Improve logging in new SQL engine (#912)

* Remove sensitive log and add log for fallback

* Update readme

README.md

@@ -44,6 +44,8 @@ Here is a documentation list with features only available in this improved SQL q
     * Improvement on Subqueries in FROM clause
 * [Window functions](./docs/user/dql/window.rst): ranking window function support
 
+To avoid impact on your side, normally you won't see any difference in query response. If you want to check if and why your query falls back to be handled by old SQL engine, please explain your query and check Elasticsearch log for "Request is falling back to old SQL engine due to ...".
+
 
 ## Setup
 

legacy/src/main/java/com/amazon/opendistroforelasticsearch/sql/legacy/plugin/RestSQLQueryAction.java

@@ -112,6 +112,10 @@ public RestChannelConsumer prepareRequest(SQLQueryRequest request, NodeClient no
                 sqlService.analyze(
                     sqlService.parse(request.getQuery())));
     } catch (SyntaxCheckException e) {
+      // When explain, print info log for what unsupported syntax is causing fallback to old engine
+      if (request.isExplainRequest()) {
+        LOG.info("Request is falling back to old SQL engine due to: " + e.getMessage());
+      }
       return NOT_SUPPORTED_YET;
     }
 

legacy/src/main/java/com/amazon/opendistroforelasticsearch/sql/legacy/plugin/RestSqlAction.java

@@ -154,8 +154,7 @@ protected RestChannelConsumer prepareRequest(RestRequest request, NodeClient cli
                     sqlRequest.getSql(), request.path(), request.params());
                 RestChannelConsumer result = newSqlQueryHandler.prepareRequest(newSqlRequest, client);
                 if (result != RestSQLQueryAction.NOT_SUPPORTED_YET) {
-                    LOG.info("[{}] Request {} is handled by new SQL query engine",
-                        LogUtils.getRequestId(), newSqlRequest);
+                    LOG.info("[{}] Request is handled by new SQL query engine", LogUtils.getRequestId());
                     return result;
                 }
                 LOG.debug("[{}] Request {} is not supported and falling back to old SQL engine",