HBase-14925 Develop HBase shell command/tool to list table's region info through command line

Signed-off-by: Ashish Singhi <ashishsinghi@apache.org>

hbase-shell/src/main/ruby/shell.rb

@@ -285,6 +285,7 @@ Shell.load_command_group(
     alter_async
     get_table
     locate_region
+    list_regions
   ],
   :aliases => {
     'describe' => ['desc']

hbase-shell/src/main/ruby/shell/commands/list_regions.rb

@@ -0,0 +1,76 @@
+#
+#
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+module Shell
+  module Commands
+    class ListRegions < Command
+      def help
+
+        return<<EOF
+        List all regions for a particular table as an array and also filter them by server name (optional) as prefix.
+        By default, it will return all the regions for the table
+
+        Examples:
+        hbase> list_regions 'table_name'
+        hbase> list_regions 'table_name', 'server_name'
+
+EOF
+        return
+      end
+
+      def command(table_name, region_server_name = "")
+        admin_instance = admin.instance_variable_get("@admin")
+        conn_instance = admin_instance.getConnection()
+        cluster_status = admin_instance.getClusterStatus()
+        hregion_locator_instance = conn_instance.getRegionLocator(TableName.valueOf(table_name))
+        hregion_locator_list = hregion_locator_instance.getAllRegionLocations()
+        results = Array.new
+
+        begin
+          hregion_locator_list.each do |hregion|
+            hregion_info = hregion.getRegionInfo()
+            server_name = hregion.getServerName()
+            if hregion.getServerName().toString.start_with? region_server_name
+              startKey = Bytes.toString(hregion.getRegionInfo().getStartKey())
+              endKey = Bytes.toString(hregion.getRegionInfo().getEndKey())
+              region_load_map = cluster_status.getLoad(server_name).getRegionsLoad()
+              region_load = region_load_map.get(hregion_info.getRegionName())
+              region_store_file_size = region_load.getStorefileSizeMB()
+              region_requests = region_load.getRequestsCount()
+              results << { "server" => hregion.getServerName().toString(), "name" => hregion_info.getRegionNameAsString(), "startkey" => startKey, "endkey" => endKey, "size" => region_store_file_size, "requests" => region_requests }
+            end
+          end
+        ensure
+          hregion_locator_instance.close()
+        end
+
+        @end_time = Time.now
+
+        printf("%-60s | %-60s | %-15s | %-15s | %-20s | %-20s", "SERVER_NAME", "REGION_NAME", "START_KEY", "END_KEY", "SIZE", "REQ");
+        printf("\n")
+        for result in results
+          printf("%-60s | %-60s | %-15s | %-15s | %-20s | %-20s", result["server"], result["name"], result["startkey"], result["endkey"], result["size"], result["requests"]);
+            printf("\n")
+        end
+        printf("%d rows", results.size)
+
+      end
+    end
+  end
+end