fix metrics for establish connection

[windtalker]

Signed-off-by: xufei xufeixw@mail.ustc.edu.cn

What problem does this PR solve?

Issue Number: close #6197

Problem Summary:

What is changed and how it works?

1. Fix handling_request_count and request_duration_seconds for establish connection
2. Refine FlashService so do not create DBContext if not needed.

Check List

Tests

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

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• SeaRise
• gengliqi

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[gengliqi]

LGTM

[windtalker]

/merge

[ti-chi-bot]

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[ti-chi-bot]

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

Commit hash: 8a455ae

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #6212.

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #6213.