PSQL Metadata
The Relational Interface in PSQL supports two versions of metadata, referred to as version 1 (V1) and version 2 (V2).
Metadata version is a property of the database that you specify when you create a database. V1 metadata is the default. When you create a database, you must specify V2 metadata if you want that version.
Metadata version applies to all data dictionary files (DDFs) within that database. A single database cannot use some DDFs with V1 metadata and others with V2 metadata. DDFs from the two versions cannot interact.
The database engine can, however, concurrently access multiple databases and each database can use either V1 metadata or V2 metadata.
All databases created with PSQL versions prior to PSQL v10 use V1 metadata. Databases created with PSQL v10 or later may use either metadata version depending on the database settings.
Comparison of Metadata Versions
Version 2 metadata allows for many identifier names to be up to 128 bytes long. Refer to Limits/Conditions of PSQL Features for additional information. In addition, V2 metadata allows for permissions on views and stored procedures. See Permissions on Views and Stored Procedures.
The data dictionary files (DDFs) for V2 metadata are named differently than for V1. In many cases, the V2 DDFs contain additional fields and changes to existing fields. See System Tables.