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alter session/system set skip_unusable_index = true/false ;The point :1, if set to true, then allow DML on table with unusable indexes(and index partitions). Or set to false to disallow DML on table.2, DML on tables with constraints which with unusable index status will failed because data maybe violated constraint if DML allowed.3, if DML not referencing on index column, DML will successfull dispite of this parameter .suppose index idx_job_emp is defined on column job.alter session set skip_un

create index logging, nologging performance test.For Speed up when creating an index for a large table. we can use nologging clause . test result:1, nologging is effective in archivelog database mode. Although, in noarchivelog database mode, by default ,create index will not produce much log , by other words, it's the same speed in noarchivelog mode whether nologging clause is supplied.2, use nologging clause , performance would improve 40% more or less accord actual environment.3, parallel is o