[Gambas-user] Size of a result in memory

[Tobias Boege]

On Wed, 18 Oct 2017, Christof Thalhofer wrote:
> Hello,
> 
> is there a simple way to get the size of a db result in memory?
> 
> If I use:
> 
>  Object.SizeOf(resultobj)
> 
> I get a very small count of bytes, way too small for the real size of
> all the tuples contained by the resultobject.
> 
> 

Object.SizeOf() gives more of a static size of an object. Have a look at
the implementation:

  767 BEGIN_METHOD(Object_SizeOf, GB_OBJECT object)
  768 
  769         void *object = VARG(object);
  770 
  771         if (check_null(object))
  772                 return;
  773 
  774         GB_ReturnInteger(CLASS_sizeof(OBJECT_class(object)));
  775 
  776 END_METHOD

It returns the size of the *class* of the object. Native classes in Gambas
manage their memory more or less by themselves, especially if they interact
with external libraries, and they don't keep track of the dynamic memory
they use.

So, you can't get the information you want, but the good news is that this
information wouldn't have helped you either way. Unless your DBMS is made
for tiny amounts of data, you shouldn't expect the dynamic memory allocated
by the Result object to be indicative of the size of the query result.
A Result object is usually just a small (almost fixed-size) object that is
associated to a database connection and a query and allows you to fetch or
navigate through the tuples. The DBMS loads the data on-demand, because
you would expect that the entirety of a database result would not fit into
your memory anyway.

You should talk to the DBMS. If that doesn't know how big the result is,
then really nobody does. But I suppose that this calculation is expensive.

Regards,
Tobi

-- 
"There's an old saying: Don't change anything... ever!" -- Mr. Monk