pkg/lightning : remove get_regions call in physical backend (#46202)

[ti-chi-bot]

This is an automated cherry-pick of #46202

What problem does this PR solve?

Problem Summary:
When lightning runs in physical import mode, it runs this sql query

SELECT REGION_ID, APPROXIMATE_SIZE FROM information_schema.TIKV_REGION_STATUS WHERE TABLE_ID = ?

This call is made by each lightning process in parallel import mode and by multiple worker threads in a lightning process. It can potentially overload the PD if number of regions are too many. However, it appears that this call may be unnecessary since its purpose is to display a warning message and increment a counter in the SplitAndScatterRegionByRanges() function. Considering that lightning physical import always operates on a new table, splitting the new region should not pose any harm.

Issue Number: close #45507

What is changed and how it works?

Remove the getRegions call from lightning

Check List

Tests

• Manual test (add detailed scripts or steps below)

1. Run lightning in parallel import mode
2. Check get_Regions call in PD dashboard. It should be 0
3. Lightning should run successfully

Release note

We saw this issue in 6.5.0

Please refer to Release Notes Language Style Guide to write a quality release note.

None

[ti-chi-bot]

This cherry pick PR is for a release branch and has not yet been approved by release team.
Adding the do-not-merge/cherry-pick-not-approved label.

To merge this cherry pick, it must first be approved by the collaborators.

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[Benjamin2037]

LGTM

[GMHDBJD]

/retest

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (release-6.5@7241e78). Click here to learn what that means.
The diff coverage is n/a.

Additional details and impacted files

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[GMHDBJD]

LGTM

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Benjamin2037, GMHDBJD

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2023-11-22 05:11:06.276935092 +0000 UTC m=+381094.942161287: ☑️ agreed by Benjamin2037.
• 2023-11-23 08:23:33.028408575 +0000 UTC m=+479041.693634769: ☑️ agreed by GMHDBJD.

[Benjamin2037]

/retest

[Benjamin2037]

/retest

[Benjamin2037]

/retest