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Posted to reviews@iotdb.apache.org by GitBox <gi...@apache.org> on 2019/07/18 02:23:23 UTC
[GitHub] [incubator-iotdb] jt2594838 commented on a change in pull request
#247: TsFile Docs
jt2594838 commented on a change in pull request #247: TsFile Docs
URL: https://github.com/apache/incubator-iotdb/pull/247#discussion_r304709106
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File path: docs/Documentation/UserGuideV0.7.0/7-TsFile/2-Usage.md
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+ KIND, either express or implied. See the License for the
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+Now, you’re ready to start doing some awesome things with TsFile. This section demonstrates the detailed usage of TsFile.
+
+### Time-series Data
+A time-series is considered as a set of quadruples. A quadruple is defined as (deltaObject, measurement, time, value).
+
+* **deltaObject**: In many situations, a device which contains many sensors can be considered as a deltaObject.
+* **measurement**: A sensor can be considered as a measurement
+
+
+Table 1 illustrates a set of time-series data. The set showed in the following table contains one deltaObject named "device\_1" with three measurements named "sensor\_1", "sensor\_2" and "sensor\_3".
+
+<center>
+<table style="text-align:center">
+ <tr><th colspan="6">device_1</th></tr>
+ <tr><th colspan="2">sensor_1</th><th colspan="2">sensor_2</th><th colspan="2">sensor_3</th></tr>
+ <tr><th>time</th><th>value</td><th>time</th><th>value</td><th>time</th><th>value</td>
+ <tr><td>1</td><td>1.2</td><td>1</td><td>20</td><td>2</td><td>50</td></tr>
+ <tr><td>3</td><td>1.4</td><td>2</td><td>20</td><td>4</td><td>51</td></tr>
+ <tr><td>5</td><td>1.1</td><td>3</td><td>21</td><td>6</td><td>52</td></tr>
+ <tr><td>7</td><td>1.8</td><td>4</td><td>20</td><td>8</td><td>53</td></tr>
+</table>
+<span>A set of time-series data</span>
+</center>
+
+**One Line of Data**: In many industrial applications, a device normally contains more than one sensor and these sensors may have values at a same timestamp, which is called one line of data.
+
+Formally, one line of data consists of a `deltaObject_id`, a timestamp which indicates the milliseconds since January 1, 1970, 00:00:00, and several data pairs composed of `measurement_id` and corresponding `value`. All data pairs in one line belong to this `deltaObject_id` and have the same timestamp. If one of the `measurements` doesn't have a `value` in the `timestamp`, use a space instead(Actually, TsFile does not store null values). Its format is shown as follow:
+
+```
+deltaObject_id, timestamp, <measurement_id, value>...
+```
+
+An example is illustrated as follow. In this example, the data type of three measurements are `INT32`, `FLOAT` and `ENUMS` respectively.
+
+```
+device_1, 1490860659000, m1, 10, m2, 12.12, m3, MAN
+```
+
+
+### Writing TsFile
+
+#### Generate a TsFile File.
+A TsFile can be generated by following three steps and the complete code will be given in the section "Example for writing TsFile".
+
+* First, use the interface to construct a TsFile instance.
+ ```
+ public TsFileWriter(File file) throws WriteProcessException, IOException
+ ```
+
+ **Parameters:**
+
+ * file : The TsFile to write
+
+* Second, add measurements
+
+ ```
+ public void addMeasurement(MeasurementDescriptor measurementDescriptor) throws WriteProcessException
+ ```
+
+ **Parameters:**
+
+ * measurementDescriptor : The measurement information including name, data type and encoding
+
+ > **Notice:** Although one measurement name can be used in multiple deltaObjects, the properties cannot be changed. I.e.
+ it's not allowed to add one measurement name for multiple times with different type or encoding.
+ Here is a bad example:
+
+ ```
+ // The measurement "sensor_1" is float type
+ addMeasurement(new MeasurementSchema("sensor_1", TSDataType.FLOAT, TSEncoding.RLE));
+ // This call will throw a WriteProcessException exception
+ addMeasurement(new MeasurementSchema("sensor_1", TSDataType.INT32, TSEncoding.RLE));
+ ```
+* Third, write data continually.
+
+ ```
+ public void write(TSRecord record) throws IOException, WriteProcessException
+ ```
+
+ Use this interface to create a new TSRecord(a timestamp and device pair).
+
+ ```
+ public TSRecord(long timestamp, String deviceId)
+ ```
+ Then create DataPoint(a measurement and value pair), and use the addTuple method to add the DataPoint to the correct
+ TsRecord.
+
+* Finally, call `close` to finish this writing process.
