Update:Remora Database Replication

• Method
  • Cake determines which db to use by the $useDbConfig var in the Model, so in order to implement rw/ro we need to change that var to the correct database. We default to the read-only Shadow db, and change to the default db only when performing a write operation, ideally, though some models may need to read from the rw db because they can't tolerate any replication lag.
  • We set a variable to store the name of the ro config, and the rw config as well, var $DbReadConfig and $DbWriteConfig.
  • This is pretty simple for the Save and Del methods.

function save($data = null, $validate = true, $fieldList = array()) {
    $this->useDbConfig=$this->useDbWriteConfig;
    $ret = parent::save($data, $validate, $fieldList);
    $this->useDbConfig=$this->useDbReadConfig;
    return $ret;
}

• • For query, use preg_match to detect a write query type(insert, update, replace) and do the right thing.

• Tests
  • Tests need to account for replication lag...
    • How long to delay? Some way to detect it?
  • We need to test everything that writes to the db, some things already have tests for this that need to be modified to deal with replication lag.
  • Writes to the /test db/ won't replicate to the real db, obviously, so we probably need to have a replicated real db and a replicated test db.
    • For this to work, we need to make the site read from the test db when called by the web tests, user agent detection?