Support begin in read-only mode for JDBC transactions

[brfrn169]

Description

This PR adds support for beginning a transaction in read-only mode for JDBC transactions.

Note that this feature is being developed in the support-begin-in-read-only-mode feature branch.

Related issues and/or PRs

• Add beginReadOnly() method to transaction abstraction #2734

Changes made

Added some inline comments. Please take a look for the details!

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

N/A

[Copilot]

Pull Request Overview

This PR adds support for starting JDBC transactions in read-only mode and updates related tests and execution logic.

• Introduces beginReadOnly overloads and a unified begin(txId, readOnly) implementation
• Updates executeTransaction to distinguish between read-only and read-write operations
• Adjusts unit tests to cover read-only behavior and cleans up integration tests

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
core/src/test/java/com/scalar/db/transaction/jdbc/JdbcTransactionManagerTest.java	Added tests for beginReadOnly variants and updated scanner tests to use read-only transactions
core/src/main/java/com/scalar/db/transaction/jdbc/JdbcTransactionManager.java	Added beginReadOnly methods, unified begin(txId, readOnly), and updated executeTransaction to accept a read-only flag
core/src/integration-test/java/com/scalar/db/transaction/jdbc/JdbcTransactionIntegrationTest.java	Removed placeholder disabled tests for read-only integration scenarios

Comments suppressed due to low confidence (4)

core/src/integration-test/java/com/scalar/db/transaction/jdbc/JdbcTransactionIntegrationTest.java:42

• Integration tests for read-only transactions have been removed; consider implementing and re-enabling tests to validate read-only begin methods in real database scenarios.

@Disabled("Implement later")

core/src/main/java/com/scalar/db/transaction/jdbc/JdbcTransactionManager.java:104

• Public methods beginReadOnly and beginReadOnly(String) lack Javadoc comments; consider adding descriptions for their behavior and parameters.

public DistributedTransaction beginReadOnly() throws TransactionException {

core/src/main/java/com/scalar/db/transaction/jdbc/JdbcTransactionManager.java:114

• [nitpick] Consider renaming the boolean parameter readOnly to isReadOnly for clearer intent in the method signature.

private DistributedTransaction begin(String txId, boolean readOnly) throws TransactionException {

core/src/main/java/com/scalar/db/transaction/jdbc/JdbcTransactionManager.java:376

• [nitpick] The executeTransaction method now requires an explicit readOnly flag for each call; consider providing an overload without the flag (defaulting to write mode) to simplify calls for common write operations.

private <R> R executeTransaction(

[brfrn169]

Call Connection.setReadOnly() for read-only transactions.

[komamitsu]

I noticed the method name setReadOnly() seems to change the rdbEngine to read-only mode. setConnectionToReadOnly() might be less confusing. What do you think?

[brfrn169]

Fixed in 60c000f. Thanks!

[brfrn169]

Wrap the transaction object with ReadOnlyDistributedTransaction.

[komamitsu]

LGTM! 👍

[feeblefakie]

LGTM! Thank you!

[Torch3333]

LGTM, thank you!