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## Where do my Druid segments end up after ingestion?

Depending on what `druid.storage.type` is set to, Druid will upload segments to some [Deep Storage](Deep-Storage.html). Local disk is used as the default deep storage.

## My realtime node is not handing segments off

Make sure that the `druid.publish.type` on your real-time nodes is set to "db". Also make sure that `druid.storage.type` is set to a deep storage that makes sense. Some example configs:

```
druid.publish.type=db

druid.db.connector.connectURI=jdbc\:mysql\://localhost\:3306/druid
druid.db.connector.user=druid
druid.db.connector.password=diurd

druid.storage.type=s3
druid.storage.bucket=druid
druid.storage.baseKey=sample
```

## How do I get HDFS to work?

Make sure to include the `druid-hdfs-storage` module as one of your extensions and set `druid.storage.type=hdfs`.

## I don't see my Druid segments on my historical nodes
You can check the coordinator console located at `<COORDINATOR_IP>:<PORT>/cluster.html`. Make sure that your segments have actually loaded on [historical nodes](Historical.html). If your segments are not present, check the coordinator logs for messages about capacity of replication errors. One reason that segments are not downloaded is because historical nodes have maxSizes that are too small, making them incapable of downloading more data. You can change that with (for example):

```
-Ddruid.segmentCache.locations=[{"path":"/tmp/druid/storageLocation","maxSize":"500000000000"}]
-Ddruid.server.maxSize=500000000000
 ```

## My queries are returning empty results

You can check `<BROKER_IP>:<PORT>/druid/v2/datasources/<YOUR_DATASOURCE>?interval=0/3000` for the dimensions and metrics that have been created for your datasource. Make sure that the name of the aggregators you use in your query match one of these metrics. Also make sure that the query interval you specify match a valid time range where data exists. Note: the broker endpoint will only return valid results on historical segments.

## How can I Reindex existing data in Druid with schema changes?

You can use IngestSegmentFirehose with index task to ingest existing druid segments using a new schema and change the name, dimensions, metrics, rollup, etc. of the segment.
See [Firehose](Firehose.html) for more details on IngestSegmentFirehose.

## How can I change the granularity of existing data in Druid?

In a lot of situations you may want to lower the granularity of older data. Example, any data older than 1 month has only hour level granularity but newer data has minute level granularity. 

To do this use the IngestSegmentFirehose and run an indexer task. The IngestSegment firehose will allow you to take in existing segments from Druid and aggregate them and feed them back into druid. It will also allow you to filter the data in those segments while feeding it back in. This means if there are rows you want to delete, you can just filter them away during re-ingestion.

Typically the above will be run as a batch job to say everyday feed in a chunk of data and aggregate it.


## More information

Getting data into Druid can definitely be difficult for first time users. Please don't hesitate to ask questions in our IRC channel or on our [google groups page](https://groups.google.com/forum/#!forum/druid-development).