25 Jan
Too Many Flashbacks
With apologies to Dr. Seuss.
Did I ever tell you the makers of RAC
had seven features and named each flashback?
Well they did, and it wasn’t a smart thing to do.
You see, when the customers wanted a clue
as to how to keep data from getting deleted
the RAC folks said “flashback” and customers heeded.
They turned on all seven of those flashback features
Each one was a slightly dissimilar creature.
Some used the UNDO, some used flashback files
Some just renamed tables to bin$ styles.
One was a place you keep things for recovering
Another was just for forensic discovering
With so many features called by the same name
when thinks broke no one knew just which one they should blame.
On a Friday three minutes past seventeen hundred,
users ask, “What’s the deal? Our data’s been plundered.”
“It looks like all names in the customer table,
are now ‘John Q Public,’ a certain mislabel.”
It was Nimrod, an intern fresh from his instruction.
What he thought was just test was really production.
“No Problem,” says Morton, the wise DBA,
“Flashback is on. I’ll restore it today.”
First Morton asked Nimrod what time he committed
his update that had any where clause omitted.
“I ran it at just past noon yesterday lunch,
It ran for so long that I went for a munch.”
By now it had been almost thirty one hours
but Morton knew that he could call on his powers,
and on the mere fact that that the undo_retention
was set to two days, a quite lengthy extension.
But woe! When he tried to engage Flashback Query,
he got “snapshot too old” and it ruined his theory
that undo_retention makes Oracle hold
all undo data no matter how old.
It turns out that there was no undo_guarantee
or autoextend which would also be key
to use all Flashback features reliant on Undo
A realization he would slowly come to.
Now Flashback Transaction and Versions Between
were out of the picture, although unforseen.
But he still had four more kinds of Flashback to try
So he thought them each through, to see if they might fly.
Undropping the table would use flashback syntax,
But that wouldn’t help, since the table was intact.
With database flashback all could be reverted
But subsequent changes would then be subverted
Do you know who was governor of California
When Flashback Data Archive came out and I’ll warn ya,
it will not help poor Morton, though it’s called Total Recall.
He’d have had to enable it for tables to see all.
The last of the flashbacks was the old FRA,
the Flashback Recovery Area they say.
And it’s just a directory where things are kept
Like logs and old backups made while Morton slept.
So after all that there was nary a way
to use Flashback of any sort to save the day.
Old-fashioned LogMiner was what Morton used
To restore all the rows that poor Nimrod abused.
With so many flashbacks and so much confusion
I bet that Oracle regrets the profusion
of so many things that they call the same name.
But now its too late and there’s no one to blame.
