On 06/02/14 18:34, Fabio M. Di Nitto wrote:
On 02/06/2014 05:13 PM, Christine Caulfield wrote:
On 05/02/14 16:02, Jan Friesse wrote:
Chrissie,
patch looks good but what will happen in following scenario:
Unless I made coding errors (entirely possible) in ATB pre-this-patch:
- 4 nodes (A B C D) and atb list is (A B C D).
- A B and C D will split. So A B will get quorum
right
- C will split from D
both are unquorate at this stage.
- C will join D. So "previous" partition is C (for D node) and D (for C)
C and D are both unquorate. even if they rejoin they will still remain
unquorate.
ATB should only work:
- previous partition was quorate
- there is a 50/50 split
- partition that has "preferred node" will win.
node, and as you can see, no A or B. So according to comment, it will
vote?
Hmm good point. Maybe I need to make the algorithm dependant on the
previous membership list being more (maybe even twice as much) as the
current one. I'll have a think.
Unless you changed behaviour in your patch, I am not sure I see the
point Jan is trying to make here.
No I haven't changed that behaviour - I was going to test Honza's
question yesterday but was suffering hardware failures. You are right
(and testing bears it out) that [C D] will not achieve quorum. I was
erring on the side of safety - as you always must with quorum :)
Chrissie
Thanks
Chrissie
Honza
Christine Caulfield napsal(a):
This patch adds more flexibility to the auto_tie_breaker feature of
votequorum. With this, not only can the lowest nodeid be used as
a tie breaker, but also the highest, or a node from a nominated list.
If there is a list of nodes, the first node in the list that was not
part of the previous partition is used. This allows the user to
specify a preferred set of nodes but prevents a split-brain if the
cluster divides evenly with a node in each half.
Signed-Off-By: Christine Caulfield <ccaulfie@xxxxxxxxxx>
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