DumpSegment tool. (apache#3182)

Fixes apache#2723.

docs/content/operations/dump-segment.md

@@ -0,0 +1,62 @@
+---
+layout: doc_page
+---
+# DumpSegment tool
+
+The DumpSegment tool can be used to dump the metadata or contents of a segment for debugging purposes. Note that the
+dump is not necessarily a full-fidelity translation of the segment. In particular, not all metadata is included, indexes
+are not included, and complex metric values may not be complete.
+
+To run the tool, point it at a segment directory and provide a file for writing output:
+
+```
+java io.druid.cli.Main tools dump-segment \
+  --directory /home/druid/path/to/segment/ \
+  --out /home/druid/output.txt
+```
+
+### Output format
+
+Data dumps generated by this tool are newline-separate JSON objects, with one object per line. For example, one line
+might look like this when pretty-printed:
+
+```
+{
+  "__time": 1442018818771,
+  "added": 36,
+  "channel": "#en.wikipedia",
+  "cityName": null,
+  "comment": "added project",
+  "count": 1,
+  "countryIsoCode": null,
+  "countryName": null,
+  "deleted": 0,
+  "delta": 36,
+  "isAnonymous": "false",
+  "isMinor": "false",
+  "isNew": "false",
+  "isRobot": "false",
+  "isUnpatrolled": "false",
+  "iuser": "00001553",
+  "metroCode": null,
+  "namespace": "Talk",
+  "page": "Talk:Oswald Tilghman",
+  "regionIsoCode": null,
+  "regionName": null,
+  "user": "GELongstreet"
+}
+```
+
+Metadata dumps generated by this tool are in the same format as returned by the
+[SegmentMetadata query](../querying/segmentmetadataquery.html).
+
+### Command line arguments
+
+|argument|description|required?|
+|--------|-----------|---------|
+|--directory file|Directory containing segment data. This could be generated by unzipping an "index.zip" from deep storage.|yes|
+|--output file|File where output will be written.|yes|
+|--filter json|JSON-encoded [query filter](../querying/filters.html). Omit to include all rows.|no|
+|--column columnName|Column to include. Specify multiple times for multiple columns, or omit to include all columns.|no|
+|--time-iso8601|Dump __time column in ISO8601 format rather than long.|no|
+|--metadata|Dump metadata instead of actual rows, will ignore --filter and --column selections.|no|

processing/src/main/java/io/druid/query/NoopQueryWatcher.java

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+/*
+ * Licensed to Metamarkets Group Inc. (Metamarkets) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. Metamarkets 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.
+ */
+
+package io.druid.query;
+
+import com.google.common.util.concurrent.ListenableFuture;
+
+public class NoopQueryWatcher implements QueryWatcher
+{
+  private static final NoopQueryWatcher INSTANCE = new NoopQueryWatcher();
+
+  public static NoopQueryWatcher instance()
+  {
+    return INSTANCE;
+  }
+
+  private NoopQueryWatcher()
+  {
+    // No instantiation
+  }
+
+  @Override
+  public void registerQuery(Query query, ListenableFuture future)
+  {
+    // Do nothing
+  }
+}