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Qt-interest Archive, March 2002
memory leak

Message 1 in thread

Subject: memory leak
From: Abdul-Rahman Masoud <abud@xxxxxx>
Date: Wed, 13 Mar 2002 11:33:03 +0100
Reply-to: masoud@xxxxxx
To: qt-interest@xxxxxxxxxxxxx

Hi everybody,

I detected a memory leak in SQL.
I am using: SuSe 7.2  Qt3.0.0, and for connecting to the PostgreSql Database 
I use unixODBC.

Now the Problem:
I use QSqlQuery to get data from the database like this:

1 QString QueryResult;
2 QSqlQuery Target( "SELECT blabla... FROM blabla WHERE blabla..." );
3 if ( Target.isActive() ) {
4    while ( Target.next() ) {
5       // I know that the table has three columns 
6        for( int i = 0; i < 3; i++ ) {
7           QueryResult = QueryResult + Target.value( i ).toString();
8        }
9}

The table is very big. Now I traced the memory with top and I saw that the 
"memory used" grows and grows. and when I stop the request the memory will 
not be released. I also changed line 7 to: 
QueryResult = QueryResult + "hello world";
I traced it the same way. The "memory used" grown also but after stopping the 
request the memory has been released.
Is this a bug in Target.value(i) or am I doing something wrong?
If so please let me know.

Best regards,
Abud

Message 2 in thread

Subject: Re: memory leak
From: Henrik Johnson <hpj@xxxxxxxxxxx>
Date: Wed, 13 Mar 2002 12:03:23 +0100
To: "Qt Interest (E-mail)" <qt-interest@xxxxxxxxxxxxx>

You allocate more and more memory yourself as the program runs. The 
variable QueryResult seems to contain all the values you read. This be 
really slow also as QuereResult grows.

/Mauritz
GlobeCom AB

Abdul-Rahman Masoud wrote:

>Hi everybody,
>
>I detected a memory leak in SQL.
>I am using: SuSe 7.2  Qt3.0.0, and for connecting to the PostgreSql Database 
>I use unixODBC.
>
>Now the Problem:
>I use QSqlQuery to get data from the database like this:
>
>1 QString QueryResult;
>2 QSqlQuery Target( "SELECT blabla... FROM blabla WHERE blabla..." );
>3 if ( Target.isActive() ) {
>4    while ( Target.next() ) {
>5       // I know that the table has three columns 
>6        for( int i = 0; i < 3; i++ ) {
>7           QueryResult = QueryResult + Target.value( i ).toString();
>8        }
>9}
>
>The table is very big. Now I traced the memory with top and I saw that the 
>"memory used" grows and grows. and when I stop the request the memory will 
>not be released. I also changed line 7 to: 
>QueryResult = QueryResult + "hello world";
>I traced it the same way. The "memory used" grown also but after stopping the 
>request the memory has been released.
>Is this a bug in Target.value(i) or am I doing something wrong?
>If so please let me know.
>
>Best regards,
>Abud
>
>--
>List archive and information: http://qt-interest.trolltech.com
>

Message 3 in thread

Subject: Re: memory leak
From: Abdul-Rahman Masoud <abud@xxxxxx>
Date: Wed, 13 Mar 2002 13:42:42 +0100
Reply-to: masoud@xxxxxx
To: hpj@xxxxxxxxxxx, "Qt Interest (E-mail)" <qt-interest@xxxxxxxxxxxxx>

I will get specific:

Everytime I get a request to get something from the database a signal will be 
emitted, which is connected to this slot
void classname::slot_bla(.......) {
   QString QueryResult;
   QSqlQuery Target( "SELECT blabla... FROM blabla WHERE blabla..." );
   if ( Target.isActive() ) {
    while ( Target.next() ) {
     // I know that the table has three columns 
      for( int i = 0; i < 3; i++ ) {
         QueryResult = QueryResult + Target.value( i ).toString();
      }
    }
  ..........
  }
  .......
}
this means after leaving the slot all the variables are destroyed because  
they are localvariables.
But that does not happen here!
As I mentioned, I have only changed "Target.value(i).toStning" into a const 
QString "hello world" and there was no leak any more.

Qt-interest Archive, March 2002memory leak

Qt-interest Archive, March 2002
memory leak