docs: update known limitation section for blue/green deployment (#1490)

Author: karenc-bq

README.md

@@ -118,26 +118,23 @@ To find all the documentation and concrete examples on how to use the AWS JDBC D
 
 #### Amazon RDS Blue/Green Deployments
 
-Although the AWS Advanced JDBC Wrapper is not compatible with [AWS Blue/Green Deployments](https://docs.aws.amazon.com/whitepapers/latest/overview-deployment-options/bluegreen-deployments.html) and does not officially support them, the combination of the AWS Advanced JDBC Wrapper and the Failover Plugin has been validated for use with clusters that employ Blue/Green Deployments. While general basic connectivity to both Blue and Green clusters is always in place, some failover cases are not fully supported.
+The AWS Advanced JDBC Wrapper **versions 2.6.0 and above** now include enhanced full support for Blue/Green Deployments. This support requires a minimum database version that includes a specific metadata table. This constraint **does not** apply to RDS MySQL.
 
-The current limitations are:
+**No action is required** if your database does not include the new metadata table -- the driver will continue to operate as before with no special blue/green functionality. If you have questions or encounter issues, please open an issue in this repository.
+
+Supported RDS PostgreSQL Versions: `rds_tools v1.7 (17.1, 16.5, 15.9, 14.14, 13.17, 12.21)` and above.<br>
+Supported Aurora PostgreSQL Versions: Engine Release `17.5, 16.9, 15.13, 14.18, 13.21` and above.<br>
+Supported Aurora MySQL Versions: Engine Release `3.07` and above.
+
+If your database version does **not** support this table, the driver will automatically detect its absence and fallback to its previous behaviour in wrapper versions <2.6.0. In this fallback mode, Blue/Green handling is subject to the same limitations listed below.
+
+AWS Advanced JDBC Wrapper **versions earlier than 2.6.0** are not compatible with [AWS Blue/Green Deployments](https://docs.aws.amazon.com/whitepapers/latest/overview-deployment-options/bluegreen-deployments.html) and do not officially support them. However, the combination of the AWS Advanced JDBC Wrapper and the Failover Plugin has been validated for use with clusters that employ Blue/Green Deployments for these versions. While general basic connectivity to both Blue and Green clusters is always in place, some failover cases are not fully supported.
+
+The limitations for versions earlier than 2.6.0 are:
 - After a Blue/Green switchover, the wrapper may not be able to properly detect the new topology and handle failover, as there are discrepancies between the metadata and the available endpoints.
 - The specific version requirements for Aurora MySQL versus Aurora PostgreSQL may vary, as the internal systems used by the wrapper can differ[^1].
 
-The development team is aware of these limitations and is working to improve the wrapper's awareness and handling of Blue/Green switchovers. In the meantime, users can consider utilizing the `enableGreenNodeReplacement` configuration parameter, which allows the driver to override incorrect topology metadata and try to connect to available new Blue endpoints.
-
-> [!WARNING]\
-> **Blue/Green Support Behaviour and Version Compatibility**
-> 
-> The AWS Advanced JDBC Wrapper now includes enhanced full support for Blue/Green Deployments. This support requires a minimum database version that includes a specific metadata table. This constraint **does not** apply to RDS MySQL.
->
-> If your database version does **not** support this table, the driver will automatically detect its absence and fallback to its previous behaviour. In this fallback mode, Blue/Green handling is subject to the same limitations listed above.
->
-> **No action is required** if your database does not include the new metadata table -- the driver will continue to operate as before. If you have questions or encounter issues, please open an issue in this repository.
->
-> Supported RDS PostgreSQL Versions: `rds_tools v1.7 (17.1, 16.5, 15.9, 14.14, 13.17, 12.21)` and above.<br>
-> Supported Aurora PostgreSQL Versions: Engine Release `17.5, 16.9, 15.13, 14.18, 13.21` and above.<br>
-> Supported Aurora MySQL Versions: Engine Release `3.07` and above.
+For these earlier versions, users can consider utilizing the `enableGreenNodeReplacement` configuration parameter, which allows the driver to override incorrect topology metadata and try to connect to available new Blue endpoints.
 
