Update Chapter4_2.md

Update Chapter4_2.md

Add a reference to the BenchmarkSQL tool

Add a reference to the BenchmarkSQL tool

Update Preface.md

Update Preface.md

Update Chapter7.md

Update Chapter7.md

Improve the description based on user feedback.

Improve the description based on user feedback.

Uniform image format

Uniform image format

Improvement documentation

Improvement documentation

Update Chapter8.md

Update Chapter8.md

Update Chapter8.md

Update Chapter8.md

Add content on improving low concurrency performance

Add content on improving low concurrency performance

Update Chapter4_2.md

Update Chapter4_2.md

Lay the foundation for low-concurrency performance improvements

Lay the foundation for low-concurrency performance improvements

Avoid potential future copyright disputes with Oracle

Avoid potential future copyright disputes with Oracle

Update README.md

Update README.md

Optimize the remaining documentation

Optimize the remaining documentation