[GRASS5] v.in.ascii

[Radim Blazek]

On 8/16/05, Helena Mitasova <hmitaso at unity.ncsu.edu> wrote:
> Radim Blazek wrote:
> > Please read my previous mails about that, IT IS implemented,
> > and IT DOES NOT call free() by default because it is faster
> > and IT CAN free the memory if it is necessary. I wrote that 2-3
> > times already.
> 
> I meant at the module level, as a user how can I tell v.in.ascii or
> v.build or any other module that builds topology to free the memory
> when needed? From your emails it seemed to me
> that this option needs to be added to the relevant modules, but I might
> have misunderstood it,
> 
> Helena

Spatial index occupies a lot of memory but it is necessary for 
topology building. Also, it takes long time to release the memory
occupied by spatial index (dig_spidx_free) . 

The function building topology (Vect_build) is usually called 
at the end of module (before Vect_close) so it is faster to call
exit() and operating system releases all the memory much faster.
By default the memory is not released.

It is possible to call Vect_set_release_support() before Vect_close()
to force  to release the memory, but it takes long time on large files.

Currently most of the modules do not release spatial index and work 
like this:
main
{
     Vect_open_new()
     //writing new vector

     Vect_build()
     Vect_close()  // memory is not released
}

you can add Vect_set_release_support():

main
{
     Vect_open_new()
     // writing new vector

     Vect_build()
     Vect_set_release_support()
     Vect_close()  // memory is released
}

but it only takes longer time. 

It make sense to release spatial index if it is used only at the beginning
of a module or in permanently running programs like QGIS.
For example:

main
{
     Vect_open_old()
     // select features using spatial index, e.g.  Vect_select_lines_by_box()
     Vect_set_release_support()
     Vect_close()  // memory is released

     // do some processing which needs memory
}


Radim