factors).