Oracle 18c新特性：PDB Snapshot Carousel (PDB快照 旋转木马)
今天在墨天轮社区看到一个关于PDB Snapshot的问题， 之前在写过一系列PDB新特性，这个功能补充一下，在一些生产容灾环境中有一种定期clone一份数据库的需求，如BCV存储快照技术 ，当然最近几年CDP, CDM技术的出现也是基于存储快照实现数据库历史时间的恢复。Oracle 在18c中同样提供了一种自动生成并清理历史数据库快照的技术PDB Snapshot Carousel，和redo group, undo archive轮训一样，下面附一张官方图一看。
技术特性
1， 可以指定创建快照的频率间隔(minutes, hours)
2, 可以指定最大快照周期个数，配置值为0时，清理所有快照
3， 快照是以轮训的方式清理，达到个数时新快照覆盖历史快照
4，快照可以手动创建也可以自动创建
5， 快照可以批定命名也可以系统自动生成
6， 快照可以在已存在的库指定刷新，也可以在创建PDB时指定刷新频率
7， 快照刷新配置可以在线修改
8， 基于快照可以clone PDB, 但不可以基于快照创建快照
9， 快照文件是一种二进制PDB archive files(unplug database后的datafile和xml描述文件生成的独立的压缩副本文件，以”.pdb”为扩展名)
10, 要求PDB 使得local undo
11, License 只支持Oracle Database Enterprise Edition以上on Engineered Systems(ODA, EXADATA) 和 on Oracle Database Cloud
功能演示
note: 我的环境用于测试修改了Exadata的限制参数，（生产环境不建议），使用的19.3 EE On-Premise。
1, 创建PDB时同时指定刷新
SQL> select pdb_name,snapshot_mode,snapshot_interval/60 from dba_pdbs
PDB_NAME SNAPSH SNAPSHOT_INTERVAL/60
-------------------- ------ --------------------
PDB1 MANUAL
PDB$SEED MANUAL
SQL> create pluggable database pdb1_snp from pdb1 file_name_convert=('pdb1','pdb1_snp') snapshot mode every 1 hours;
create pluggable database pdb1_snp from pdb1 file_name_convert=('pdb1','pdb1_snp') snapshot mode every 1 hours
*
ERROR at line 1:
ORA-12754: Feature PDB SNAPSHOT CAROUSEL is disabled due to missing capability .
SQL> @pd exadata
Show all parameters and session values from x$ksppi/x$ksppcv...
NUM N_HEX NAME VALUE DESCRIPTION
---------- ----- -------------------------------------------------------- ------------------------------ ---------------------------------------------------------------------------------------------------
482 1E2 _rm_exadata_pdb_cpu_cnt FALSE Use PDB CPU cnt for Exadata smart scan
483 1E3 _rm_exadata_partition_fc FALSE Partition flash cache for Exadata
484 1E4 _rm_exadata_pdb_cpu_cnt_mult 2 Multiplication factor for PDB cpu count
912 390 _exadata_feature_on FALSE Exadata Feature On
1236 4D4 _lm_exadata_fence_type TRUE if FALSE disable Exadata fence type
2062 80E _enable_flash_logging TRUE Enable Exadata Smart Flash Logging
2863 B2F _cell_offload_hybridcolumnar TRUE Query offloading of hybrid columnar compressed tables to exadata
4031 FBF _bloom_serial_filter ON enable serial bloom filter on exadata
4828 12DC _asm_offload_all FALSE Offload all write operations to Exadata cells, when supported
5136 1410 _auto_manage_exadata_disks TRUE Automate Exadata disk management
10 rows selected.
SQL> alter system set "_exadata_feature_on"=true scope=spfile;
System altered.
SQL> startup force
ORACLE instance started.
Total System Global Area 1073738488 bytes
Fixed Size 9143032 bytes
Variable Size 763363328 bytes
Database Buffers 297795584 bytes
Redo Buffers 3436544 bytes
Database mounted.
Database opened.
