Extend 'A Practical Guide For SQL Tuning' with table partitioning

Change Request

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

1. Describe what you find is inappropriate or missing in the existing docs.
   As a follow up to #19108, also write a part where table partitioning is explained and what its best practice can be used for SQL tuning

2. Describe your suggestion or addition.
   It should mention:

• Benefits of table partitioning
  • partition pruning can skip all partitions not matching the predicates of the query, also for TiFlash
  • DROP PARTITION very efficient way of deleting a whole partition, similar to DROP TABLE, without having to go through the transaction layer.
  • EXCHANGE PARTITION
• Drawbacks of table partitioning
  • non-global secondary indexes will do index lookups for each matching partition
• Global index
  • Remove the limitation that 'all unique indexes needs to include all partitioning columns'
  • A single table level index so not one lookup per partition
  • Needs index reorganization when dropping / reorganizing partitions, so not meta-data only DROP PARTITION.

3. Provide some reference materials (such as documents and websites) if you could.

Locate the existing “A Practical Guide For SQL Tuning” page and review the context from issue #19108 before planning the addition. Cover partition pruning, DROP PARTITION, EXCHANGE PARTITION, non-global secondary-index drawbacks, and global-index trade-offs; the documentation is done when each requested benefit, limitation, and use case is explained accurately.