*: show memory usage in "show processlist"

[zz-jason]

after this PR:

TiDB(localhost) > show processlist;
+------+------+-----------+------+---------+------+-------+--------------------------------+----------+
| Id   | User | Host      | db   | Command | Time | State | Info                           | Mem      |
+------+------+-----------+------+---------+------+-------+--------------------------------+----------+
|    3 | root | 127.0.0.1 | test | Query   |    0 | 2     | show processlist               |        0 |
|    1 | root | 127.0.0.1 | test | Query   |  162 | 2     | select * from t t1, t t2, t t3 | 19906560 |
+------+------+-----------+------+---------+------+-------+--------------------------------+----------+
2 rows in set (0.01 sec)

[zz-jason]

@winoros @XuHuaiyu @shenli PTAL

[winkyao]

CI failed

[winkyao]

reset LGTM

[zz-jason]

/run-all-tests

[alivxxx]

Could we do it in SetProcessInfo?

[zz-jason]

No we can not. Memory usage is dynamically changed value, we should calculate the memory usage when "show processlist" is called not when a query is being executed.

[alivxxx]

LGTM