Add doc for MeasurementSchema in Tablet (#1534)

* fix tablet doc

example/session/src/main/java/org/apache/iotdb/SessionExample.java

@@ -238,11 +238,12 @@ public class SessionExample {
    * Users need to control the count of Tablet and write a batch when it reaches the maxBatchSize
    */
   private static void insertTablet() throws IoTDBConnectionException, StatementExecutionException {
-    // The schema of sensors of one device
+    // The schema of measurements of one device
+    // only measurementId and data type in MeasurementSchema take effects in Tablet
     List<MeasurementSchema> schemaList = new ArrayList<>();
-    schemaList.add(new MeasurementSchema("s1", TSDataType.INT64, TSEncoding.RLE));
-    schemaList.add(new MeasurementSchema("s2", TSDataType.INT64, TSEncoding.RLE));
-    schemaList.add(new MeasurementSchema("s3", TSDataType.INT64, TSEncoding.RLE));
+    schemaList.add(new MeasurementSchema("s1", TSDataType.INT64));
+    schemaList.add(new MeasurementSchema("s2", TSDataType.INT64));
+    schemaList.add(new MeasurementSchema("s3", TSDataType.INT64));
 
     Tablet tablet = new Tablet("root.sg1.d1", schemaList, 100);
 
@@ -269,11 +270,12 @@ public class SessionExample {
   }
 
   private static void insertTablets() throws IoTDBConnectionException, StatementExecutionException {
-    // The schema of sensors of one device
+    // The schema of measurements of one device
+    // only measurementId and data type in MeasurementSchema take effects in Tablet
     List<MeasurementSchema> schemaList = new ArrayList<>();
-    schemaList.add(new MeasurementSchema("s1", TSDataType.INT64, TSEncoding.RLE));
-    schemaList.add(new MeasurementSchema("s2", TSDataType.INT64, TSEncoding.RLE));
-    schemaList.add(new MeasurementSchema("s3", TSDataType.INT64, TSEncoding.RLE));
+    schemaList.add(new MeasurementSchema("s1", TSDataType.INT64));
+    schemaList.add(new MeasurementSchema("s2", TSDataType.INT64));
+    schemaList.add(new MeasurementSchema("s3", TSDataType.INT64));
 
     Tablet tablet1 = new Tablet("root.sg1.d1", schemaList, 100);
     Tablet tablet2 = new Tablet("root.sg1.d2", schemaList, 100);

tsfile/src/main/java/org/apache/iotdb/tsfile/write/record/Tablet.java

@@ -74,7 +74,8 @@ public class Tablet {
    * constructor (all Tablet should be the same size).
    *
    * @param deviceId   the name of the device specified to be written in
-   * @param timeseries the list of measurement schemas for creating the tablet
+   * @param timeseries the list of measurement schemas for creating the tablet,
+   *                   only measurementId and type take effects
    */
   public Tablet(String deviceId, List<MeasurementSchema> timeseries) {
     this(deviceId, timeseries, DEFAULT_SIZE);
@@ -87,7 +88,7 @@ public class Tablet {
    *
    * @param deviceId     the name of the device specified to be written in
    * @param schemas   the list of measurement schemas for creating the row
-   *                     batch
+   *                  batch, only measurementId and type take effects
    * @param maxRowNumber the maximum number of rows for this tablet
    */
   public Tablet(String deviceId, List<MeasurementSchema> schemas, int maxRowNumber) {