Prepared Statemet executeQuery() getting slower and slower

Question

Hi,
I have a servlet that do the following:
1.- Construct the where clause for a query with the data the user has sent.
2.- Get a connection from the pool.
3.- Load a temporary table with a select that uses the where clause created on the first step.
4.- Create a prepared statement as simple as "select * from temp_table where rownum < 500"
5.- While there is still data on the temporary table, loop
5.1.- Extract the information of the result set the Prepared Statemet executeQuery() returns.
5.2.- Delete the rows of the temporary table that had been read on the 5.1 step
5.3.- Check if there is more data
6.- Close the result set, statements, ...
The first runs of the loop are very fast, on the order of 500 ms. When the servlet has executed some times the loop, each run of the loop starts getting slower and slower, growing the time of the loop with each run.
Do anyone knows why the loop takes longer and longer with each run?
Regards,
CptnAgua

Answer 1

          ...     initialization of the servlet and reading the parameters
          // The connection object is created and get a connection
          // from the application servlet pool
        ConexionBaseDatos bbdd;
        bbdd = new ConexionBaseDatos();
        try {
            bbdd.conecta();
        } catch (Exception e) {
               ... exception code
        String sql;
        String where = " where 1=1";       
               the where clause is created depending on the parameters received by the sevlet
        String insert;
          // here all the variables are created and most of them initialized
        insert = "insert into temp_table select * from conciliation_v x " + where;
        Statement stmt = null;
        PreparedStatement prepStmt = null;
        ResultSet rs = null;       
        SimpleDateFormat formatoFecha = null;
        Date hoy = null;
        FileWriter fstream = null;
        BufferedWriter file = null;
        String rowid_update = "";
        String rowid_select = "";
        formatoFecha = new SimpleDateFormat("yyyyMMddHHmmss");
        hoy = new Date();
        nombreFichero = "";          
          // the floder where the servlet is going to store the output is read
          // from the server.xml
        nombreFichero =
                this.getInitParameter("DirectorioEscritura") + nombreFichero;
        File fichero = new File(nombreFichero);
          // if the file already exists, the servlet stops.
        if (fichero.exists()) {
            out.println("El fichero especificado ya existe.");
               ... exception code
            LogManager.shutdown();
            return;
        sql = "select * from temp_table where rownum < 500";
        fstream = new FileWriter(nombreFichero);
        file = new BufferedWriter(fstream);
        try {
               // here the temp table is filled with the update string already defined
            stmt = bbdd.getStmt();           
            stmt.executeUpdate(insert);           
               // and the query is preparsed
            prepStmt = bbdd.getPrepStmt(sql);
            prepStmt.setFetchSize(500);                       
        } catch (SQLException e) {
               ... exception code
        String linea;
        String field1 = "";
        String field2 = "";
        String field3 = "";
        String field4 = "";
        String field5 = "";
        String field6 = "";
        String field7 = "";
        String field8 = "";
        String field9 = "";
        String field10 = "";
        String field11 = "";
        String field12 = "";
        String field13 = "";       
        boolean hayValores = true;       
          // the loop starts          
        while (hayValores) {
            hayValores = false;           
            try {
                // The preparsed statement is executed
                rs = prepStmt.executeQuery();               
            } catch (SQLException e) {
                         ... exception code
            try {
                while (rs.next()) {
                    hayValores = true;
                    try {
                        field1 =
                                lPad(rs.getString("field1"), 10); //50
                        field2 =
                                lPad(rs.getString("field2"), 18); //18
                        field3 =
                                lPad(rs.getString("field3"), 10); //0
                        field4 =
                                lPad(rs.getString("field4"), 50); //50
                        field5 =
                                lPad(rs.getString("field5"),
                                     20); //10 + number
                        field6 =
                                lPad(rs.getString("field6"), 16); //number
                        field7 =
                                lPad(rs.getString("field7"),
                                     10); // 10
                        field8 =
                                lPad(rs.getString("field8"), 10); //10
                        field9 = lPad(rs.getString("field9"), 1); //1
                        field10 = lPad(rs.getString("field10"), 10); // 0
                        field11 = lPad(rs.getString("field11"), 10); // 0
                        field12 = lPad(rs.getString("field12"), 10); // 0
                        field13 = lPad(rs.getString("field13"), 10); // 0
                        rowid_update =
                                rowid_update + "rowid = '" + rs.getString("a_rowid") +
                                "' OR ";
                        rowid_select =
                                rowid_select + "'" + rs.getString("a_rowid") +
                    } catch (Exception exp) {
                                   ... exception code
                    linea =
                            field1 + field2 + field3 + field4 +
                            field5 + field6 +
                            field7 + field8 +
                            field9 + field10 + field11 + field12 + field13 +
                            "\r\n";
                    file.write(linea);                   
            } catch (Exception e) {
                         ... exception code
            file.flush();
            if (hayValores) {
                String delete;
                delete =
                        "delete from temp_table where a_rowid in (" +
                        rowid_select.substring(0, rowid_select.length() - 2) +
                rowid_select = "";
                try {                   
                    stmt.executeUpdate(delete);
                } catch (Exception exp) {
                              ... exception code
        file.close();
        try {
            rs.close();
        } catch (Exception e) {
                    ... exception code
        try {
            prepStmt.close();
        } catch (Exception e3) {
                    ... exception code
               Do the already extracted lines must be flagged as extracted?
        if (tipoExtraccion.toUpperCase().equals("AUTO") ||
            marca.toUpperCase().equals("S")) {
            if (!(rowid_update.equals(""))) {
                rowid_update =
                        rowid_update.substring(0, rowid_update.length() - 3);
                String update =
                    "UPDATE sys_conciliation.conciliation " + "SET FECHA_INTEGRADO = SYSDATE " +
                    "WHERE " + rowid_update;               
                try {
                    stmt.executeUpdate(update);
                    bbdd.commit();
                } catch (SQLException e) {
                              ... exception code
        try {
            bbdd.close();
        } catch (Exception e) {
                    ... exception code
        try {
            stmt.close();
        } catch (Exception e) {
                    ... exception code
        out.println("OK");
        out.close();
        LogManager.shutdown();
    public String rPad(String campo, int longitud) {
        if (campo == null) {
            campo = "";
        int lcampo = campo.length();
        if (lcampo > longitud)
            return (campo.substring(0, longitud));
        if (lcampo == longitud)
            return (campo);
        String nuevoCampo = campo;
        for (int a = 0; a < longitud - lcampo; a++) {
            nuevoCampo = nuevoCampo + " ";
        return (nuevoCampo);
    public String lPad(String campo, int longitud) {
        if (campo == null) {
            campo = "";
        int lcampo = campo.length();
        if (lcampo > longitud)
            return (campo.substring(0, longitud));
        if (lcampo == longitud)
            return (campo);
        String nuevoCampo = campo;
        for (int a = 0; a < longitud - lcampo; a++) {
            nuevoCampo = " " + nuevoCampo;
        return (nuevoCampo);
}Message was edited by:
CptnAgua