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doc: clarify hierarchy of objects: global, db, schema, etc.

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The previous wording was confusing because it wasn't in decreasing order
and had to backtrack.  Also clarify role/user wording.

Reported-by: jbird@nuna.com

Discussion: https://postgr.es/m/158057750885.1123.2806779262588618988@wrigleys.postgresql.org

Backpatch-through: 9.5
This commit is contained in:
Bruce Momjian 2020-03-31 18:10:39 -04:00
parent 046fd4f364
commit 009e422c1b
2 changed files with 14 additions and 17 deletions
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15
doc/src/sgml/ddl.sgml
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@ -2625,19 +2625,18 @@ SELECT * FROM information WHERE group_id = 2 FOR UPDATE;
</indexterm>
<para>
A <productname>PostgreSQL</productname> database cluster
contains one or more named databases. Users and groups of users are
shared across the entire cluster, but no other data is shared across
databases. Any given client connection to the server can access
only the data in a single database, the one specified in the connection
request.
A <productname>PostgreSQL</productname> database cluster contains
one or more named databases. Roles and a few other object types are
shared across the entire cluster. A client connection to the server
can only access data in a single database, the one specified in the
connection request.
</para>
<note>
<para>
Users of a cluster do not necessarily have the privilege to access every
database in the cluster. Sharing of user names means that there
cannot be different users named, say, <literal>joe</literal> in two databases
database in the cluster. Sharing of role names means that there
cannot be different roles named, say, <literal>joe</literal> in two databases
in the same cluster; but the system can be configured to allow
<literal>joe</literal> access to only some of the databases.
</para>

16
doc/src/sgml/manage-ag.sgml
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@ -22,15 +22,13 @@
</indexterm>
<para>
A database is a named collection of <acronym>SQL</acronym> objects
(<quote>database objects</quote>). Generally, every database
object (tables, functions, etc.) belongs to one and only one
database. (However there are a few system catalogs, for example
<literal>pg_database</literal>, that belong to a whole cluster and
are accessible from each database within the cluster.) More
accurately, a database is a collection of schemas and the schemas
contain the tables, functions, etc. So the full hierarchy is:
server, database, schema, table (or some other kind of object,
A small number of objects, like role, database, and tablespace
names, are defined at the cluster level and stored in the
<literal>pg_global</literal> tablespace. Inside the cluster are
multiple databases, which are isolated from each other but can access
cluster-level objects. Inside each database are multiple schemas,
which contain objects like tables and functions. So the full hierarchy
is: cluster, database, schema, table (or some other kind of object,
such as a function).
</para>