Re: memory management

From:

Ingo Menger <quetzalcotl@consultant.com>

Newsgroups:

comp.lang.java.programmer

Date:

Wed, 31 Oct 2007 03:55:56 -0700

Message-ID:

<1193828156.379069.280790@y42g2000hsy.googlegroups.com>

On 31 Okt., 11:32, Thomas Kellerer <YQDHXVLMU...@spammotel.com> wrote:

josh, 31.10.2007 11:14:

On 31 Ott, 10:56, Thomas Kellerer <YQDHXVLMU...@spammotel.com> wrote:

josh, 31.10.2007 10:22:

Hi, I have the following problem:
in a while loop I get from a db some records and in the same time
I put them with an insert preparedStatement in
a destination db but the jave process increase the memory until it
goes in out of memory.
How can I optimize that? also If I increase Tomcat java memory when I
process more than 500 records
tha java memory is already at 700mb of usage!

My guess is that you are buffering the retrieved rows somehow (or
keeping references to them). You will need to show us your code.

Thomas

ok I post the code:

st_from = conn.createStatement();

rs_from = st_from.executeQuery(query_from);

ps_into = conn_t.prepareStatement(insert_into);

int i_out_record = 0;
int i_in_record = 0;

while(rs_from.next())
{

i_out_record++;

                   out_record += "SELECT su record (" + i_out_record + ")";
                   in_record += "INSERT su record (";

                   row_error = rs_from.getString(campi_from[0]); // se errore su quale
id

                   for(int i=0; i < campi_from.length; i++)
                   {
                           out_record += campi_from[i] + "=" +
rs_from.getString(campi_from[i]) + "::" ;

                           ps_into.setString(i+1, rs_from.getString(campi_from[i])); //
prepara l'insert

                           in_values += campi_to[i] + "=" + rs_from.getString(campi_from[i])
+ "::" ;
                   }
                   out_record = out_record.substring(0, out_record.length()-2); //
tolgo il cancelletto finale

                   int res = ps_into.executeUpdate();

                   if(res != 0)
                   {
                           i_in_record++;
                           in_record += i_in_record + ")" + in_values;

                           // chiudi la statement
                           //ps_into.close();
                   }

                   out_record += "\n";
                   in_record += "\n";

                   /*
                   if(i_out_record > 10)
                           break;
                           */
           }

           String log = "Per la tabella origine " + tabellaFrom + " processati
in uscita record: " + i_out_record + "\n";
           log += "Per la tabella destinazione " + tabellaTo + " processati in
entrata record: " + i_in_record + "\n";
           log += "-----------------------------------------------------------
\n";
           log += out_record + in_record;

           //out.print(st);
           out.print(log);

After a quick look, I'd say the following lines are your problem:

>out_record += "SELECT su record (" + i_out_record + ")";
>in_record += "INSERT su record (";
>in_record += i_in_record + ")" + in_values;

As far as I can tell, this will create huge strings with the complete
result set, as they are declared outside the loop (actually twice the
result set because one for the out_Record and one for the in_record).

Actually 4-fold, since at the end he does:

               log += out_record + in_record;
                //out.print(st);
                out.print(log);

Just changing this will save 50% memory:

                out.print(out_record);
                out.print(in_record);

But, of course, the out_record and in_record logging is totally bad.
First, avoid + on strings. Use a StringBuilder instead.
If this doesn't solve the problem, write the out_record and in_record
directly to a file. For example, through a PrintWriter.