Automatic memory management(AMM) in oracle 11g

   Oracle has improvised the memory management in all the versions from 9i. We have pga_aggregate_target parameter to govern the programable global area management. The same automation in memory allocation is enforced in sga from 10g. But in oracle 11g this goes even better that is AMM, which oracle uses to dynamically allocate memory between PGA and SGA. 
  
    The 2 parameters that rule the AMM are MEMORY_MAX_TARGET and MEMORY_TARGET. Memory_max_target is static parameter and memory_max_target is dynamic. Any non zero value for memory_target will enable the AMM feature. This feature is very much helpful for OLTP environments running with share server configuration.

Index rebuild

alter index index_name tablespace tbs_name rebuild online parallel 2;

The parallel parameter works only in Enterprise edition of oracle.

Because parallelism doesnt comes free with Standard Edition. Same way the compression techniques used in oralce, for example compressed backup, compressed table(LOB), compressed expdp, compressed archive log files for standby.

Index rebuild with online option requires disk space equal to the size of the index in-order to make the index usable for the current running sessions which ever required.

 

Oracle FAQ's

Recover a deleted rows from undo without flashback.

select * from testtable versions between timestamp to_timestamp('22-feb-2012 03:25:35' ,'dd-mon-rrrr HH24:MI:SS') and to_timestamp('22-feb-2012 03:28:35' ,'dd-mon-rrrr HH24:MI:SS')

This query will return the deleted rows of the test table in the mentioned time. This will work even without flashback on.