Why Memory Engine is much larger than InnoDB engine store?

Question

I have a table stored about 100,000 rows data in InnoDB engine. I just copy the data to a memory engine table, but I find that the size of the new one is much large than orignal table. Why?

| Rows | Engine | Size |

| 96702 | Memory|741MB|

|96952|InnoDB|28MB|

WHY?

Answer 1

Memory engine tables use a fixed-length row-storage format. Variable-length types such as VARCHAR are stored using a fixed length.

Note: Loading your data from an InnoDB engine into a Memory engine is really a SQL anti-pattern (because of data duplication). You really should configure the InnoDB buffer pool on your MySQL server. InnoDB will then outperform a Memory engine with many clients because a Memory engine is row locking based

See the documentation on Memory engine's .