Christopher Cobb wrote:
>
> This is the fatal flaw in a two-phased commit. As far as I know, a two-phased
>commit can never solve this problem (even though this is the problem it is apparently
>designed to solve).
>
> It can come 'close' in a logical sense if everything but the very last possible
>atomic write is performed during phase 1.
>
> However, it can never fully deal with transmission or media failures in the later
>parts of the phase 2 commits. The whole point is that you cannot undo a commit.
>
> If anyone else knows different, please speak up.
2-phase commit is not designed to cope with media failures - it is designed to
cope with crashes. Media failures are definitely not 100% fixable. If your
entire system is nuked no amount of software will get the data back.
If by transmission failures you mean communication failures between two parts of
a distributed transaction then 2-pc does solve them - when communication is
eventually resored the transactions will be committed or backed out correctly.
Ian McCallion
Alexis Systemsa Limited
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