Re: Record size

Hilary Forbes <hforbes(at)dmr(dot)co(dot)uk> writes:
> Now the question. Does the number of fields that you have in a record and indeed their size affect performance on a SELECT statement when only a subset of fields is being extracted? So suppose that I have

> f1 integer
> f2 varchar(4)
> f3 varchar(20)
> f4 text

> and f4 contains reams of data. (well eg 4k). If I just want f1 and f2, will the performance of the SELECT statement be affected by the fact that f4 is large in physical size? If so, I would be better having two parallel tables one with fields f1,f2,f3 and one with f1,f4 as most of the time I don't want to read in the f4.

Most of the possible benefit applies automatically, because large values
of f4 will be "toasted" (moved out of line). I don't think it's worth
contorting your table structure for. You might care to run some
experiments to verify that theory, though. (But update first;
experiments against 7.0 don't necessarily prove anything about 7.3 ...)

> As a secondary question, presumably it is better to have a permanently compiled view in the database defined as

> CREATE VIEW myview as SELECT f1,f2,f3 from mytable

> rather than issuing the query each time direct to the underlying table?

There's essentially no difference in performance. Views are not
pre-optimized.

regards, tom lane