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Atomic Commits

How to do atomic commits? Two-phase commit.

Two-phase commit

Two-phase commit has a single coordinator and multiple participants.

First phase:

  • The coordinator sends a prepare request to each of the nodes, asking them whether they are able to commit.
  • If all participants reply yes, the coordinator sends a commit request in phase 2 (writing this on disk), and the commit takes place.
    • If the commit request fails or times out, the coordinator must retry forever until it succeeds.
  • If any of the participants replies no, then the coordinator sends an abort request.

Problems with 2PC: If the coordinator fails after it has sent out prepare requests to everyone, the participants are kind of stuck — they can’t abort anymore, because they must wait to hear back from the coordinator whether the transaction was committed or aborted.

Created from: Raft & Paxos 202211231100

uid: 202211232128 tags: #distributed-systems #software-engineering

Date
February 22, 2023
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