title: Two phase commit in MongoDB
body: <p>Having carefully reading <a href="http://docs.mongodb.org/manual/tutorial/perform-two-phase-commits/" rel="noreferrer">the online documentation</a>, I still have a lot of questions about two phase commit in MongoDB.</p>
  
  <p>In the section <strong>Recovering from Failure Scenarios</strong>, why are there only two classes of failures? In my thinking failure can happen in any of these step so there should be a lot more than two classes here. For example what if, (in <strong>Apply Transaction to Both Accounts</strong> section), after updating account A the database server failed. That means account A lost some money without anything happen on account B. And we would have inconsistent transaction?</p>