Manage TiCDC Cluster and Replication Tasks

This document describes how to upgrade TiCDC cluster and modify the configuration of TiCDC cluster using TiUP, and how to manage the TiCDC cluster and replication tasks using the command-line tool cdc cli.

You can also use the HTTP interface (the TiCDC OpenAPI feature) to manage the TiCDC cluster and replication tasks. For details, see TiCDC OpenAPI.

Upgrade TiCDC using TiUP

This section introduces how to upgrade the TiCDC cluster using TiUP. In the following example, assume that you need to upgrade TiCDC and the entire TiDB cluster to v6.1.7.

tiup update --self && \
tiup update --all && \
tiup cluster upgrade <cluster-name> v6.1.7

Notes for upgrade

• The changefeed configuration has changed in TiCDC v4.0.2. See Compatibility notes for the configuration file for details.
• If you encounter any issues, see Upgrade TiDB using TiUP - FAQ.

Modify TiCDC configuration using TiUP

This section introduces how to modify the configuration of TiCDC cluster using the tiup cluster edit-config command of TiUP. The following example changes the value of gc-ttl from the default 86400 to 3600, namely, one hour.

First, run the following command. You need to replace <cluster-name> with your actual cluster name.

tiup cluster edit-config <cluster-name>

Then, enter the vi editor page and modify the cdc configuraion under server-configs. The configuration is shown below:

 server_configs:
  tidb: {}
  tikv: {}
  pd: {}
  tiflash: {}
  tiflash-learner: {}
  pump: {}
  drainer: {}
  cdc:
    gc-ttl: 3600

After the modification, run the tiup cluster reload -R cdc command to reload the configuration.

Use TLS

For details about using encrypted data transmission (TLS), see Enable TLS Between TiDB Components.

Use cdc cli to manage cluster status and data replication task

This section introduces how to use cdc cli to manage a TiCDC cluster and data replication tasks. cdc cli is the cli sub-command executed using the cdc binary. The following description assumes that:

• cli commands are executed directly using the cdc binary;
• PD listens on 10.0.10.25 and the port is 2379.

If you deploy TiCDC using TiUP, replace cdc cli in the following commands with tiup ctl:<cluster-version> cdc.

Manage TiCDC service progress (capture)

• Query the capture list:

  cdc cli capture list --pd=http://10.0.10.25:2379
  

  [
    {
      "id": "806e3a1b-0e31-477f-9dd6-f3f2c570abdd",
      "is-owner": true,
      "address": "127.0.0.1:8300"
    },
    {
      "id": "ea2a4203-56fe-43a6-b442-7b295f458ebc",
      "is-owner": false,
      "address": "127.0.0.1:8301"
    }
  ]
  

  • id: The ID of the service process.
  • is-owner: Indicates whether the service process is the owner node.
  • address: The address via which the service process provides interface to the outside.

Manage replication tasks (changefeed)

State transfer of replication tasks

The state of a replication task represents the running status of the replication task. During the running of TiCDC, replication tasks might fail with errors, be manually paused, resumed, or reach the specified TargetTs. These behaviors can lead to the change of the replication task state. This section describes the states of TiCDC replication tasks and the transfer relationships between states.

The states in the above state transfer diagram are described as follows:

• Normal: The replication task runs normally and the checkpoint-ts proceeds normally.
• Stopped: The replication task is stopped, because the user manually pauses the changefeed. The changefeed in this state blocks GC operations.
• Error: The replication task returns an error. The replication cannot continue due to some recoverable errors. The changefeed in this state keeps trying to resume until the state transfers to Normal. The changefeed in this state blocks GC operations.
• Finished: The replication task is finished and has reached the preset TargetTs. The changefeed in this state does not block GC operations.
• Failed: The replication task fails. Due to some unrecoverable errors, the replication task cannot resume and cannot be recovered. The changefeed in this state does not block GC operations.

The numbers in the above state transfer diagram are described as follows.

