Merge master about 6.6(7ec73fd)

[CalvinNeo]

What problem does this PR solve?

Issue Number: close #xxx

Problem Summary:

This PR is to adopt Flashback fix:

1. First merge 9726e5. No flashback fix included, do this because we want less work when we actually merge flashback fix.
2. Then merge 7ec73fd. This is flashback fix.
   Origin 453b9df.

What is changed and how it works?

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

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you all sign our Contributor License Agreement before we can accept your contribution.
7 out of 18 committers have signed the CLA.

✅ hongyunyan
✅ HuSharp
✅ glorv
✅ CalvinNeo
✅ YangKeao
✅ breezewish
✅ LittleFall
❌ ethercflow
❌ tonyxuqqi
❌ BusyJay
❌ Connor1996
❌ tabokie
❌ bufferflies
❌ MyonKeminta
❌ iosmanthus
❌ YuJuncen
❌ andreid-db
❌ JmPotato
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