[Info-vax] Oracle on VMS

[Arne Vajhøj]

On 11/20/2016 1:01 AM, IanD wrote:
> Yes, modern DB's do cache execution plans, RDB I believe was the
> first to come up with the idea of a query optimizer and unlike MySQL
> (or how it used to be) with RDB you can access the query optimiser
> for free and it's cincluded in the price and even make changes to it
> to force your own behavior if you believe the DB got it wrong on it's
> strategy (usually happens when it gets the number of tuples wrong on
> complex joins etc)

Query optimizer is generally included in the price today (also for
MySQL @ $0).

But I am not aware of any database where you can change the plan.

> I wonder with the push for dynamic languages how much optimisation is
> worth it at compile time versus having a smarter optimiser at run
> time? I guess some information could be supplied to the DB in advance
> because RDB creates a strategy at run time and formulates it's
> strategy then - being forewarned wth inside knowledge from an EXE
> might help?

With the nature of SQL then I would expect the database to be
better than the application to optimize.

Fundamentally the SQL just defines the data needed. If we
assume that the SQL does not request data that is not actually
needed, then there should be little that the application
can tell the database.

Arne