QSqlQuery::next() is too slow.

1. Using QSqlQuery to access Orcale database from a remote DB Server, the code slice like following:
QSqlQuery query("SELECT * FROM artist");
while (query.next())
{
doSomething();
}

2. The problem is:
query.next() function was running too slow.
In my case, I used next() function to get about 7000 records, it spent about 7 seconds, and I'm sure it is not a problem of network.
Does it a bug of qt? or can anyone give me a suggestion?