RE: multi-master replication
- From: "Marquez, Chris" <cmarquez@xxxxxxxxxxxxxxxx>
- To: <greg.loughmiller@xxxxxxxxxxxx>, <oracle-l@xxxxxxxxxxxxx>
- Date: Thu, 20 Oct 2005 16:12:23 -0400
Greg,
"Data/Transaction Replication" in even a modest complex environment can be a
nightmare.
In my experience "Data/Transaction Replication" works best in system with few
internal constraints/dependencies and external programs.
Pushing the same 300 inserts into two databases in two like tables is simple.
But have one database send 150 inserts to one db, while the other db 150
inserts the other way and the both later do updates, on all the data, while all
using-firing-triggering internal or external events, while pulling form
individual sequences, and maintaining data validity/consistency, all done
Asynchronously is where the idea of "Data/Transaction Replication" "falls
down". I'm not just talking Oracle constraints and triggers...I mean other
dependent transactional programs/validation and the middle tier too.
Oracle Advanced "Data/Transaction" Replication is can work very well...I have
used it...used if for Failover too. I hear that Quests SharPlex
"Data/Transaction" can work well to.
The problem is that most systems are built and run serially. When we have a
"final" result data set and try to "push it" through a like serially system we
must un-do or halt many of the serial process that normally would effect that
(now complete) transaction...this becomes a head ache and why many are never
able to us "Data/Transaction Replication" as a Disaster Recovery option. How
well "Data/Transaction Replication" works for your system depends on how much
manipulation, constraints, dependences, and consistency your data/transaction
will/must incur through the serial process.
Another major issue is "Asynchronously Bi-directional Replication". Even in
very simple system with NO dependences/constraints/triggers we still need to
maintain data consistency...no duplicate transactions/data. "(Data) Conflict
Resolution" rules/plans are painful idea in itself, but must be addressed.
Yet another issue is *change*.
We tried 100% replication on two db's for 2 years and never got to 100%. The
db/schema changed so much and so often that we were always un-doing and
re-doing the replication...a good idea that was not practical it implement and
maintain.
Finally "Data/Transaction Replication" is administratively intense for both day
to day data issues and monitoring. And honestly it took a bit of time to truly
understand and be comfortable with command-line Oracle Multi-Master
Replication...I would not just trust a GUI on this one at all. Also
Data/Transaction Replication doesn't often support application upgrades and nor
rolling upgrades.
Not to turn you off to "Data/Transaction Replication", but many do not see the
hurdles until they are knee deep into it.
The devil is in the details for sure. The more simple, static, uni-directional
the system, the better chance you have with successful "Data/Transaction
Replication".
I have not used Oracle Steams but from what I understand it is still what I
consider "Data/Transaction Replication"...and is conceptually and technically
similar to Quests SharPlex.
I have not used Quests SharPlex, but I did have technical meeting with their
reps. In the end (of the meeting) I found all the same issues and "things" the
effect Oracle Multi-Master Replication effected them to.
Again not that it doesn't work, but with data replication look for/ask for the
issues and problems before the benefits for sure.
hth
Chris Marquez
Oracle DBA
-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx on behalf of Loughmiller, Greg
Sent: Thu 10/20/2005 10:57 AM
To: 'oracle-l@xxxxxxxxxxxxx'
Subject: multi-master replication
hey folks,
I believe I may have sent this out before - so go ahead and hammer me
accordingly:-) But I have an interesting requirement for an effort......
Has anyone had any experience in trying to do multi-master replication to
keep multiple databases in sync? The assumption is that there would be
multiple application/database infrastructures - and the data needs to be
consistent between the *stacks*. And in one specific scenario - there could
be several million txn's per a 12 hour window of the day:-). A couple of the
goals and objectives for this chaos are to try to be data center agnostic
for the application-thus the need for the data to be consistent. The
additional assumption is that this would provide a level of HA in the event
there is a problem with one or more application stack (hmmm..... smells like
RAC, taste like RAC - maybe it is RAC but not data center agnostic). The
version of Oracle is 9206(for now), on Solaris, using HDS/EMC storage.....
So I guess my questions are:
1. Can streams keep up in this type of transactional volume?
2. I have my own opinion of this matter - but have you all seen other
methods to maintain the data in such a fashion?
3. Other technologies for this type of problem?
4. Or better yet - other potential solutions (don't do multi master but
do X,Y,Z )
My personal opinion with the limited exposure to Streams is that it probably
could not maintain that type of throughput, as well as placing additional
stress on the host as well as the DB. So I thought would throw this out
there to get some opinions, thrashing, or ideas from the list.....
Thanks in advance
Greg Loughmiller
Other related posts:
