show vitess_tablets is incorrect after reparenting

[deepthi]

Overview of the Issue

vtgate's show vitess_tablets command does not show the timestamp for a new master.

Reproduction Steps

Run local example (101_initial_cluster.sh). Connect to vtgate.

$ mysql
mysql> show vitess_tablets;
+-------+----------+-------+------------+---------+------------------+------------------+----------------------+
| Cell  | Keyspace | Shard | TabletType | State   | Alias            | Hostname         | MasterTermStartTime  |
+-------+----------+-------+------------+---------+------------------+------------------+----------------------+
| zone1 | commerce | 0     | MASTER     | SERVING | zone1-0000000100 |<hostname redacted>| 2020-06-09T18:08:09Z |
| zone1 | commerce | 0     | REPLICA    | SERVING | zone1-0000000101 |<hostname redacted>|                      |
| zone1 | commerce | 0     | RDONLY     | SERVING | zone1-0000000102 |<hostname redacted>|                      |
+-------+----------+-------+------------+---------+------------------+------------------+----------------------+
3 rows in set (0.00 sec)

From another shell, reparent to tablet 101

$ vtctlclient PlannedReparentShard -keyspace_shard=commerce/0 -new_master=zone1-0000000101
I0609 11:14:31.899712   25100 main.go:64] I0609 18:14:31.897724 reparent.go:559] Checking replication on master-elect zone1-0000000101
I0609 11:14:31.919441   25100 main.go:64] I0609 18:14:31.919056 reparent.go:594] demote current master cell:"zone1" uid:100 
I0609 11:14:32.780261   25100 main.go:64] I0609 18:14:32.779588 reparent.go:692] populating reparent journal on new master zone1-0000000101
I0609 11:14:32.780739   25100 main.go:64] I0609 18:14:32.779916 reparent.go:675] setting new master on replica zone1-0000000102
I0609 11:14:32.780794   25100 main.go:64] I0609 18:14:32.779966 reparent.go:675] setting new master on replica zone1-0000000100

Now look at tablet status again

mysql> show vitess_tablets;
+-------+----------+-------+------------+---------+------------------+------------------+----------------------+
| Cell  | Keyspace | Shard | TabletType | State   | Alias            | Hostname         | MasterTermStartTime  |
+-------+----------+-------+------------+---------+------------------+------------------+----------------------+
| zone1 | commerce | 0     | MASTER     | SERVING | zone1-0000000101 |<hostname redacted>|                      |
| zone1 | commerce | 0     | REPLICA    | SERVING | zone1-0000000100 |<hostname redacted>| 2020-06-09T18:08:09Z |
| zone1 | commerce | 0     | RDONLY     | SERVING | zone1-0000000102 |<hostname redacted>|                      |
+-------+----------+-------+------------+---------+------------------+------------------+----------------------+
3 rows in set (0.00 sec)

Notice that tablet 101 is now MASTER but it's MasterTermStartTime is still empty.

Binary version

$ vtgate --version
Version: 945e105aa (Git branch 'master') built on Tue Jun  9 12:35:29 PDT 2020 by <redacted> using go1.13.6 linux/amd64

Operating system and Environment details

$ uname -a
Linux <hostname redacted> 4.15.0-101-generic #102-Ubuntu SMP Mon May 11 10:07:26 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux

[deepthi]

Desired output:
Before reparenting:

mysql> show vitess_tablets;
+-------+----------+-------+------------+---------+------------------+------------------+---------------------------+
| Cell  | Keyspace | Shard | TabletType | State   | Alias            | Hostname         | MasterTermStartTime       |
+-------+----------+-------+------------+---------+------------------+------------------+---------------------------+
| zone1 | commerce | 0     | MASTER     | SERVING | zone1-0000000100 |<hostname redacted>| 2020-06-09T20:41:31Z     |
| zone1 | commerce | 0     | REPLICA    | SERVING | zone1-0000000101 |<hostname redacted>|                          |
| zone1 | commerce | 0     | RDONLY     | SERVING | zone1-0000000102 |<hostname redacted>|                          |
+-------+----------+-------+------------+---------+------------------+------------------+---------------------------+
3 rows in set (0.00 sec)

After reparenting:

mysql> show vitess_tablets;
+-------+----------+-------+------------+---------+------------------+------------------+---------------------------+
| Cell  | Keyspace | Shard | TabletType | State   | Alias            | Hostname         | MasterTermStartTime       |
+-------+----------+-------+------------+---------+------------------+------------------+---------------------------+
| zone1 | commerce | 0     | MASTER     | SERVING | zone1-0000000101 |<hostname redacted>| 2020-06-09T20:43:47Z     |
| zone1 | commerce | 0     | REPLICA    | SERVING | zone1-0000000100 |<hostname redacted>|                          |
| zone1 | commerce | 0     | RDONLY     | SERVING | zone1-0000000102 |<hostname redacted>|                          |
+-------+----------+-------+------------+---------+------------------+------------------+---------------------------+
3 rows in set (0.00 sec)