Thursday, April 10, 2008

Just a DBA in a developers world...

Sometimes I wonder where this whole web development thing is going...

I was asked to setup some backup and recovery tools for the BerkeleyDB Java Edition (JE).

Hmm... DB... I could probably argue that DB should be dropped from the name if you add Java edition to it. I suppose maybe it's Oracle's plan to drop BerkeleyDB for the newer improved BerkeleyDB Java Edition (JE). Maybe that's why there won't be a BDB storage engine for MySQL beyond 5.1...

So after reading way to many pages of Oracle docs, I try just using a shell script with some fancy tar work and cross my fingers. That doesn't work, so I call on the Java developers to write a little copy tool using a jdb backup class buried somewhere way down deep in those java class libraries somewhere, plug that it to my script, and now we have backups.

All this to make sure we have instant DBA recovery for one of our Java applications, that uses Hibernate, that talks to Terracotta, that uses the BerkeleyDB JE. No complexity there...

Of course, the next thing they ask is does that mean we can restore to a point in time?

Well, that all depends. If we crash Terracotta crashes, and the filesystem is intact, the BerkeleyDB JE has the ability to roll it's logs forward and restore to the point in time of the last valid transaction at the time of the crash.

That won't do us much good, however, if we need to actually restore from a backup and then roll the logs forward, because BerkeleyDB is a append only write model: Meaning that the log and the data are one in the same, so I can't get copy's of the transaction logs on a periodic basis without getting the data as well. So, unless we plan on running backups every 15 minutes or so, we better not be expecting to restore to a point in time.

So the next question is (of course):

How are we supposed to use Terracotta as a highly recoverable persistent data store then?

My Answer (these are my opinions, as a DBA, of course):

Don't, if you expect your persistent data store to act like a relational database engine.... :)

But don't worry... it's the DBA's responsibility to make sure the data is all recoverable... right?
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