Sunday, March 27, 2011

Oracle RDBMS Patch set 11.2.0.2 new behaviour on datafile and Automatic Memory Management

New Behaviour for datafile:

In patch set 11.2.0.2 a new behaviour for datafile write errors has been implemented.With this release ANY write error to a datafile will cause the instance to abort.

Before 11.2.0.2 those errors usually led to an offline datafile if the database operates in archivelog mode (your production database do, don’t they?!) and the datafile does not belong to the SYSTEM tablespace. Internal discussion found this behaviour not up-to-date and alligned with RAC systems and modern storages.
Therefore it has been changed and a new underscore parameter got introduced.

_DATAFILE_WRITE_ERRORS_CRASH_INSTANCE=TRUE

This is the default setting´and the new behaviour beginning with Oracle 11.2.0.2

If you would like to revert to the pre-11.2.0.2 behaviour you’ll have to set in your init.ora/spfile this parameter to false. But keep in mind that there’s a reason why this has been changed.
More info in MOSC Note: 7691270.8

New Behaviour for Automatic Mamory Management (AMM):

Unfortunately a “new feature” in 11gR2 turns AMM on unless a hidden parameter called _memory_imm_mode_without_autosga is set to FALSE.

This means if you have disabled AMM , upgrades to 11gR2, you can find that AMM has reappeared, even if you think that you have disabled it. [Oracle11gR2 AMM restart]

There is a MOSC note about AMM in 11gR2 that notes that this regression back to AMM is the expected behavior in 11.2 for immediate memory allocation requests and that Oracle added this behavior as a 11gR2 new feature when automatic memory management was disabled.

More info MOSC Note:1269139.1, “SGA Re-Sizes Occurring Despite AMM/ASMM Being Disabled(MEMORY_TARGET/SGA_TARGET=0)”