Add docs for virtual database tags (#307)
* Add docs for virtual database tags
* Update CHANGES.md
diff --git a/CHANGES.md b/CHANGES.md
index 46411e5..bcd3a46 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -15,7 +15,8 @@
#### Documentation
* Update `configuration` doc about overriding default value as empty map/list accordingly.
-* Update plugin dev tags for cache relative tags
+* Update plugin dev tags for cache relative tags.
+* Add plugin dev docs for virtual database tags.
All issues and pull requests are [here](https://github.com/apache/skywalking/milestone/150?closed=1)
diff --git a/docs/en/setup/service-agent/java-agent/Java-Plugin-Development-Guide.md b/docs/en/setup/service-agent/java-agent/Java-Plugin-Development-Guide.md
index 20e9ce6..289a20e 100644
--- a/docs/en/setup/service-agent/java-agent/Java-Plugin-Development-Guide.md
+++ b/docs/en/setup/service-agent/java-agent/Java-Plugin-Development-Guide.md
@@ -186,6 +186,19 @@
}
```
+#### Vitural Database Relative Tags
+SkyWalking analysis Database(SQL-like) performance metrics through the following tags.
+
+```java
+ public static final StringTag DB_TYPE = new StringTag(3, "db.type");
+ public static final StringTag DB_STATEMENT = new StringTag(5, "db.statement");
+```
+
+* `db.type` records database type, such as sql, cassandra, Elasticsearch.
+* `db.statement`records the sql statement of the database access.
+
+Read [backend's virtual database doc](https://skywalking.apache.org/docs/main/next/en/setup/service-agent/virtual-database/) for more details.
+
#### Vitural Cache Relative Tags
Skywalking analysis cache performance related metrics through the following tags.
