CREATE TABLE test1 AS
    SELECT CAST(substr(cst.msisdn, 4) AS char(8)) suffix, cst.id profile
      FROM customers cst
     WHERE cst.msisdn LIKE '123________'
       AND ROWNUM < 10000;

CREATE CLUSTER test2 (suffix char(8))
SIZE 16
SINGLE TABLE
HASHKEYS 26000000
TABLESPACE TICKETS;

CREATE CLUSTER test2 (suffix char(8))
*
ERROR at line 1:
ORA-02454: Number of hash keys per block (505) exceeds maximum of 256

CREATE CLUSTER profile_cluster (suffix char(8))
SIZE 32
SINGLE TABLE
HASHKEYS 13000000
TABLESPACE TICKETS
PARALLEL 6;

  INSERT INTO cust_profile_map
    SELECT /*+ FULL(cst) PARALLEL(cst, 6) */
           CAST(substr(cst.msisdn, 4) AS char(8)), cst.id
      FROM customers cst
     WHERE cst.msisdn LIKE '123________';

ACCEPT cluster_name PROMPT 'Cluster Name: '

COLUMN table_name NEW_VALUE table_name

SELECT  table_name
FROM    user_tables
WHERE   cluster_name = upper('&cluster_name')
/

COLUMN db_block_size NEW_VALUE db_block_size

SELECT  value AS db_block_size
FROM    v$parameter
WHERE   name = 'db_block_size'
/

COLUMN nblocks NEW_VALUE nblocks
SELECT  round((&db_block_size / key_size) * hashkeys) AS nblocks
FROM    user_clusters
WHERE   cluster_name = upper('&cluster_name')
/

SELECT  count(*)        AS overflow_blocks
,       sum(row_count)  AS overflow_rows
FROM (
        SELECT  file#
        ,       block#
        ,       row_count
        ,       row_number() OVER (ORDER BY file#, block#) AS block_seq
        FROM (
                SELECT  dbms_rowid.rowid_relative_fno(ROWID) AS file#
                ,       dbms_rowid.rowid_block_number(ROWID) AS block#
                ,       count(*) row_count
                FROM    &table_name
                GROUP BY
                        dbms_rowid.rowid_relative_fno(ROWID)
                ,       dbms_rowid.rowid_block_number(ROWID)
        )
)
WHERE   block_seq > &nblocks
/