Replicate Data to Kafka

This document describes how to create a changefeed that replicates incremental data to Apache Kafka using TiCDC.

Create a replication task

Create a replication task by running the following command:

cdc cli changefeed create \
    --server=http://10.0.10.25:8300 \
    --sink-uri="kafka://127.0.0.1:9092/topic-name?protocol=canal-json&kafka-version=2.4.0&partition-num=6&max-message-bytes=67108864&replication-factor=1" \
    --changefeed-id="simple-replication-task"

Create changefeed successfully!
ID: simple-replication-task
Info: {"sink-uri":"kafka://127.0.0.1:9092/topic-name?protocol=canal-json&kafka-version=2.4.0&partition-num=6&max-message-bytes=67108864&replication-factor=1","opts":{},"create-time":"2020-03-12T22:04:08.103600025+08:00","start-ts":415241823337054209,"target-ts":0,"admin-job-type":0,"sort-engine":"unified","sort-dir":".","config":{"case-sensitive":true,"filter":{"rules":["*.*"],"ignore-txn-start-ts":null,"ddl-allow-list":null},"mounter":{"worker-num":16},"sink":{"dispatchers":null},"scheduler":{"type":"table-number","polling-time":-1}},"state":"normal","history":null,"error":null}

• --server: The address of any TiCDC server in the TiCDC cluster.
• --changefeed-id: The ID of the replication task. The format must match the ^[a-zA-Z0-9]+(\-[a-zA-Z0-9]+)*$ regular expression. If this ID is not specified, TiCDC automatically generates a UUID (the version 4 format) as the ID.
• --sink-uri: The downstream address of the replication task. For details, see Configure sink URI with kafka.
• --start-ts: Specifies the starting TSO of the changefeed. From this TSO, the TiCDC cluster starts pulling data. The default value is the current time.
• --target-ts: Specifies the ending TSO of the changefeed. To this TSO, the TiCDC cluster stops pulling data. The default value is empty, which means that TiCDC does not automatically stop pulling data.
• --config: Specifies the changefeed configuration file. For details, see TiCDC Changefeed Configuration Parameters.

Configure sink URI for Kafka

Sink URI is used to specify the connection information of the TiCDC target system. The format is as follows:

[scheme]://[userinfo@][host]:[port][/path]?[query_parameters]

Sample configuration:

--sink-uri="kafka://127.0.0.1:9092/topic-name?protocol=canal-json&kafka-version=2.4.0&partition-num=6&max-message-bytes=67108864&replication-factor=1"

The following are descriptions of sink URI parameters and values that can be configured for Kafka:

Best practices

• It is recommended that you create your own Kafka Topic. At a minimum, you need to set the maximum amount of data of each message that the Topic can send to the Kafka broker, and the number of downstream Kafka partitions. When you create a changefeed, these two settings correspond to max-message-bytes and partition-num, respectively.
• If you create a changefeed with a Topic that does not yet exist, TiCDC will try to create the Topic using the partition-num and replication-factor parameters. It is recommended that you specify these parameters explicitly.
• In most cases, it is recommended to use the canal-json protocol.

TiCDC uses the authentication and authorization of Kafka

The following are examples when using Kafka SASL authentication:

• SASL/PLAIN

  --sink-uri="kafka://127.0.0.1:9092/topic-name?kafka-version=2.4.0&sasl-user=alice-user&sasl-password=alice-secret&sasl-mechanism=plain"
  

• SASL/SCRAM

  SCRAM-SHA-256 and SCRAM-SHA-512 are similar to the PLAIN method. You just need to specify sasl-mechanism as the corresponding authentication method.

• SASL/GSSAPI

  SASL/GSSAPI user authentication:

  --sink-uri="kafka://127.0.0.1:9092/topic-name?kafka-version=2.4.0&sasl-mechanism=gssapi&sasl-gssapi-auth-type=user&sasl-gssapi-kerberos-config-path=/etc/krb5.conf&sasl-gssapi-service-name=kafka&sasl-gssapi-user=alice/for-kafka&sasl-gssapi-password=alice-secret&sasl-gssapi-realm=example.com"
  

  Values of sasl-gssapi-user and sasl-gssapi-realm are related to the principle specified in kerberos. For example, if the principle is set as alice/for-kafka@example.com, then sasl-gssapi-user and sasl-gssapi-realm are specified as alice/for-kafka and example.com respectively.

  SASL/GSSAPI keytab authentication:

  --sink-uri="kafka://127.0.0.1:9092/topic-name?kafka-version=2.4.0&sasl-mechanism=gssapi&sasl-gssapi-auth-type=keytab&sasl-gssapi-kerberos-config-path=/etc/krb5.conf&sasl-gssapi-service-name=kafka&sasl-gssapi-user=alice/for-kafka&sasl-gssapi-keytab-path=/var/lib/secret/alice.key&sasl-gssapi-realm=example.com"
  

  For more information about SASL/GSSAPI authentication methods, see Configuring GSSAPI.

