Re: surrogate key or not?

Markus,

Oh, so you want USEFUL answers. OK.

> Now when I want to search for a type in types or another table that
> references types(type_id), under what circumstances is it advisable to
> have a surrogate integer key and not use the unique type name?

When using the actual name will be a performance problem.

> Is
> searching for an integer as fast as is searching for a string when both
> have an index?

Not usually, no. The index on the text values will simply be larger than the
one on 4-byte INTs, which means it's "slower", assuming you run out of memory
some of the time. If your whole DB fits in RAM, it's not worth worrying
about.

> How many records in the type table do I need to make a
> surrogate key a not unsignificantly faster way to retrieve a row?

It needs to be large enougth that the difference in data types makes a
difference in whether or not it will fit into sort_mem, and how likely it is
to be already cached in memory.

> What
> about joins?

Double jeopardy; you're using the column twice so double the storage
difference. Otherwise, it's just the same issue; does it still fit in RAM
or not?

> Are these the right questions?

Also you'll want to consider the speed of CASCADE operations whenever a
type_name changes. If these changes occur extremely infrequently, then you
can ignore this as well.

--
-Josh Berkus
Aglio Database Solutions
San Francisco