char vs varchar for performance in stock database

Question

I'm using mySQL to set up a database of stock options. There are about 330,000 rows (each row is 1 option). I'm new to SQL so I'm trying to decide on the field types for things like option symbol (varies from 4 to 5 characters), stock symbol (varies from 1 to 5 characters), company name (varies from 5 to 60 characters).

I want to optimize for speed. Both creating the database (which happens every 5 minutes as new price data comes out -- i don't have a real-time data feed, but it's near real-time in that i get a new text file with 330,000 rows delivered to me every 5 minutes; this new data completely replaces the prior data), and also for lookup speed (there will be a web-based front end where many users can run ad hoc queries).

If I'm not concerned about space (since the db lifetime is 5 minutes, and each row contains maybe 300 bytes, so maybe 100MBs for the whole thing) then what is the fastest way to structure the fields?

Same question for numeric fields, actually: Is there a performance difference between int(11) and int(7)? Does one length work better than another for queries and sorting?

Thanks!

Answer 1

In MyISAM, there is some benefit to making fixed-width records. VARCHAR is variable width. CHAR is fixed-width. If your rows have only fixed-width data types, then the whole row is fixed-width, and MySQL gains some advantage calculating the space requirements and offset of rows in that table. That said, the advantage may be small and it's hardly worth a possible tiny gain that is outweighed by other costs (such as cache efficiency) from having fixed-width, padded CHAR columns where VARCHAR would store more compactly.

The breakpoint where it becomes more efficient depends on your application, and this is not something that can be answered except by you testing both solutions and using the one that works best for your data under your application's usage.

Regarding INT(7) versus INT(11), this is irrelevant to storage or performance. It is a common misunderstanding that MySQL's argument to the INT type has anything to do with size of the data -- it doesn't. MySQL's INT data type is always 32 bits. The argument in parentheses refers to how many digits to pad if you display the value with ZEROFILL. E.g. INT(7) will display 0001234 where INT(11) will display 00000001234. But this padding only happens as the value is displayed, not during storage or math calculation.