• TLS/SSL encryption

  If the Kafka broker has TLS/SSL encryption enabled, you need to add the -enable-tls=true parameter to --sink-uri. If you want to use self-signed certificates, you also need to specify ca, cert and key in --sink-uri.

• ACL authorization

  The minimum set of permissions required for TiCDC to function properly is as follows.

  • The Create, Write, and Describe permissions for the Topic resource type.
  • The DescribeConfigs permission for the Cluster resource type.

Integrate TiCDC with Kafka Connect (Confluent Platform)

To use the data connectors provided by Confluent to stream data to relational or non-relational databases, you need to use the avro protocol and provide a URL for Confluent Schema Registry in schema-registry.

Sample configuration:

--sink-uri="kafka://127.0.0.1:9092/topic-name?&protocol=avro&replication-factor=3" --schema-registry="http://127.0.0.1:8081" --config changefeed_config.toml

[sink]
dispatchers = [
 {matcher = ['*.*'], topic = "tidb_{schema}_{table}"},
]

For detailed integration guide, see Quick Start Guide on Integrating TiDB with Confluent Platform.

Customize the rules for Topic and Partition dispatchers of Kafka Sink

Matcher rules

Take the following configuration of dispatchers as an example:

[sink]
dispatchers = [
  {matcher = ['test1.*', 'test2.*'], topic = "Topic expression 1", partition = "ts" },
  {matcher = ['test3.*', 'test4.*'], topic = "Topic expression 2", partition = "index-value" },
  {matcher = ['test1.*', 'test5.*'], topic = "Topic expression 3", partition = "table"},
  {matcher = ['test6.*'], partition = "ts"}
]

• For the tables that match the matcher rule, they are dispatched according to the policy specified by the corresponding topic expression. For example, the test3.aa table is dispatched according to "Topic expression 2"; the test5.aa table is dispatched according to "Topic expression 3".
• For a table that matches multiple matcher rules, it is dispatched according to the first matching topic expression. For example, the test1.aa table is distributed according to "Topic expression 1".
• For tables that do not match any matcher rule, the corresponding data change events are sent to the default topic specified in --sink-uri. For example, the test10.aa table is sent to the default topic.
• For tables that match the matcher rule but do not specify a topic dispatcher, the corresponding data changes are sent to the default topic specified in --sink-uri. For example, the test6.aa table is sent to the default topic.

Topic dispatchers

You can use topic = "xxx" to specify a Topic dispatcher and use topic expressions to implement flexible topic dispatching policies. It is recommended that the total number of topics be less than 1000.

The format of the Topic expression is [prefix]{schema}[middle][{table}][suffix].

• prefix: optional. Indicates the prefix of the Topic Name.
• {schema}: required. Used to match the schema name.
• middle: optional. Indicates the delimiter between schema name and table name.
• {table}: optional. Used to match the table name.
• suffix: optional. Indicates the suffix of the Topic Name.

prefix, middle and suffix can only include the following characters: a-z, A-Z, 0-9, ., _ and -. {schema} and {table} are both lowercase. Placeholders such as {Schema} and {TABLE} are invalid.

Some examples:

• matcher = ['test1.table1', 'test2.table2'], topic = "hello_{schema}_{table}"
  • The data change events corresponding to test1.table1 are sent to the topic named hello_test1_table1.
  • The data change events corresponding to test2.table2 are sent to the topic named hello_test2_table2.
• matcher = ['test3.*', 'test4.*'], topic = "hello_{schema}_world"
  • The data change events corresponding to all tables in test3 are sent to the topic named hello_test3_world.
  • The data change events corresponding to all tables in test4 are sent to the topic named hello_test4_world.
• matcher = ['*.*'], topic = "{schema}_{table}"
  • All tables listened by TiCDC are dispatched to separate topics according to the "schema_table" rule. For example, for the test.account table, TiCDC dispatches its data change log to a Topic named test_account.

Dispatch DDL events

Schema-level DDLs

DDLs that are not related to a specific table are called schema-level DDLs, such as create database and drop database. The events corresponding to schema-level DDLs are sent to the default topic specified in --sink-uri.

Table-level DDLs

DDLs that are related to a specific table are called table-level DDLs, such as alter table and create table. The events corresponding to table-level DDLs are sent to the corresponding topic according to dispatcher configurations.

For example, for a dispatcher like matcher = ['test.*'], topic = {schema}_{table}, DDL events are dispatched as follows:

• If a single table is involved in the DDL event, the DDL event is sent to the corresponding topic as is. For example, for the DDL event drop table test.table1, the event is sent to the topic named test_table1.
• If multiple tables are involved in the DDL event (rename table / drop table / drop view may involve multiple tables), the DDL event is split into multiple events and sent to the corresponding topics. For example, for the DDL event rename table test.table1 to test.table10, test.table2 to test.table20, the event rename table test.table1 to test.table10 is sent to the topic named test_table1 and the event rename table test.table2 to test.table20 is sent to the topic named test.table2.

