Re: Replication Ideas

On Thu, 2003-08-28 at 16:00, Jan Wieck wrote:
> Ron Johnson wrote:
>
> > Notes:
> > a) this is, of course, not *sufficient* for multi-master
> > b) yes, you need a fast, low latency network for the DLM chatter.
>
> "Fast" is an understatement. The DLM you're talking about would (in our
> case) need to use Spread's AGREED_MESS or SAFE_MESS service type,
> meaning guarantee of total order. A transaction that needs any type of
> lock sends that request into the DLM group and then waits. The incoming
> stream of lock messages determines success or failure. With the overhead
> of these service types I don't think one single communication group for
> all database backends in the whole cluster guaranteeing total order will
> be that efficient.

I guess it's the differing protocols involved.  DEC made clustering
(including Rdb/VMS) work over an 80Mbps protocol, back in The Day,
and HPaq says that it works fine now over fast ethernet.

> > This is a tried and true method of synchronization.  DEC Rdb/VMS
> > has been using it for 19 years as the underpinnings of it's cluster
> > technology, and Oracle licensed it from them (well, really Compaq)
> > for it's 9i RAC.
>
> Are you sure they're using it that way?

Not as sure as I am that the sun will rise in the east tomorrow,
but, yes, I am highly confident that O modified DLM for use in
9i RAC.  Note that O purchased Rdb/VMS from DEC back in 1994, along
with the Engineers, so they have long knowledge of how it works
in VMS.  One of the reasons they bought Rdb was to merge the tech-
nology into RDBMS.

--
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Ron Johnson, Jr. ron.l.johnson@cox.net
Jefferson, LA USA

"they love our milk and honey, but preach about another way of living"
Merle Haggard, "The Fighting Side Of Me"