Schemas: status report, call for developers
Current CVS tip has most of the needed infrastructure for SQL-spec
schema support: you can create schemas, and you can create objects
within schemas, and search-path-based lookup for named objects works.
There's still a number of things to be done in the backend, but it's
time to start working on schema support in the various frontends that
have been broken by these changes. I believe that pretty much every
frontend library and client application that looks at system catalogs
will need revisions. So, this is a call for help --- I don't have the
time to fix all the frontends, nor sufficient familiarity with many
of them.
JDBC and ODBC metadata code is certainly broken; so are the catalog
lookups in pgaccess, pgadmin, and so on. psql and pg_dump are broken
as well (though I will take responsibility for fixing pg_dump, and will
then look at psql if no one else has done it by then). I'm not even
sure what else might need to change.
Here's an example of what's broken:
test=# create schema foo;
CREATE
test=# create table foo.mytab (f1 int, f2 text);
CREATE
test=# create schema bar;
CREATE
test=# create table bar.mytab (f1 text, f3 int);
CREATE
test=# \d mytab
Table "mytab"
Column | Type | Modifiers
--------+---------+-----------
f1 | text |
f1 | integer |
f2 | text |
f3 | integer |
psql's \d command hasn't the foggiest idea that there might now be more
than one pg_class entry with the same relname. It needs to be taught
about that --- but even before that, we need to work out schema-aware
definitions of the wildcard expansion rules for psql's backslash
commands that accept wildcarded names. In the above example, probably
"\d mytab" should have said "no such table" --- because neither foo nor
bar were in my search path, so I should not see them unless I give a
qualified name (eg, "\d foo.mytab" or "\d bar.mytab"). For commands
that accept wildcard patterns, what should happen --- should "\z my*"
find these tables, if they're not in my search path? Is "\z f*.my*"
sensible to support? I dunno yet.
If you've got time to work on fixing frontend code, or even helping
to work out definitional questions like these, please check out current
CVS tip or a nightly snapshot tarball and give it a try. (But do NOT
put any valuable data into current sources --- until pg_dump is fixed,
you won't be able to produce a useful backup of a database that uses
multiple schemas.)
Some documentation can be found at
http://developer.postgresql.org/docs/postgres/sql-naming.html
http://developer.postgresql.org/docs/postgres/sql-createschema.html
http://developer.postgresql.org/docs/postgres/sql-grant.html
http://developer.postgresql.org/docs/postgres/runtime-config.html#RUNTIME-CONFIG-GENERAL (see SEARCH_PATH)
but more needs to be written. (In particular, I think the Tutorial
could stand to have a short section added about schemas; and the Admin
Guide ought to be revised to discuss running one database with per-user
schemas as a good alternative to per-user databases. Any volunteers to
write that stuff?)
Some things that don't work yet in the backend:
1. There's no DROP SCHEMA. (If you need to, you can drop the contained
objects and then manually delete the pg_namespace row for the schema.)
No ALTER SCHEMA RENAME either (though you can just UPDATE the
pg_namespace row if you need that).
2. CREATE SCHEMA with sub-statements isn't up to SQL spec requirements
yet. Best bet is to create the schema and then create contained objects
separately, as in the above example.
3. I'm not sure that the newly-defined GRANT privileges are all checked
everywhere they should be. Also, the default privilege settings
probably need fine-tuning still.
4. We probably need more helper functions and/or predefined system views
to make it possible to fix the frontends in a reasonable way --- for
example, it's still quite difficult for something looking at pg_class to
determine which tables are visible in the current search path. Thoughts
about what should be provided are welcome.
regards, tom lane
<snip>
Here's an example of what's broken:
test=# create schema foo;
CREATE
test=# create table foo.mytab (f1 int, f2 text);
CREATE
test=# create schema bar;
CREATE
test=# create table bar.mytab (f1 text, f3 int);
CREATE
test=# \d mytab
Table "mytab"
Column | Type | Modifiers
--------+---------+-----------
f1 | text |
f1 | integer |
f2 | text |
f3 | integer |
I would think this should produce the following:
Table "bar.mytab"
Column | Type | Modifiers
--------+---------+-----------
f1 | text |
f1 | integer |
Table "foo.mytab"
Column | Type | Modifiers
--------+---------+-----------
f2 | text |
f3 | integer |
What do you think?
