dr: cannot add new stores in primary

[lhy1024]

Bug Report

What did you do?

test dr-auto-sync

1. down dr
2. add new stores in primary

What did you expect to see?

tikv can add new peers in new stores

What did you see instead?

tikv cannot add new peers and log print "drop msg"

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

v6.5.4

[lhy1024]

pd/pkg/replication/replication_mode.go

Lines 581 to 583 in a85f29c

	if s.GetRegionCount() == s.GetLearnerCount() {
	continue
	}

For new stores, if its learner count is equal to the region count, the code will not put it into AvailableStores, so tikv will drop msg.

Unfortunately, all peers in the new store are learners, which is normal.

Workaround: switch majority mode