MySQL schema change to support fractional time

[bpkroth]

Pull Request

Title

MySQL schema change to support fractional time

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Description

• Changes the storage schema to support a variant for MySQL that can handle fractional time.
• Adds a custom column comparator to be able to pick that up by default in the future.
• Adjusts tests to check for fractional time support.

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Type of Change

• 🛠️ Bug fix
• ✨ New feature
• 🔄 Refactor
• 🧪 Tests

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Testing

• A lot of manual testing with docker.
• Additional CI tests
• Existing CI tests

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Additional Notes (optional)

Part of a series of changes, should be merged after #983

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[Copilot]

Pull Request Overview

Adds support for fractional seconds in MySQL storage columns and aligns the test suite to use a new docker_hostname fixture.

• Updated all relevant DateTime columns to use mysql.DATETIME(fsp=6) variants and removed microsecond truncation in trial creation.
• Introduced a custom Alembic type comparator and schema-reset helpers for testing.
• Refactored test fixtures/configs: replaced per-module SSH host fixtures with a shared docker_hostname, updated JSON configs, and adjusted telemetry tests for fractional timestamps.

Reviewed Changes

Copilot reviewed 29 out of 29 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
tests/services/remote/ssh/test_ssh_host_service.py	Consolidated imports to include wait_docker_service_socket.
tests/services/remote/ssh/fixtures.py	Switched from ssh_test_server_hostname to shared docker_hostname.
tests/services/remote/ssh/conftest.py	Removed obsolete hostname fixture alias.
tests/services/remote/ssh/init.py	Dropped duplicate helper and plugin imports.
tests/environments/remote/conftest.py	Removed unused hostname fixture.
tests/environments/local/local_env_telemetry_test.py	Updated timestamp format strings to include microseconds.
tests/environments/local/composite_local_env_test.py	Updated timestamp format strings to include microseconds.
tests/conftest.py	Added docker_hostname fixture—missing sys import causes a bug.
tests/config/schedulers/test_load_scheduler_config_examples.py	Replaced concrete SqlStorage type with the Storage interface.
tests/init.py	Duplicate imports and two definitions of wait_docker_service_socket.
storage/sql/storage.py	Added _reset_schema test helper.
storage/sql/schema.py	Refactored string-length constants and added DATETIME(fsp=6).
storage/sql/experiment.py	Removed forced truncation of microseconds in _new_trial.
storage/sql/alembic/versions/..._support_fractional_seconds_with_mysql.py	Auto-generated Alembic revision for fractional-second support.
storage/sql/alembic/env.py	Added custom_compare_types comparator and updated env configuration.
storage/sql/alembic/README.md	Expanded and clarified migration instructions.
storage/sql/alembic.ini	Updated hooks and uncommented URL options.
config/storage/postgresql.jsonc	Corrected database name.
config/storage/mysql.jsonc	Corrected database name.

Comments suppressed due to low confidence (4)

mlos_bench/mlos_bench/tests/conftest.py:38

• The docker_hostname fixture references sys.platform but sys is not imported at the top of this file. Add import sys.

if sys.platform != "win32" and resolve_host_name(HOST_DOCKER_NAME):

mlos_bench/mlos_bench/tests/init.py:19

• [nitpick] Duplicate import of Services as DockerServices. Remove the redundant import to clean up the module namespace.

from pytest_docker.plugin import Services as DockerServices

mlos_bench/mlos_bench/tests/init.py:109

• This helper is defined twice in this file (also around line 151). Consolidate to a single definition to avoid confusion.

def wait_docker_service_socket(docker_services: DockerServices, hostname: str, port: int) -> None:

mlos_bench/mlos_bench/storage/sql/alembic/env.py:15

• [nitpick] Importing two different Column classes under similar names may be confusing. Consider renaming the alias (e.g., InspectedColumn) for clarity.

from sqlalchemy.schema import Column as SchemaColumn