Oracle database index on a table may be not good.

Table 1-5. Impact of multiple indexes on insert performance
Number of inserts and indexes Runtime
Inserting 256 rows with 0 indexes 1.101 seconds
Inserting 512 rows with 0 indexes 1.161 seconds
Inserting 256 rows with 5 indexes 3.936 seconds
Inserting 512 rows with 5 indexes 12.788 seconds
Inserting 256 rows with 10 indexes 12.558 seconds
Inserting 512 rows with 10 indexes 22.132 seconds