Question

I have a problem with processing all rows from database (PostgreSQL). I get an error: org.postgresql.util.PSQLException: Ran out of memory retrieving query results. I think that I need to read all rows in small pieces, but it doesn’t work – it reads only 100 rows (code below). How to do that?

    int i = 0;      
    Statement s = connection.createStatement();
    s.setMaxRows(100); // bacause of: org.postgresql.util.PSQLException: Ran out of memory retrieving query results.
    ResultSet rs = s.executeQuery("select * from " + tabName);      
    for (;;) {
        while (rs.next()) {
            i++;
            // do something...
        }
        if ((s.getMoreResults() == false) && (s.getUpdateCount() == -1)) {
            break;
        }           
    }

Answer 1

Use a CURSOR in PostgreSQL or let the JDBC-driver handle this for you.

LIMIT and OFFSET will get slow when handling large datasets.