Sequences Performance Issue

Question

Hello.
I have a problem in the sequences.
Retrieving the next value of the sequence consumes 5 milliseconds of the procedure execution time.
When the sequence value goes high for millions... retrieving the sequence next value consumes about 300 milliseconds !!!!!
The sequence is cached, with values 20, .... and also tested with cache value 1000 and the performance is the same. the sequence currently cached with value 20
Why it takes 300 milliseconds, while it was consumes only 5 milliseconds?
Any Idea

Answer 1

So selecting the sequence can be almost a hundred times slower, depending on how large the sequence value is. Somehow I don;t think so unless it is a bug in your version. What happens if you do this?
SQL> create sequence s start with 100000 increment by 1 cache 1000;
Sequence created.
Elapsed: 00:00:00.00
SQL> declare
  2    n number;
  3  begin
  4    for i in 1 .. 100000 loop
  5      select s.nextval into n from dual;
  6    end loop;
  7  end;
  8  /
PL/SQL procedure successfully completed.
Elapsed: 00:00:05.07
SQL> /
PL/SQL procedure successfully completed.
Elapsed: 00:00:05.06
SQL> /
PL/SQL procedure successfully completed.
Elapsed: 00:00:05.02
SQL> drop sequence s;
Sequence dropped.
Elapsed: 00:00:00.05
SQL> create sequence s start with 10000000000 increment by 1 cache 1000;
Sequence created.
Elapsed: 00:00:00.00
SQL> declare
  2    n number;
  3  begin
  4    for i in 1 .. 100000 loop
  5      select s.nextval into n from dual;
  6    end loop;
  7  end;
  8  /
PL/SQL procedure successfully completed.
Elapsed: 00:00:05.02
SQL> /
PL/SQL procedure successfully completed.
Elapsed: 00:00:05.05
SQL> /
PL/SQL procedure successfully completed.
Elapsed: 00:00:05.01
SQL>