- Bill Cunningham
Bill Cunningham <billc@ballydev.com> writes:
I would think this should produce the following:
test=# \d mytab
Table "bar.mytab"
Column | Type | Modifiers
--------+---------+-----------
f1 | text |
f1 | integer |
Table "foo.mytab"
Column | Type | Modifiers
--------+---------+-----------
f2 | text |
f3 | integer |
Even when schemas bar and foo are not in your search path? (And,
perhaps, not even accessible to you?)
My gut feeling is that "\d mytab" should tell you about the same
table that "select * from mytab" would find. Anything else is
probably noise to you --- if you wanted to know about foo.mytab,
you could say "\d foo.mytab".
However, \d is not a wildcardable operation AFAIR. For the commands
that do take wildcard patterns (like \z), I'm not as sure what should
happen.
regards, tom lane
I think DBD::Pg driver very much depends on system tables.
Hope, Jeffrey (current maintainer) is online.
regards,
Oleg
On Tue, 30 Apr 2002, Tom Lane wrote:
Current CVS tip has most of the needed infrastructure for SQL-spec
schema support: you can create schemas, and you can create objects
within schemas, and search-path-based lookup for named objects works.
There's still a number of things to be done in the backend, but it's
time to start working on schema support in the various frontends that
have been broken by these changes. I believe that pretty much every
frontend library and client application that looks at system catalogs
will need revisions. So, this is a call for help --- I don't have the
time to fix all the frontends, nor sufficient familiarity with many
of them.JDBC and ODBC metadata code is certainly broken; so are the catalog
lookups in pgaccess, pgadmin, and so on. psql and pg_dump are broken
as well (though I will take responsibility for fixing pg_dump, and will
then look at psql if no one else has done it by then). I'm not even
sure what else might need to change.Here's an example of what's broken:
test=# create schema foo;
CREATE
test=# create table foo.mytab (f1 int, f2 text);
CREATE
test=# create schema bar;
CREATE
test=# create table bar.mytab (f1 text, f3 int);
CREATE
test=# \d mytab
Table "mytab"
Column | Type | Modifiers
--------+---------+-----------
f1 | text |
f1 | integer |
f2 | text |
f3 | integer |psql's \d command hasn't the foggiest idea that there might now be more
than one pg_class entry with the same relname. It needs to be taught
about that --- but even before that, we need to work out schema-aware
definitions of the wildcard expansion rules for psql's backslash
commands that accept wildcarded names. In the above example, probably
"\d mytab" should have said "no such table" --- because neither foo nor
bar were in my search path, so I should not see them unless I give a
qualified name (eg, "\d foo.mytab" or "\d bar.mytab"). For commands
that accept wildcard patterns, what should happen --- should "\z my*"
find these tables, if they're not in my search path? Is "\z f*.my*"
sensible to support? I dunno yet.If you've got time to work on fixing frontend code, or even helping
to work out definitional questions like these, please check out current
CVS tip or a nightly snapshot tarball and give it a try. (But do NOT
put any valuable data into current sources --- until pg_dump is fixed,
you won't be able to produce a useful backup of a database that uses
multiple schemas.)Some documentation can be found at
http://developer.postgresql.org/docs/postgres/sql-naming.html
http://developer.postgresql.org/docs/postgres/sql-createschema.html
http://developer.postgresql.org/docs/postgres/sql-grant.html
http://developer.postgresql.org/docs/postgres/runtime-config.html#RUNTIME-CONFIG-GENERAL (see SEARCH_PATH)
but more needs to be written. (In particular, I think the Tutorial
could stand to have a short section added about schemas; and the Admin
Guide ought to be revised to discuss running one database with per-user
schemas as a good alternative to per-user databases. Any volunteers to
write that stuff?)Some things that don't work yet in the backend:
1. There's no DROP SCHEMA. (If you need to, you can drop the contained
objects and then manually delete the pg_namespace row for the schema.)
