support PostgreSQL >= 9.5 upsert capability

extensions-core/postgresql-metadata-storage/src/main/java/io/druid/metadata/storage/postgresql/PostgreSQLConnector.java

@@ -31,6 +31,7 @@ import org.skife.jdbi.v2.Handle;
 import org.skife.jdbi.v2.tweak.HandleCallback;
 import org.skife.jdbi.v2.util.StringMapper;
 
+import java.sql.DatabaseMetaData;
 import java.sql.SQLException;
 
 public class PostgreSQLConnector extends SQLMetadataConnector
@@ -41,6 +42,8 @@ public class PostgreSQLConnector extends SQLMetadataConnector
 
   private final DBI dbi;
 
+  private volatile Boolean canUpsert;
+
   @Inject
   public PostgreSQLConnector(Supplier<MetadataStorageConnectorConfig> config, Supplier<MetadataStorageTablesConfig> dbTables)
   {
@@ -68,6 +71,18 @@ public class PostgreSQLConnector extends SQLMetadataConnector
     return SERIAL_TYPE;
   }
 
+  protected boolean canUpsert(Handle handle) throws SQLException
+  {
+    if (canUpsert == null) {
+      DatabaseMetaData metaData = handle.getConnection().getMetaData();
+      canUpsert = metaData.getDatabaseMajorVersion() > 9 || (
+          metaData.getDatabaseMajorVersion() == 9 &&
+          metaData.getDatabaseMinorVersion() >= 5
+      );
+    }
+    return canUpsert;
+  }
+
   @Override
   public boolean tableExists(final Handle handle, final String tableName)
   {
@@ -95,6 +110,19 @@ public class PostgreSQLConnector extends SQLMetadataConnector
           @Override
           public Void withHandle(Handle handle) throws Exception
           {
+            if (canUpsert(handle)) {
+              handle.createStatement(
+                  String.format(
+                      "INSERT INTO %1$s (%2$s, %3$s) VALUES (:key, :value) ON CONFLICT (%2$s) DO UPDATE SET %3$s = EXCLUDED.%3$s",
+                      tableName,
+                      keyColumn,
+                      valueColumn
+                  )
+              )
+                    .bind("key", key)
+                    .bind("value", value)
+                    .execute();
+            } else {
               handle.createStatement(
                   String.format(
                       "BEGIN;\n" +
@@ -110,6 +138,7 @@ public class PostgreSQLConnector extends SQLMetadataConnector
                     .bind("key", key)
                     .bind("value", value)
                     .execute();
+            }
             return null;
           }
         }