Oracle Bulk Operation Data ____oracle

a large number of insert data below is inserted in the table tables 300,000 of data, if the first time to build the index is 57s, not indexed time is 58s, so and indexing and inserting data is not related.

Insert into table Select 1, ' TMP ' | | Lpad (rownum,7,0),,, ' null ', ' null ', Null,null,null,null, ' 0a972c8afe0a4fee9607fef52e42454c ', sysdate, ' 0a972c8afe0a4fee9607fef52e42454c ', Sysdate,2,null,null,null,null,null,null,null,null,null,null,null,null,null, ' Null ', 2,2,2,2,1,1,2 from dual connect by level <= 300000;

query large amounts of data create a federated index, which is valid from the previous back, if it is invalidated from the rear, and the order in which the index is valid is the previous backward

Create INDEX Someindex on dsep_c_allw_2016 (id,unit_id,disc_id)

Delete Index

Drop INDEX Someindex

This sentence below explains the execution of the statement.

Explain plan for  select count (IDS) from table_name
SELECT * FROM table (dbms_xplan.display);