I agree with Mark and Ryan. Here's a few thoughts from me:
- Don't do it! It's complex and a bit dangerous. Get it wrong and you have 2
(or more) corrupt DB's.
- Don't use Table-based sequences (e.g. for a no-gap sequence): you can't have
no-gap sequences.
- If you are using SEQUENCEs, don't replicate them but ensure they can't
produce the same value in each DB. In the past I have used stepped increments
(DB-1: start with 1 increment by 10: DB-2 start with 2 increment by 10: DB-3
start with 3... etc) so rows from DB-1 always end in a 1, etc... Don't start
one at 1,000,000,000,000 and the next at 2,000,000,000,000.
- database should be in forced logging mode with plenty of supplemental
logging to support the keys - so you're going to get (a bit) more redo.
- Every table should have a PK or UK. If it doesn't, add a surrogate one.
Trying
to uniquely identify rows with multiple columns will require lots of
extra redo supplemental logging (all columns) at the very least.
- consider how you will *prove* you have the same data in all DB's. What is
your reconciliation process?
- Can you replicate the DDL for schema change? This can make life a lot simpler
(I'm not knowledgeable about DBVisit, only Goldengate) when keeping the DB's
aligned if the tool will do it for you. Doing it manually can be particularly
painful.
- you will get conflicts. you need to consider the conflict resolution rules
carefully as when you have a conflict that is not auto-resolved by a rule, all
replication will stop until you resolve it introducing significant replication
delay.
- You will probably have problems with encrypted or compressed tablespaces -
check with the vendor.
- Remember, a replicated DB is not a backed-up DB. As I have had to explain to
a client in the past.
Look at MOS Article "1296168.1" which gives a scripts which will review your
current schema for GoldenGate Classic Capture, which is basically the same
method as used by DBVisit to extract transaction change vectors.
regards
Neil Chandler
[snip]
On Sep 26, 2016, at 5:04 PM, Vadim Keylis <vkeylis2009@xxxxxxxxx>
wrote:
Good afternoon everyone. I am
working on designing POC bi-directional replication
between two data centers using dbvisit application. What
are the general best practices when designing database
for bidirectional replication ? What are the general
design consideration should be made from your experience
for bi-directional replication?
Thanks so much in advance,
Vadim
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