Provide a comparison tool for checking compatibility changes between TiDB versions

[likidu]

Why: To help customers and users upgrade the TiDB database smoothly.

https://docs.pingcap.com/tidb/dev/system-variables

• All variables for a certain version
• Diff between two version
• Fuzzy search variable name

A PR has been created for this: #445

[likidu]

@lilin90 We can use git diff to compare the same file from two branches and output to a markdown file.

Here is a simple bash for this:

git diff -U6000 --word-diff release-7.4 release-7.1 -- system-variables.md --no-index |\
tail +6  |\
sed 's/\[-/~~/g;s/-]/~~/g;' |\
sed 's/{\+/__/g;s/+}/__/g' > ~/Repos/sys-var-new.md

The -U6000 is just provide the lines to compare, we can use wc -l <file> to calculate the actual lines of the file for each branch and use the greater number to have a more precise value.

Attached the output of this command to see the result.

sys-var-new.md

[likidu]

User further asks about easy-to-find info of deprecated system variables.

[likidu]

For MySQL, this one that is quite useful for version compatibility checks: https://dev.mysql.com/doc/mysqld-version-reference/en/options-variables.html.

[likidu]

Another solution: https://kit.mogdb.io/