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Article:
  Advanced MySQL Replication Techniques
Subject:   Consistency problem?
Date:   2007-03-14 08:43:53
From:   UloPe
Hi,


thank you for you interesting article.


I have a quation though.


Lets assume we have 4 servers (A,B,C,D) setup to replicate as follows: A->B->C->-D->A


As I understand your setup the following will happen if we pull the plug on C:
D should switch over to B as its master.


But here is the question: what happens if there are updates made on B while C is already dead? As soon (i.e. 30-59 sec if checkinterval is 30 s) as D detects that C is gone it will tell B to "reset master" and switch over, thereby missing all the changes that happend on A and B for maybe nearly a minute.


Am I correct in that assumption or did i miss something?


Thanks.


Ulrich

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  • Giuseppe Maxia photo Consistency problem?
    2007-03-14 09:44:35  Giuseppe Maxia | O'Reilly Blogger [View]

    You are right.
    Please be aware that my article is just a proof of concept. It is not an example of what you should do in production, because of this problem.
    Currently, you can't detect the master log position using only SQL routines. You should use external applications for that.
    At the moment, the technology available in MySQL stored routines is not able to handle such information unassisted.

    Best regards

    Giuseppe