With Oracle 12c Oracle introduced the concept of common objects which avoids redundancy of metadata and data. Which makes CDB maintenance and up-gradation easy.
Common objects exist in Oracle-supplied schemas and therefore cannot be user-defined.
In the Application container, we can create metadata-linked or data-linked common objects.
There can be following types of common objects we can create with Application Container :
Triggers, tables, object table, object views, stored function, stored procedure etc.
There are four types of sharing mode available for common objects.
- METADATA
- DATA
- EXTENDED
- NONE
METADATA: This is the default sharing mode in the application container. Objects created with this sharing mode share common metadata across PDBs. Metadata ob objects are stored in the Application Container and Data are stored in Application PDB. With this sharing mode, we can have different data stored in object PDB wise.
With this SHARING MODE metadata of objects are stored in Application Root.
We can change default sharing mode using default_sharing initialization parameter.
DATA: We need to give SHARING=METADATA clause while creating an object to use this sharing mode. If we use DATA sharing mode metadata of object as well as data are shared commonly across all PDBs and Application root.
With this SHARING MODE data and metadata, both are stored in Application Root.
Extended: We need to give SHARING=EXTENDED DATA while creating an object. With this sharing mode application pdb can have common data with other PDBs and can have its own pdb specific data.
With this SHARING MODE metadata are stored in Application Root. Common data of all PDBs are stored in application root and pdb specific data are stored in Application PDB.
None: With this sharing mode application root object will not be shared to application PDBs .
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