clone_schema

clone_schema is a PostgreSQL tool for making a copy of a schema. It includes all objects associated with a schema.

Handles following objects:

• Tables - structure (UDT columns, indexes, constraints, keys) and optionally, data
• Views, Materialized Views - Structure and data
• Sequences, Serial, Identity, Replica Identity
• Functions/Procedures
• Types (composite and enum)
• Collations, Domains, Rules, Policies
• Triggers, Trigger Functions
• Comments
• ACLs (Permissions/Grants)
  

Arguments:

• source schema

  Required: text - schema name

• target schema

  Required: text - table name

• action

  Required: One of 'DATA','NODATA','DDLONLY'

• Enumerated list

  Optional: 'NOOWNER','NOACL','VERBOSE','FILECOPY'

Returns: INTEGER (0 for success, positive non-zero number for an error)

Examples
Clone the schema with no data:

select clone_schema('sample', 'sample_clone', 'NODATA');

Clone the schema with data:

select clone_schema('sample', 'sample_clone', 'DATA');
select clone_schema('sample', 'sample_clone', 'DATA','VERBOSE'); -- verbose mode shows row copy progress

Just generate DDL:

select clone_schema('sample', 'sample_clone', 'DDLONLY');

In the generated output for DDLONLY, modify the output as follows:

• remove the lines that start with NOTICE:
• remove any other lines that do not begin with INFO:
• Then, remove the first 7 characters of the these lines that begin with INFO:
  

The result should be a clean DDL output.

Ownership/Privileges
By default, ownership and privileges are also cloned from source to target schema. To override, specify NOOWNER and/or NOACL (similar to how pg_dump works). When NOOWNER is specified, the one running the script is the default owner unless overridden by a SET ROLE command before running this script.

Copying Data You may get faster results copying data to/from disk instead of in-memory copy. FILECOPY is a workaround for tables with complex UDT-type columns that fail to copy. It only works for On-Prem PG Instances since it relies on using the COPY command to write to and read from disk on which the PostgreSQL server resides.
Although pg_clone_schema supports data copy, it is not very efficient for large datasets. It only copies tables one at a time. Using pg_dump/pg_restore in directory mode using parallel jobs would be a lot more efficient for large datasets.

Sequences, Serial, and Identity
Serial is treated the same way as sequences are with explicit sequence definitions. Although you can create a serial column with the serial keyword, when you export it through pg_dump, it loses its serial definition and looks like a plain sequence. This program also attempts to set the nextval (using setval) for all 3 types which have a valid last_value from the pg_sequences table.

Function Dependency Issues
If functions depend on other functions, creation may fail unless the referenced functions already exist. Possible solutions:

• Change the function language from SQL to PL/pgSQL.
• Set check_function_bodies = false.
  
  

The second option is usually preferred because SQL functions can benefit from optimizer features that may be lost when converting to PL/pgSQL. Simply execute this SET command before running clone_schema. In general, it is recommended to leave it ON at the global level, and override it at the session level for dependency case issues like this.

Regression Testing Overview

Regression Testing is done in the following order:

• Execute the sampledb.sql script to create the clone_testing database and the sample schema within it as the basis for the source schema.
• Clone the sample schema in the 3 ways possible (NODATA, DATA, DDLONLY).
• Run the schema_object_counts.sql queries to compare object counts and rows from the source and target schemas.
• Repeat all of the above for all supported versions of PG.

Assumptions

• Testing and validation is done only through the Community version of PostgreSQL.
• The target schema uses the same tablespace(s) as the source schema.

Limitations

• Only works for PG Versions 10 and up.
• Large Objects (LOs) are not suported, but bytea binary objects (associated with TOAST tables) are supported. See notes below.
• You should not clone the "public" schema. The resulting output may not be accurate even if it finishes without any errors.
• You should not use multiple, user-defined schema objects and expect cloning one schema to another to work. This project does not support that at the present time. It only supports 3 schemas basically: the source schema, the target schema, and objects defined in the public schema referenced by those user-defined schemas.
• This utility does not alter the contents within objects such as functions, procedures, triggers, etc. So any hard-coded schema references within them are not changed during the cloning process.
• Index and key names are not all the same in the cloned schema since some of the tables are created with the CREATE TABLE ... (LIKE ...) construct. Those index names are automatically fabricated by PG with naming format that is prepended with table and column names separated by underscores and ending with "_idx" or "_key". In DDLOnly mode, this will cause errors when attempting to make comments on indexes. Follow the NOTE in DDL output for lines you may want to comment out or fix.
• Foreign Tables are not handled at the present time. They must be done manually.
• Functional dependency order is not supported. If you have functions that depend on other functions, just make sure that you define them as language as PLPGSQL. Then the order does not matter, but if you define them as language SQL, dependency order is in play and you may get errors.

Note on Binary Data

This tool fully supports the bytea data type. However, Large Objects (LOs) referenced via OIDs are not currently supported for cloning. If your schema relies on pg_largeobject, the OID references will be copied, but the underlying binary data will not be duplicated.

Sponsor: http://elephas.io/

Compare cloning with EnterpriseDB's version that only works with their Advanced Server: https://www.enterprisedb.com/edb-docs/d/edb-postgres-advanced-server/user-guides/user-guide/11/EDB_Postgres_Advanced_Server_Guide.1.078.html