To handle issue after big delete, since region merge feature is alrea…

…dy released, update on it (#16365)

faq/migration-tidb-faq.md

@@ -170,7 +170,7 @@ Yes.
 
 ### Why does the query speed getting slow after deleting data?
 
-Deleting a large amount of data leaves a lot of useless keys, affecting the query efficiency. Currently the Region Merge feature is in development, which is expected to solve this problem. For details, see the [deleting data section in TiDB Best Practices](https://en.pingcap.com/blog/tidb-best-practice/#write).
+Deleting a large amount of data leaves a lot of useless keys, affecting the query efficiency. The [Region Merge feature](/best-practices/massive-regions-best-practices.md#method-3-enable-region-merge) can solve this problem. For more details, see the [deleting data section in TiDB Best Practices](https://en.pingcap.com/blog/tidb-best-practice/#write).
 
 ### What is the most efficient way of deleting data?