Notes and Constraints
This section describes the notes and constraints on DMS for Kafka.
Instance
Item |
Notes and Constraints |
---|---|
Kafka ZooKeeper |
Kafka clusters are managed using ZooKeeper. Opening ZooKeeper may cause misoperations and service losses. Currently, ZooKeeper is used only within Kafka clusters and does not provide services externally. |
Version |
|
Logging in to the VM where the Kafka brokers reside |
Not supported |
Storage |
|
Bandwidth or broker quantity |
The bandwidth and broker quantity can be increased but cannot be decreased. |
VPC, subnet, and AZ |
After an instance is created, its VPC, subnet, and AZ cannot be modified. |
Kerberos authentication |
Not supported |
Topic
Item |
Notes and Constraints |
---|---|
Total number of topic partitions |
The total number of topic partitions is related to the instance specifications. For details, see Specifications. Kafka manages messages by partition. If there are too many partitions, message creation, storage, and retrieval will be fragmented, affecting the performance and stability. If the total number of partitions of topics reaches the upper limit, you cannot create more topics. |
Number of partitions in a topic |
Based on the open-source Kafka constraints, the number of partitions in a topic can be increased but cannot be decreased. |
Topic quantity |
The topic quantity is related to the total number of topic partitions and number of partitions in each topic. For details, see Specifications. |
Automatic topic creation |
Supported. If automatic topic creation is enabled, the system automatically creates a topic when a message is created in or retrieved from a topic that does not exist. This topic has the following default settings: 3 partitions, 3 replicas, aging time 72 hours, and synchronous replication and flushing disabled. After you change the value of the log.retention.hours, default.replication.factor, or num.partitions parameter, automatically created topics later use the new value. For example, if num.partitions is set to 5, an automatically created topic will have the following settings: 5 partitions, 3 replicas, aging time 72 hours, and synchronous replication and flushing disabled. |
Synchronous replication |
If a topic has only one replica, synchronous replication cannot be enabled. |
Replica quantity |
Single-replica topics are not recommended. If an instance node is faulty, an internal service error may be reported when you query messages in a topic with only one replica. Therefore, you are not advised to use a topic with only one replica. |
Aging time |
The value of the log.retention.hours parameter takes effect only if the aging time has not been set for the topic. For example, if the aging time of Topic01 is set to 60 hours and log.retention.hours is set to 72 hours, the actual aging time of Topic01 is 60 hours. |
Batch importing and exporting topics |
Batch export is supported, but batch import is not supported. |
Topic name |
If a topic name starts with a special character, for example, an underscore (_) or a number sign (#), monitoring data cannot be displayed. |
Delay queues |
Not supported |
Consumer Group
Item |
Notes and Constraints |
---|---|
Creating consumer groups, consumers, and producers |
Consumer groups, consumers, and producers are generated automatically when you use the instance. |
Resetting the consumer offset |
Messages may be retrieved more than once after the offset is reset. |
Consumer group name |
If a consumer group name starts with a special character, for example, an underscore (_) or a number sign (#), monitoring data cannot be displayed. |
Message
Item |
Notes and Constraints |
---|---|
Message size |
The maximum length of a message is 10 MB. If the length exceeds 10 MB, the production fails. |
User
Item |
Notes and Constraints |
---|---|
Number of users |
A maximum of 20 SASL_SSL users can be created for a Kafka instance. |
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