Обсуждение: A few comparison terms just to be sure.

Hi everyone.
For a long time I've been an Oracle developer and administrator but recently
I became seduced by what I read about Postgresql. So I downloaded and
installed a server and I'm reading the docs right now, ready to start
practicing.
Just to feel at home, I would like to make a few comparisons between oracle
and postgresql and I hope somebody can confirm if I'm right or not.
The questions:
1- What I know as an oracle database (a group of schemas), in postgresql is
called a cluster. Is that right?
2- what I know as "schema", in postgresql is called a "database"?
3- Every user is the superuser of his own schema/database but is there a
SYS/SYSMAN/SYSTEM (DBA) user who has access to all "databases"? I place
where I can log in and control what everyone is doing?
4- What in Oracle is the SYSTEM/SYSAUX schema (where all oracle's own
objects reside) is the "postgres" database (I didn't find this schema
although I read about in the docs: chapter 16.2)?

I know these are pretty simple question and I'm really thankful in advance
for any comments.

Regards.

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"Dale Cooper" <sa_dale_cooper@hotmail.com> writes:
> The questions:
> 1- What I know as an oracle database (a group of schemas), in postgresql is
> called a cluster. Is that right?

No.  A group of schemas is a database, a group of databases is a cluster
(a/k/a installation).  I think the SQL-spec term for what we call a
database is a "catalog"; not sure if Oracle uses that terminology.

> 2- what I know as "schema", in postgresql is called a "database"?

No, it's called a schema.  (Or at least it is if Oracle uses the spec
terminology.)

> 3- Every user is the superuser of his own schema/database but is there a
> SYS/SYSMAN/SYSTEM (DBA) user who has access to all "databases"? I place
> where I can log in and control what everyone is doing?

In the first place, an ordinary user isn't "the superuser" of anything;
he may own a table or a schema or a database but that doesn't give him
superuser privileges, only the ability to drop or modify that object.
The OS user that created the installation is a true superuser --- the
documentation always refers to this user as "postgres" but you don't
necessarily have to run Postgres under that username.

> 4- What in Oracle is the SYSTEM/SYSAUX schema (where all oracle's own
> objects reside) is the "postgres" database (I didn't find this schema
> although I read about in the docs: chapter 16.2)?

Perhaps you are looking for the pg_catalog schema.  See chapter 43
(system catalogs).

            regards, tom lane

>From: Tom Lane <tgl@sss.pgh.pa.us>
>To: "Dale Cooper" <sa_dale_cooper@hotmail.com>
>CC: pgsql-novice@postgresql.org
>Subject: Re: [NOVICE] A few comparison terms just to be sure. Date: Sun, 01
>Jul 2007 17:54:38 -0400
>
>"Dale Cooper" <sa_dale_cooper@hotmail.com> writes:
> > The questions:
> > 1- What I know as an oracle database (a group of schemas), in postgresql
>is
> > called a cluster. Is that right?
>
>No.  A group of schemas is a database, a group of databases is a cluster
>(a/k/a installation).  I think the SQL-spec term for what we call a
>database is a "catalog"; not sure if Oracle uses that terminology.
>
> > 2- what I know as "schema", in postgresql is called a "database"?
>
>No, it's called a schema.  (Or at least it is if Oracle uses the spec
>terminology.)
>
> > 3- Every user is the superuser of his own schema/database but is there a
> > SYS/SYSMAN/SYSTEM (DBA) user who has access to all "databases"? I place
> > where I can log in and control what everyone is doing?
>
>In the first place, an ordinary user isn't "the superuser" of anything;
>he may own a table or a schema or a database but that doesn't give him
>superuser privileges, only the ability to drop or modify that object.
>The OS user that created the installation is a true superuser --- the
>documentation always refers to this user as "postgres" but you don't
>necessarily have to run Postgres under that username.
>
> > 4- What in Oracle is the SYSTEM/SYSAUX schema (where all oracle's own
> > objects reside) is the "postgres" database (I didn't find this schema
> > although I read about in the docs: chapter 16.2)?
>
>Perhaps you are looking for the pg_catalog schema.  See chapter 43
>(system catalogs).
>
>            regards, tom lane
Thanks Tom for your time and really quick answer (it seems I need to keep up
reading :)).

Regards.

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