max_execution_time doesn't contain get tso time

[aytrack]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

from https://asktug.com/t/topic/1023086

1. set max_execution_time = 3000
2. execute sql get tso from pd exceed 3s
   

2. What did you expect to see? (Required)

the query should interrupted after 3s

3. What did you see instead (Required)

the query run longer than 3s

4. What is your TiDB version? (Required)

master

[yibin87]

/severity major

[yibin87]

/remove-severity moderate

[guo-shaoge]

After asking help from @MyonKeminta , this is related to transaction and pd-client module.

1. DurationWaitTs is the get tso duration.
2. tf.future.Wait() is the main waiting function, it's an pd-client interface, but this interface doesn't has any method to interrupt get tso process.
3. need change pd-client to add method to interrupt getting tso process: tsoRequest

[cfzjywxk]

@guo-shaoge
I think the severity could be lowered, in most cases it would be a big problem.