No ALTER SCHEMA RENAME either (though you can just UPDATE the
pg_namespace row if you need that).2. CREATE SCHEMA with sub-statements isn't up to SQL spec requirements
yet. Best bet is to create the schema and then create contained objects
separately, as in the above example.3. I'm not sure that the newly-defined GRANT privileges are all checked
everywhere they should be. Also, the default privilege settings
probably need fine-tuning still.4. We probably need more helper functions and/or predefined system views
to make it possible to fix the frontends in a reasonable way --- for
example, it's still quite difficult for something looking at pg_class to
determine which tables are visible in the current search path. Thoughts
about what should be provided are welcome.regards, tom lane
---------------------------(end of broadcast)---------------------------
TIP 4: Don't 'kill -9' the postmaster
Regards,
Oleg
_____________________________________________________________
Oleg Bartunov, sci.researcher, hostmaster of AstroNet,
Sternberg Astronomical Institute, Moscow University (Russia)
Internet: oleg@sai.msu.su, http://www.sai.msu.su/~megera/
phone: +007(095)939-16-83, +007(095)939-23-83
-----Original Message-----
From: Tom Lane [mailto:tgl@sss.pgh.pa.us]
Sent: 30 April 2002 18:32
To: pgsql-hackers@postgresql.org; pgsql-interfaces@postgresql.org
Subject: [INTERFACES] Schemas: status report, call for developersCurrent CVS tip has most of the needed infrastructure for
SQL-spec schema support: you can create schemas, and you can
create objects within schemas, and search-path-based lookup
for named objects works. There's still a number of things to
be done in the backend, but it's time to start working on
schema support in the various frontends that have been broken
by these changes. I believe that pretty much every frontend
library and client application that looks at system catalogs
will need revisions. So, this is a call for help --- I don't
have the time to fix all the frontends, nor sufficient
familiarity with many of them.JDBC and ODBC metadata code is certainly broken; so are the
catalog lookups in pgaccess, pgadmin, and so on. psql and
pg_dump are broken as well (though I will take responsibility
for fixing pg_dump, and will then look at psql if no one else
has done it by then). I'm not even sure what else might need
to change.
Thanks Tom, this is just the post I've been waiting for!
To anyone thinking of hacking pgAdmin at the moment -> now would
probably not be the best time as I will be *seriously* restructuring
pgSchema.
Regards, Dave.
Import Notes
Resolved by subject fallback
Tom Lane wrote:
Bill Cunningham <billc@ballydev.com> writes:
I would think this should produce the following:
test=# \d mytab
Table "bar.mytab"
Column | Type | Modifiers
--------+---------+-----------
f1 | text |
f1 | integer |Table "foo.mytab"
Column | Type | Modifiers
--------+---------+-----------
f2 | text |
f3 | integer |Even when schemas bar and foo are not in your search path? (And,
perhaps, not even accessible to you?)My gut feeling is that "\d mytab" should tell you about the same
table that "select * from mytab" would find. Anything else is
probably noise to you --- if you wanted to know about foo.mytab,
you could say "\d foo.mytab".However, \d is not a wildcardable operation AFAIR. For the commands
that do take wildcard patterns (like \z), I'm not as sure what should
happen.regards, tom lane
So we now have a default schema name of the current user? For example:
foobar@somewhere> psql testme
testme=# select * from mytab
Table "foobar.mytab"
Column | Type | Modifiers
--------+---------+-----------
f2 | text |
f3 | integer |
like that? This is exactly how DB2 operates, implict schemas for each user.
- Bill Cunningham
Bill Cunningham <billc@ballydev.com> writes:
So we now have a default schema name of the current user?
... This is exactly how DB2 operates, implict schemas for each user.
You can operate that way. It's not the default though; the DBA will
have to explicitly do a CREATE SCHEMA for each user. For instance:
test=# CREATE USER tgl;
CREATE USER
test=# CREATE SCHEMA tgl AUTHORIZATION tgl;
CREATE
test=# \c - tgl
You are now connected as new user tgl.
test=> select current_schemas();
current_schemas
-----------------
{tgl,public} -- my search path is now tgl, public
(1 row)
-- this creates tgl.foo:
test=> create table foo(f1 int);
CREATE
test=> select * from foo;
f1
----
(0 rows)
test=> select * from tgl.foo;
f1
----
(0 rows)
If you don't create schemas then you get backwards-compatible behavior
(all the users end up sharing the "public" schema as their current
schema).
