sysvar: add a sysvar (#10958)
sysvar: add a sysvar (#10958)

* sysvar: add a sysvar

* Update system-variables.md

Co-authored-by: Aolin <50c5dcd6645c407e0928aca2ce24e0b7d94bb2c9@pingcap.com>

Co-authored-by: Aolin <50c5dcd6645c407e0928aca2ce24e0b7d94bb2c9@pingcap.com>
pingcap/docs,pingcap/docs,pingcap/docs