On 10/29/21 09:43, Peter J. Holzer wrote:
On 2021-10-29 09:03:04 -0400, Mladen Gogala wrote:
On 10/29/21 08:49, Peter J. Holzer wrote:
I don't think that's equivalent. An Oracle instance is a runtime concept
(the collection of server processes on a single machine serving a single
database (the collection of files on the disk)) whereas a PostgreSQL cluster is
both a data and a runtime concept (config + data files for several
databases with some shared data + the processes serving them). Also
instance:database is n:1 while cluster to database is 1:n. Very
different.
Peter, Oracle instance manages collection of the databases and is ensuring
recoverabilty using redo logs, which are completely analogous to WAL logs,
if managed a bit differently. Let's not be nitpicking here. Oracle instance
is completely analogous to Postgres cluster. If you ask me, the word cluster
was picked to avoid the word "instance"
I'm quoting Tom Kyte here:
| In fact, it is true to say that an instance will mount and open at
| most a single database in its entire lifetime!
While that article is originally from 2009, it was last changed in 2021,
and I'd trust Tom to change something as fundamental if it wasn't true
anymore.
hp
Few days ago, in july 2013, Oracle has introduced version 12c with
multi-tenant option.
http://appstech.com/2013/08/oracle-announces-general-availability-of-oracle-database-12c-the-first-database-designed-for-the-cloud/
Each Oracle instance can now manage up to 255 pluggable databases which
are, for all intents and purposes, equivalent to Postgres databases, if
somewhat more awkward. The "unplug" and "plug in" operations leave a lot
of room for improvement. That makes Oracle instance functionally
equivalent to the Postgres cluster. Current Oracle version, 21c no
longer supports flat architecture, without pluggable databases.
--
Mladen Gogala
Database Consultant
Tel: (347) 321-1217
https://dbwhisperer.wordpress.com
