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Deadlock

Oracle Enqueue Rules Leading to Deadlock Changes Again in 12.1?

August 1, 2013 Four years ago while co-writing two chapters for an Oracle Database book, an interesting test case was put together to demonstrate how enqueues are handled when multiple sessions are competing for some of the same database resources – the test case was intended to demonstrate the neat, orderly, and predictable process implemented by Oracle Database.  Oracle Database 10.2.0.1 […]

Oracle Enqueue Rules Leading to Deadlock Changes Again in 12.1?

August 1, 2013 Four years ago while co-writing two chapters for an Oracle Database book, an interesting test case was put together to demonstrate how enqueues are handled when multiple sessions are competing for some of the same database resources – the test case was intended to demonstrate the neat, orderly, and predictable process implemented by Oracle Database.  Oracle Database 10.2.0.1 […]

Faulty Quotes 7 – Deadlock Kills Sessions?

January 4, 2012 (Back to the Previous Post in the Series) I thought that I would begin this blog article with a bit of a test case that demonstrates a very simple deadlock between two sessions. In Session 1 (create the test table with a primary key and insert a single row): CREATE TABLE T1 (   [...]

Knowing the trend of Deadlock occurrences from the Alert Log

Recently, my client deployed a new application and had this intermittent “Deadlock Storm” …

A trace file was sent and I was able to pinpoint the cause of the deadlock and the session that caused it.
The deadlock was a TX enqueue with mode of 4 (S – share) which could be verified by looking at the following lines of the Process State dump:

   last wait for 'enq: TX - row lock contention' blocking sess=0x 7000000cb239d60 seq=7849 wait_time=2929705 seconds since wait started=3
            name|mode=54580004, usn<<16 | slot=a0028, sequence=283f2

the "enqueue and lock mode" is explained as:
mode=54580004 (see above)
5458 (hex) = TX (ascii)
0004 (hex) = mode 4 (S – share)