Why is my table size more than 4x larger than expected? (rows*bytes/row)

Question

I'm looking at a simple table in MySQL that has 4 columns with the following sizes,

unsigned bigint (8 bytes)
unsigned bigint (8 bytes)
unsigned smallint (2 bytes)
unsigned tinyint (1 byte)

So I would expect 19 bytes/row.

There are 1,654,150 rows in this table so the size of the data should be 31,428,850 bytes (or about 30 megabytes).

But I can see via phpMyAdmin that the data is taking up 136.3 MiB (not including the size of the Index on bigint 1, smallint, tinyint which is 79 MiB).

Storage Engine is InnoDB and Primary Key is bigint 1, bigint 2 (a user ID and a unique item id).

Edit: As requested in the comments, here is the result of a SHOW CREATE TABLE storage

CREATE TABLE `storage` (
 `fbid` bigint(20) unsigned NOT NULL,
 `unique_id` bigint(20) unsigned NOT NULL,
 `collection_id` smallint(5) unsigned NOT NULL,
 `egg_id` tinyint(3) unsigned NOT NULL,
 PRIMARY KEY (`fbid`,`unique_id`),
 KEY `fbid` (`fbid`,`collection_id`,`egg_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8

Why is my table size more than 4x larger than expected? (rows*bytes/row)

3 Answers