TMySQL50Connection memory leak
lazarus / 16-Databases

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DimProfi · 2012-06-08 00:26

Code: [Select]procedure TForm1.Button2Click(Sender: TObject);
var
    conn:TMySQL50Connection;
    query:TSQLQuery;
    trans:TSQLTransaction;
     c:integer;
begin
  for c:=0 to 100000 do
  begin
         conn:=TMySQL50Connection.Create(nil);
         conn.HostName:='localhost';
         conn.DatabaseName:='?database?';
         conn.UserName:='root';
         conn.Password:='';

         trans:=TSQLTransaction.Create(nil);
         trans.DataBase:=conn;

         query:=TSQLQuery.Create(nil);
         query.DataBase:=conn;
         query.Transaction:=trans;
         conn.Open;

         query.SQL.clear;
         query.SQL.Add('select * from ?table? LIMIT 1000');
         query.ExecSQL;

         FreeAndNil(query);
         FreeAndNil(trans);

          conn.Close;
          FreeAndNil(conn);
     end;
   showmessage('ok!');
end;


1. Replace "?database?" and "?table?" with your some of your mysql
database (I used XAMPP for Windows on localhost for this test to speed
up)

2. Start Task-Manager, look at Memory-Usage for 5-10 Minutes. It grows
and grows about 1 MB in 3 Minutes and it doesnt stops after 30
minutes.

Thats not good for my software which runs 2-3 month and frequently
connecting to the database.

But the main question is: is it a bug? how can i eliminate it?

I tested with Lazarus 0.9.30.4 x86_64-win64  on windows 7 64bit.

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Lacak2 · 2012-06-08 05:19

Do changes something, when you use instead of:

         query.ExecSQL;

         query.Open;

?

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DimProfi · 2012-06-08 05:31

Quote from: Lacak2 on June 08, 2012, 07:19:17 amDo changes something,
when you use instead of:

         query.ExecSQL;

         query.Open;

?

Ok, I made it. As expected, no changes. RAM usage grows about 1 MB in
30 second.

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ludob · 2012-06-08 05:33

Checked your code with heaptrc, the cmem memory manager and a memory
monitor tool: there is no leak in the pascal code. However the memory
increase (confirmed with cmem) is apparently coming from libmysql
(5.0.22 on my system). See http://bugs.mysql.com/bug.php?id=45002 or
http://bugs.mysql.com/bug.php?id=47841 for pascal.

Edit: found that the leak is memory allocated in libmysql but not
linked to above bug reports. When calling ExecSQL with a command that
returns a result set, the result set is not cleared with
Mysql_free_result. The suggestion made by Lacak2 (query.open, instead
of query.execsql)  is working for me: closing the dataset calls
Mysql_free_result, no more memory increase. FPC 2.7.1
So this is wrong usage of datasets and yes, it is also a bug in
TMySQLxxConnection. I'll report the bug and try to create a patch for
it.

Edit: http://bugs.freepascal.org/view.php?id=22228

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DimProfi · 2012-06-08 12:02

Thanks a lot!

So i will try to minimize a leak