Shulou(Shulou.com)06/01 Report--

I. brief introduction:

①: in the 12C R1 version, undo only supports Global Shared Undo mode, and all container share a UNDO tablespace. This mode is currently retained only for upgrade transition.

②: PDB Local UNDO schema is introduced in 12C R2. Each container has its own UNDO tablespace, and for RAC, each container has its own UNDO tablespace, which is recommended. There is a local undo option in DBCA, and it is checked by default.

Benefits of the local undo model:

①: reduces contention for undo tablespaces while making it easy to unplug and insert

②: the following new features are supported only with local undo: Refresh PDB, Flashback PDB, (Hot Clone, Relocate PDB in open read/write mode)

③: point-in-time recovery PDB

-- Note: if you want to convert local UNO to shared UNO, the database must be started in upgrade mode, otherwise an error will be reported.

2. From local undo to shared undo:

①: check to see if local undo is enabled: (local undo is enabled by default, because this option is checked by default during installation) SQL > col PROPERTY_NAME for A25 position SQL > col PROPERTY_VALUE for A25 position SQL > select PROPERTY_NAME,PROPERTY_VALUE from database_properties where property_name='LOCAL_UNDO_ENABLED' PROPERTY_NAME PROPERTY_VALUE--LOCAL_UNDO_ENABLED TRUE Note: in the Oracle12.1 version, undo only supports Global Shared Undo mode, but not local undo option ②: restart the database, start it in upgrade mode: SQL > shutdown immediateSQL > startup upgradeSQL > alter database local undo off -change the mode of local undo. The database must be started in upgrade mode. SQL > shutdown immediateSQL > startupSQL > col PROPERTY_NAME for a25th SQL > select PROPERTY_NAME,PROPERTY_VALUE from database_properties where property_name='LOCAL_UNDO_ENABLED';PROPERTY_NAME PROPERTY_VALUE--LOCAL_UNDO_ENABLED FALSE--- Note: from the previous query, we know that local_undo has been closed. ③: delete the undo tablespace in pdb: SQL > show pdbs CON_ID CON_NAME OPEN MODE RESTRICTED- 2 PDB$SEED READ ONLY NO 3 TESTPDB READ WRITE NOSQL > alter session set container=testpdb SQL > select tablespace_name from dba_tablespaces;-View the current tablespace, TABLESPACE_NAME--SYSTEMSYSAUXUNDOTBS1TEMPUSERSTEST6 rows selected.SQL > select name from v$datafile where name like'% undo%' -you can see that there are currently two undo tablespaces, one of which belongs to CDB One is PDB's own NAME----/opt/oracle/oradata/orcl/undotbs01.dbf/opt/oracle/oradata/orcl/testpdb/undotbs01.dbfSQL > drop tablespace UNDOTBS1 including contents and datafiles. -Delete the undo tablespace in pdb, (must go to pdb to execute this command) Tablespace dropped.SQL > select name from v$datafile where name like'% undo%' -at this point, if you look at the undo tablespace, only one of the CDB is left, NAME----/opt/oracle/oradata/orcl/undotbs01.dbfSQL > show con_name. CON_NAME--TESTPDB

2. From shared undo to local undo:

SQL > shutdown immediateSQL > startup upgrade-must start database SQL > alter database local undo on; with upgrade-enable local undo mode SQL > shutdown immediateSQL > startupSQL > col PROPERTY_NAME for A25 position SQL > col PROPERTY_VALUE for A25 position SQL > select PROPERTY_NAME,PROPERTY_VALUE from database_properties where property_name='LOCAL_UNDO_ENABLED' PROPERTY_NAME PROPERTY_VALUE--LOCAL_UNDO_ENABLED TRUESQL > alter pluggable database testpdb open;SQL > alter session set container=testpdb;SQL > select name from v$datafile where name like'% undo%' NAME- -/ opt/oracle/oradata/orcl/testpdb/system01_i1_undo.dbf

Description:

When loacl undo is opened, undo tablespaces are automatically created for the current PDB, and if you create a new pdb before, the system automatically creates its own undo tablespaces. The name and size of the created tablespace are determined by the configuration information in PDB$SEED.

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