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In order to fix these issues, we should introduce a new RPC named incrementalAlterConfigs.  The new RPC should operate incrementally, modifying only the configuration values that are specified.  We should deprecate AlterConfigs.

Proposed Changes

The new IncrementalAlterConfigs API in AdminClient will take a collection of operations describing the configuration modifications.  There are four types of operations.

• Set: set a configuration to a value.  The value must not be null.
• Delete: delete a configuration key
• Append: if a configuration key is a list of values, add to the list.
• Subtract: if a configuration key is a list of values, subtract from the list.

Public Interfaces

@InterfaceStability.Evolving
public class AlterConfigOp {

    public enum OpType {
        SET((byte) 0), DELETE((byte) 1), APPEND((byte) 2), SUBTRACT((byte) 3);

        private static final Map<Byte, OpType> OP_TYPES = Collections.unmodifiableMap(
                Arrays.stream(values()).collect(Collectors.toMap(OpType::id, Function.identity()))
        );

        private final byte id;

        OpType(final byte id) {
            this.id = id;
        }

        public byte id() {
            return id;
        }

        public static OpType forId(final byte id) {
            return OP_TYPES.get(id);
        }
    }

    private final ConfigEntry configEntry;
    private final OpType opType;

    public AlterConfigOp(ConfigEntry configEntry, OpType operationType) {
        this.configEntry = configEntry;
        this.opType =  operationType;
    }

    public ConfigEntry configEntry() {
        return configEntry;
    };

    public OpType opType() {
        return opType;
    };
}


public IncrementalAlterConfigsResult incrementalAlterConfigs(
		Map<ConfigResource, Collection<AlterConfigOp>> configs,
        final IncrementalAlterConfigsOptions options);

...

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Similar to AlterConfigsResult, IncrementalAlterConfigsResult will have a values function which allows callers to determine the result of a specific configuration resource modifications, and an all function which will throw an exception if any operation failed.

@InterfaceStability.Evolving
public class IncrementalAlterConfigsResult {
    private final Map<ConfigResource, KafkaFuture<Void>> futures;

    IncrementalAlterConfigsResult(Map<ConfigResource, KafkaFuture<Void>> futures) {
        this.futures = futures;
    }

    /**
     * Return a map from resources to futures which can be used to check the status of the operation on each resource.
     */
    public Map<ConfigResource, KafkaFuture<Void>> values() {
        return futures;
    }

    /**
     * Return a future which succeeds only if all the alter configs operations succeed.
     */
    public KafkaFuture<Void> all() {
        return KafkaFuture.allOf(futures.values().toArray(new KafkaFuture[0]));
    }
}

...

@InterfaceStability.Evolving
public class IncrementalAlterConfigsOptions extends AbstractOptions<IncrementalAlterConfigsOptions> {
    private boolean validateOnly = false;

    /**
     * Set the request timeout in milliseconds for this operation or {@code null} if the default request timeout for the
     * AdminClient should be used.
     */
    public IncrementalAlterConfigsOptions timeoutMs(Integer timeoutMs) {
        this.timeoutMs = timeoutMs;
        return this;
    }

    /**
     * Return true if the request should be validated without altering the configs.
     */
    public boolean shouldValidateOnly() {
        return validateOnly;
    }

    /**
     * Set to true if the request should be validated without altering the configs.
     */
    public IncrementalAlterConfigsOptions validateOnly(boolean validateOnly) {
        this.validateOnly = validateOnly;
        return this;
    }
}

Proposed Changes

The new IncrementalAlterConfigs API in AdminClient will take a collection of operations describing the configuration modifications.  There are four types of operations.

• Set: set a configuration to a value.  The value must not be null.
• Delete: delete a configuration key
• Append: if a configuration key is a list of values, add to the list.
• Subtract: if a configuration key is a list of values, subtract from the list.

Similar to AlterConfigsResult, IncrementalAlterConfigsResult will have a values function which allows callers to determine the result of a specific configuration resource modifications, and an all function which will throw an exception if any operation failed.

Similar to AlterConfigsOptions, IncrementalAlterConfigsOptions will include a timeout value and a dry-run flag.

Similar to existing alterConfigs API, we will to keep the "transactionality" of updating several configs  for the same ConfigResource at once. We guarantee that we never do a partial update of a collection of configs
for a ConfigResource from a single request. On validation/update error, we will return the error for the ConfigResource.

Protocol APIs

There will be a new IncrementalAlterConfigsRequest.

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• If a configuration key was specified more than once in the request for given ConfigResource, we fail ConfigResource update with the INVALID_REQUEST will be returned for all occurrences of the configuration key.
• If APPEND or SUBTRACT was specified for a configuration key that does not take a list of elements, we fail ConfigResource update with the INVALID_REQUEST will be returned for the configuration key.

Compatibility, Deprecation, and Migration Plan

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