Partition dispatchers

You can use partition = "xxx" to specify a partition dispatcher. It supports four dispatchers: default, ts, index-value, and table. The dispatcher rules are as follows:

• default: When multiple unique indexes (including the primary key) exist or the Old Value feature is enabled, events are dispatched in the table mode. When only one unique index (or the primary key) exists, events are dispatched in the index-value mode.
• ts: Use the commitTs of the row change to hash and dispatch events.
• index-value: Use the value of the primary key or the unique index of the table to hash and dispatch events.
• table: Use the schema name of the table and the table name to hash and dispatch events.

[sink]
dispatchers = [
   {matcher = ['*.*'], dispatcher = "ts"},
   {matcher = ['*.*'], partition = "ts"},
]

{matcher = ['*.*'], dispatcher = "ts", partition = "table"},

Scale out the load of a single large table to multiple TiCDC nodes

This feature splits the data replication range of a single large table into multiple ranges, according to the data volume and the number of modified rows per minute, and it makes the data volume and the number of modified rows replicated in each range approximately the same. This feature distributes these ranges to multiple TiCDC nodes for replication, so that multiple TiCDC nodes can replicate a large single table at the same time. This feature can solve the following two problems:

• A single TiCDC node cannot replicate a large single table in time.
• The resources (such as CPU and memory) consumed by TiCDC nodes are not evenly distributed.

Sample configuration:

[scheduler]
# The default value is "false". You can set it to "true" to enable this feature.
enable-table-across-nodes = true
# When you enable this feature, it only takes effect for tables with the number of regions greater than the `region-threshold` value.
region-threshold = 100000
# When you enable this feature, it takes effect for tables with the number of rows modified per minute greater than the `write-key-threshold` value.
# Note:
# * The default value of `write-key-threshold` is 0, which means that the feature does not split the table replication range according to the number of rows modified in a table by default.
# * You can configure this parameter according to your cluster workload. For example, if it is configured as 30000, it means that the feature will split the replication range of a table when the number of modified rows per minute in the table exceeds 30000.
# * When `region-threshold` and `write-key-threshold` are configured at the same time:
#   TiCDC will check whether the number of modified rows is greater than `write-key-threshold` first.
#   If not, next check whether the number of Regions is greater than `region-threshold`.
write-key-threshold = 30000

You can query the number of Regions a table contains by the following SQL statement:

SELECT COUNT(*) FROM INFORMATION_SCHEMA.TIKV_REGION_STATUS WHERE DB_NAME="database1" AND TABLE_NAME="table1" AND IS_INDEX=0;

Handle messages that exceed the Kafka topic limit

Kafka topic sets a limit on the size of messages it can receive. This limit is controlled by the max.message.bytes parameter. If TiCDC Kafka sink sends data that exceeds this limit, the changefeed reports an error and cannot proceed to replicate data. To solve this problem, TiCDC provides the following solution.

Send handle keys only

Starting from v7.3.0, TiCDC Kafka sink supports sending only the handle keys when the message size exceeds the limit. This can significantly reduce the message size and avoid changefeed errors and task failures caused by the message size exceeding the Kafka topic limit. Handle Key refers to the following:

• If the table to be replicated has primary key, the primary key is the handle key.
• If the table does not have primary key but has NOT NULL Unique Key, the NOT NULL Unique Key is the handle key.

Currently, this feature supports two encoding protocols: Canal-JSON and Open Protocol. When using the Canal-JSON protocol, you must specify enable-tidb-extension=true in sink-uri.

The sample configuration is as follows:

[sink.kafka-config.large-message-handle]
# This configuration is introduced in v7.3.0.
# Empty by default, which means when the message size exceeds the limit, the changefeed fails.
# If this configuration is set to "handle-key-only", when the message size exceeds the limit, only the handle key is sent in the data field. If the message size still exceeds the limit, the changefeed fails.
large-message-handle-option = "handle-key-only"

Consume messages with handle keys only

The message format with handle keys only is as follows:

{
    "id": 0,
    "database": "test",
    "table": "tp_int",
    "pkNames": [
        "id"
    ],
    "isDdl": false,
    "type": "INSERT",
    "es": 1639633141221,
    "ts": 1639633142960,
    "sql": "",
    "sqlType": {
        "id": 4
    },
    "mysqlType": {
        "id": "int"
    },
    "data": [
        {
          "id": "2"
        }
    ],
    "old": null,
    "_tidb": {     // TiDB extension fields
        "commitTs": 163963314122145239,
        "onlyHandleKey": true
    }
}

When a Kafka consumer receives a message, it first checks the onlyHandleKey field. If this field exists and is true, it means that the message only contains the handle key of the complete data. In this case, to get the complete data, you need to query the upstream TiDB and use tidb_snapshot to read historical data.