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Paxos is more powerful and in the famous writing "Consensus on Transaction Commit" : http://research.microsoft.com/pubs/64636/tr-2003-96.pdf, Jim Gray and Leslie Lamport describe 2PC as a special case of Paxos.

Why do relational database use 2PC in real world? Also 2PC is not fault tolerant because it uses a single coordinator whose failure can cause the protocol to block.

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    $\begingroup$ Google's Spanner is a relational database and it uses Paxos. $\endgroup$
    – jkff
    Commented Dec 4, 2014 at 20:16
  • $\begingroup$ Probably because its implementation isn't trivial on strong transactional systems. Even tho, this is changing lately, ie: citusdata.com/blog/2016/04/13/masterless-distributed-queue $\endgroup$
    – 3manuek
    Commented Sep 4, 2017 at 16:50

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One of the reasons is the message complexity. For N nodes, 2PC will require 3N to be exchanged whereas Paxos requires 4N. Also, Paxos adds sequence numbers to each message which adds a significant overhead to the overall execution.

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  • $\begingroup$ Thanks for the answer. A follow up question, Wikipedia mentions : "he greatest disadvantage of the two-phase commit protocol is that it is a blocking protocol. If the coordinator fails permanently, some cohorts will never resolve their transactions: After a cohort has sent an agreement message to the coordinator, it will block until a commit or rollback is received." How do real world production services resolve these problems? $\endgroup$
    – Nitish Upreti
    Commented Dec 4, 2014 at 20:52

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