On 11/21/19 6:51 AM, Laurenz Albe wrote:
On Thu, 2019-11-21 at 06:55 -0500, stan wrote:
You can use tablespaces in PostgreSQL, which are directories on a
different file system, to put your data elsewhere.
But that has very limited use-cases, and normally you don't
create a tablespace.
About isolation:
- The different databases in a cluster are physically located in
the same tablespace, but they are logically strictly separated.
You cannot connect to one database and access another database from there.
dblink(https://www.postgresql.org/docs/11/dblink.html) and
FDW(https://www.postgresql.org/docs/11/sql-createforeigntable.html)
would beg to differ.
- There can be several schemas in a database.
There are several schemas in a database. In a new database:
test=# \dnS
List of schemas
Name | Owner
--------------------+----------
information_schema | postgres
pg_catalog | postgres
pg_temp_1 | postgres
pg_toast | postgres
pg_toast_temp_1 | postgres
public | postgres
You can access a table in a schema if you have the required privilege
on both the schema and the table.
This is entirely independent of physical storage, which is provided
by tablespaces. Tables from different databases can be located in the
same tablespace and vice versa.
Think of "database" and "schema" as a logical separation in SQL.
You cannot backup and restore an individual tablespace, only the
whole cluster.
Yours,
Laurenz Albe
--
Adrian Klaver
[email protected]
