MySQL's Two-Phase Commit Implementation Is Broken

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If an XA transaction has reached the PREPARED state and the MySQL server is +killed (for example, with kill -9 on Unix) or shuts down abnormally, the +transaction can be continued after the server restarts. However, if the +client reconnects and commits the transaction, the transaction will be +absent from the binary log even though it has been committed. This means the +data and the binary log have gone out of synchrony. An implication is that +XA cannot be used safely together with replication.
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(Emphasis mine.)

If you're solving the kinds of problems where two-phase commit and XA +transaction management look attractive, then you very likely have the kinds of +uptime requirements that make replication mandatory. “It works, but not with +replication” is effectively “it doesn't work.”

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It is possible that the server will roll back a pending XA transaction, even +one that has reached the PREPARED state. This happens if a client connection +terminates and the server continues to run, or if clients are connected and +the server shuts down gracefully.
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XA transaction managers assume that if every resource successfully reaches the +PREPARED state, then every resource will be able to commit the transaction +“eventually.” Resources that unilaterally roll back PREPARED transactions +violate this assumption pretty badly.

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