+
+ ```
+ public void close() throws IOException
+ ```
+
+#### Example for writing TsFile
+
+You should install TsFile to your local maven repository.
+
+See reference: [Installation](./1-Installation.md)
+
+A more thorough example can be found at `/tsfile/example/src/main/java/org/apache/iotdb/tsfile/TsFileWrite.java`
+
+```java
+package org.apache.iotdb.tsfile;
+
+import java.io.File;
+import org.apache.iotdb.tsfile.file.metadata.enums.TSDataType;
+import org.apache.iotdb.tsfile.file.metadata.enums.TSEncoding;
+import org.apache.iotdb.tsfile.write.TsFileWriter;
+import org.apache.iotdb.tsfile.write.record.TSRecord;
+import org.apache.iotdb.tsfile.write.record.datapoint.DataPoint;
+import org.apache.iotdb.tsfile.write.record.datapoint.FloatDataPoint;
+import org.apache.iotdb.tsfile.write.record.datapoint.IntDataPoint;
+import org.apache.iotdb.tsfile.write.schema.MeasurementSchema;
+/**
+ * An example of writing data to TsFile
+ * It uses the interface:
+ * public void addMeasurement(MeasurementSchema MeasurementSchema) throws WriteProcessException
+ */
+public class TsFileWrite {
+
+ public static void main(String args[]) {
+ try {
+ String path = "test.tsfile";
+ File f = new File(path);
+ if (f.exists()) {
+ f.delete();
+ }
+ TsFileWriter tsFileWriter = new TsFileWriter(f);
+
+ // add measurements into file schema
+ tsFileWriter
+ .addMeasurement(new MeasurementSchema("sensor_1", TSDataType.FLOAT, TSEncoding.RLE));
+ tsFileWriter
+ .addMeasurement(new MeasurementSchema("sensor_2", TSDataType.INT32, TSEncoding.TS_2DIFF));
+ tsFileWriter
+ .addMeasurement(new MeasurementSchema("sensor_3", TSDataType.INT32, TSEncoding.TS_2DIFF));
+ // construct TSRecord
+ TSRecord tsRecord = new TSRecord(1, "device_1");
+ DataPoint dPoint1 = new FloatDataPoint("sensor_1", 1.2f);
+ DataPoint dPoint2 = new IntDataPoint("sensor_2", 20);
+
+ //For time 1 in device_1, the data will be 1.2, 20, null
+ tsRecord.addTuple(dPoint1);
+ tsRecord.addTuple(dPoint2);
+
+ // write a TSRecord to TsFile
+ tsFileWriter.write(tsRecord);
+ // close TsFile
+ tsFileWriter.close();
+ } catch (Throwable e) {
+ e.printStackTrace();
+ System.out.println(e.getMessage());
+ }
+ }
+}
+
+```
+
+### Interface for Reading TsFile
+
+#### Before the Start
+
+The set of time-series data in section "Time-series Data" is used here for a concrete introduction in this section. The set showed in the following table contains one deltaObject named "device\_1" with three measurements named "sensor\_1", "sensor\_2" and "sensor\_3". And the measurements has been simplified to do a simple illustration, which contains only 4 time-value pairs each.
+
+<center>
+<table style="text-align:center">
+ <tr><th colspan="6">device_1</th></tr>
+ <tr><th colspan="2">sensor_1</th><th colspan="2">sensor_2</th><th colspan="2">sensor_3</th></tr>
+ <tr><th>time</th><th>value</td><th>time</th><th>value</td><th>time</th><th>value</td>
+ <tr><td>1</td><td>1.2</td><td>1</td><td>20</td><td>2</td><td>50</td></tr>
+ <tr><td>3</td><td>1.4</td><td>2</td><td>20</td><td>4</td><td>51</td></tr>
+ <tr><td>5</td><td>1.1</td><td>3</td><td>21</td><td>6</td><td>52</td></tr>
+ <tr><td>7</td><td>1.8</td><td>4</td><td>20</td><td>8</td><td>53</td></tr>
+</table>
+<span>A set of time-series data</span>
+</center>
+
+#### Definition of Path
+
+A path represents a series instance in TsFile. In the example given above, "device\_1.sensor\_1" is a path.
Review comment:
I would suggest a more specific description like:
A path is a dot-separated string which uniquely identifies a time-series in TsFile, e.g., "root.area\_1.device\_1.sensor\_1". The last section "sensor\_1" is called "measurementId" while the remaining parts "root.area\_1.device\_1" is called deviceId. As mentioned above, the same measurement in different devices has the same data type and ending, and devices are also unique.
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