• Subject: Two-way mirroring
  • From: Terry Herrin <therrin@xxxxxxxxx>
  • Date: Thu, 04 Nov 1999 20:57:27 -0500

"Edward Koziol" <koziol@chaney.net> wrote:
>They can do it and so can DataMirror...

It would be interesting to know how these products handle multiple
updates to the same data.  For example, if system A updates a field in
a record with value "X", and system B updates that same field and
record with value "Y", what value are you going to use when you go to
resynch the databases later?  Are you going to compare the journal
entries from both systems to determine which update happened later,
and then use that value?  Or what if system A deletes a record that
was updated by system B?  Do we just delete that record and not bother
with why system B was doing an update to it?  Whatever choices are
made in the above examples, assumptions will be made according to a
set of rules.  How am I to know those rules are the way I want my data
to behave?  This sounds like it would be a great thing to have, but to
me it opens up a whole Pandora's box of issues.

Terry Herrin
Sr. Programmer/Analyst
New Hanover Regional Medical Center
Wilmington, NC
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