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This article demonstrates how to reproduce  ORA-02475  error , and explains why it happens and how to resolve this issue.

1. Create cluster tables and indexes.

SQL> CREATE CLUSTER emp_dept (deptno NUMBER(3)) TABLESPACE users;

Cluster created.

SQL> CREATE TABLE dept 
     (
        deptno NUMBER(3) PRIMARY KEY,
        deptname VARCHAR2(15) NOT NULL
     )
     CLUSTER emp_dept (deptno);

Table created.

SQL> CREATE TABLE emp 
     (
        empno NUMBER(10) PRIMARY KEY,
        ename VARCHAR2(15) NOT NULL,
       deptno NUMBER(3) REFERENCES dept
     )
     CLUSTER emp_dept (deptno);

Table created.

SQL> CREATE INDEX emp_dept_index
         ON CLUSTER emp_dept
         TABLESPACE users ;

Index created.

SQL> insert into dept values ( 1,'DEPT1 1');

1 row created.

SQL> insert into dept values (2,'DEPT1 2');

1 row created.

SQL> insert into dept values (3, 'DEPT1 3');

1 row created.

SQL> commit;

Commit complete.

2.  Insert records into cluster table EMP until gets ORA-02475 error.

SQL> set serveroutput on;
begin
    for i in 1 .. 1000000000
    loop
       begin
           insert into emp values (i,'emp '||i, 3);
           commit;
       exception
       when others
       then
           dbms_output.put_line( SQLERRM );
          exit;
       end;
   end loop;
end;
/

ORA-02475: maximum cluster chain block count of 65534 has been exceeded

PL/SQL procedure successfully completed.