Project: Druid (App Definition and Development / Database)
File: dump-segment.md

id: dump-segment title: "dump-segment tool" <!-- ~ 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. --> The DumpSegment tool can be used to dump the metadata or contents of an Apache Druid 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, 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 -classpath "/my/druid/lib/*" -Ddruid.extensions.loadList="[]" org.apache.druid.cli.Main \ tools dump-segment \ --directory /home/druid/path/to/segment/ \ --out /home/druid/output.txt ``` If you use JDK 11 and above, you need to add the following additional parameters ``` --add-opens java.base/java.lang=ALL-UNNAMED --add-opens java.base/sun.nio.ch=ALL-UNNAMED ``` The following is an example ``` java --add-opens java.base/java.lang=ALL-UNNAMED --add-opens java.base/sun.nio.ch=ALL-UNNAMED \ -classpath "/my/druid/lib/*" \ -Ddruid.extensions.loadList="[]" org.apache.druid.cli.Main \ tools dump-segment \ --directory /home/druid/path/to/segment/ \ --out /home/druid/output.txt ``` By default, or with `--dump rows`, this tool dumps rows of the segment as newline-separate JSON objects, with one object per line, using the default serialization for each column. Normally all columns are included, but if you like, you can limit the dump to specific columns with `--column name`. 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" } ``` With `--dump metadata`, this tool dumps metadata instead of rows. Metadata dumps generated by this tool are in the same format as returned by the . With `--dump bitmaps`, this tool will dump bitmap indexes instead of rows. Bitmap dumps generated by this tool include dictionary-encoded string columns only. The output contains a field "bitmapSerdeFactory" describing the type of bitmaps used in the segment, and a field "bitmaps" containing the bitmaps for each value of each column. These are base64 encoded by default, but you can also dump them as lists of row numbers with `--decompress-bitmaps`. Normally all columns are included, but if you like, you can limit the dump to specific columns with `--column name`. Sample output: ``` { "bitmapSerdeFactory": { "type": "roaring" }, "bitmaps": { "isRobot": { "false": "//aExfu+Nv3X...", "true":

} } } ``` With `--dump nested`, this tool can be used to examine Druid . Using `nested` always requires exactly one `--column name` argument, and takes an optional argument to specify a specific nested field in , `--nested-path $.path.to.field`. If `--nested-path` is not specified, the output will contain the list of nested fields and their types, the global value dictionaries, and the list of null rows. Sample output: ```json { "nest": { "fields": [ { "path": "$.x", "types": [ "LONG" ] }, { "path": "$.y", "types": [ "DOUBLE" ] }, { "path": "$.z", "types": [ "STRING" ] } ], "dictionaries": { "strings": [ { "globalId": 0, "value": null }, { "globalId": 1, "value": "a" }, { "globalId": 2, "value": "b" } ], "longs": [ { "globalId": 3, "value": 100 }, { "globalId": 4, "value": 200 }, { "globalId": 5, "value": 400 } ], "doubles": [ { "globalId": 6, "value": 1.1 }, { "globalId": 7, "value": 2.2 }, { "globalId": 8, "value": 3.3 } ], "nullRows": [] } } } ``` If `--nested-path` is specified, the output will instead contain the types of the nested field, the local value dictionary, including the 'global' dictionary id and value, the uncompressed bitmap index for each value (list of row numbers which contain the value), and a dump of the column itself, which contains the row number, raw JSON form of the nested column itself, the local dictionary id of the field for that row, and the value for the field for the row. Sample output: ```json { "bitmapSerdeFactory": { "type": "roaring" }, "nest": { "$.x": { "types": [ "LONG" ], "dictionary": [ { "localId": 0, "globalId": 0, "value": null, "rows": [ 4 ] }, { "localId": 1, "globalId": 3, "value": "100", "rows": [ 3 ] }, { "localId": 2, "globalId": 4, "value": "200", "rows": [ 0, 2 ] }, { "localId": 3, "globalId": 5, "value": "400", "rows": [ 1 ] } ], "column": [ { "row": 0, "raw": { "x": 200, "y": 2.2 }, "fieldId": 2, "fieldValue": "200" }, { "row": 1, "raw": { "x": 400, "y": 1.1, "z": "a" }, "fieldId": 3, "fieldValue": "400" }, { "row": 2, "raw": { "x": 200, "z": "b" }, "fieldId": 2, "fieldValue": "200" }, { "row": 3, "raw": { "x": 100, "y": 1.1, "z": "a" }, "fieldId": 1, "fieldValue": "100" }, { "row": 4, "raw": { "y": 3.3, "z": "b" }, "fieldId": 0, "fieldValue": null } ] } } } ``` |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 to write to, or omit to write to stdout.|yes| |--dump TYPE|Dump either 'rows' (default), 'metadata', 'bitmaps', or 'nested' for examining nested columns.|no| |--column columnName|Column to include. Specify multiple times for multiple columns, or omit to include all columns.|no| |--filter json|JSON-encoded . Omit to include all rows. Only used if dumping rows.|no| |--time-iso8601|Format time column in ISO8601 format rather than long. Only used if dumping rows.|no| |--decompress-bitmaps|Dump bitmaps as arrays rather than base64-encoded compressed bitmaps. Only used if dumping bitmaps.|no| |--nested-path|Specify a specific nested column field using . Only used if dumping a nested column.|no|