ways to improve the performance of this scenario

Question

I have a map with huge amount of data being populated (around 300,000 records in approx)

and iterating it as below ,

    for (Map.Entry&         


        

Answer 1

The for loop is taking time due to two reasons.
1) Individual Email improve it by less Transport connection
2) Individual commits improve it by

So Ideal is to handle both, I would recommend do it for batch of 1000, then play with numbers

Example

int BATCH_SIZE = 1000
conn = DriverManager.getConnection("username","password");
conn.setAutoCommit(false);
Statement stmt = conn.createStatement(
        ResultSet.TYPE_SCROLL_INSENSITIVE,
        ResultSet.CONCUR_UPDATABLE);
int count = 0;

Map emails_map = new HashMap(BATCH_SIZE);
for (Map.Entry> entry : testMap
        .entrySet()) {
    String email = get_useremail();
    String const_val = do_magic(); // this is how you are computing some constant
    String body = construct_body();

    count++;
    String SQL = "YOUR UPDATE STATEMENT";
    stmt.executeUpdate(SQL);  
    emails_map.put(email, body); // can create 
    if (count % BATCH_SIZE == 0) {
        //commits all transcations
        conn.commit();
        //bulk send emails sending 
        //http://stackoverflow.com/questions/13287515/how-to-send-bulk-mails-using-javax-mail-api-efficiently-can-we-use-reuse-auth

        bulk_emails_send(emails_map)
    }

}


public void bulk_emails_send(Map emails_map) {
    // Get the default Session object through your setting
    Session session = Session.getDefaultInstance(properties);
    Transport t = session.getTransport();
    t.connect();
    try {
        for (String email_id in emails_map) {
            Message m = new MimeMessage(session);
            //add to, from , subject, body
            m.saveChanges();
            t.sendMessage(m, m.getAllRecipients());
        }
    } finally {
        t.close();
    }
}