docs/UserGuide/FAQ/Frequently-asked-questions.md

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# Frequently Asked Questions

**How can I identify my version of IoTDB?**

There are several ways to identify the version of IoTDB that you are using:

* Launch IoTDB's Command Line Interface:

```
> ./start-cli.sh -p 6667 -pw root -u root -h localhost
 _____       _________  ______   ______    
|_   _|     |  _   _  ||_   _ `.|_   _ \   
  | |   .--.|_/ | | \_|  | | `. \ | |_) |  
  | | / .'`\ \  | |      | |  | | |  __'.  
 _| |_| \__. | _| |_    _| |_.' /_| |__) | 
|_____|'.__.' |_____|  |______.'|_______/  version x.x.x
```

* Check pom.xml file:

```
<version>x.x.x</version>
```

* Use JDBC API:

```
String iotdbVersion = tsfileDatabaseMetadata.getDatabaseProductVersion();
```

* Use Command Line Interface:

```
IoTDB> show version
show version
+---------------+
|version        |
+---------------+
|x.x.x          |
+---------------+
Total line number = 1
It costs 0.241s
```

**Where can I find IoTDB logs?**

Suppose your root directory is:

```
$ pwd
/workspace/iotdb

$ ls -l
server/
cli/
pom.xml
Readme.md
...
```

Let `$IOTDB_HOME = /workspace/iotdb/server/target/iotdb-server-{project.version}`

Let `$IOTDB_CLI_HOME = /workspace/iotdb/cli/target/iotdb-cli-{project.version}`

By default settings, the logs are stored under ```IOTDB_HOME/logs```. You can change log level and storage path by configuring ```logback.xml``` under ```IOTDB_HOME/conf```.

**Where can I find IoTDB data files?**

By default settings, the data files (including tsfile, metadata, and WAL files) are stored under ```IOTDB_HOME/data/datanode```.

**How do I know how many time series are stored in IoTDB?**

Use IoTDB's Command Line Interface:

```
IoTDB> show timeseries root
```

In the result, there is a statement shows `Total timeseries number`, this number is the timeseries number in IoTDB.

In the current version, IoTDB supports querying the number of time series. Use IoTDB's Command Line Interface:

```
IoTDB> count timeseries root
```

If you are using Linux, you can use the following shell command:

```
> grep "0,root" $IOTDB_HOME/data/system/schema/mlog.txt |  wc -l
>   6
```

**Can I use Hadoop and Spark to read TsFile in IoTDB?**

Yes. IoTDB has intense integration with Open Source Ecosystem. IoTDB supports [Hadoop](https://github.com/apache/iotdb/tree/master/hadoop), [Spark](https://github.com/apache/iotdb/tree/master/spark-tsfile) and [Grafana](https://github.com/apache/iotdb/tree/master/grafana-plugin) visualization tool.

**How does IoTDB handle duplicate points?**

A data point is uniquely identified by a full time series path (e.g. ```root.vehicle.d0.s0```) and timestamp. If you submit a new point with the same path and timestamp as an existing point, IoTDB updates the value of this point instead of inserting a new point. 

**How can I tell what type of the specific timeseries?**

Use ```SHOW TIMESERIES <timeseries path>``` SQL in IoTDB's Command Line Interface:

For example, if you want to know the type of all timeseries, the \<timeseries path> should be `root`. The statement will be:

```
IoTDB> show timeseries root
```

If you want to query specific sensor, you can replace the \<timeseries path> with the sensor name. For example:

```
IoTDB> show timeseries root.fit.d1.s1
```

Otherwise, you can also use wildcard in timeseries path:

```
IoTDB> show timeseries root.fit.d1.*
```

**How can I change IoTDB's Cli time display format?**

The default IoTDB's Cli time display format is readable (e.g. ```1970-01-01T08:00:00.001```), if you want to display time in timestamp type or other readable format, add parameter ```-disableISO8601``` in start command:

```
> $IOTDB_CLI_HOME/sbin/start-cli.sh -h 127.0.0.1 -p 6667 -u root -pw root -disableISO8601
```

**How to handle error `IndexOutOfBoundsException` from `org.apache.ratis.grpc.server.GrpcLogAppender`?**

It is an internal error introduced by Ratis 2.4.1 dependency, and we can safely ignore this exception as it will
not affect normal operations. We will fix this message in the incoming releases.