Changefeed Sinks

Enterprise changefeeds emit messages to configurable downstream sinks. CockroachDB supports the following sinks:

See CREATE CHANGEFEED for more detail on the query parameters available when setting up a changefeed.

For a step-by-step example connecting a changefeed to a sink, see the Changefeed Examples page.

Sink URI

The sink URI follows the basic format of:

'{scheme}://{host}:{port}?{query_parameters}'
URI Component Description
scheme The type of sink: kafka, gcpubsub, any cloud storage sink, or webhook sink.
host The sink's hostname or IP address.
port The sink's port.
query_parameters The sink's query parameters.

To set a different sink URI to an existing changefeed, use the sink option with ALTER CHANGEFEED.

Kafka

Example of a Kafka sink URI:

'kafka://broker.address.com:9092?topic_prefix=bar_&tls_enabled=true&ca_cert=LS0tLS1CRUdJTiBDRVJUSUZ&sasl_enabled=true&sasl_user={sasl user}&sasl_password={url-encoded password}&sasl_mechanism=SASL-SCRAM-SHA-256'

The following table lists the available parameters for Kafka URIs:

URI Parameter Description
topic_name The topic name to which messages will be sent. See the following section on Topic Naming for detail on how topics are created.
topic_prefix Adds a prefix to all topic names.

For example, CREATE CHANGEFEED FOR TABLE foo INTO 'kafka://...?topic_prefix=bar_' would emit rows under the topic bar_foo instead of foo.
tls_enabled If true, enable Transport Layer Security (TLS) on the connection to Kafka. This can be used with a ca_cert (see below).

Default: false
ca_cert The base64-encoded ca_cert file. Specify ca_cert for a Kafka sink.

Note: To encode your ca.cert, run base64 -w 0 ca.cert.
client_cert The base64-encoded Privacy Enhanced Mail (PEM) certificate. This is used with client_key.
client_key The base64-encoded private key for the PEM certificate. This is used with client_cert.

Note: Client keys are often encrypted. You will receive an error if you pass an encrypted client key in your changefeed statement. To decrypt the client key, run: openssl rsa -in key.pem -out key.decrypt.pem -passin pass:{PASSWORD}. Once decrypted, be sure to update your changefeed statement to use the new key.decrypt.pem file instead.
sasl_enabled If true, the authentication protocol can be set to SCRAM or PLAIN using the sasl_mechanism parameter. You must have tls_enabled set to true to use SASL.

Default: false
sasl_mechanism Can be set to SASL-SCRAM-SHA-256, SASL-SCRAM-SHA-512, or SASL-PLAIN. A sasl_user and sasl_password are required.

Default: SASL-PLAIN
sasl_user Your SASL username.
sasl_password Your SASL password
insecure_tls_skip_verify If true, disable client-side validation of responses. Note that a CA certificate is still required; this parameter means that the client will not verify the certificate. Warning: Use this query parameter with caution, as it creates MITM vulnerabilities unless combined with another method of authentication.

Default: false

This table shows the parameters for changefeeds to a specific sink. The CREATE CHANGEFEED page provides a list of all the available options.

Topic naming

By default, a Kafka topic has the same name as the table on which a changefeed was created. If a changefeed was created on multiple tables, the changefeed will write to multiple topics corresponding to those table names.

To modify the default topic naming, you can specify a topic prefix, an arbitrary topic name, or use the full_table_name option. Using the topic_name parameter, you can specify an arbitrary topic name and feed all tables into that topic.

You can either manually create a topic in your Kafka cluster before starting the changefeed, or the topic will be automatically created when the changefeed connects to your Kafka cluster.

Note:

You must have the Kafka cluster setting auto.create.topics.enable set to true for automatic topic creation. This will create the topic when the changefeed sends its first message. If you create the consumer before that, you will also need the Kafka consumer configuration allow.auto.create.topics to be set to true.

Kafka has the following topic limitations:

  • Legal characters are numbers, letters, and [._-].
  • The maximum character length of a topic name is 249.
  • Topics with a period (.) and underscore (_) can collide on internal Kafka data structures, so you should use either but not both.
  • Characters not accepted by Kafka will be automatically encoded as unicode characters by CockroachDB.

Kafka sink configuration

The kafka_sink_config option allows configuration of a changefeed's message delivery, Kafka server version, and batching parameters.

Warning:

Each of the following settings have significant impact on a changefeed's behavior, such as latency. For example, it is possible to configure batching parameters to be very high, which would negatively impact changefeed latency. As a result it would take a long time to see messages coming through to the sink. Also, large batches may be rejected by the Kafka server unless it's separately configured to accept a high max.message.bytes.

kafka_sink_config='{"Flush": {"MaxMessages": 1, "Frequency": "1s"}, "Version": "0.8.2.0", "RequiredAcks": "ONE" }'

"Flush"."MaxMessages" and "Flush"."Frequency" are configurable batching parameters depending on latency and throughput needs. For example, if "MaxMessages" is set to 1000 and "Frequency" to 1 second, it will flush to Kafka either after 1 second or after 1000 messages are batched, whichever comes first. It's important to consider that if there are not many messages, then a "1s" frequency will add 1 second latency. However, if there is a larger influx of messages these will be flushed quicker.

