Estimate the index size before creating an Oracle index (dbms_space.create_index_cost)

Estimate the index size before an Oracle index is created. Estimate the index size before a field in a table is created. The best way is to create an index in the test database for prediction. If no test is performed

Estimate the index size before an Oracle index is created. Estimate the index size before a field in a table is created. The best way is to create an index in the test database for prediction. If no test is performed

Estimate the index size before creating an Oracle Index

Estimate the size of a field in a table before creating an index. The best way is to create an index in the test database for prediction. If no test environment is available, you can use dbms_space.create_index_cost to estimate its size.

Syntax:

DBMS_SPACE.CREATE_INDEX_COST (
Ddl IN VARCHAR2,
Used_bytes out number,
Alloc_bytes out number,
Plan_table IN VARCHAR2 default null );

Example:

SQL> create table xyc_test (id int, name varchar (32 ));

The table has been created.

SQL> begin
2 for I in 1 .. 100000 loop
3 insert into xyc_test values (I, 'yundun ');
4 end loop;
5 commit;
6 end;
7/

The PL/SQL process is successfully completed.

SQL> exec dbms_stats.gather_table_stats (user, 'xyc _ test ');

The PL/SQL process is successfully completed.

SQL> variable used_bytes number;
SQL> variable alloc_bytes number;
SQL> exec DBMS_SPACE.CREATE_INDEX_COST ('create index x_idx on xyc_test (id) ',: used_bytes,: alloc_bytes );

The PL/SQL process is successfully completed.

SQL> print: used_bytes
500000
---- Estimate the allocation size
SQL> print: alloc_bytes
3145728

SQL> create index x_idx on xyc_test (id );

The index has been created.
---- The actual allocation size, which may be related to the amount of data.
SQL> select bytes from user_segments where segment_name = 'x _ idx ';
2097152

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