OF-3277: Introduce helper method to determine database 'limit' keyword

[guusdk]

The SQL LIMIT clause is not portable across the databases Openfire supports. SQL Server, for example, uses SELECT TOP.

Up until now, code had to interrogate the type of database to find out what variant to be used. In this commit, this information is exposed as metadata.

Small changes have been applid to the pubsub persistence implementation. It is expected that the Monitoring plugin (and others) benefit from this, too.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

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📥 Commits

Reviewing files that changed from the base of the PR and between 3e6245d and bc0caf5.

📒 Files selected for processing (3)

• xmppserver/src/main/java/org/jivesoftware/database/DbConnectionManager.java
• xmppserver/src/main/java/org/jivesoftware/openfire/pubsub/DefaultPubSubPersistenceProvider.java
• xmppserver/src/test/java/org/jivesoftware/database/DbConnectionManagerTest.java

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📝 Walkthrough

Walkthrough

This PR adds a public API to DbConnectionManager for database-specific result-set limit syntax and applies it to eliminate hardcoded database checks. A new ResultSetLimitKeyword enum maps each database type (SQL Server, Oracle, DB2, ANSI) to its keyword (TOP, FETCH_FIRST, or LIMIT) and metadata indicating whether the keyword is prefix- or suffix-style. DefaultPubSubPersistenceProvider.getPublishedItems() is refactored to use this API when selecting between prepared statements and binding the max parameter. New JUnit tests validate the keyword mappings and prefix behavior across database types.

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description check	✅ Passed	The pull request description accurately describes the changeset and its motivation: exposing database-specific SQL LIMIT keyword metadata to avoid hard-coded database type checks.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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[Copilot]

Pull request overview

This PR (OF-3277) centralizes database-specific SQL row-limiting behavior by exposing metadata from DbConnectionManager, reducing the need for scattered database-type checks (eg. LIMIT vs SQL Server TOP).

Changes:

• Added ResultSetLimitKeyword metadata (keyword + prefix/suffix positioning) to DbConnectionManager / DatabaseType.
• Updated PubSub persistence logic to select the appropriate query variant based on the new metadata.
• Added unit tests that validate the mapping for SQL Server, Oracle, DB2, and ANSI-style databases.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.

File	Description
xmppserver/src/main/java/org/jivesoftware/database/DbConnectionManager.java	Introduces ResultSetLimitKeyword and helper methods to expose per-database row-limiting keyword metadata.
xmppserver/src/main/java/org/jivesoftware/openfire/pubsub/DefaultPubSubPersistenceProvider.java	Replaces database-type branching with the new row-limiting keyword metadata when loading last published items.
xmppserver/src/test/java/org/jivesoftware/database/DbConnectionManagerTest.java	Adds test coverage for the new keyword/prefix metadata across key database types.

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[stokito]

Looks like start of re-inventing Hibernate Dialect.
Maybe we can't use it because of it's bad performance but maybe something can be helpful there
https://github.com/hibernate/hibernate-orm/blob/main/hibernate-core/src/main/java/org/hibernate/dialect/pagination/SQLServer2012LimitHandler.java