How Does GaussDB(DWS) Implement Workload Isolation?

Workload Isolation

In GaussDB(DWS), you can isolate workloads through database and schema configurations. Their differences are as follows:

• Databases cannot communicate with each other and share very few resources. Their connections and permissions can be isolated.
• Schemas share more resources than databases do. User permissions on schemas and subordinate objects can be flexibly configured using the GRANT and REVOKE syntax.

DATABASE

A database is a physical collection of database objects. Resources of different databases are completely isolated (except some shared objects). Databases are used to isolate workloads. Objects in different databases cannot access each other. For example, objects in Database B cannot be accessed in Database A. Therefore, when logging in to a cluster, you must connect to the specified database.

SCHEMA

In a database, database objects are logically divided and isolated based on schemas.

With permission management, you can access and operate objects in different schemas in the same session. Schemas contain objects that applications may access, such as tables, indexes, data in various types, functions, and operators.

Database objects with the same name cannot exist in the same schema, but object names in different schemas can be the same.

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gaussdb=> CREATE SCHEMA myschema;
CREATE SCHEMA
gaussdb=> CREATE SCHEMA myschema_1;
CREATE SCHEMA

gaussdb=> CREATE TABLE myschema.t1(a int, b int) DISTRIBUTE BY HASH(b);
CREATE TABLE
gaussdb=> CREATE TABLE myschema.t1(a int, b int) DISTRIBUTE BY HASH(b);
ERROR:  relation "t1" already exists
gaussdb=> CREATE TABLE myschema_1.t1(a int, b int) DISTRIBUTE BY HASH(b);
CREATE TABLE

Schemas logically divide workloads. These workloads are interdependent with the schemas. Therefore, if a schema contains objects, deleting it will cause errors with dependency information displayed.

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gaussdb=> DROP SCHEMA myschema_1;
ERROR: cannot drop schema myschema_1 because other objects depend on it 
Detail: table myschema_1.t1 depends on schema myschema_1 
Hint: Use DROP ... CASCADE to drop the dependent objects too.

When a schema is deleted, the CASCADE option is used to delete the objects that depend on the schema.

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gaussdb=> DROP SCHEMA myschema_1 CASCADE;
NOTICE:  drop cascades to table myschema_1.t1
gaussdb=> DROP SCHEMA

USER/ROLE

Users and roles are used to implement permission control on the database server (cluster). They are the owners and executors of cluster workloads and manage all object permissions in clusters. A role is not confined in a specific database. However, when it logs in to the cluster, it must explicitly specify a user name to ensure the transparency of the operation. A user's permissions to a database can be specified through permission management.

A user is the subject of permissions. Permission management is actually the process of deciding whether a user is allowed to perform operations on database objects.

Permissions Management

Permission management in GaussDB(DWS) falls into three categories:

• System permission

  System permissions are also called user attributes, including SYSADMIN, CREATEDB, CREATEROLE, AUDITADMIN, and LOGIN.

  They can be specified only by the CREATE ROLE or ALTER ROLE syntax. The SYSADMIN permission can be granted and revoked using GRANT ALL PRIVILEGE and REVOKE ALL PRIVILEGE, respectively. System permissions cannot be inherited by a user from a role, and cannot be granted using PUBLIC.

• Permissions

  Grant a role's or user's permissions to one or more roles or users. In this case, every role or user can be regarded as a set of one or more database permissions.

  If WITH ADMIN OPTION is specified, the member can in turn grant permissions in the role to others, and revoke permissions in the role as well. If a role or user granted with certain permissions is changed or revoked, the permissions inherited from the role or user also change.

  A database administrator can grant permissions to and revoke them from any role or user. Roles having CREATEROLE permission can grant or revoke membership in any role that is not an administrator.

• Object permission

  Permissions on a database object (table, view, column, database, function, schema, or tablespace) can be granted to a role or user. The GRANT command can be used to grant permissions to a user or role. These permissions granted are added to the existing ones.

Schema Isolation Example

Example 1:

By default, the owner of a schema has all permissions on objects in the schema, including the delete permission. The owner of a database has all permissions on objects in the database, including the delete permission. Therefore, you are advised to strictly control the creation of databases and schemas. Create databases and schemas as an administrator and assign related permissions to users.

1. Assign the permission to create schemas in the testdb database to user user_1 as user dbadmin.

   1 2	testdb=> GRANT CREATE ON DATABASE testdb to user_1; GRANT

2. Switch to user user_1.

   1 2	testdb=> SET SESSION AUTHORIZATION user_1 PASSWORD '********'; SET

   Create a schema named myschema_2 in the testdb database as user_1.

   1 2	testdb=> CREATE SCHEMA myschema_2; CREATE SCHEMA

3. Switch to the administrator dbadmin.

   1 2	testdb=> RESET SESSION AUTHORIZATION; RESET

   Create table t1 in schema myschema_2 as the administrator dbadmin.

   1 2	testdb=> CREATE TABLE myschema_2.t1(a int, b int) DISTRIBUTE BY HASH(b); CREATE TABLE

4. Switch to user user_1.

   1 2	testdb=> SET SESSION AUTHORIZATION user_1 PASSWORD '********'; SET

   Delete table t1 created by administrator dbadmin in schema myschema_2 as user user_1.

   1 2	testdb=> drop table myschema_2.t1; DROP TABLE

Example 2:

Due to the logical isolation of schemas, database objects need to be verified at both the schema level and the object level.

1. Grant the permission on the myschema.t1 table to user_1.

   1 2	gaussdb=> GRANT SELECT ON TABLE myschema.t1 TO user_1; GRANT

2. Switch to user user_1.

   1 2	SET SESSION AUTHORIZATION user_1 PASSWORD '********'; SET

   Query the table myschema.t1.

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   gaussdb=> SELECT * FROM myschema.t1; ERROR: permission denied for schema myschema LINE 1: SELECT * FROM myschema.t1;

3. Switch to the administrator dbadmin.

   1 2	gaussdb=> RESET SESSION AUTHORIZATION; RESET

   Grant the permission on the myschema.t1 table to user user_1.

   1 2	gaussdb=> GRANT USAGE ON SCHEMA myschema TO user_1; GRANT

4. Switch to user user_1.

   1 2	gaussdb=> SET SESSION AUTHORIZATION user_1 PASSWORD '********'; SET

   Query the table myschema.t1.

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   gaussdb=> SELECT * FROM myschema.t1; a | b ---+--- (0 rows)