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This KIP proposes to migrate to incrementalAlterConfigs API for syncing topic configurations in MirrorMaker. The incrementalAlterConfigs API has been around for several years since it was introduced in Kafka 2.3.0 and addresses the shortcoming of the deprecated alterConfigs  API. In order not to break the compatibility, we will introduce a new setting to MirrorMaker to give the option to enable incrementalAlterConfigs API for syncing topic configurations. This new setting is expected to serve as a temporary measure until the next major release when the API is always used. 

It also proposes includes a proposal to add an option the ability to use the target cluster's default for the target topic configurations instead of , rather than using the source cluster's default. For example, if the user wants to use the target cluster default, the  ConfigPropertyFilter would be used instance, users would be able to configure ConfigPropertyFilter to check if the configuration on the source topic has been dynamically set and decide which cluster default should be usedis the default and decide whether or not to replicate it to the target topic. 

Proposed Changes

1) Add a new method updateTopicConfigsUsingIncrementalAlterConfigs() to MirrorSourceConnector.java which takes a list topic configurations as a parameter and calls incrementalAlterConfigs() to the target cluster. 

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