Improve sysvar documentation

Change Request

This repository is ONLY used to solve issues related to DOCS.
For other issues (related to TiDB, PD, etc), please move to other repositories.

Please answer the following questions before submitting your issue. Thanks!

1. Describe what you find is inappropriate or missing in the existing docs.

In the PR #3152 the following comments were left unhandled:

• Has the value of auto been removed from tidb_enable_table_partition? @tiancaiamao
• Can we safely set tidb_row_format_version to a lower value in a newer versioned TiDB cluster? @coocood
• Is there an example where windowing_use_high_precision has different behavior / performance? @SunRunAway

2. Describe your suggestion or addition.

See above.

3. Provide some reference materials (documents, websites, etc) if you could.

#3152

[tiancaiamao]

auto is not removed from tidb_enable_table_partition, the semantic of on is changed.
I explained why in the PR pingcap/tidb#16497
@nullnotnil

[github-actions]

This issue is stale because it has been open for 60 days with no activity. If no comment has been made and the lifecycle/stale label is not removed, this issue will be closed in 15 days.

[github-actions]

This issue is stale because it has been open for 60 days with no activity. If no comment has been made and the lifecycle/stale label is not removed, this issue will be closed in 15 days.

[TomShawn]

@coocood @SunRunAway PTAL

[coocood]

Yes, we can safely set tidb_row_format_version to a lower value in a newer versioned TiDB cluster.