Re: Memory exeception - Mailing list pgsql-jdbc

Hi Barry

Looks good! I thought cursors are only available in embedded SQL. So this approach
seems to work for me.
Thanks for your help.

Peter

Barry Lind wrote:

> Peter,
>
> You certainly can do this with java.  I do in my code in many places.
> Consider the following example that processes all rows in the table
> 'bar' by fetching 10 rows at a time.
>
> thanks,
> --Barry
>
> PreparedStatement l_cursorstmt = connection.PrepareStatement("declare
> foo_cursor cursor for select foo from bar");
> PreparedStatement l_fetchstmt = connection.PrepareStatement("fetch
> forward 10 from foo_cursor");
>
> //open the cursor
> l_cursorstmt.execute();
>
> ResultSet l_rset;
> int l_count;
> do {
>    //continue looping until you get no rows returned in a fetch
>    l_count = 0;
>    //fetch rows from the cursor using the fetch statement
>    l_rset = l_fetchstmt.executeQuery();
>    while (l_rset.next) {
>      l_count++;
>      //process the rows here
>    }
> } while (l_count > 0);
>
> //don't forget to close the cursor
> PreparedStatement l_closestmt = connection.PrepareStatement("close
> foo_cursor");
> l_closestmt.execute();
>
> Peter Wasem wrote:
>
> > Hi Barry
> >
> > This is exactly what I observed. The physical memory dropped down to almost
> > zero (but no swap was used) before the exception was thrown. I'm not sure if I
> > can use cursors (other than ResultSet) since my application is Java-based.
> >
> > Thanks
> >
> > Barry Lind wrote:
> >
> >
> >>Peter,
> >>
> >>Postgres will return the entire result into memory first before
> >>processing the first row of data.  If you don't want this behavior you
> >>should use explicit cursors and fetch statements to get data a few rows
> >>at a time.  See the postgres documentation on the 'cursor' and 'fetch'
> >>sql statements.
> >>
> >>thanks,
> >>--Barry
> >>
> >>Peter Wasem wrote:
> >>
> >>
> >>>Hi
> >>>
> >>>I have a problem in processing large numbers of rows in ResultSets.
> >>>Here's the code fragment where the problem occurs:
> >>>
> >>>...
> >>>    ResultSet rset = stmt.executeQuery( "select ... from ... where ...
> >>>order by ..." ) ;
> >>>    while(rset.next() )
> >>>    { // Process the row }
> >>>...
> >>>
> >>>The query addresses some 100'000 rows. When stmt.executeQuery() is
> >>>executed suddenly an exception occurs.
> >>>The same program works fine with other JDBC drivers.
> >>>
> >>>Any ideas ?
> >>>
> >>>Greetings
> >>>Peter
> >>>
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