Wednesday, October 1, 2014

Replication from Oracle to MariaDB the simple way - Part 4

Now it's time to get serious about replicating to MariaDB from Oracle, and we are real close now, right? What I needed was a means of keeping track of what happens in a transaction, such as a LOG table of some kind, and then an idea of applying this log to MariaDB when there is a COMMIT in Oracle. And thing is, these two don't have to be related. So I can have a table which I write to and also have a Materialized View that is refreshed on COMMIT on, and I need a log table or something. And when the Materialized View is refreshed, as there is a COMMIT, then the log can be applied. From a schematic point-of-view, it looks something like this:
This looks more complex than it is, actually, all that is needed is some smart PL/SQL and this will work. I have not done much of any kind of testing, except checking that the basics work, but the PL/SQL needed I have done for you, and the order table triggers and what have you not is also created for you by a shell script that can do this for any table.

As for the DUMMY table that I have to use to get a trigger on COMMIT, this doesn't have to have that many rows, I actually just INSERT into it once per transaction, and then I INSERT the transaction id, which I get from Oracle. This table will have some junk in it after a while, all the transactions that were started and COMMITted will have an entry here. But in my code for this, I have included a simple job that purges this table from inactive transactions.

Best of all is that this works even with Oracle Express, so no need to pay for "Advanced Replication", not that I consider it really advanced or anything. I'd really like to know what you think about these ideas? Would it work? I know it's not perfect, far from it, for for the intent of having a MariaDB table reasonable well syncronized with an Oracle, this should work. Or? The solution is on one hand simple and lightweight, but I have given up on the number of features and possibly also the design affects performance a bit.But it should be good enough for many uses I think?

Let me hear what you think, I'm just about to release this puppy!



Jobin said...

Hi Karlsson,
I was following your posts from 1 to 3. the ideas were well explained. But on this 4th one, I see very little explanation.

It will be nice if you can explain the overall setup with exact commands as you done for chapter 3.

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