Vit Spinka technical blog

An interesting questions is: what is in fact the difference between unique and non-unique indexes? For a long discussion, see Richard Foote's blog . Here, we look at the on-disk differences. Let's start with environment setup and block dump creation: connect system create user itest identified by itest; grant dba to itest; create tablespace ITEST; alter user itest default tablespace itest; connect itest/itest create table TDATA (pk varchar2(20)); begin for i in 1..10000 loop insert into TDATA values ('VAL'||i); end loop; commit; end; create index TIDX1 on TDATA(pk); (I chose varchar2 type so that the actual characters are clearly seen in the dump. Also, I created a fresh new tablespace so the block numbers are small and probably consecutive.) Now, find the extents involved: select * from dba_extents where owner=user; And dump the blocks (take numbers from the query above - relative_fno, block_id): alter system dump datafile 14 block min 33 block max 62; Save the trace,