refactor: respect data_home as root data home directory

[zyy17]

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What's changed and what's your intention?

respect data_home as root data home directory:

1. When logs_dir is not specified, use ${data_home}/${logs_dir} as default logs dir;
2. Rename METASRV_HOME to METASRV_DATA_DIR and change its default value to metasrv/. The actual metasrv_home will be ${data_home}/${METASRV_DATA_DIR};
3. Normalize some constants about *DIR;

PR Checklist

Please convert it to a draft if some of the following conditions are not met.

• I have written the necessary rustdoc comments.
• I have added the necessary unit tests and integration tests.
• This PR requires documentation updates.
• API changes are backward compatible.
• Schema or data changes are backward compatible.

[Copilot]

Pull Request Overview

This PR centralizes path configuration by introducing DEFAULT_DATA_HOME as the root data directory, renaming and refactoring component‐specific home and log directories to use this base, and updating code, tests, and example configs to join subdirectories under data_home.

• Introduce DEFAULT_DATA_HOME and DEFAULT_LOGGING_DIR constants and remove hardcoded paths
• Rename METASRV_HOME to METASRV_DATA_DIR and update MetasrvOptions defaults
• Update CLI commands to set logging.dir under data_home when unset and refresh example configs/docs

Reviewed Changes

Copilot reviewed 17 out of 17 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/meta-srv/src/metasrv/builder.rs	Build metasrv_home by joining data_home and METASRV_DATA_DIR
src/meta-srv/src/metasrv.rs	Rename METASRV_HOME → METASRV_DATA_DIR, use DEFAULT_DATA_HOME
src/datanode/src/config.rs	Remove local DEFAULT_DATA_HOME, import global constant
src/common/telemetry/src/logging.rs	Add DEFAULT_LOGGING_DIR, clear default dir for runtime override
src/common/config/src/lib.rs	Add DEFAULT_DATA_HOME constant
src/cmd/tests/load_config_test.rs	Update tests to use DEFAULT_DATA_HOME/DEFAULT_LOGGING_DIR
src/cmd/src/{standalone,metasrv,frontend,flownode,datanode}.rs	Set logging.dir to <data_home>/logs/ if empty
config/*.example.toml, config/config.md	Refresh example paths with trailing slashes and new defaults

Comments suppressed due to low confidence (2)

src/cmd/tests/load_config_test.rs:61

• Example configs now use a trailing slash for the WAL directory, but WAL_DIR may not include it. Ensure WAL_DIR constant includes a trailing slash or update the test to expect the trailing slash so the loaded value matches the TOML example.

Path::new(DEFAULT_DATA_HOME).join(WAL_DIR).to_string_lossy().to_string(),

src/cmd/src/standalone.rs:408

• [nitpick] Consider adding a unit or integration test to verify that logging.dir is correctly set to <data_home>/logs/ when the option is left empty, to prevent regressions in this new fallback logic.

if opts.logging.dir.is_empty() {

[Copilot]

Pull Request Overview

This PR refactors directory configurations to respect data_home as the root data directory by updating default constants and configuration paths. Key changes include:

• Using data_home to compute default paths for logs, WAL, and metasrv directories.
• Renaming METASRV_HOME to METASRV_DATA_DIR for clarity.
• Normalizing configuration files and tests to align with the new default directory constants.

Reviewed Changes

Copilot reviewed 16 out of 16 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/store-api/src/path_utils.rs	Normalizes WAL_DIR by removing the trailing slash.
src/meta-srv/src/metasrv/builder.rs	Updates metasrv home construction using data_home and METASRV_DATA_DIR.
src/meta-srv/src/metasrv.rs	Replaces METASRV_HOME with METASRV_DATA_DIR and updates logging defaults.
src/datanode/src/config.rs	Leverages DEFAULT_DATA_HOME from common_config.
src/common/telemetry/src/logging.rs	Updates LoggingOptions default directory configuration.
src/common/config/src/lib.rs	Adds DEFAULT_DATA_HOME constant.
src/cmd/tests/load_config_test.rs	Aligns test configurations with updated default directory constants.
src/cmd/src/standalone.rs	Sets logging directory using data_home if not provided.
src/cmd/src/metasrv.rs	Sets logging directory using data_home if unset.
src/cmd/src/frontend.rs	Sets logging directory using data_home if unset.
src/cmd/src/flownode.rs	Sets logging directory using data_home if unset.
src/cmd/src/datanode.rs	Sets logging directory using data_home if unset.
config/standalone.example.toml	Normalizes storage.data_home configuration.
config/metasrv.example.toml	Normalizes data_home configuration.
config/datanode.example.toml	Normalizes storage.data_home configuration.
config/config.md	Updates documentation to reflect new data_home defaults.

Comments suppressed due to low confidence (1)

src/store-api/src/path_utils.rs:21

• Removing the trailing slash from WAL_DIR may affect path concatenations if downstream consumers expect a trailing separator. Verify that all usages correctly handle this change or adjust the constant or consumers accordingly.

pub const WAL_DIR: &str = "wal";

[MichaelScofield]

Is this a breaking change if users are using the default configuration?

[zyy17]

It's not a breaking change.

In the original implementation, it uses the following code to create a data home for metasrv:

let metasrv_home = options.data_home.to_string();

This PR change to(METASRV_DATA_DIR is metasrv):

        let metasrv_home = Path::new(&options.data_home)
            .join(METASRV_DATA_DIR)
            .to_string_lossy()
            .to_string();

The final config is the same.

[zyy17]

After some thought, it's not breaking change for default configs. However, it could be a breaking change for the scenarios that specify data_home, although it isn't very common in most deployments.

What do you think? @fengjiachun @killme2008, should we break it or not?