This is purely for the sake of partitioning. In this example, I’ll quickly partition the wordpress comments table into partitions. The hash partition ensures data are evenly distributed across partitions.
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mysql> alter table wp_comments partition by hash(comment_ID) partitions 3; Query OK, 13 rows affected (0.04 sec) Records: 13 Duplicates: 0 Warnings: 0 |
Now check that queries are only reaching out to necessary partitions
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mysql> explain partitions select * from wp_comments where comment_id = 1\G *************************** 1. row *************************** id: 1 select_type: SIMPLE table: wp_comments partitions: p1 type: const possible_keys: PRIMARY key: PRIMARY key_len: 8 ref: const rows: 1 Extra: 1 row in set (0.00 sec) |
The hash function can be overridden with any function that returns an integer. For example, I can use mod(some_id,2) to divide some_id into two groups – even…
