simplify implementation, getDb returns instance if db not found

Author: azhou-datadog

dd-java-agent/agent-bootstrap/src/main/java/datadog/trace/bootstrap/instrumentation/jdbc/DBInfo.java

@@ -193,7 +193,7 @@ public String getInstance() {
   }
 
   public String getDb() {
-    return db;
+    return db != null ? db : instance;
   }
 
   public String getHost() {

dd-java-agent/instrumentation/jdbc/src/main/java/datadog/trace/instrumentation/jdbc/DBMCompatibleConnectionInstrumentation.java

@@ -132,13 +132,7 @@ public static String onEnter(
           DECORATE.DBM_ALWAYS_APPEND_SQL_COMMENT || "sqlserver".equals(dbInfo.getType());
       sql =
           SQLCommenter.inject(
-              sql,
-              dbService,
-              dbInfo.getType(),
-              dbInfo.getHost(),
-              DECORATE.isOracle(dbInfo) ? DECORATE.getDbInstance(dbInfo) : dbInfo.getDb(),
-              null,
-              append);
+              sql, dbService, dbInfo.getType(), dbInfo.getHost(), dbInfo.getDb(), null, append);
       return inputSql;
     }
 

dd-java-agent/instrumentation/jdbc/src/main/java/datadog/trace/instrumentation/jdbc/JDBCDecorator.java

@@ -219,13 +219,6 @@ public String getDbService(final DBInfo dbInfo) {
     return dbService(dbInfo.getType(), dbInstance(dbInfo));
   }
 
-  public String getDbInstance(final DBInfo dbInfo) {
-    if (null == dbInfo) {
-      return null;
-    }
-    return dbInstance(dbInfo);
-  }
-
   public static DBInfo parseDBInfoFromConnection(final Connection connection) {
     if (connection == null || !FETCH_DB_METADATA_ON_QUERY) {
       // we can log here, but it risks to be too verbose

dd-java-agent/instrumentation/jdbc/src/main/java/datadog/trace/instrumentation/jdbc/StatementInstrumentation.java

@@ -147,26 +147,23 @@ public static AgentScope onEnter(
           }
 
           final String dbService;
-          final String dbName;
           if (isOracle) {
             String oracleService = DECORATE.getDbService(dbInfo);
             if (oracleService != null) {
               oracleService =
                   traceConfig(span).getServiceMapping().getOrDefault(oracleService, oracleService);
             }
             dbService = oracleService;
-            dbName = DECORATE.getDbInstance(dbInfo);
           } else {
             dbService = span.getServiceName();
-            dbName = dbInfo.getDb();
           }
           sql =
               SQLCommenter.inject(
                   sql,
                   dbService,
                   dbInfo.getType(),
                   dbInfo.getHost(),
-                  dbName,
+                  dbInfo.getDb(),
                   injectTraceInComment ? traceParent : null,
                   appendComment);
         }