• ① Run the changefeed pause command.
• ② Run the changefeed resume command to resume the replication task.
• ③ Recoverable errors occur during the changefeed operation, and the operation is resumed automatically.
• ④ Run the changefeed resume command to resume the replication task.
• ⑤ Unrecoverable errors occur during the changefeed operation.
• ⑥ changefeed has reached the preset TargetTs, and the replication is automatically stopped.
• ⑦ changefeed suspended longer than the duration specified by gc-ttl, and cannot be resumed.
• ⑧ changefeed experienced an unrecoverable error when trying to execute automatic recovery.

Create a replication task

Run the following commands to create a replication task:

cdc cli changefeed create --pd=http://10.0.10.25:2379 --sink-uri="mysql://root:123456@127.0.0.1:3306/" --changefeed-id="simple-replication-task" --sort-engine="unified"

Create changefeed successfully!
ID: simple-replication-task
Info: {"sink-uri":"mysql://root:123456@127.0.0.1:3306/","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}

• --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. Configure --sink-uri according to the following format. Currently, the scheme supports mysql/tidb/kafka/pulsar/s3/local.

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

  When a URI contains special characters, you need to process these special characters using URL encoding.

• --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.

• --sort-engine: Specifies the sorting engine for the changefeed. Because TiDB and TiKV adopt distributed architectures, TiCDC must sort the data changes before writing them to the sink. This option supports unified (by default)/memory/file.

  • unified: When unified is used, TiCDC prefers data sorting in memory. If the memory is insufficient, TiCDC automatically uses the disk to store the temporary data. This is the default value of --sort-engine.
  • memory: Sorts data changes in memory. It is NOT recommended to use this sorting engine, because OOM is easily triggered when you replicate a large amount of data.
  • file: Entirely uses the disk to store the temporary data. This feature is deprecated. It is NOT recommended to use it in any situation.

• --config: Specifies the configuration file of the changefeed.

• sort-dir: Specifies the temporary file directory used by the sorting engine. Note that this option is not supported since TiDB v4.0.13, v5.0.3 and v5.1.0. Do not use it any more.

Configure sink URI with mysql/tidb

Sample configuration:

--sink-uri="mysql://root:123456@127.0.0.1:3306/?worker-count=16&max-txn-row=5000&transaction-atomicity=table"

The following are descriptions of parameters and parameter values that can be configured for the sink URI with mysql/tidb:

Configure sink URI with kafka

Sample configuration:

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

The following are descriptions of parameters and parameter values that can be configured for the sink URI with 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 and Write 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.

Configure sink URI with pulsar

Sample configuration:

--sink-uri="pulsar://127.0.0.1:6650/topic-name?connectionTimeout=2s"

The following are descriptions of parameters that can be configured for the sink URI with pulsar:

For more parameters of Pulsar, see pulsar-client-go ClientOptions and pulsar-client-go ProducerOptions.

Use the task configuration file

For more replication configuration (for example, specify replicating a single table), see Task configuration file.

You can use a configuration file to create a replication task in the following way:

cdc cli changefeed create --pd=http://10.0.10.25:2379 --sink-uri="mysql://root:123456@127.0.0.1:3306/" --config changefeed.toml

In the command above, changefeed.toml is the configuration file for the replication task.

Query the replication task list

Run the following command to query the replication task list:

cdc cli changefeed list --pd=http://10.0.10.25:2379

[{
    "id": "simple-replication-task",
    "summary": {
      "state": "normal",
      "tso": 417886179132964865,
      "checkpoint": "2020-07-07 16:07:44.881",
      "error": null
    }
}]

• checkpoint indicates that TiCDC has already replicated data before this time point to the downstream.
• state indicates the state of the replication task.
  • normal: The replication task runs normally.
  • stopped: The replication task is stopped (manually paused).
  • error: The replication task is stopped (by an error).
  • removed: The replication task is removed. Tasks of this state are displayed only when you have specified the --all option. To see these tasks when this option is not specified, run the changefeed query command.
  • finished: The replication task is finished (data is replicated to the target-ts). Tasks of this state are displayed only when you have specified the --all option. To see these tasks when this option is not specified, run the changefeed query command.

