MySQL Database replication

We can implement this in codeigniter using database groups.
Below is a sample execution.

Create two active groups – one for read and one for write.

File: system/application/config/database.php

$active_group = "write";
$active_record = TRUE;

$db['read']['hostname'] = "localhost";
$db['read']['username'] = "root";
$db['read']['password'] = "";
$db['read']['database'] = "read_database_name";
$db['read']['dbdriver'] = "mysql";
$db['read']['dbprefix'] = "";
$db['read']['pconnect'] = TRUE;
$db['read']['db_debug'] = FALSE;
$db['read']['cache_on'] = FALSE;
$db['read']['cachedir'] = "";
$db['read']['char_set'] = "utf8";
$db['read']['dbcollat'] = "utf8_general_ci";

$db['write']['hostname'] = "localhost";
$db['write']['username'] = "root";
$db['write']['password'] = "";
$db['write']['database'] = "write_database_name";
$db['write']['dbdriver'] = "mysql";
$db['write']['dbprefix'] = "";
$db['write']['pconnect'] = TRUE;
$db['write']['db_debug'] = FALSE;
$db['write']['cache_on'] = FALSE;
$db['write']['cachedir'] = "";
$db['write']['char_set'] = "utf8";
$db['write']['dbcollat'] = "utf8_general_ci";

Create separate database connections to access read and write databases separately where needed (constructor is generally a good place for this).

$read_db = $this->load->database('read', TRUE);
$write_db = $this->load->database('write', TRUE);

You can now go about running queries in the usual way.

/* For reads */
$query = $read_db->get('table_name');

foreach ($query->result() as $row)
{
    echo $row->title;
}

/* For writes */
$data = array(
               'title' => $title,
               'name' => $name,
               'date' => $date
            );

$write_db->insert('mytable', $data);

In case you want to try this on an application you are already running, you can leave the “default” connection group intact and create only the “read” connection group. Use it where you think you are running read heavy queries.

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We have changed the release model so that instead of focusing on quality and features our release is now defined by timeliness and features. Quality is not regarded to be that important.

and

Zero critical bugs is impossible: Sure, zero bugs is desirable. And at times, we internally glorify MySQL’s past, with “production level alpha releases”. Those were the days, but those days also had less complex and less interwoven features, and fewer developers to manage.

I wonder where MySQL is headed.

So as Monty says, you are better off not upgrading to version 5.1 if you do not plan to use its new features, atleast not without testing it for a few weeks.

Links:
Oops, we did it again (MySQL 5.1 released as GA with crashing bugs)
Why You Want to Switch to MySQL 5.1
MySQL 5.1 Stability

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A simple way out of this is to run the missing DDLs on the slave and push the counter by a step. This is not recommended as this might cause data inconsistency.

Use the below sql to skip the counter by 1.

SET GLOBAL SQL_SLAVE_SKIP_COUNTER = 1; START SLAVE;

Just remember to use the value 1 for any SQL statement that does not use AUTO_INCREMENT or LAST_INSERT_ID(), otherwise you will need to use the value 2. Statements that use AUTO_INCREMENT or LAST_INSERT_ID() take up 2 events in the binary log.

To skip lots of duplicate errors, you can set this in my.cnf

slave-skip-errors = 1062

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