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From:Marcus Bointon Date:October 27 2011 9:55am
Subject:Re: Master-Master -> duplicate entry
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On 27 Oct 2011, at 09:51, Johan De Meersman wrote:

> Say what? If that's the case, you haven't set up your replication correctly. There
> are quite a few reasons to not use both masters concurrently, but this is not one of
> them.

Not at all. The point of redundancy (via replication or DRBD) is to maintain consistent
and available data in the face of a server or replication failure. If you only write to
one master at a time you have that. If you write to both you have neither - i.e. it's
actually worse than having no redundancy at all, hence my statement. Because there is no
performance gain and there is an increased risk of data loss it's not just pointless,
it's actively bad. It's a bit like using RAID-0, but without the speedup! With writes to
both there's no way of avoiding the split-brain scenario you describe and it's really
hard to recover from (I've been there!). No advantages plus lots of disadvantages sounds
like a bad combo to me.

There are some attempts to introduce a semi-synchronous replication system for MySQL that
waits until transactions are replicated (possibly to a quorum of slaves, much like
Cassandra) before committing (or at least before returning a result to the client).

Marcus
-- 
Marcus Bointon
Synchromedia Limited: Creators of http://www.smartmessages.net/
UK info@hand CRM solutions
marcus@stripped | http://www.synchromedia.co.uk/



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