druid/docs/content/operations/insert-segment-to-db.md

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layout: doc_page
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# insert-segment-to-db Tool

`insert-segment-to-db` is a tool that can insert segments into Druid metadata storage. It is intended to be used
to update the segment table in metadata storage after people manually migrate segments from one place to another.
It can also be used to insert missing segments into Druid, or even recover metadata storage by telling it where the
segments are stored.

**Note:** This tool simply scans the deep storage directory to reconstruct the metadata entries used to locate and
identify each segment. It does not have any understanding about whether those segments _should actually_ be written to
the metadata storage. In certain cases, this can lead to undesired or inconsistent results. Some examples of things to
watch out for:
  - Dropped datasources will be re-enabled.
  - The latest version of each segment set will be loaded by Druid, which in some cases may not be the version you
    actually want. An example of this is a bad compaction job that generates segments which need to be manually rolled
    back by removing that version from the metadata table. If these segments are not also removed from deep storage,
    they will be imported back into the metadata table and overshadow the correct version.
  - Some indexers such as the Kafka indexing service have the potential to generate more than one set of segments that
    have the same segment ID but different contents. When the metadata is first written, the correct set of segments is
    referenced and the other set is normally deleted from deep storage. It is possible however that an unhandled
    exception could result in multiple sets of segments with the same segment ID remaining in deep storage. Since this
    tool does not know which one is the 'correct' one to use, it will simply select the newest segment set and ignore
    the other versions. If the wrong segment set is picked, the exactly-once semantics of the Kafka indexing service
    will no longer hold true and you may get duplicated or dropped events.

With these considerations in mind, it is recommended that data migrations be done by exporting the original metadata
storage directly, since that is the definitive cluster state. This tool should be used as a last resort when a direct
export is not possible.

**Note:** This tool expects users to have Druid cluster running in a "safe" mode, where there are no active tasks to interfere
with the segments being inserted. Users can optionally bring down the cluster to make 100% sure nothing is interfering.

In order to make it work, user will have to provide metadata storage credentials and deep storage type through Java JVM argument
or runtime.properties file. Specifically, this tool needs to know:

```
druid.metadata.storage.type
druid.metadata.storage.connector.connectURI
druid.metadata.storage.connector.user
druid.metadata.storage.connector.password
druid.storage.type
```

Besides the properties above, you also need to specify the location where the segments are stored and whether you want to
update descriptor.json (`partitionNum_descriptor.json` for HDFS data storage). These two can be provided through command line arguments.

`--workingDir` (Required)

    The directory URI where segments are stored. This tool will recursively look for segments underneath this directory
    and insert/update these segments in metdata storage.
    Attention: workingDir must be a complete URI, which means it must be prefixed with scheme type. For example,
    hdfs://hostname:port/segment_directory

`--updateDescriptor` (Optional)

    if set to true, this tool will update `loadSpec` field in `descriptor.json` (`partitionNum_descriptor.json` for HDFS data storage) if the path in `loadSpec` is different from
    where `desciptor.json` (`partitionNum_descriptor.json` for HDFS data storage) was found. Default value is `true`.

Note: you will also need to load different Druid extensions per the metadata and deep storage you use. For example, if you
use `mysql` as metadata storage and HDFS as deep storage, you should load `mysql-metadata-storage` and `druid-hdfs-storage`
extensions.


Example:

Suppose your metadata storage is `mysql` and you've migrated some segments to a directory in HDFS, and that directory looks
like this,

```
Directory path: /druid/storage/wikipedia

├── 2013-08-31T000000.000Z_2013-09-01T000000.000Z
│   └── 2015-10-21T22_07_57.074Z
│           ├── 0_descriptor.json
│           └── 0_index.zip
├── 2013-09-01T000000.000Z_2013-09-02T000000.000Z
│   └── 2015-10-21T22_07_57.074Z
│           ├── 0_descriptor.json
│           └── 0_index.zip
├── 2013-09-02T000000.000Z_2013-09-03T000000.000Z
│   └── 2015-10-21T22_07_57.074Z
│           ├── 0_descriptor.json
│           └── 0_index.zip
└── 2013-09-03T000000.000Z_2013-09-04T000000.000Z
    └── 2015-10-21T22_07_57.074Z
            ├── 0_descriptor.json
            └── 0_index.zip
```

To load all these segments into `mysql`, you can fire the command below,

```
java 
-Ddruid.metadata.storage.type=mysql 
-Ddruid.metadata.storage.connector.connectURI=jdbc\:mysql\://localhost\:3306/druid 
-Ddruid.metadata.storage.connector.user=druid 
-Ddruid.metadata.storage.connector.password=diurd 
-Ddruid.extensions.loadList=[\"mysql-metadata-storage\",\"druid-hdfs-storage\"] 
-Ddruid.storage.type=hdfs
-cp $DRUID_CLASSPATH 
org.apache.druid.cli.Main tools insert-segment-to-db --workingDir hdfs://host:port//druid/storage/wikipedia --updateDescriptor true
```

In this example, `mysql` and deep storage type are provided through Java JVM arguments, you can optionally put all
of them in a runtime.properites file and include it in the Druid classpath. Note that we also include `mysql-metadata-storage`
and `druid-hdfs-storage` in the extension list.

After running this command, the segments table in `mysql` should store the new location for each segment we just inserted.
Note that for segments stored in HDFS, druid config must contain core-site.xml as described in [Druid Docs](http://druid.io/docs/latest/tutorials/cluster.html), as this new location is stored with relative path.

It is also possible to use `s3` as deep storage. In order to work with it, specify `s3` as deep storage type and load 
[`druid-s3-extensions`](../development/extensions-core/s3.html) as an extension.

```
java
-Ddruid.metadata.storage.type=mysql 
-Ddruid.metadata.storage.connector.connectURI=jdbc\:mysql\://localhost\:3306/druid 
-Ddruid.metadata.storage.connector.user=druid 
-Ddruid.metadata.storage.connector.password=diurd
-Ddruid.extensions.loadList=[\"mysql-metadata-storage\",\"druid-s3-extensions\"]
-Ddruid.storage.type=s3
-Ddruid.s3.accessKey=... 
-Ddruid.s3.secretKey=...
-Ddruid.storage.bucket=your-bucket
-Ddruid.storage.baseKey=druid/storage/wikipedia
-Ddruid.storage.maxListingLength=1000
-cp $DRUID_CLASSPATH
org.apache.druid.cli.Main tools insert-segment-to-db --workingDir "druid/storage/wikipedia" --updateDescriptor true
```

 Note that you can provide the location of segments with either `druid.storage.baseKey` or `--workingDir`. If both are 
 specified, `--workingDir` gets higher priority. `druid.storage.maxListingLength` is to determine the length of a
 partial list in requesting a object listing to `s3`, which defaults to 1000.