sql - oracle autoincrement with sequence and trigger is not working correctly

Question

here is my problemI have this code to make an autoincrement variable in oracle database:

CREATE TABLE Korisnici
    (
        id_korisnika number PRIMARY KEY,
        ime_korisnika varchar2(200),
        prezime_korisnika varchar2(200),
        broj_telefona varchar2(30),
        adresa_korisnika varchar2(400)
    )
    /

create sequence test_seq
start with 1 
increment by 1;

CREATE OR REPLACE TRIGGER test_trigger
BEFORE INSERT ON Korisnici FOR EACH ROW
BEGIN
  SELECT test_seq.NEXTVAL
  INTO :NEW.id_korisnika
  FROM DUAL;
END;
/

If I start from begining everything works great, I have numbers as 1,2,3,4.... I close the program, open it again, so oracle database connection is once again started. I add one more input and I have numbers like 20,21,22,23... I put program on my android and connect from different device, when I input one user I have 30,31,33,34...

Why is this happening? And how to fix it?

Thank you

EDIT:

Here is my proc for reading data from database

CREATE OR REPLACE PROCEDURE Citanje_korisnika( p_rc OUT SYS_REFCURSOR )
AS
BEGIN
  OPEN p_rc
   FOR SELECT *
         FROM Korisnici;
END;

I am a bit of newbie in oracle database.

Answer 1

Specifying the SEQUENCE with NOCACHE will stop a session caching 20 numbers at a time and help.

create sequence test_seq
start with 1 
increment by 1
NOCACHE;

However, if you're hoping for a completely contiguous sequence this is very difficult to achieve - numbers taken from the sequence are "lost" if (for example) an insert is rolled back.

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Based on your comment, I wonder if you're forgetting to COMMIT?