HBASE-23018 - [HBCK2] Add useful messages when report/fixing missing …

…regions in meta (#31)

Signed-off-by: Michael Stack <stack@apache.org>

hbase-hbck2/src/main/java/org/apache/hbase/HBCK2.java

@@ -219,6 +219,13 @@ Pair<List<String>, List<ExecutionException>> addMissingRegionsInMetaForTables(St
       try(ClusterConnection conn = connect();
         final Admin admin = conn.getAdmin()) {
         Map<TableName,List<Path>> report = reportTablesWithMissingRegionsInMeta(nameSpaceOrTable);
+        if(report.size() < 1) {
+          LOG.info("\nNo missing regions in meta are found. Worth using " +
+                  "reportMissingRegionsInMeta first.\nYou are likely passing non-existent " +
+                  "namespace or table. Note that table names should include the namespace " +
+                  "portion even for tables in the default namespace. " +
+                  "See also the command usage.\n");
+        }
         for (TableName tableName : report.keySet()) {
           if(admin.tableExists(tableName)) {
             futures.add(executorService.submit(new Callable<List<String>>() {
@@ -786,6 +793,12 @@ private static String toString(List<?> things) {
 
   private String formatMissingRegionsInMetaReport(Map<TableName,List<Path>> report) {
     final StringBuilder builder = new StringBuilder();
+    if(report.size() < 1) {
+      builder.append("\nNo reports are found. You are likely passing non-existent " +
+              "namespace or table. Note that table names should include the namespace " +
+              "portion even for tables in the default namespace. See also the command usage.\n");
+      return builder.toString();
+    }
     builder.append("Missing Regions for each table:\n\t");
     report.keySet().stream().forEach(table -> {
       builder.append(table);