[Dbix-class] Prefetch question

Bill Moseley moseley at hank.org
Wed Dec 16 17:52:16 GMT 2009

On Wed, Dec 16, 2009 at 8:43 AM, Bernhard Graf <dbic4 at augensalat.de> wrote:

> Prefetching is a convenient thing, but may also need a lot of resources.
> E.g. I have a users table, that belongs_to("country"). Table 'country'
> has more information (e.g. full name, int. phone code, time zones, etc).
> The users table may have zillions of rows, whereas the the country table
> is quite small (and nearly all users belong to a handful of countries).
> With prefetching I get the same country data over and over again.
> Without prefetching DBIC delays country fetches until I access
> $user->country, but then also fetches the same country data all the time.
> Is it possible not to prefetch country, but tell DBIC to cache delayed
> fetches of related data, so that each related country row is really only
> fetched once for this user resultset?

Isn't this what Class::DBI attempted to do with it's object index?  That is,
if it needed to fetch $user->county but that $country had already been
fetched then it used the in-memory copy.  I always disabled that feature as
it seems to cause more breakage than not.

I assume you are fetching a page of users to display?   Say 20 rows? I'd be
interested to see a benchmark between doing it in one query (with prefetch)
and then one query and then twenty additional queries to fetch each country.

-- =

Bill Moseley
moseley at hank.org
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