# Additional Knowledge: Dml Data Reading Process


![left](./student-guide/diagram/03-09-1.png)

------------------------------------------------------------

Through the monitoring just now, it has been possible to troubleshoot that the problem is in some components other than TiDB Server, so what are the important key steps in the SQL execution process that need to be investigated one by one? Then what monitoring are these key steps locked to?

In the DML statement reading process, the user's SQL is read by the protocol layer of the TiDB server. After that, TSO is obtained in the PD, parsed, compiled, and then entered TiKV for execution. Therefore, check if there is a problem with PD that causes SQL to slow, parse, compile, and read TiKV. Is there a problem with the data.