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From:Johan De Meersman Date:October 28 2011 7:03am
Subject:Re: Master-Master -> duplicate entry
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----- Original Message -----
> From: "Rick James" <rjames@stripped>
> 
> The potential flaw in semi-sync is that it acks once the data gets to
> the relay log; it does not wait for the write to be applied to the
> table.  Granted, it would take two serious crashes to cause loss of a
> write.

Correct, thank you :-)

It amazes me how many people run replication, but how little is actually understood about
it :-)

MySQL's semi-synchronous feature is not that a quorum of slaves confirms the update (as
Cassandra does, like Marcus points out); it is semi-synchronous because the slave must
acknowledge that it has _received_ the update (ie, written to the relay log), whereas a
fully synchronous replication requires that the slave acknowledges that it has _applied_
the update.

When the master writes statements to the binary log, most non-deterministic expressions
(autoincrement, now(), ...) get replaced by the actual values that were applied; thus
ensuring that the slave does indeed apply exactly the same data. Not *all* of those get
translated, though - a typical example being "insert as select" where the select has no
explicit ordering - and those cases, if you have them, can be accomodated by using
row-based replication instead of statement-based. Look at the documentation before making
a decision :-)




-- 
Bier met grenadyn
Is als mosterd by den wyn
Sy die't drinkt, is eene kwezel
Hy die't drinkt, is ras een ezel
Thread
Master-Master -> duplicate entryRicardo Freitas26 Oct
  • Re: Master-Master -> duplicate entrynavid@navid.it26 Oct
    • Re: Master-Master -> duplicate entryRicardo26 Oct
  • Re: Master-Master -> duplicate entryRick James27 Oct
    • Re: Master-Master -> duplicate entryRicardo27 Oct
      • Re: Master-Master -> duplicate entryMarcus Bointon27 Oct
        • Re: Master-Master -> duplicate entryJohan De Meersman27 Oct
          • Re: Master-Master -> duplicate entryRicardo27 Oct
          • Re: Master-Master -> duplicate entryRicardo27 Oct
          • Re: Master-Master -> duplicate entryMarcus Bointon27 Oct
            • RE: Master-Master -> duplicate entryRicardo Freitas27 Oct
              • Re: Master-Master -> duplicate entrynavid@navid.it27 Oct
              • Re: Master-Master -> duplicate entryMarcus Bointon27 Oct
                • RE: Master-Master -> duplicate entryRicardo Freitas27 Oct
                  • Re: Master-Master -> duplicate entryMarcus Bointon27 Oct
                    • RE: Master-Master -> duplicate entryRicardo Freitas27 Oct
                    • Re: Master-Master -> duplicate entryRicardo27 Oct
                      • Re: Master-Master -> duplicate entryMarcus Bointon27 Oct
                        • RE: Master-Master -> duplicate entryRicardo Freitas27 Oct
                          • Re: Master-Master -> duplicate entryMarcus Bointon27 Oct
                            • Re: Master-Master -> duplicate entry (UUID lecture)Rick James27 Oct
            • Re: Master-Master -> duplicate entryJohan De Meersman28 Oct
        • Re: Master-Master -> duplicate entryRicardo27 Oct
  • Re: Master-Master -> duplicate entrylist27 Oct
    • RE: Master-Master -> duplicate entryRicardo Freitas27 Oct
      • Re: Master-Master -> duplicate entryMarcus Bointon27 Oct
        • Re: Master-Master -> duplicate entryMySQL)27 Oct
    • Re: Master-Master -> duplicate entryRick James27 Oct
      • Re: Master-Master -> duplicate entryMarcus Bointon27 Oct
        • Re: Master-Master -> duplicate entryRick James27 Oct
          • Re: Master-Master -> duplicate entryJohan De Meersman28 Oct
            • Re: Master-Master -> duplicate entryRick James28 Oct
              • Re: Master-Master -> duplicate entryMats Kindahl31 Oct
      • Re: Master-Master -> duplicate entrylist27 Oct