Does using a smallint datatype in a mysql table over a regular int actually improve memory usage? Wouldn't the hardware just allocate a full 64 bit word size for all data anyway? If it doesn't allocate a full word, then wouldn't we see a performance decrease from having to parse out multiple smallints or tinyints from a 64 bit word allocated in memory?

Basically, is there any design/memory/performance benefit to using the following table over the one after it, assuming we know the range of the values stored in the Status column will never exceed the max/min range of smallint? Any insight would be appreciated:

create table `TestTableWithSmallInt` (

`ID` bigint(20) NOT NULL AUTO_INCREMENT,

`Status` smallint(11) DEFAULT 0,

PRIMARY KEY (`ID`)

) ENGINE=InnoDB DEFAULT CHARSET=utf8;

create table `TestTableWithInt` (

`ID` bigint(20) NOT NULL AUTO_INCREMENT,

`Status` int(11) DEFAULT 0,

PRIMARY KEY (`ID`)

) ENGINE=InnoDB DEFAULT CHARSET=utf8;

解决方案

You'll theoretically save two bytes per row, a SMALLINT is a 16-bit signed integer versus the INT which is 32-bit signed. The various types have varying storage requirements.

Normally the savings between INT and SMALLINT produces such a slim performance improvement that you'll have a hard time measuring it, especially if there's a small number of fields you're trimming this way.

For the opposite, you'll only want to use a BIGINT when it's conceivable that you might exhaust the number space of an AUTO_INCREMENT flagged field.

You should probably declare them in their bare types, without a length, to get the best fit. INT is preferable to INT(11) and SMALLINT(11) is misleading as it's impossible to get that much precision from a 16-bit value.