WIth the JDBC transaction manager, use the storage default transaction isolation level instead of SERIALIZABLE

[Torch3333]

Description

When the JDBC transaction manager is used, we set the default transaction isolation level to SERIALIZABLE if the user does not specify one in the config with scalar.db.jdbc.isolation_level.
We now consider this is not necessary anymore and the default storage transaction isolation can be used if scalar.db.jdbc.isolation_level is not set.

Related issues and/or PRs

• Support TiDB #3001 (comment)

Changes made

• For the JDBC transaction manager, do not set the SERIALIZABLE transaction isolation level by default. The transaction isolation level is set by the storage.

Checklist

The following is a best-effort checklist. If any items in this checklist are not applicable to this PR or are dependent on other, unmerged PRs, please still mark the checkboxes after you have read and understood each item.

• I have commented my code, particularly in hard-to-understand areas.
• I have updated the documentation to reflect the changes.
• I have considered whether similar issues could occur in other products, components, or modules if this PR is for bug fixes.
• Any remaining open issues linked to this PR are documented and up-to-date (Jira, GitHub, etc.).
• Tests (unit, integration, etc.) have been added for the changes.
• My changes generate no new warnings.
• Any dependent changes in other PRs have been merged and published.

Additional notes (optional)

N/A

Release notes

When using the JDBC transaction manager, do not set the JDBC transaction isolation level to SERIALIZABLE when the configuration scalar.db.jdbc.isolation_level is not set. The default is now the default value set by the storage.

[Copilot]

Pull Request Overview

This PR changes the default transaction isolation level behavior for JDBC transaction manager. Instead of forcing SERIALIZABLE isolation level when scalar.db.jdbc.isolation_level is not configured, it now allows the storage to use its own default transaction isolation level.

Key Changes

• Removed the hardcoded SERIALIZABLE transaction isolation level setting from the JDBC data source initialization
• Transaction isolation level now defaults to the storage's native default when not explicitly configured

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[brfrn169]

LGTM! Thank you!

[feeblefakie]

LGTM! Thank you!

[komamitsu]

LGTM, thank you!