Oracle Database 12c中引入了 In-Database Archiving的新特性， 该特性允许用户通过对表上的数据行标记为inactive不活跃的，以归档数据。 这些inactive的数据行可以通过压缩进一部优化，且对应用来说默认不可见。 可以通过一个session级别的参数来控制数据的可见与否。
通过In-Database Archiving数据库内归档特性可以在单库中存放更长周期的数据， 而损耗很少的应用性能。 归档数据还可以通过压缩来进一步提升备份效能。
要管理一张表的In-Database Archiving，必须为表启用ROW ARCHIVAL 并操作ORA_ARCHIVE_STATE 这个隐藏字段 。 此外用户还可以指定session级别的 ROW ARCHIVAL VISIBILITY为ACTIVE 或者ALL。
下面为演示示例：
/* Set visibility to ACTIVE to display only active rows of a table.*/
ALTER SESSION SET ROW ARCHIVAL VISIBILITY = ACTIVE;
CREATE TABLE employees_indbarch
(employee_id NUMBER(6) NOT NULL,
first_name VARCHAR2(20), last_name VARCHAR2(25) NOT NULL,
email VARCHAR2(25) NOT NULL, phone_number VARCHAR2(20),
hire_date DATE NOT NULL, job_id VARCHAR2(10) NOT NULL, salary NUMBER(8,2),
commission_pct NUMBER(2,2), manager_id NUMBER(6), department_id NUMBER(4)) ROW ARCHIVAL;
INSERT INTO employees_indbarch(employee_id, first_name, last_name, email,
hire_date, job_id, salary, manager_id, department_id)
VALUES (251, 'Scott', 'Tiger', 'scott.tiger@example.com', '21-MAY-2009',
'IT_PROG', 50000, 103, 60);
INSERT INTO employees_indbarch(employee_id, first_name, last_name, email,
hire_date, job_id, salary, manager_id, department_id)
VALUES (252, 'Jane', 'Lion', 'jane.lion@example.com', '11-JUN-2009',
'IT_PROG', 50000, 103, 60);
commit;
/* Show all the columns in the table, including hidden columns */
SELECT SUBSTR(COLUMN_NAME,1,22), SUBSTR(DATA_TYPE,1,20), COLUMN_ID AS COL_ID,
SEGMENT_COLUMN_ID AS SEG_COL_ID, INTERNAL_COLUMN_ID AS INT_COL_ID, HIDDEN_COLUMN, CHAR_LENGTH
FROM USER_TAB_COLS WHERE TABLE_NAME='EMPLOYEES_INDBARCH';
SELECT SUBSTR(COLUMN_NAME,1,22) NAME, SUBSTR(DATA_TYPE,1,20) DATA_TYPE, COLUMN_ID AS COL_ID,
SEGMENT_COLUMN_ID AS SEG_COL_ID, INTERNAL_COLUMN_ID AS INT_COL_ID, HIDDEN_COLUMN, CHAR_LENGTH
FROM USER_TAB_COLS WHERE TABLE_NAME='EMPLOYEES_INDBARCH';
NAME DATA_TYPE COL_ID SEG_COL_ID INT_COL_ID HID CHAR_LENGTH
---------------------- -------------------- ---------- ---------- ---------- --- -----------
ORA_ARCHIVE_STATE VARCHAR2 1 1 YES 4000
EMPLOYEE_ID NUMBER 1 2 2 NO 0
FIRST_NAME VARCHAR2 2 3 3 NO 20
LAST_NAME VARCHAR2 3 4 4 NO 25
EMAIL VARCHAR2 4 5 5 NO 25
PHONE_NUMBER VARCHAR2 5 6 6 NO 20
HIRE_DATE DATE 6 7 7 NO 0
JOB_ID VARCHAR2 7 8 8 NO 10
SALARY NUMBER 8 9 9 NO 0
COMMISSION_PCT NUMBER 9 10 10 NO 0
MANAGER_ID NUMBER 10 11 11 NO 0
DEPARTMENT_ID NUMBER 11 12 12 NO 0
/* Decrease the ORA_ARCHIVE_STATE column size to improve formatting in queries */
COLUMN ORA_ARCHIVE_STATE FORMAT a18;
/* The default value for ORA_ARCHIVE_STATE is '0', which means active */
SELECT employee_id, ORA_ARCHIVE_STATE FROM employees_indbarch;
EMPLOYEE_ID ORA_ARCHIVE_STATE
----------- ------------------
251 0
252 0
/* Insert a value into ORA_ARCHIVE_STATE to set inactive */
UPDATE employees_indbarch SET ORA_ARCHIVE_STATE = '20' WHERE employee_id = 252;
/* Only active records are in the following query */
SELECT employee_id, ORA_ARCHIVE_STATE FROM employees_indbarch;
EMPLOYEE_ID ORA_ARCHIVE_STATE
----------- ------------------
251 0
/* Set visibility to ALL to display all records */
ALTER SESSION SET ROW ARCHIVAL VISIBILITY = ALL;