Using the default values or not setting fields in kafka_sink_config will mean that changefeed messages emit immediately.

The configurable fields are as follows:

Field Type Description Default
Flush.MaxMessages INT Sets the maximum number of messages the producer can send in a single broker request. Any messages beyond the configured limit will be blocked. Increasing this value allows all messages to be sent in a batch. 1
Flush.Messages INT Configure the number of messages the changefeed should batch before flushing. 0
Flush.Bytes INT When the total byte size of all the messages in the batch reaches this amount, it should be flushed. 0
Flush.Frequency INTERVAL When this amount of time has passed since the first received message in the batch without it flushing, it should be flushed. "0s"
"Version" STRING Sets the appropriate Kafka cluster version, which can be used to connect to Kafka versions < v1.0 (kafka_sink_config='{"Version": "0.8.2.0"}'). "1.0.0.0"
"RequiredAcks" STRING Specifies what a successful write to Kafka is. CockroachDB guarantees at least once delivery of messages — this value defines the delivery. The possible values are:

"ONE": a write to Kafka is successful once the leader node has committed and acknowledged the write. Note that this has the potential risk of dropped messages; if the leader node acknowledges before replicating to a quorum of other Kafka nodes, but then fails.

"NONE": no Kafka brokers are required to acknowledge that they have committed the message. This will decrease latency and increase throughput, but comes at the cost of lower consistency.

"ALL": a quorum must be reached (that is, most Kafka brokers have committed the message) before the leader can acknowledge. This is the highest consistency level.
"ONE"

Google Cloud Pub/Sub

Note:

The Google Cloud Pub/Sub sink is currently in beta. For more information, read about compatible changefeed options and the Create a changefeed connected to a Google Cloud Pub/Sub sink example.

New in v22.1: Changefeeds can deliver messages to a Google Cloud Pub/Sub sink, which is integrated with Google Cloud Platform.

A Pub/Sub sink URI follows this example:

'gcpubsub://{project name}?region={region}&topic_name={topic name}&AUTH=specified&CREDENTIALS={base64-encoded key}'

URI Parameter Description
project name The Google Cloud Project name.
region (Required) The single region to which all output will be sent.
topic_name (Optional) The topic name to which messages will be sent. See the following section on Topic Naming for detail on how topics are created.
AUTH The authentication parameter can define either specified (default) or implicit authentication. To use specified authentication, pass your Service Account credentials with the URI. To use implicit authentication, configure these credentials via an environment variable. See Use Cloud Storage for Bulk Operations for examples of each of these.
CREDENTIALS (Required with AUTH=specified) The base64-encoded credentials of your Google Service Account credentials.

This table shows the parameters for changefeeds to a specific sink. The CREATE CHANGEFEED page provides a list of all the available options.

When using Pub/Sub as your downstream sink, consider the following:

  • It only supports JSON message format.
  • Your Google Service Account must have the Pub/Sub Editor role assigned at the project level.
  • You must specify the region parameter in the URI to maintain ordering guarantees. Unordered messages are not supported, see Known Limitations for more information.
  • Changefeeds connecting to a Pub/Sub sink do not support the topic_prefix option.

Pub/Sub topic naming

When running a CREATE CHANGEFEED statement to Pub/Sub, it will try to create a topic automatically. When you do not specify the topic in the URI with the topic_name parameter, the changefeed will use the table name to create the topic name. If the topic already exists in your Pub/Sub sink, the changefeed will write to it. You can also use the full_table_name option to create a topic using the fully qualified table name.

You can manually create a topic in your Pub/Sub sink before starting the changefeed. See the Creating a changefeed to Google Cloud Pub/Sub example for more detail. To understand restrictions on user-specified topic names, see Google's documentation on Guidelines to name a topic or subscription.

For a list of compatible parameters and options, see Parameters on the CREATE CHANGEFEED page.

Cloud storage sink

Use a cloud storage sink to deliver changefeed data to OLAP or big data systems without requiring transport via Kafka.

Some considerations when using cloud storage sinks:

  • Cloud storage sinks only work with JSON and emit newline-delimited JSON files.
  • Cloud storage sinks can be configured to store emitted changefeed messages in one or more subdirectories organized by date. See file partitioning and the General file format examples.
  • The supported cloud schemes are: s3, gs, azure, http, and https.
  • Both http:// and https:// are cloud storage sinks, not webhook sinks. It is necessary to prefix the scheme with webhook- for webhook sinks.

Examples of supported cloud storage sink URIs:

Amazon S3

's3://{BUCKET NAME}/{PATH}?AWS_ACCESS_KEY_ID={KEY ID}&AWS_SECRET_ACCESS_KEY={SECRET ACCESS KEY}'

Azure Storage

'azure://{CONTAINER NAME}/{PATH}?AZURE_ACCOUNT_NAME={ACCOUNT NAME}&AZURE_ACCOUNT_KEY={URL-ENCODED KEY}'

Google Cloud Storage

'gs://{BUCKET NAME}/{PATH}?AUTH=specified&CREDENTIALS={ENCODED KEY}'

The following table lists the available parameters for cloud storage sink URIs:

URI Parameter Description
file_size The file will be flushed (i.e., written to the sink) when it exceeds the specified file size. This can be used with the WITH resolved option, which flushes on a specified cadence.

