Add support for beginning transactions in read-only mode

[brfrn169]

Description

This PR adds support for beginning transactions in read-only mode. It simply merges the support-begin-in-read-only-mode feature branch into the master branch, and the code has already been reviewed.

Related issues and/or PRs

• Add beginReadOnly() method to transaction abstraction #2734
• Support begin in read-only mode for JDBC transactions #2738
• Support begin in read-only mode for Consensus Commit transactions #2739

Changes made

• Merged the support-begin-in-read-only-mode feature branch to the master branch

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

Added support for beginning transactions in read-only mode.

[Copilot]

Pull Request Overview

This PR adds support for beginning transactions in read‐only mode by extending the transaction manager interfaces and implementations across multiple modules. It introduces new methods (beginReadOnly/startReadOnly) in core transaction manager classes, updates JDBC connection handling for read‐only mode, and adds a new error code for mutation attempts in read‐only transactions.

Reviewed Changes

Copilot reviewed 26 out of 26 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
core/src/main/java/com/scalar/db/transaction/singlecrudoperation/SingleCrudOperationTransactionManager.java	Added read‐only methods that throw an UnsupportedOperationException.
core/src/main/java/com/scalar/db/transaction/jdbc/JdbcTransactionManager.java	Updated begin and executeTransaction methods to support a readOnly parameter.
core/src/main/java/com/scalar/db/transaction/consensuscommit/TwoPhaseConsensusCommitManager.java	Modified CrudHandler construction to include a readOnly flag.
core/src/main/java/com/scalar/db/transaction/consensuscommit/Snapshot.java	Expanded inline documentation for transaction sets.
core/src/main/java/com/scalar/db/transaction/consensuscommit/CrudHandler.java	Introduced conditional behavior based on a readOnly flag for handling read set and scan validation.
core/src/main/java/com/scalar/db/transaction/consensuscommit/ConsensusCommitManager.java	Added read‐only transaction methods and wrapped transactions when in read‐only mode.
core/src/main/java/com/scalar/db/storage/jdbc/RdbEngineStrategy.java	Renamed method to setConnectionToReadOnly and adjusted its signature.
core/src/main/java/com/scalar/db/storage/jdbc/JdbcDatabase.java	Updated calls to use the renamed setConnectionToReadOnly method.
core/src/main/java/com/scalar/db/storage/jdbc/JdbcAdmin.java	Updated methods to set JDBC connections to read‐only mode via the renamed method.
core/src/main/java/com/scalar/db/storage/dynamo/SelectStatementHandler.java	Added documentation for the new fetchSize parameter.
core/src/main/java/com/scalar/db/service/TransactionService.java	Exposed read‐only transaction methods that delegate to the underlying manager.
core/src/main/java/com/scalar/db/common/error/CoreError.java	Introduced a new error code for mutations attempted in read‐only transactions.
core/src/main/java/com/scalar/db/common/ReadOnlyDistributedTransaction.java	Provided a read‐only transaction proxy that forbids mutation operations.
core/src/main/java/com/scalar/db/common/DecoratedDistributedTransactionManager.java	Forwarded read‐only transaction methods from the decorated manager.
core/src/main/java/com/scalar/db/api/DistributedTransactionManager.java	Extended the interface to include read‐only transaction methods with appropriate Javadoc.

Comments suppressed due to low confidence (3)

core/src/main/java/com/scalar/db/transaction/singlecrudoperation/SingleCrudOperationTransactionManager.java:79

• Consider adding a clarifying comment explaining why read-only transactions are not supported in this transaction manager, to aid future maintainers in understanding the design decision.

@Override

core/src/main/java/com/scalar/db/common/error/CoreError.java:934

• Ensure that the new error code '0211' for MUTATION_NOT_ALLOWED_IN_READ_ONLY_TRANSACTION is documented in the project’s error handling guidelines for consistency.

MUTATION_NOT_ALLOWED_IN_READ_ONLY_TRANSACTION(

core/src/main/java/com/scalar/db/transaction/consensuscommit/ConsensusCommitManager.java:244

• Since the CrudHandler is constructed with a readOnly flag and the transaction is further wrapped in a ReadOnlyDistributedTransaction, please verify that this double application is intentional and consider adding a comment to clarify the rationale.

if (readOnly) {

[Torch3333]

LGTM, thank you!

[feeblefakie]

LGTM! Thank you!

[komamitsu]

LGTM! 👍