John Watson's blog
Concurrent inserts into a table will often result in crippling buffer busy wait problems as sessions serialize on access to the last block(s) of the table segment. Using hash clusters can remove the issue.
Many people are terrified of global indexes, one reason being that partition DDLs on the table will either render them unusable, or take forever as they are updated. Deferred global index maintenance solves this, and should be an important driver for the 12c upgrade.
Why use interpreted PL/SQL when native compiled PL/SQL is so much faster? No reason at all - except that interpreted is the default, and most DBAs never change this. They should.
Can this parameter really boost performance? This simple test suggests that it can.
Unified Audit is a major architectural change: fast, easy, and impossible for the DBA to bypass. On upgrade to Oracle 12c, you really should enable it. The earlier method that we all use is pretty awful.
The concept of an adaptive plan is that execution of a statement can start with one plan, and (during execution) switch to another. A pretty amazing capability. No need to run the statement to completion and try again: correct it in flight.
I was at the Connecticut Oracle User Group re-launch meeting last week, talking about some of the 12c new features that I specially like: those related to what I call "the self-learning database".
Why does the CBO get it wrong? Often because it has insufficient information. No matter how often you analyze your tables, if your queries use multi-column predicates, the CBO will mis-calculate the cardinalities. You have to understand your data, and create extended statistics to correlate the columns. How many people do this? Hardly any. Not a problem any more: release 12c can do this for you. If you configure it appropriately.
A necessary part of a cluster is the cluster interconnect: the private network between the cluster nodes. This component is critical for both reliability and scalability, and configuring it for fault tolerance and capacity is a matter of burning importance for the DBA and his System Administrator (not to mention the end users). One question is, should this be managed by the operating system or by Oracle?
I have seen articles that misrepresent a Flex Cluster, even this book Expert Oracle RAC 12c which is written by people who know better (Oracle ACE directors, an OCM, an Oak Table member) gets it wrong, because of a reliance on beta documentation.