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Please keep the discussion on the mailing list rather than commenting on the wiki (wiki discussions get unwieldy fast).

[This FLIP proposal is a joint work between Xuannan Su and Rui Fan ]

Motivation

As Flink progresses to 2.0, we want to enhance the user experience with the existing configuration. In FLIP-77, we introduced ConfigOption with DataType and strongly encourage users to utilize ConfigOption instead of string keys for accessing and setting Flink configurations. Presently, many string configuration keys have been deprecated and replaced with ConfigOptions; however, some string configuration keys are still in use.

To ensure a better experience with the existing configuration in Flink 2.0, this FLIP will migrates migrate all user-facing string configuration keys to ConfigOptions. Additionally, we want to modify the Configuration infrastructure to promote the use of ConfigOption over string configuration keys among developers and users.

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1. Update ConfigConstants.java to deprecate and replace string configuration keys:

2. Remove Mark unused constants in ConfigConstants.java as deprecated and remove in 2.0:

• LOCAL_NUMBER_JOB_MANAGER

• DEFAULT_LOCAL_NUMBER_JOB_MANAGER

• HA_JOB_MANAGER_PORT

• DEFAULT_EXECUTION_RETRIES

• DEFAULT_FILESYSTEM_SCHEME

• DEFAULT_FILESYSTEM_OVERWRITE

• DEFAULT_STATE_BACKEND

• ENV_FLINK_BIN_DIR

...

3. Update FileInputFormat.java, FileOutputFormat.java, BinaryInputFormat.java, and BinaryOutputFormat.java to deprecate and replace string configuration keys:

• We will introduce InputOutputFormatOptions class at org.apache.flink.api.common.io.

• FileInputFormat.java

• FileOutputFormat.java

• BinaryInputFormat.java

• BinaryOutputFormat.java

4. Update Configuration to encourage the usage of ConfigOption over string configuration key

• Deprecate getXXX(String key, XXX defaultValue) and setXXX(String key, XXX value), except getString(String key, String defaultValue) and , setString(String key, String value), getBytes(String key, byte[] defaultValue), and setBytes(String key, byte[] bytes).
  
• Update the comment in both getString(String key, String defaultValue) and setString(String key, String value) to encourage user users to use ConfigOption.

@Public
public class Configuration extends ExecutionConfig.GlobalJobParameters
        implements IOReadableWritable,
                java.io.Serializable,
                Cloneable,
                ReadableConfig,
                WritableConfig {
...

    /**
     * Returns the value associated with the given key as a string. Getting value with string key is
     * discouraged. Please use {@link #get(ConfigOption)} or {@link #getOptional(ConfigOption)}.
     *
     * @param key the key pointing to the associated value
     * @param defaultValue the default value which is returned in case there is no value associated
     *     with the given key
     * @return the (default) value associated with the given key
     */
    public String getString(String key, String defaultValue) {
        return getRawValue(key)
                .map(o -> ConfigurationUtils.convertToString(o, standardYaml))
                .orElse(defaultValue);		...
    }

    /**
     * Adds the given key/value pair to the configuration object. Setting value with string key is
     * discouraged. Please use {@link #set(ConfigOption, Object)}.
     *
     * @param key the key of the key/value pair to be added
     * @param value the value of the key/value pair to be added
     */
    public void setString(String key, String value) {
        setValueInternal(key, value);...
    }
}

Proposed Changes

1. Migrate all usage of deprecated string key in ConfigConstants to ConfigOption.

2. Remove all the internal usage of string configuration keys, e.g., DistributedCache, TaskConfig, StreamConfig, YarnClusterDescriptor, etc.

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