Re: Does Sybase have something like Oracle's RAC for hot failover?

Comments in-line.

Joe Weinstein wrote:

RAC is not a Sybase like HA failover and there is no relationship
between the Sybase capability and that of Oracle's RAC. Sybase HA
failover is more equivalent to Oracle's DataGuard failover.

With the Sybase solution you do not have shared-everything. With
Sybase you do not have load balancing. With Sybase there is a
primary node and the balance are secondary. With Oracle that concept
does not exist. All nodes stand on a equal footing.

With Sybase, after failover, all existing client connections are lost.
With Oracle all existing client connections are maintained. The end-user
experience is seemless with a DML statement restarted on another live
node.


I undertand now that RAC != Sybase HA (yet). 

It would be nice if Sybase offered an equivalent capability.

However RAC is not nirvana,
and the above seems to confuse/co-mingle Oracle RAC with Oracle TAF.


Actually not but we'll get there. RAC != TAF. TAF also works with
DataGuard and in other situations as TAF is Net Services.

With RAC alone, connections to a failing RAC node are simply dead. 

Well yeah. If you yank the power cord the node is dead. But the end
user never knows it.

There is a connect-time option for the Oracle client code to try
a named series of RAC nodes to find on that is currently running,
(failover and/or load-balancing). When a RAC conneciton dies, any
ongoing local transaction or global transaction that has not yet reached
the prepared state is gone.


Where did you get this misinformation? It is absolutely untrue.

My standard lecture demo of RAC node failure is to live-demo transparent
failover ... transparent means transparent.

However, there are bugs and problems: These in-doubt transactions will
not be known *and in a recoverable state* for upwards of a minute, 

Sorry but this is pure nonsense. I've never seen a TAF failover take
more than 2 seconds ... generally they are subsecond. I teach RAC
classes and my students generally build 4-8 two node clusters each and
every month. Not once has any one of them ever experienced what you
describe.

Also, in a wierd turn-about, Oracle uses PAGE_LEVEL
LOCKING like old Sybase!


You've really got to stop smoking whatever it is you are smoking. To
start with Oracle has no concept of pages ... they are blocks. And
you couldn't lock a block in Oracle by any method short of writing a
program that interrogated the block, determined what rows it contained
and then locked each individual row. Seriously Joe ... where are you
getting this stuff?

   TAF is different. It is "Transparent Application Failover", and
purports to make connections failover in-flight, so applications
can just continue to do their work.


Exactly.

This is a noble goal, but TAF is
a cynical misnomer for most real clients. Below is a link to
Oracle documents which partially admits to the computational and
session state that is lost over the 'transparent failover'
> http://metalink.oracle.com/metalink/plsql/ml2_documents.showDocument?p_database_id=NOT&p_id=97926.1) 


"Admits"? You have misunderstood what you read.

What happens behind the scenes is irrelevant to the end-user experience.
Which is subsecond and truly transparent.
--
Daniel A. Morgan
http://www.psoug.org
damorgan@xxxxxxxxxxxxxxxx
(replace x with u to respond)
.

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