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This article mainly explains "what are the differences between CDB and PDB parameters". Interested friends may wish to take a look. The method introduced in this paper is simple, fast and practical. Next, let the editor take you to learn "what are the differences between CDB and PDB parameters?"

1. CDB and PDB share a parameter file, and CDB uses spfileSID.ora, then what you see when you show parameter spfile in PDB is that spfileSID.ora,CDB uses spfile.ora, then what you see when you show parameter spfile in PDB is that spfile.ora,CDB uses initSID.ora, then you can't see any files when you show parameter spfile in PDB, and the parameter information of PDB will not appear in the spfile or pfile file, but will be inherited directly from CDB.

2. CDB performs alter system modification parameters regardless of whether or not CONTAINER is added, and no matter whether the contain value is ALL or CURRENT,PDB. PDB performs alter system modification parameters, which only takes effect on the PDB. PDB alter system modification parameters cannot be added with CONTAINER = ALL, otherwise the error ORA-65050: Common DDLs only allowed in root,CONTAINER = ALL can only be executed in the CDB container.

The following two statements are equivalent because the default value for CONTAINER is CURRENT

ALTER SYSTEM SET parameter_name=value

ALTER SYSTEM SET parameter_name=value CONTAINER=CURRENT

The following two statements are equivalent in CDB because CDB has been modified, and so has PDB

ALTER SYSTEM SET parameter_name=value

ALTER SYSTEM SET parameter_name=value CONTAINER=ALL

3. The parameter that PDB can perform alter system modification must be the parameter corresponding to this parameter, otherwise it will report an error ORA-65040: the information of the parameter that operation not allowed from within a pluggable database,PDB performs alter system modification is stored in the PDB_SPFILE$ of CDB, not in the PDB_SPFILE$ of PDB, and the PDB_SPFILE$ table of PDB is always empty. PDB performs alter system-modified parameters regardless of database restart, CDB re-modification, cloning, unplug, etc., this parameter will continue to take effect in the PDB, that is to say, after manually modifying the parameter of a PDB, this parameter is not controlled by the CDB parameter in this PDB, and then modifying the parameter of CDB cannot modify the parameter value of the PDB, because the parameter and the information of the PDB have been stored in the data dictionary.

PDB inherits the parameter value from CDB, unless the parameter has been overridden at the PDB level, the parameter information overridden at the PDB level is stored in the PDB_SPFILE$ of the CDB, and the PDB first refers to the parameter of the PDB_SPFILE$ PDB in the CDB. If the PDB_SPFILE$ of the CDB is cleared, PDB automatically inherits the parameter value from CDB. Each container has a PDB_SPFILE$, or PDB_SPFILE$, that exists at both the CDB and PDB levels, but only the PDB_SPFILE$ of CDB has a value, and the PDB_SPFILE$ of PDB is empty.

Of course, if scope is added as memory when a PDB performs alter system modification, the information will not be written into the PDB_SPFILE$ of CDB. The parameter is invalid after PDB is restarted, just like 11g.

4. After PDB executes unplug, the parameter information of the PDB is written into the xml file. At this time, the parameter information of the PDB is still in the PDB_SPFILE$ of the CDB, and the show pdbs can also see the PDB, that is, when a PDB is unplugged, its own initialization parameters will not be copied to the PDB's own PDB_SPFILE$, but still exist in the PDB_SPFILE$ of CDB. When the drop pluggable database is executed, the PDB_SPFILE$ of the CDB cannot see the record of the PDB, the record of the PDB is cleared, and the show pdbs cannot see the PDB. When the PDB is re-create using xml to the CDB, the parameter is reloaded back into the PDB and written into the PDB_SPFILE$ of CDB.

5. V$system_parameter can view the parameters of CDB and all PDB (except PDB$SEED). Each container is distinguished by con_id.

Question and answer:

1. Does the modification parameter at CDB level affect the PDB level?

Yes, all PDB will be affected unless a PDB modifies the parameter individually

2. Does the modification parameter at PDB level affect the CDB level?

No, the CDB level and other PDB will not be affected.

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