primary changed twice when pdms rolling update

[Lily2025]

Bug Report

What did you do?

1、update the config of tso

What did you expect to see?

the primary changed once when tso rolling update

What did you see instead?

the primary changed twice when tso rolling update

What version of PD are you using (pd-server -V)?

./pd-server -V
Release Version: v8.0.0-alpha
Edition: Community
Git Commit Hash: bc92c13
Git Branch: heads/refs/tags/v8.0.0-alpha
UTC Build Time: 2024-03-27 11:37:04
2024-03-28T15:26:29.929+0800

[Lily2025]

/type bug
/severity major
/assign HuSharp

[HuSharp]

For tiup

1. When we have 3 pdms, pdms-0/pdms-1/pdms-2, and pdms-2 is primary
2. upgrade pdms-2 firstly maybe transfer primary to pdms-0
3. uprade pdms-0 will transfer primary again

We can upgrade pdms primary in last place(named defer feature) can avoid unnecessary primary transfer

Ref pingcap/tiup#2414

For operator

tidb-operator does not have the ability to defer feature, it can only upgrade the pods in order.

Furthermore, Thinking about this situation:

1. When we have 3 pdms, pdms-0/pdms-1/pdms-2, and pdms-2 is primary
2. upgrade pdms-2 firstly maybe transfer primary to pdms-1
3. upgrade pdms-1 maybe transfer primary to pdms-0.

To fix it, Assume that current primary ordinal is x, and range is [0, n]

1. Find the max suitable ordinal in (x, n], because they have been upgraded
2. If no suitable ordinal, find the min suitable ordinal in [0, x) to reduce the count of transfer

Ref pingcap/tidb-operator#5643