FreeLists / oracle-l / Index unusable

["Stephens, Chris" <chris_stephens@xxxxxxxxxxxx>]

2x this week a non-partitioned pk index has become unusable preventing
inserts into the table.
 
there has been no ddl on the table.
 
i can only find documentation on what causes partitioned indexes to be
unusable.
 
anybody know of a possible reason for this to be occuring?

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