merge should consider offline store

[BusyJay]

Bug Report

What did you do?

Delete a store by

store delete store_id

What did you expect to see?

No new replicas are scheduled to the deleted stores.

What did you see instead?

New replicas are schedule to deleted stores from time to time. Apparently, merge scheduler doesn't if stores are offline or not.

[2021/09/14 07:50:14.593 +00:00] [INFO] [operator_controller.go:543] ["operator finish"] [region-id=208025] [takes=6.063414281s] [operator="\"replace-rule-offline-leader-peer {mv peer: store [367567] to [6]} (kind:replica,region,leader, region:208025(2144,851), createAt:2021-09-14 07:50:08.530475804 +0000 UTC m=+324583.120329687, startAt:2021-09-14 07:50:08.530563423 +0000 UTC m=+324583.120417305, currentStep:5, steps:[add learner peer 532133 on store 6, transfer leader from store 367567 to store 5, use joint consensus, promote learner peer 532133 on store 6 to voter, demote voter peer 480732 on store 367567 to learner, leave joint state, promote learner peer 532133 on store 6 to voter, demote voter peer 480732 on store 367567 to learner, remove peer on store 367567]) finished\""] [additional-info=]
[2021/09/14 07:50:50.948 +00:00] [INFO] [operator_controller.go:430] ["add operator"] [region-id=208025] [operator="\"merge-region {merge: region 208025 to 516311} (kind:merge,region, region:208025(2144,857), createAt:2021-09-14 07:50:50.94888579 +0000 UTC m=+324625.538739654, startAt:0001-01-01 00:00:00 +0000 UTC, currentStep:0, steps:[add learner peer 532180 on store 367567, use joint consensus, promote learner peer 532180 on store 367567 to voter, demote voter peer 532133 on store 6 to learner, leave joint state, promote learner peer 532180 on store 367567 to voter, demote voter peer 532133 on store 6 to learner, remove peer on store 6, merge region 208025 into region 516311])\""] [additional-info=]

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

$ ./deploy/pd-2379/bin/pd-server --version
Release Version: v5.1.1
Edition: Community
Git Commit Hash: 7cba1912b317a533e18b16ea2ba9a14ed2891129
Git Branch: heads/refs/tags/v5.1.1
UTC Build Time:  2021-07-23 01:16:18

[HunDunDM]

It may also be scheduled on the low space Store.