- When the Controller cannot retrieve any assignments from Impala (without an error), return an HTTP-"MULTI_STATUS" with an empty "AssignmentsResponse", instead of an "INTERNAL_SERVER_ERROR".

- Fix an error-message.

src/main/java/eu/openaire/urls_controller/controllers/UrlController.java

@@ -177,10 +177,12 @@ public class UrlController {
             String errorMsg = "No results retrieved from the \"findAssignmentsQuery\" for worker with id: " + workerId + ". Will increase the \"maxAttempts\" to " + maxAttemptsPerRecordAtomic.incrementAndGet() + " for the next requests.";
             logger.error(errorMsg);
             String tmpErrMsg = dropCurrentAssignmentTable();
-            if ( tmpErrMsg != null )
-                errorMsg += "\n" + tmpErrMsg;
             ImpalaConnector.databaseLock.unlock();
-            return ResponseEntity.status(HttpStatus.INTERNAL_SERVER_ERROR).body(errorMsg);
+            if ( tmpErrMsg != null ) {
+                errorMsg += "\n" + tmpErrMsg;   // The additional error-msg is already logged.
+                return ResponseEntity.status(HttpStatus.INTERNAL_SERVER_ERROR).body(errorMsg);
+            } else
+                return ResponseEntity.status(HttpStatus.MULTI_STATUS).body(new AssignmentsResponse((long) -1, null));
         } else if ( assignmentsSize < assignmentsLimit ) {
             logger.warn("The retrieved results were fewer (" + assignmentsSize + ") than the \"assignmentsLimit\" (" + assignmentsLimit + "), for worker with id: " + workerId + ". Will increase the \"maxAttempts\" to " + maxAttemptsPerRecordAtomic.incrementAndGet() + " for the next requests.");
         }
@@ -374,7 +376,7 @@ public class UrlController {
             jdbcTemplate.execute(dropCurrentAssignmentsQuery);
             return null;    // All good. No error-message.
         } catch (Exception e) {
-            return ImpalaConnector.handleQueryException("dropCurrentAssignmentsQuery", dropCurrentAssignmentsQuery, e);
+            return ImpalaConnector.handleQueryException("dropCurrentAssignmentsQuery", dropCurrentAssignmentsQuery, e); // The error is already logged inside.
         }
     }
 

src/main/java/eu/openaire/urls_controller/util/ParquetFileUtils.java

@@ -417,7 +417,7 @@ public class ParquetFileUtils {
             // See: https://docs.cloudera.com/documentation/enterprise/latest/topics/impala_load_data.html
 
         } catch (Throwable e) {
-            String errorMsg = "Error while importing parquet data into the Impala Database, through WebHDFS!\n" + e;
+            String errorMsg = "Error while uploading parquet file \"" + parquetFileFullLocalPath + "\" to HDFS!\n" + e;
             logger.error(errorMsg);
             return errorMsg;
         }