store/tikv: pipe the split and scatter task

[nolouch]

Signed-off-by: nolouch [email protected]

What problem does this PR solve?

close #22969

Problem Summary:
Splitting and Scattering at the same time will cause multiple conflicts on the same region.

What is changed and how it works?

pipeline all splits task and scatter tasks

Release note

• Make the time consuming of split table more stable

I have run multiple times  to split 4000 regions, and the time is stale about `1m30s`
2021/03/17 17:25:57 split single sql result: [map[SCATTER_FINISH_RATIO:1 TOTAL_SPLIT_REGION:2001]]
2021/03/17 17:25:57 split all sql run total cost: 1m28.908304306s
2021/03/17 17:25:57 split all sql run success!!!

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has not been approved.

To complete the pull request process, please ask the reviewers in the list to review by filling /cc @reviewer in the comment.
After your PR has acquired the required number of LGTMs, you can assign this pull request to the committer in the list by filling /assign @committer in the comment to help you merge this pull request.

The full list of commands accepted by this bot can be found here.

Reviewer can indicate their review by writing /lgtm in a comment.
Reviewer can cancel approval by writing /lgtm cancel in a comment.

[crazycs520]

Suggested change

	for _, r := range spResp.Regions {
	tid := int64(0)
	if tableID != nil {
	tid = *tableID
	}
	tid := int64(0)
	if tableID != nil {
	tid = *tableID
	}
	for _, r := range spResp.Regions {

[crazycs520]

Suggested change

	tid := int64(0)
	if tableID != nil {
	tid = *tableID
	}

[jackysp]

So it's still using

tidb/store/tikv/split_region.go

Line 217 in 579421f

_, err := s.pdClient.ScatterRegions(bo.ctx, []uint64{regionID}, opts...)

the batch API to scatter regions one by one. Which may make the scatter not work?

[jackysp]

I mean #22788 .
OK, I'm off topic.

[Yisaer]

The current region scatter may not work in a specific case which described in tikv/pd#3422 , I think it's not related to the api.

[ti-chi-bot]

@nolouch: PR needs rebase.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.