Query a specific replication task

To query a specific replication task, run the changefeed query command. The query result includes the task information and the task state. You can specify the --simple or -s argument to simplify the query result that will only include the basic replication state and the checkpoint information. If you do not specify this argument, detailed task configuration, replication states, and replication table information are output.

cdc cli changefeed query -s --pd=http://10.0.10.25:2379 --changefeed-id=simple-replication-task

{
 "state": "normal",
 "tso": 419035700154597378,
 "checkpoint": "2020-08-27 10:12:19.579",
 "error": null
}

In the command and result above:

• state is the replication state of the current changefeed. Each state must be consistent with the state in changefeed list.
• tso represents the largest transaction TSO in the current changefeed that has been successfully replicated to the downstream.
• checkpoint represents the corresponding time of the largest transaction TSO in the current changefeed that has been successfully replicated to the downstream.
• error records whether an error has occurred in the current changefeed.

cdc cli changefeed query --pd=http://10.0.10.25:2379 --changefeed-id=simple-replication-task

{
  "info": {
    "sink-uri": "mysql://127.0.0.1:3306/?max-txn-row=20\u0026worker-count=4",
    "opts": {},
    "create-time": "2020-08-27T10:33:41.687983832+08:00",
    "start-ts": 419036036249681921,
    "target-ts": 0,
    "admin-job-type": 0,
    "sort-engine": "unified",
    "sort-dir": ".",
    "config": {
      "case-sensitive": true,
      "enable-old-value": false,
      "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
  },
  "status": {
    "resolved-ts": 419036036249681921,
    "checkpoint-ts": 419036036249681921,
    "admin-job-type": 0
  },
  "count": 0,
  "task-status": [
    {
      "capture-id": "97173367-75dc-490c-ae2d-4e990f90da0f",
      "status": {
        "tables": {
          "47": {
            "start-ts": 419036036249681921
          }
        },
        "operation": null,
        "admin-job-type": 0
      }
    }
  ]
}

In the command and result above:

• info is the replication configuration of the queried changefeed.
• status is the replication state of the queried changefeed.
  • resolved-ts: The largest transaction TS in the current changefeed. Note that this TS has been successfully sent from TiKV to TiCDC.
  • checkpoint-ts: The largest transaction TS in the current changefeed. Note that this TS has been successfully written to the downstream.
  • admin-job-type: The status of a changefeed:
    • 0: The state is normal.
    • 1: The task is paused. When the task is paused, all replicated processors exit. The configuration and the replication status of the task are retained, so you can resume the task from checkpiont-ts.
    • 2: The task is resumed. The replication task resumes from checkpoint-ts.
    • 3: The task is removed. When the task is removed, all replicated processors are ended, and the configuration information of the replication task is cleared up. Only the replication status is retained for later queries.
• task-status indicates the state of each replication sub-task in the queried changefeed.

Pause a replication task

Run the following command to pause a replication task:

cdc cli changefeed pause --pd=http://10.0.10.25:2379 --changefeed-id simple-replication-task

In the above command:

• --changefeed-id=uuid represents the ID of the changefeed that corresponds to the replication task you want to pause.

Resume a replication task

Run the following command to resume a paused replication task:

cdc cli changefeed resume --pd=http://10.0.10.25:2379 --changefeed-id simple-replication-task

In the above command:

• --changefeed-id=uuid represents the ID of the changefeed that corresponds to the replication task you want to resume.

Remove a replication task

Run the following command to remove a replication task:

cdc cli changefeed remove --pd=http://10.0.10.25:2379 --changefeed-id simple-replication-task

In the above command:

• --changefeed-id=uuid represents the ID of the changefeed that corresponds to the replication task you want to remove.

Update task configuration

Starting from v4.0.4, TiCDC supports modifying the configuration of the replication task (not dynamically). To modify the changefeed configuration, pause the task, modify the configuration, and then resume the task.

cdc cli changefeed pause -c test-cf --pd=http://10.0.10.25:2379
cdc cli changefeed update -c test-cf --pd=http://10.0.10.25:2379 --sink-uri="mysql://127.0.0.1:3306/?max-txn-row=20&worker-count=8" --config=changefeed.toml
cdc cli changefeed resume -c test-cf --pd=http://10.0.10.25:2379

Currently, you can modify the following configuration items:

• sink-uri of the changefeed.
• The changefeed configuration file and all configuration items in the file.
• Whether to use the file sorting feature and the sorting directory.
• The target-ts of the changefeed.