Default: 16MB
partition_format New in v22.1: Specify how changefeed file paths are partitioned in cloud storage sinks. Use partition_format with the following values:

  • daily is the default behavior that organizes directories by dates (2022-05-18/, 2022-05-19/, etc.).
  • hourly will further organize directories by hour within each date directory (2022-05-18/06, 2022-05-18/07, etc.).
  • flat will not partition the files at all.

For example: CREATE CHANGEFEED FOR TABLE users INTO 'gs://...?AUTH...&partition_format=hourly'

Default: daily
S3_storage_class New in v22.1: Specify the Amazon S3 storage class for files created by the changefeed. See Create a changefeed with an S3 storage class for the available classes and an example.

Default: STANDARD
topic_prefix Adds a prefix to all topic names.

For example, CREATE CHANGEFEED FOR TABLE foo INTO 's3://...?topic_prefix=bar_' would emit rows under the topic bar_foo instead of foo.

This table shows the parameters for changefeeds to a specific sink. The CREATE CHANGEFEED page provides a list of all the available options.

Use Cloud Storage for Bulk Operations provides more detail on authentication to cloud storage sinks.

Webhook sink

Note:

The webhook sink is currently in beta. The following section provides usage considerations.

Use a webhook sink to deliver changefeed messages to an arbitrary HTTP endpoint.

Example of a webhook sink URL:

'webhook-https://{your-webhook-endpoint}?insecure_tls_skip_verify=true'

The following table lists the parameters you can use in your webhook URI:

URI Parameter Description
ca_cert The base64-encoded ca_cert file. Specify ca_cert for a webhook sink.

Note: To encode your ca.cert, run base64 -w 0 ca.cert.
client_cert The base64-encoded Privacy Enhanced Mail (PEM) certificate. This is used with client_key.
client_key The base64-encoded private key for the PEM certificate. This is used with client_cert.

Note: Client keys are often encrypted. You will receive an error if you pass an encrypted client key in your changefeed statement. To decrypt the client key, run: openssl rsa -in key.pem -out key.decrypt.pem -passin pass:{PASSWORD}. Once decrypted, be sure to update your changefeed statement to use the new key.decrypt.pem file instead.
insecure_tls_skip_verify If true, disable client-side validation of responses. Note that a CA certificate is still required; this parameter means that the client will not verify the certificate. Warning: Use this query parameter with caution, as it creates MITM vulnerabilities unless combined with another method of authentication.

Default: false

This table shows the parameters for changefeeds to a specific sink. The CREATE CHANGEFEED page provides a list of all the available options.

The following are considerations when using the webhook sink:

  • Only supports HTTPS. Use the insecure_tls_skip_verify parameter when testing to disable certificate verification; however, this still requires HTTPS and certificates.
  • Only supports JSON output format.
  • There is no concurrency configurability.

Webhook sink configuration

The webhook_sink_config option allows the changefeed flushing and retry behavior of your webhook sink to be configured.

The following details the configurable fields:

Field Type Description Default
Flush.Messages INT When the batch reaches this configured size, it should be flushed (batch sent). 0
Flush.Bytes INT When the total byte size of all the messages in the batch reaches this amount, it should be flushed. 0
Flush.Frequency INTERVAL When this amount of time has passed since the first received message in the batch without it flushing, it should be flushed. "0s"
Retry.Max INT or STRING The maximum amount of time the sink will retry a single HTTP request to send a batch. This value must be positive (> 0). If infinite retries are desired, use inf. "0s"
Retry.Backoff INTERVAL The initial backoff the sink will wait after the first failure. The backoff will double (exponential backoff strategy), until the max is hit. "500ms"
Warning:

Setting either Messages or Bytes with a non-zero value without setting Frequency, will cause the sink to assume Frequency has an infinity value. If either Messages or Bytes have a non-zero value, then a non-zero value for Frequency must be provided. This configuration is invalid and will cause an error, since the messages could sit in a batch indefinitely if the other conditions do not trigger.

Some complexities to consider when setting Flush fields for batching:

  • When all batching parameters are zero ("Messages", "Bytes", and "Frequency") the sink will interpret this configuration as "send batch every time." This would be the same as not providing any configuration at all:
{
  "Flush": {
    "Messages": 0,
    "Bytes": 0,
    "Frequency": "0s"
  }
}
  • If one or more fields are set as non-zero values, any fields with a zero value the sink will interpret as infinity. For example, in the following configuration, the sink will send a batch whenever the size reaches 100 messages, or, when 5 seconds has passed since the batch was populated with its first message. Bytes defaults to 0 in this case, so a batch will never trigger due to a configured byte size:
{
  "Flush": {
    "Messages": 100,
    "Frequency": "5s"
  }
}

See also


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