show processlist 'mem' column always zero

[morgo]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. What did you do?

In TiDB, the show processlist command has a column for 'mem'. It is always zero:

mysql> show processlist;
+------+------+-----------+------+---------+------+-------+------------------+------+
| Id   | User | Host      | db   | Command | Time | State | Info             | Mem  |
+------+------+-----------+------+---------+------+-------+------------------+------+
|    1 | root | 127.0.0.1 | test | Query   |    0 | 2     | show processlist |    0 |
+------+------+-----------+------+---------+------+-------+------------------+------+
1 row in set (0.00 sec)

2. What did you expect to see?

I suggest we remove it, since it is not a MySQL compatibility requirement (MySQL uses performance schema to show memory), and looks bad that it is always zero.

Long term when views exist, it would be nice to add a sys-like feature to TiDB.

3. What did you see instead?

Mem column.

4. What version of TiDB are you using (tidb-server -V or run select tidb_version(); on TiDB)?

mysql> SELECT tidb_version()\G
*************************** 1. row ***************************
tidb_version(): Release Version: v2.1.0-rc.3-241-ge5dc251dd
Git Commit Hash: e5dc251dd3e6826f8c23bef645ea2a3b10a970f7
Git Branch: newmaster
UTC Build Time: 2018-11-27 04:41:52
GoVersion: go version go1.11 linux/amd64
Race Enabled: false
TiKV Min Version: 2.1.0-alpha.1-ff3dd160846b7d1aed9079c389fc188f7f5ea13e
Check Table Before Drop: false
1 row in set (0.00 sec)

[morgo]

Fixed in #8543