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Posted to reviews@iotdb.apache.org by GitBox <gi...@apache.org> on 2019/07/17 08:19:54 UTC
[GitHub] [incubator-iotdb] qiaojialin commented on a change in pull request
#247: TsFile Docs
qiaojialin commented on a change in pull request #247: TsFile Docs
URL: https://github.com/apache/incubator-iotdb/pull/247#discussion_r304272184
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File path: docs/Documentation/UserGuideV0.7.0/7-TsFile/2-Usage.md
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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
+
+ Or use a json object
+ ```
+ public void addMeasurementByJson(JSONObject measurement) throws WriteProcessException
+ ```
+ **Parameters:**
+
+ * measurement : The Json object including name, data type, encoding, and compression type. See schema Json section
+ below.
+
+ > **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
+ ```
+
+#### Format of Schema JSON
+`SchemaJSON` is a schema array specifying a list of allowable time series. The schema describes each measurement's `measurement_id`, `data_type`, `encoding`, `compression type` , and
+properties according to the specific data type.
+
+An example is shown as follow:
+
+``` json
+{
+ "schema": [
+ {
+ "measurement_id": "m1",
+ "data_type": "INT32",
+ "encoding": "RLE"
+ },
+ {
+ "measurement_id": "m2",
+ "data_type": "FLOAT",
+ "encoding": "TS_2DIFF",
+ "max_point_number": 2
+ },
+ {
+ "measurement_id": "m3",
+ "data_type": "ENUMS",
+ "encoding": "BITMAP",
+ "enum_values":["MAN","WOMAN"]
+ },
+ {
+ "measurement_id": "m4",
+ "data_type": "INT64",
+ "encoding": "RLE",
+ "compressor": "SNAPPY"
+ }
+ ],
+}
+```
+`SchemaJSON` consists of a `JSONArray` of schema objects . For each schema object, which corresponds to a time series, its field description is shown as follow:
+
+| key | is required| description | allowed values|
+| :-------- | --------:| :------:| :------:|
+| measurement_id |**required** |name of the time series |any combination of letters, numbers and other symbols like `_` `.` |
+| data_type |**required** |data type|`BOOLEAN`, `INT32`, `INT64`, `FLOAT`, `DOUBLE`, `ENUM` and `TEXT`(namely `String`)|
+| encoding |**required** | encoding approach for time domain. |`PLAIN`(for all data types), {`TS_2DIFF`, `RLE`}(for `INT32`, `INT64`, `FLOAT`, `DOUBLE`, `ENUM`), `BITMAP`(`ENUM`)|
+| compressor |**required** | the type of compression.| `SNAPPY` and `UNCOMPRESSED`|
+| enum_values |required if `data_type` is `ENUM` | the fields of `ENUM` | in format of `["MAN","WOMAN"]`|
+| max\_point\_number |optional | the number of reserved decimal digits. It's useful if the data type is `FLOAT`, `DOUBLE` or `BigDecimal`| natural number, defaults to 2|
+|max\_string\_length |optional | maximal length of string. It's useful if the data type is `TEXT`. | positive integer, defaults to 128|
+
+
+
+#### Example for writing TsFile
+
+You should install TsFile to your local maven repository.
+
+See reference: [Installation](./1-Installation.md)
+
+
+
+##### Writing TsFile by using json schema
+
+```java
+package org.apache.iotdb.tsfile;
+
+import java.io.File;
+import java.io.IOException;
+import com.alibaba.fastjson.JSONArray;
+import com.alibaba.fastjson.JSONObject;
+import org.apache.iotdb.tsfile.exception.write.WriteProcessException;
+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
+ */
+public class TsFileWrite {
+ /**
+ * There are two ways to construct a TsFile instance,they generate the identical TsFile file.
+ * This method uses the first interface:
+ * public void addMeasurementByJson(JSONObject measurement) throws WriteProcessException
+ * The corresponding json string is provided below.