Manage processing units of replication sub-tasks (processor)

• Query the processor list:

  cdc cli processor list --pd=http://10.0.10.25:2379
  

  [
          {
                  "id": "9f84ff74-abf9-407f-a6e2-56aa35b33888",
                  "capture-id": "b293999a-4168-4988-a4f4-35d9589b226b",
                  "changefeed-id": "simple-replication-task"
          }
  ]
  

• Query a specific changefeed which corresponds to the status of a specific replication task:

  cdc cli processor query --pd=http://10.0.10.25:2379 --changefeed-id=simple-replication-task --capture-id=b293999a-4168-4988-a4f4-35d9589b226b
  

  {
    "status": {
      "tables": {
        "56": {    # ID of the replication table, corresponding to tidb_table_id of a table in TiDB
          "start-ts": 417474117955485702
        }
      },
      "operation": null,
      "admin-job-type": 0
    },
    "position": {
      "checkpoint-ts": 417474143881789441,
      "resolved-ts": 417474143881789441,
      "count": 0
    }
  }
  

  In the command above:

  • status.tables: Each key number represents the ID of the replication table, corresponding to tidb_table_id of a table in TiDB.
  • resolved-ts: The largest TSO among the sorted data in the current processor.
  • checkpoint-ts: The largest TSO that has been successfully written to the downstream in the current processor.

Task configuration file

This section introduces the configuration of a replication task.

# Specifies whether the database names and tables in the configuration file are case-sensitive.
# The default value is true.
# This configuration item affects configurations related to filter and sink.
case-sensitive = true

# Specifies whether to output the old value. New in v4.0.5. Since v5.0, the default value is `true`.
enable-old-value = true

[filter]
# Ignores the transaction of specified start_ts.
# ignore-txn-start-ts = [1, 2]

# Filter rules.
# Filter syntax: https://docs.pingcap.com/tidb/stable/table-filter#syntax.
rules = ['*.*', '!test.*']

[mounter]
# mounter thread counts, which is used to decode the TiKV output data.
worker-num = 16

[sink]
# For the sink of MQ type, you can use dispatchers to configure the event dispatcher.
# Since v6.1, TiDB supports two types of event dispatchers: partition and topic. For more information, see the following section.
# The matching syntax of matcher is the same as the filter rule syntax. For details about the matcher rules, see the following section.

# 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 sink of MQ type, you can specify the protocol format of the message.
# Currently the following protocols are supported: canal-json, open-protocol, and avro.
# protocol = "canal-json"

Notes for compatibility

• In TiCDC v4.0.0, ignore-txn-commit-ts is removed and ignore-txn-start-ts is added, which uses start_ts to filter transactions.
• In TiCDC v4.0.2, db-dbs/db-tables/ignore-dbs/ignore-tables are removed and rules is added, which uses new filter rules for databases and tables. For detailed filter syntax, see Table Filter.

Customize the rules for Topic and Partition dispatchers of Kafka Sink

Matcher rules

In the example of the previous section:

• 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"},

Output the historical value of a Row Changed Event New in v4.0.5

In the default configuration, the Row Changed Event of TiCDC Open Protocol output in a replication task only contains the changed value, not the value before the change. Therefore, the output value cannot be used by the consumer ends of TiCDC Open Protocol as the historical value of a Row Changed Event.

Starting from v4.0.5, TiCDC supports outputting the historical value of a Row Changed Event. To enable this feature, specify the following configuration in the changefeed configuration file at the root level:

enable-old-value = true

This feature is enabled by default since v5.0. To learn the output format of the TiCDC Open Protocol after this feature is enabled, see TiCDC Open Protocol - Row Changed Event.

Replicate tables with the new framework for collations enabled

Starting from v4.0.15, v5.0.4, v5.1.1 and v5.2.0, TiCDC supports tables that have enabled new framework for collations.

Replicate tables without a valid index

Since v4.0.8, TiCDC supports replicating tables that have no valid index by modifying the task configuration. To enable this feature, configure in the changefeed configuration file as follows:

enable-old-value = true
force-replicate = true

Unified Sorter

Unified sorter is the sorting engine in TiCDC. It can mitigate OOM problems caused by the following scenarios:

• The data replication task in TiCDC is paused for a long time, during which a large amount of incremental data is accumulated and needs to be replicated.
• The data replication task is started from an early timestamp so it becomes necessary to replicate a large amount of incremental data.

