executor: show better placement schedule state

[xhebox]

Signed-off-by: xhe [email protected]

What problem does this PR solve?

Issue Number: close #30960

Problem Summary: Depends on tikv/pd#4508. Now we have "PENDING" to indicate PD did not start the schedule at all. It is possibly caused by busy looping or unmet condition, whatever, it is not scheduling.

I'll complete the document in another PR, since there are other document changes.

What is changed and how it works?

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)

mysql [email protected]:(none)> create table test.t1 (a int) FOLLOWERS=4;
Query OK, 0 rows affected
Time: 0.200s
mysql [email protected]:(none)> show placement;
+---------------+-------------+------------------+
| Target        | Placement   | Scheduling_State |
+---------------+-------------+------------------+
| TABLE test.t1 | FOLLOWERS=4 | PENDING       |
+---------------+-------------+------------------+

• No code

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

None

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[xhebox]

/cc @morgo

PTAL, not about the code logic, but the name of third state. Currently I made it "WAITING". This primarily comes from the truth that it is not equal to "UNABLE TO SCHEDULE".

PD could only tell that it is not scheduling, i.e. it paused the schedule somehow due to other conditions. PD could recover from "WAITING" to "INPROGRESS"/"SCHEDULED" at anytime, or vice versa.

Reviewers of PD also said about "WAITING" and "INPROGRESS" is too similar. But "unable to schedule" feels like it won't schedule again at all. What about 'NOT SCHEDULING'? I really ran out of words in my mind.

[morgo]

PTAL, not about the code logic, but the name of third state. Currently I made it "WAITING". This primarily comes from the truth that it is not equal to "UNABLE TO SCHEDULE".

I see. I think PENDING is the correct word here. It is common to say that "the case is pending out a decision".

[xhebox]

PTAL, not about the code logic, but the name of third state. Currently I made it "WAITING". This primarily comes from the truth that it is not equal to "UNABLE TO SCHEDULE".

I see. I think PENDING is the correct word here. It is common to say that "the case is pending out a decision".

Neat!

[morgo]

@xhebox great job btw, thanks for working on this!

[sre-bot]

Code Coverage Details: https://codecov.io/github/pingcap/tidb/commit/6959a31fee5ec2fb950f22a6dcb6f9528ea40423

[xhebox]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 2b6d702

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