how update may cause index block split

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Hi, We have a 10.2.0.3 RAC and frequently got enq: TX - index contention.
The index are as follows

SCHLP1  ORDER_DATE,ORDER_CODE,ORDER_INTRNL_LINE_NUM,SCHED_NUM,UNIQUE_NUM
SCHLI2  ORDER_DATE,ORDER_CODE,ORDER_INTRNL_LINE_NUM,SCHED_NUM,LOAD_NUM
SCHLI3  ORDER_DATE,ORDER_CODE,TKT_CODE

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