SELECT employee_id, ORA_ARCHIVE_STATE FROM employees_indbarch;
EMPLOYEE_ID ORA_ARCHIVE_STATE
----------- ------------------
251 0
252 20
SQL> desc employees_indbarch
Name Null? Type
----------------------------------------- -------- ----------------------------
EMPLOYEE_ID NOT NULL NUMBER(6)
FIRST_NAME VARCHAR2(20)
LAST_NAME NOT NULL VARCHAR2(25)
EMAIL NOT NULL VARCHAR2(25)
PHONE_NUMBER VARCHAR2(20)
HIRE_DATE NOT NULL DATE
JOB_ID NOT NULL VARCHAR2(10)
SALARY NUMBER(8,2)
COMMISSION_PCT NUMBER(2,2)
MANAGER_ID NUMBER(6)
DEPARTMENT_ID NUMBER(4)
1* select COLUMN_NAME,COLUMN_ID,DATA_TYPE from dba_tab_cols where table_name=upper('employees_indbarch')
SQL> /
COLUMN_NAME COLUMN_ID DATA_TYPE
-------------------- --------- --------------------
DEPARTMENT_ID 11 NUMBER
MANAGER_ID 10 NUMBER
COMMISSION_PCT 9 NUMBER
SALARY 8 NUMBER
JOB_ID 7 VARCHAR2
HIRE_DATE 6 DATE
PHONE_NUMBER 5 VARCHAR2
EMAIL 4 VARCHAR2
LAST_NAME 3 VARCHAR2
FIRST_NAME 2 VARCHAR2
EMPLOYEE_ID 1 NUMBER
ORA_ARCHIVE_STATE VARCHAR2
SQL> select dump(ORA_ARCHIVE_STATE,16),dump(EMPLOYEE_ID,16),dbms_rowid.rowid_block_number(rowid),dbms_rowid.rowid_relative_fno(rowid) from employees_indbarch;
DUMP(ORA_ARCHIVE_STA DUMP(EMPLOYEE_ID,16) DBMS_ROWID.ROWID_BLOCK_NUMBER(ROWID) DBMS_ROWID.ROWID_RELATIVE_FNO(ROWID)
-------------------- -------------------- ------------------------------------ ------------------------------------
Typ=1 Len=1: 30 Typ=2 Len=3: c2,3,34 109465 1
Typ=1 Len=2: 32,30 Typ=2 Len=3: c2,3,35 109465 1
SQL> alter system flush buffer_cache;
System altered.
SQL> alter system dump datafile 1 block 109465;
System altered.
tl: 73 fb: --H-FL-- lb: 0x0 cc: 12
col 0: [ 1] 30
col 1: [ 3] c2 03 34
col 2: [ 5] 53 63 6f 74 74
col 3: [ 5] 54 69 67 65 72
col 4: [23]
73 63 6f 74 74 2e 74 69 67 65 72 40 65 78 61 6d 70 6c 65 2e 63 6f 6d
col 5: *NULL*
col 6: [ 7] 78 6d 05 15 01 01 01
col 7: [ 7] 49 54 5f 50 52 4f 47
col 8: [ 2] c3 06
col 9: *NULL*
col 10: [ 3] c2 02 04
col 11: [ 2] c1 3d
tab 0, row 1, @0x1ecc
tl: 70 fb: --H-FL-- lb: 0x2 cc: 12
col 0: [ 2] 32 30
col 1: [ 3] c2 03 35
col 2: [ 4] 4a 61 6e 65
col 3: [ 4] 4c 69 6f 6e
col 4: [21]
6a 61 6e 65 2e 6c 69 6f 6e 40 65 78 61 6d 70 6c 65 2e 63 6f 6d
col 5: *NULL*
col 6: [ 7] 78 6d 06 0b 01 01 01
col 7: [ 7] 49 54 5f 50 52 4f 47
col 8: [ 2] c3 06
col 9: *NULL*
col 10: [ 3] c2 02 04
col 11: [ 2] c1 3d
可以看到这里 ORA_ARCHIVE_STATE是实际存放在块里的row piece上的第一个字段，类型为varchar2(4000);
In-Database Archiving的限制：
- ILM is not supported with OLTP table compression for in-database archiving. Segment-level ILM and compression is supported if partitioned on the ORA_ARCHIVE_STATE column.
ORA_ARCHIVE_STATE相关：
/* constants specifying ROW ARCHIVAL state */
archive_state_active constant varchar2(1) := ‘0’;
archive_state_archived constant varchar2(1) := ‘1’;
/*
* description – Given a value for the ORA_ARCHIVE_STATE column this
* function returns the mapping for the value.
*
* value – “0”, “1” or other values from the ORA_ARCHIVE_STATE column of
* a row archival enabled table
* returns either “archive_state_active” or “archive_state_archived”
*/
ILM is not supported with OLTP table compression for in-database archiving.ILM指的是什么？