 [^1]: Aurora MySQL requires v3.07 or later.
 

wrapper/src/main/java/software/amazon/jdbc/dialect/RdsMultiAzDbClusterPgDialect.java

@@ -39,24 +39,19 @@ public class RdsMultiAzDbClusterPgDialect extends PgDialect {
   private static final String TOPOLOGY_QUERY =
       "SELECT id, endpoint, port FROM rds_tools.show_topology('aws_jdbc_driver-" + DriverInfo.DRIVER_VERSION + "')";
 
-  private static final String WRITER_NODE_FUNC_EXIST_QUERY =
-      "SELECT 1 AS tmp FROM information_schema.routines"
-          + " WHERE routine_schema='rds_tools' AND routine_name='multi_az_db_cluster_source_dbi_resource_id'";
-
   // For reader nodes, the query should return a writer node ID. For a writer node, the query should return no data.
   private static final String FETCH_WRITER_NODE_QUERY =
       "SELECT multi_az_db_cluster_source_dbi_resource_id FROM rds_tools.multi_az_db_cluster_source_dbi_resource_id()"
           + " WHERE multi_az_db_cluster_source_dbi_resource_id !="
           + " (SELECT dbi_resource_id FROM rds_tools.dbi_resource_id())";
 
+  private static final String IS_RDS_CLUSTER_QUERY =
+      "SELECT multi_az_db_cluster_source_dbi_resource_id FROM rds_tools.multi_az_db_cluster_source_dbi_resource_id()";
+
   private static final String FETCH_WRITER_NODE_QUERY_COLUMN_NAME = "multi_az_db_cluster_source_dbi_resource_id";
 
   private static final String NODE_ID_QUERY = "SELECT dbi_resource_id FROM rds_tools.dbi_resource_id()";
 
-  private static final String NODE_ID_FUNC_EXIST_QUERY =
-      "SELECT 1 AS tmp FROM information_schema.routines"
-          + " WHERE routine_schema='rds_tools' AND routine_name='dbi_resource_id'";
-
   private static final String IS_READER_QUERY = "SELECT pg_is_in_recovery()";
 
   @Override
@@ -69,39 +64,11 @@ public ExceptionHandler getExceptionHandler() {
 
   @Override
   public boolean isDialect(final Connection connection) {
-    Statement stmt = null;
-    ResultSet rs = null;
-    try {
-      stmt = connection.createStatement();
-      rs = stmt.executeQuery(WRITER_NODE_FUNC_EXIST_QUERY);
-
-      if (rs.next()) {
-        rs.close();
-        stmt.close();
-
-        stmt = connection.createStatement();
-        rs = stmt.executeQuery(NODE_ID_FUNC_EXIST_QUERY);
-
-        return rs.next();
-      }
-      return false;
+    try (Statement stmt = connection.createStatement();
+        ResultSet rs = stmt.executeQuery(IS_RDS_CLUSTER_QUERY)) {
+      return rs.next() && rs.getString(1) != null;
     } catch (final SQLException ex) {
       // ignore
-    } finally {
-      if (stmt != null) {
-        try {
-          stmt.close();
-        } catch (SQLException ex) {
-          // ignore
-        }
-      }
-      if (rs != null) {
-        try {
-          rs.close();
-        } catch (SQLException ex) {
-          // ignore
-        }
-      }
     }
     return false;
   }

wrapper/src/test/java/software/amazon/jdbc/DialectTests.java

@@ -252,6 +252,7 @@ void testRdsPgIsDialectIsAurora() throws SQLException {
   void testRdsTazPgIsDialectSuccess() throws SQLException {
     when(mockStatement.executeQuery(any())).thenReturn(successResultSet);
     when(successResultSet.next()).thenReturn(true);
+    when(successResultSet.getString(1)).thenReturn("id");
     assertTrue(rdsTazPgDialect.isDialect(mockConnection));
   }
 
@@ -269,11 +270,10 @@ void testRdsTazPgIsDialectQueryReturnedEmptyResultSet() throws SQLException {
   }
 
   @Test
-  void testRdsTazPgIsDialectWriterNodeQueryFailed() throws SQLException {
-    when(mockStatement.executeQuery(any())).thenReturn(successResultSet, failResultSet);
-    when(successResultSet.next()).thenReturn(true);
+  void testRdsTazPgIsDialectIsRdsClusterQueryFailed() throws SQLException {
+    when(mockStatement.executeQuery(any())).thenReturn(failResultSet);
+    when(successResultSet.next()).thenReturn(false);
     assertFalse(rdsTazPgDialect.isDialect(mockConnection));
-    verify(successResultSet, times(1)).next();
     verify(failResultSet, times(1)).next();
   }