Grid: set column value very SLOW

Hi!

I have a program with a grid. In this grid I can set all the values of a column with a single action.

I do like this:

Code:

var g = Ext.getCmp('id_myGrid');
var s = g.getStore();
var tot = s.getCount();
tot--;
var records = s.getRange(0,tot);


Ext.each(records, function(record) {
    record.set("col_01",val);
});

It works, but is VERY SLOW!!! (in a grid with 40 rows, the execution time is more than 60 seconds!)

So I think I'm doing something wrong...

Can you help me, please?

Thanks in advance.