QSqlQuery Memory issues. QSqlQuery::exec() and QSqlDatabase::open()/close();

[johnnyturbo3]

Hi,

I'm checking the memory usage of an application I've made. It makes numerous calls to read and write values to and from a database. I've observed the following:

* QSqlQuery::exec() uses some KB of RAM to execute a given query, but does not release the memory after it goes out of scope.

* QSqlDatabase:: open() & close() do not help free resources as the documentation suggest. If anything, close() causes resources (at least memory) to remain 'trapped' on the heap/stack.

For example, here is a typical segment of code I've been using to access my database.

QStringList values;
db.open();
QString strQuery = "SELECT DISTINCT " + field + " FROM " + table + str;
 
QSqlQuery query(db);
query.prepare(strQuery);
 
if(query.exec() == true)
{
  while(query.next())
  {
    values.push_back(query.value(0).toString());
  }
}
 
db.close();

QStringList values;
db.open();
QString strQuery = "SELECT DISTINCT " + field + " FROM " + table + str;

QSqlQuery query(db);
query.prepare(strQuery);

if(query.exec() == true)
{
  while(query.next())
  {
    values.push_back(query.value(0).toString());
  }
}

db.close();

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Having experimented with I find the code below 'traps' less memory:

QStringList values;
QString strQuery = "SELECT DISTINCT " + field + " FROM " + table + str;
 
QSqlQuery query(strQuery, db);
 
  while(query.next())
  {
    values.push_back(query.value(0).toString());
  }

QStringList values;
QString strQuery = "SELECT DISTINCT " + field + " FROM " + table + str;

QSqlQuery query(strQuery, db);

  while(query.next())
  {
    values.push_back(query.value(0).toString());
  }

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However, a small amount of memory is still not released. Has anyone else experienced anything like this? Comments?

[johnnyturbo3]

It seems that in order to release this memory you must create the QSqlQuery variable as a pointer, and delete this pointer before you close the database:

QStringList values;
db.open();
QString strQuery = "SELECT DISTINCT " + field + " FROM " + table + str;
 
QSqlQuery *query = new QSqlQuery(db);
query->prepare(strQuery);
 
if(query->exec() == true)
{
  while(query->next())
  {
    values.push_back(query->value(0).toString());
  }
}
 
delete query;
db.close();

QStringList values;
db.open();
QString strQuery = "SELECT DISTINCT " + field + " FROM " + table + str;

QSqlQuery *query = new QSqlQuery(db);
query->prepare(strQuery);

if(query->exec() == true)
{
  while(query->next())
  {
    values.push_back(query->value(0).toString());
  }
}

delete query;
db.close();

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The memory is then released after the database closes.