+ * {
+ * "schema": [
+ * {
+ * "measurement_id": "sensor_1",
+ * "data_type": "FLOAT",
+ * "encoding": "RLE",
+ * "compressor" : "UNCOMPRESSED"
+ * },
+ * {
+ * "measurement_id": "sensor_2",
+ * "data_type": "INT32",
+ * "encoding": "TS_2DIFF",
+ * "compressor" : "UNCOMPRESSED"
+ * },
+ * {
+ * "measurement_id": "sensor_3",
+ * "data_type": "INT32",
+ * "encoding": "TS_2DIFF",
+ * "compressor" : "UNCOMPRESSED"
+ * }
+ * ]
+ * }
+ */
+ public static void main(String args[]) {
+ try {
+ String path = "testWithJson.tsfile";
+ String jsonText = "{\n" +
+ " \"schema\": [\n" +
+ " {\n" +
+ " \"measurement_id\": \"sensor_1\",\n" +
+ " \"data_type\": \"FLOAT\",\n" +
+ " \"encoding\": \"RLE\",\n" +
+ " \"compressor\" : \"UNCOMPRESSED\"\n" +
+ " },\n" +
+ " {\n" +
+ " \"measurement_id\": \"sensor_2\",\n" +
+ " \"data_type\": \"INT32\",\n" +
+ " \"encoding\": \"TS_2DIFF\",\n" +
+ " \"compressor\" : \"UNCOMPRESSED\"\n" +
+ "\n" +
+ " },\n" +
+ " {\n" +
+ " \"measurement_id\": \"sensor_3\",\n" +
+ " \"data_type\": \"INT32\",\n" +
+ " \"encoding\": \"TS_2DIFF\", \n" +
+ " \"compressor\" : \"UNCOMPRESSED\"\n" +
+ "\n" +
+ " }\n" +
+ " ]\n" +
+ "}";
+ File f = new File(path);
+ if (f.exists()) {
+ f.delete();
+ }
+ TsFileWriter tsFileWriter = new TsFileWriter(f);
+ JSONObject j = JSONObject.parseObject(jsonText);
+ JSONArray schemas = j.getJSONArray("schema");
+ // add measurements into file schema
+ for (int i = 0; i < schemas.size(); ++i) {
+ tsFileWriter.addMeasurementByJson(schemas.getJSONObject(i));
+ }
+ // construct TSRecord
+ TSRecord tsRecord = new TSRecord(1, "device_1");
+ DataPoint dPoint1 = new FloatDataPoint("sensor_1", 1.2f);
+ DataPoint dPoint2 = new IntDataPoint("sensor_2", 20);
+ DataPoint dPoint3;
+ tsRecord.addTuple(dPoint1);
+ tsRecord.addTuple(dPoint2);
+
+ // write a TSRecord to TsFile
+ tsFileWriter.write(tsRecord);
+
+ tsRecord = new TSRecord(2, "device_1");
+ dPoint2 = new IntDataPoint("sensor_2", 20);
+ dPoint3 = new IntDataPoint("sensor_3", 50);
+ tsRecord.addTuple(dPoint2);
+ tsRecord.addTuple(dPoint3);
+ tsFileWriter.write(tsRecord);
+
+ tsRecord = new TSRecord(3, "device_1");
+ dPoint1 = new FloatDataPoint("sensor_1", 1.4f);
+ dPoint2 = new IntDataPoint("sensor_2", 21);
+ tsRecord.addTuple(dPoint1);
+ tsRecord.addTuple(dPoint2);
+ tsFileWriter.write(tsRecord);
+
+ tsRecord = new TSRecord(4, "device_1");
+ dPoint1 = new FloatDataPoint("sensor_1", 1.2f);
+ dPoint2 = new IntDataPoint("sensor_2", 20);
+ dPoint3 = new IntDataPoint("sensor_3", 51);
+ tsRecord.addTuple(dPoint1);
+ tsRecord.addTuple(dPoint2);
+ tsRecord.addTuple(dPoint3);
+ tsFileWriter.write(tsRecord);
+
+ tsRecord = new TSRecord(6, "device_1");
+ dPoint1 = new FloatDataPoint("sensor_1", 7.2f);
+ dPoint2 = new IntDataPoint("sensor_2", 10);
+ dPoint3 = new IntDataPoint("sensor_3", 11);
+ tsRecord.addTuple(dPoint1);
+ tsRecord.addTuple(dPoint2);
+ tsRecord.addTuple(dPoint3);
+ tsFileWriter.write(tsRecord);
+
+ tsRecord = new TSRecord(7, "device_1");
+ dPoint1 = new FloatDataPoint("sensor_1", 6.2f);
+ dPoint2 = new IntDataPoint("sensor_2", 20);
+ dPoint3 = new IntDataPoint("sensor_3", 21);
+ tsRecord.addTuple(dPoint1);
+ tsRecord.addTuple(dPoint2);
+ tsRecord.addTuple(dPoint3);
+ tsFileWriter.write(tsRecord);
+
+ tsRecord = new TSRecord(8, "device_1");
+ dPoint1 = new FloatDataPoint("sensor_1", 9.2f);
+ dPoint2 = new IntDataPoint("sensor_2", 30);
+ dPoint3 = new IntDataPoint("sensor_3", 31);
+ tsRecord.addTuple(dPoint1);
+ tsRecord.addTuple(dPoint2);
+ tsRecord.addTuple(dPoint3);
+ tsFileWriter.write(tsRecord);
+
+ // close TsFile
+ tsFileWriter.close();
+ } catch (Throwable e) {
+ e.printStackTrace();
+ System.out.println(e.getMessage());
+ }
+ }
+}
+
+```
+
+##### Writing TsFile directly without defining the schema by json
Review comment:
```suggestion
##### Writing TsFile with defining the schema by API
```
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