add deleting data doc (#510)

docs/interacting/deleting-data.md

@@ -0,0 +1,52 @@
+# Delete Data in [Measures](../concept/data-model.md#measures) and [Streams](../concept/data-model.md#streams)
+
+Due to the design of BanyanDB, the `Property` data provides [CRUD](./bydbctl/property.md) operations,
+but the data in the `Measures and Streams` can not be deleted directly.
+The data will be deleted automatically based on the [Groups](../concept/data-model.md#groups) `TTL` setting.
+
+The TTL means the `time to live` of the data in the group. 
+Each group has an internal trigger which is triggered by writing events. If there is no further data, the expired data can’t get removed.
+
+For example, the following command will create a group with a TTL of 7 days:
+```shell
+bydbctl group create -f - <<EOF
+metadata:
+  name: sw_metric
+catalog: CATALOG_MEASURE
+resource_opts:
+  shard_num: 2
+  segment_interval:
+    unit: UNIT_DAY
+    num: 1
+  ttl:
+    unit: UNIT_DAY
+    num: 7
+EOF
+```
+The data in this group will keep 7 days.
+
+If you want to change the `TTL` of the data in this group to be 1 day, use the command:
+
+```shell
+bydbctl group update -f - <<EOF
+metadata:
+  name: sw_metric
+catalog: CATALOG_MEASURE
+resource_opts:
+  shard_num: 2
+  segment_interval:
+    unit: UNIT_DAY
+    num: 1
+  ttl:
+    unit: UNIT_DAY
+    num: 1
+EOF
+```
+
+More ttl units can be found in the [IntervalRule.Unit](../api-reference.md#intervalruleunit).
+
+You can also manage the Group by other clients such as [Web-UI](./web-ui/schema/group.md) or [Java-Client](java-client.md).
+
+## The API reference 
+- [Group Registration Operations](../api-reference.md#groupregistryservice)
+- [ResourceOpts Definition](../api-reference.md#resourceopts)

docs/menu.yml

@@ -94,6 +94,8 @@ catalog:
             path: "/interacting/web-ui/property"
       - name: "Java Client"
         path: "/interacting/java-client"
+      - name: "Deleting Data"
+        path: "/interacting/deleting-data"
   - name: "Operation and Maintenance"
     catalog:
       - name: "Configure BanyanDB"