Are these clusters physically together using dedicate LAN lines .... or
are they synchronizing over the Interwait?
Ron Johnson wrote:
>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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