Hint

Background

Apache ShardingSphere uses ThreadLocal to manage primary database routing marks for mandatory routing. A primary database routing mark can be added to HintManager through programming, and this value is valid only in the current thread.

Hint is mainly used to perform mandatory data operations in the primary database for read/write splitting scenarios.

Procedure

1. Call HintManager.getInstance() to obtain HintManager instance.
2. Call HintManager.setWriteRouteOnly() method to set the primary database routing marks.
3. Execute SQL statements to complete routing and execution.
4. Call HintManager.close() to clear the content of ThreadLocal.

Sample

Primary Route with Hint

Get HintManager

The same as sharding based on hint.

Configure Primary Database Route

• Use hintManager.setWriteRouteOnly to configure primary database route.

Clean Hint Value

The same as data sharding based on hint.

Code:

String sql = "SELECT * FROM t_order";
try (HintManager hintManager = HintManager.getInstance();
     Connection conn = dataSource.getConnection();
     PreparedStatement preparedStatement = conn.prepareStatement(sql)) {
    hintManager.setWriteRouteOnly();
    try (ResultSet rs = preparedStatement.executeQuery()) {
        while (rs.next()) {
            // ...
        }
    }
}

Route to the specified database with Hint

Get HintManager

The same as sharding based on hint.

Configure Database Route

• Use hintManager.setDataSourceName to configure database route.

Code:

String sql = "SELECT * FROM t_order";
try (HintManager hintManager = HintManager.getInstance();
     Connection conn = dataSource.getConnection();
     PreparedStatement preparedStatement = conn.prepareStatement(sql)) {
    hintManager.setDataSourceName("ds_0");
    try (ResultSet rs = preparedStatement.executeQuery()) {
        while (rs.next()) {
            // ...
        }
    }
}

Related References

• Core Feature: Read/write Splitting
• Developer Guide: Read/write Splitting