[mysql-dde] Re: The mutual conflict problem
- From: "Peter B. Volk" <PeterB.Volk@xxxxxxx>
- To: <mysql-dde@xxxxxxxxxxxxx>
- Date: Mon, 12 Dec 2005 16:01:12 +0100
Ok I guess the list strips the images down:
here are the links:
www.inf.tu-dresden.de/~s7205538/dde/unique_management.jpg
www.inf.tu-dresden.de/~s7205538/dde/unique_management_sequenc.jpg
Peter
----- Original Message -----
From: "Peter B. Volk" <PeterB.Volk@xxxxxxx>
To: <mysql-dde@xxxxxxxxxxxxx>
Sent: Monday, December 12, 2005 3:56 PM
Subject: [mysql-dde] Re: The mutual conflict problem
> Hey,
> Well I could be solved by having GI-Key Masters. I've added 2 diagramms to
> show a few details.
>
> Peter
> ----- Original Message -----
> From: "Fabricio Mota" <fabricio.oliveira@xxxxxxxxxxxxxxxx>
> To: "dde" <mysql-dde@xxxxxxxxxxxxx>
> Sent: Monday, December 12, 2005 2:19 PM
> Subject: [mysql-dde] The mutual conflict problem
>
>
> > Hey Guy!
> > We have a problem with uniqueness management with any approach we use.
> That is:
> >
> > Suppose Clients C1 and C2, connected respectivelly through servers S1
and
> S2.
> > Both clients try to insert a value k, into a unique-indexed column.
> Suppose they try to insert the value approximately during the same time.
> >
> > If we think about to validate global uniqueness among servers before to
> insert, then:
> >
> > 1 - C1 tries to insert it through S1 / at same time, C2 tries it through
> S2.
> > 2 - S1 validates k / C1 locally. Uniqueness is ok. S2 validates k / C2
> locally, too. Both are ok.
> > 3 - S1 request S2 about uniqueness of k. At aproximately the same time,
S2
> request the same for S1.
> > 4a - if we consider a fully isolated transaction approach, then S1 will
> perform C1 command, and S2 will perform C2 command, too. That's an
> inconsistence!
> > 4b - if we consider the value k is shared during transactions, both
> servers will abort, because k is already there during remote validation,
> causing a mutual abort.
> >
> > If we think about to validate global uniqueness among servers after to
> insert, replicating global indexes, then:
> >
> > 1 - C1 tries to insert it through S1 / at same time, C2 tries it through
> S2.
> > 2 - S1 validates k / C1 locally. Uniqueness is ok. S2 validates k / C2
> locally, too. Both are ok.
> > 3 - S1 tries to sync S2 about its new value k. At aproximately the same
> time, S2 tries to sync S1, too.
> > 4a - if we consider a fully isolated transaction approach, then S1 will
> update S2 with its k, and S2 will update S1 with its own k, too. That's an
> inconsistence, again.
> > 4b - if we consider the value k is shared during transactions, both
> servers will abort, because k is already there during remote validation,
> causing a mutual abort.
> >
> > If we consider the hypothesis 4b, what criterion could be used for both
> server to agree in which transaction to abort?
> >
> > Or so, what could we do in respect to it?
> >
> > Fabricio Mota
> > Analista de Sistemas
> > FCPC - Divisão de Planejamento do Cadastro Comercial
> > MySql-DDE discussion list
> > www.freelists.org/
> >
>
>
>
>
> MySql-DDE discussion list
> www.freelists.org/
>
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