For the changefeeds created using cdc cli after v4.0.13, Unified Sorter is enabled by default; for the changefeeds that have existed before v4.0.13, the previous configuration is used.

To check whether or not the Unified Sorter feature is enabled on a changefeed, you can run the following example command (assuming the IP address of the PD instance is http://10.0.10.25:2379):

cdc cli --pd="http://10.0.10.25:2379" changefeed query --changefeed-id=simple-replication-task | grep 'sort-engine'

In the output of the above command, if the value of sort-engine is "unified", it means that Unified Sorter is enabled on the changefeed.

Eventually consistent replication in disaster scenarios

Starting from v6.1.1, this feature becomes GA. Starting from v5.3.0, TiCDC supports backing up incremental data from an upstream TiDB cluster to an object storage or an NFS of the downstream cluster. When the upstream cluster encounters a disaster and becomes unavailable, TiCDC can restore the downstream data to the recent eventually consistent state. This is the eventually consistent replication capability provided by TiCDC. With this capability, you can switch applications to the downstream cluster quickly, avoiding long-time downtime and improving service continuity.

Currently, TiCDC can replicate incremental data from a TiDB cluster to another TiDB cluster or a MySQL-compatible database system (including Aurora, MySQL, and MariaDB). In case the upstream cluster crashes, TiCDC can restore data in the downstream cluster within 5 minutes, given the conditions that TiCDC replicates data normally before the crash, and the replication lag is small. It allows data loss of 10s at most, that is, RTO <= 5 min, and P95 RPO <= 10s.

TiCDC replication lag increases in the following scenarios:

• The TPS increases significantly in a short time
• Large or long transactions occur in the upstream
• The TiKV or TiCDC cluster in the upstream is reloaded or upgraded
• Time-consuming DDL statements, such as add index, are executed in the upstream
• The PD is configured with aggressive scheduling strategies, resulting in frequent transfer of Region leaders, or frequent Region merge or Region split

Prerequisites

• Prepare a highly available object storage or NFS for storing TiCDC's real-time incremental data backup files. These files can be accessed in case of a disaster in the upstream.
• Enable this feature for changefeeds that need to have eventual consistency in disaster scenarios. To enable it, you can add the following configuration to the changefeed configuration file.

[consistent]
# Consistency level. Options include:
# - none: the default value. In a non-disaster scenario, eventual consistency is only guaranteed if and only if finished-ts is specified.
# - eventual: Uses redo log to guarantee eventual consistency in case of the primary cluster disasters.
level = "eventual"

# Individual redo log file size, in MiB. By default, it's 64. It is recommended to be no more than 128.
max-log-size = 64

# The interval for flushing or uploading redo logs to Amazon S3, in milliseconds. It is recommended that this configuration be equal to or greater than 2000.
flush-interval = 2000

# # The path under which redo log backup is stored. The scheme can be nfs (NFS directory), or Amazon S3, GCS, and Azure (uploaded to object storage).
storage = "$SCHEME://logbucket/test-changefeed?endpoint=http://$ENDPOINT/"

Disaster recovery

When a disaster happens in the primary cluster, you need to recover manually in the secondary cluster by running the cdc redo command. The recovery process is as follows.

1. Ensure that all the TiCDC processes have exited. This is to prevent the primary cluster from resuming service during data recovery and prevent TiCDC from restarting data synchronization.
2. Use cdc binary for data recovery. Run the following command:

cdc redo apply --tmp-dir="/tmp/cdc/redo/apply" \
    --storage="s3://logbucket/test-changefeed?endpoint=http://10.0.10.25:24927/" \
    --sink-uri="mysql://normal:123456@10.0.10.55:3306/"

In this command:

• tmp-dir: Specifies the temporary directory for downloading TiCDC incremental data backup files.
• storage: Specifies the address for storing the TiCDC incremental data backup files, either an URI of object storage or an NFS directory.
• sink-uri: Specifies the secondary cluster address to restore the data to. Scheme can only be mysql.