SQL> archive log list
Database log mode No Archive Mode
Automatic archival Disabled
Archive destination /u01/app/oracle/product/19.2.0/db_1/dbs/arch
Oldest online log sequence 12
Current log sequence 14
SQL> create pluggable database pdb1_snp from pdb1 file_name_convert=('pdb1','pdb1_snp') snapshot mode every 1 hours;
create pluggable database pdb1_snp from pdb1 file_name_convert=('pdb1','pdb1_snp') snapshot mode every 1 hours
*
ERROR at line 1:
ORA-65036: pluggable database PDB1 not open in required mode
SQL> ho oerr ora 65036
65036, 00000, "pluggable database %s not open in required mode"
// *Cause: Attempted to perform an operation on a pluggable database in
// incorrect open mode.
// *Action: Open the pluggable database in the mode required for this operation
//
SQL> alter pluggable database pdb1 open;
Pluggable database altered.
SQL>SELECT property_name, property_value
FROM database_properties
3 WHERE property_name = 'LOCAL_UNDO_ENABLED';
PROPERTY_NAME PROPERTY_VALUE
------------------------------ ------------------------------
LOCAL_UNDO_ENABLED TRUE
SQL> create pluggable database pdb1_snp from pdb1 file_name_convert=('pdb1','pdb1_snp') snapshot mode every 1 hours;
Pluggable database created.
SQL> select pdb_name,snapshot_mode,snapshot_interval/60 from dba_pdbs;
PDB_NAME SNAPSH SNAPSHOT_INTERVAL/60
-------------------- ------ --------------------
PDB1 MANUAL
PDB$SEED MANUAL
PDB1_SNP AUTO 1
2， 现用的PDB创建snapshot
SQL> r
1 SELECT r.CON_ID, p.PDB_NAME, PROPERTY_NAME,
2 PROPERTY_VALUE AS value, DESCRIPTION
3 FROM CDB_PROPERTIES r, CDB_PDBS p
4 WHERE r.CON_ID = p.CON_ID
5 AND PROPERTY_NAME LIKE 'MAX_PDB%'
6* ORDER BY PROPERTY_NAME
CON_ID PDB_NAME PROPERTY_NAME VALUE DESCRIPTION
------ --------- ----------------- -------------------- -------------------------------------------
3 PDB1 MAX_PDB_SNAPSHOTS 8 maximum number of snapshots for a given PDB
3 PDB1 MAX_PDB_STORAGE UNLIMITED Maximum Space Usage of Datafiles and Local
Tempfiles in Container
SQL> ALTER PLUGGABLE DATABASE SET MAX_PDB_SNAPSHOTS=4;
ALTER PLUGGABLE DATABASE SET MAX_PDB_SNAPSHOTS=4
*
ERROR at line 1:
ORA-65046: operation not allowed from outside a pluggable database
SQL> @cc pdb1
ALTER SESSION SET container = pdb1;
Session altered.
SQL> ALTER PLUGGABLE DATABASE SET MAX_PDB_SNAPSHOTS=4;
Pluggable database altered.
SQL> ALTER PLUGGABLE DATABASE SNAPSHOT MODE EVERY 20 minutes;
Pluggable database altered.
SQL> select pdb_name,snapshot_mode,snapshot_interval/60 from dba_pdbs;
PDB_NAME SNAPSH SNAPSHOT_INTERVAL/60
--------- ------ --------------------
PDB1 AUTO .333333333
Tip：
Creating a Snapshot with a User-Specified Name
ALTER PLUGGABLE DATABASE SNAPSHOT cdb1_pdb1_b4wedload;
Creating a Snapshot with a System-Specified Name
ALTER PLUGGABLE DATABASE SNAPSHOT;
3, 查询快照
SQL> SELECT CON_ID, CON_NAME, SNAPSHOT_NAME, SNAPSHOT_SCN AS snap_scn, SNAPSHOT_TIME, FULL_SNAPSHOT_PATH FROM DBA_PDB_SNAPSHOTS ORDER BY SNAP_SCN;
因为虚机存储满，不再演示生成的文件，自己可以测试都是.pdb文件， 目前是不支持ASM中的，可以考虑ACFS。
— enjoy
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