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deadlocks

DML Tablescans

This note is a follow-up to a recent comment a blog note about Row Migration:

So I wonder what is the difference between the two, parallel dml and serial dml with parallel scan, which makes them behave differently while working with migrated rows. Why might the strategy of serial dml with parallel scan case not work in parallel dml case? I am going to make a service request to get some clarifications but maybe I miss something obvious?

The comment also referenced a couple of MoS notes:

RI Locks

RI = Referential Integrity: also known informally as parent/child integrity, and primary (or unique) key/foreign key checking.

I’m on a bit of a roll with things that I must have explained dozens or even hundreds of times in different environments without ever formally explaining them on my blog. Here’s a blog item I could have done with to response to  a question that came up on the OTN database forum over the weekend.

What happens in the following scenario:

Deadlocks

A recent question on the OTN forum asked about narrowing down the cause of deadlocks, and this prompted me to set up a little example. Here’s a deadlock graph of a not-quite-standard type:

Shrink Space

Here’s a lovely effect looking at v$lock (on 11.2.0.4)

MOUS 2013 Presentations

Just a quick note/announcement, that we had our annual Michigan Oracle Users Summit yesterday at the VisTaTech Center on the campus of Schoolcraft College, in Livonia, MI.  It was a good conference, and I think everyone who made it out, enjoyed their time there and saw some excellent presentations.

I did two presentations, Understanding and Interpreting Deadlocks and All About Indexes.  The presentations will be available at the MOUS website, but I also wanted to make them available here.  (See the links above.)

P.S.  I finally, just today, got my storage for my GoldenGate test boxes, so, I’ll be proceeding with that testing soon.  Stay tuned for my next blog post in that series, in a week or so.

Application Design is the only Reason for Deadlocks? Think Again

#38761d;">[Updated on 4/20/2013 after feedback from #38761d;">Charles Hooper#38761d;">, #38761d;">Jonathan Lewis#38761d;">, #6aa84f;">Lau#38761d;">rent Schneider and #38761d;">Mohamed Houri#38761d;"> and with some minor cosmetic enhancements of outputs]

Deadlocks

Here’s a deadlock graph that might cause a little confusion:

Lock Bug

Here’s an oddity that I ran into a little while ago while trying to prepare a sample trace file showing a particular locking pattern; it was something that I’d done before, but trace files can change with different versions of Oracle so I decided to use a copy of 11.2.0.2 that happened to be handy at the time to check if anything had changed since the previous (11gR1) release. I never managed to finish the test; here are the steps I got through: