After being SQL DBA 4+ years now since 2 years I am trying to be a DBA mean cross platform database administrator. So trying multiple technologies. MySQL, mongodb and Oracle too. My today's post is on oracle, true fiction working on large data-set. Actually I was testing CRUD and aggregations on oracle 11g over 21 millions records (21326826). I had a table employee having huge amount of data and there is a column city which have null values on 21 millions records. The story begins when I was trying to update these null value with some information. Column have already secondary index we have created on city column because result of group by was slow on city so for better response time we have created index on city column. Physical architecture of database and tables space are default . Table is present in user tablespace. We have not changed any configuration of oracle before, I am totally new on oracle.