See the development-docs pages I mentioned before for details.
regards, tom lane
For commands
that accept wildcard patterns, what should happen --- should "\z my*"
find these tables, if they're not in my search path? Is "\z f*.my*"
sensible to support? I dunno yet.
Technical question - this query:
SELECT nspname AS schema,
relname AS object
FROM pg_class c
INNER JOIN pg_namespace n
ON c.relnamespace=n.oid
WHERE relkind in ('r', 'v', 'S') AND
relname NOT LIKE 'pg$_%%' ESCAPE '$'
produces a result like this:
schema | object
--------+--------
public | abc
foo | abc
foo | xyz
bar | xyz
(4 rows)
How can I restrict the query to the schemas in the
current search path, i.e. the schema names returned
by SELECT current_schemas() ?
Ian Barwick
JDBC and ODBC metadata code is certainly broken; so are the
catalog lookups in pgaccess, pgadmin, and so on. psql and
pg_dump are broken as well (though I will take responsibility
for fixing pg_dump, and will then look at psql if no one else
has done it by then). I'm not even sure what else might need
to change.
phpPgAdmin (WebDB) will be broken as well. I think myself and at least a
few other committers lurk here tho.
Other things that will break:
TOra
Various KDE interfaces
Chris
test=# CREATE USER tgl;
CREATE USER
test=# CREATE SCHEMA tgl AUTHORIZATION tgl;
CREATE
What about "CREATE USER tgl WITH SCHEMA;" ?
Which will implicitly do a "CREATE SCHEMA tgl AUTHORIZATION tgl;"
Chris
produces a result like this:
schema | object
--------+--------
public | abc
foo | abc
foo | xyz
bar | xyz
(4 rows)How can I restrict the query to the schemas in the
current search path, i.e. the schema names returned
by SELECT current_schemas() ?
Now, if we had functions-returning-sets, this would all be easy as all you'd
need to do would be to join it with the function returning the set of
schemas in your search path :)
Chris
"Christopher Kings-Lynne" <chriskl@familyhealth.com.au> writes:
What about "CREATE USER tgl WITH SCHEMA;" ?
Uh, what about it? It's not a standard syntax AFAIK.
If I were running an installation where I wanted "one schema per user"
as default, I'd rather have an "auto_create_schema" SET parameter that
told CREATE USER to do the dirty work for me automatically.
But the sneaky part of this is that users are installation-wide,
whereas schemas are only database-wide. To make this really work
painlessly, you'd want some kind of mechanism that'd auto-create
a schema for the user in every database he's allowed access to.
How can we define that cleanly?
regards, tom lane
On Wed, May 01, 2002 at 10:05:23AM +0800, Christopher Kings-Lynne wrote:
phpPgAdmin (WebDB) will be broken as well. I think myself and at least a
few other committers lurk here tho.Other things that will break:
TOra
Various KDE interfaces
GNUe will break, as well.
Ross
I think it would be much faster simply to list of the programs that
use Postgresql internals that won't break.
--
Rod
----- Original Message -----
From: "Ross J. Reedstrom" <reedstrm@rice.edu>
To: "Christopher Kings-Lynne" <chriskl@familyhealth.com.au>
Cc: "Dave Page" <dpage@vale-housing.co.uk>; "Tom Lane"
<tgl@sss.pgh.pa.us>; <pgsql-hackers@postgresql.org>;
<pgsql-interfaces@postgresql.org>; <pgadmin-hackers@postgresql.org>
Sent: Tuesday, April 30, 2002 11:28 PM
Subject: Re: [HACKERS] [INTERFACES] Schemas: status report, call for
developers
On Wed, May 01, 2002 at 10:05:23AM +0800, Christopher Kings-Lynne
wrote:
phpPgAdmin (WebDB) will be broken as well. I think myself and at
least a
few other committers lurk here tho.
Other things that will break:
TOra
Various KDE interfacesGNUe will break, as well.
Ross
---------------------------(end of
broadcast)---------------------------
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"Ross J. Reedstrom" <reedstrm@rice.edu> writes:
GNUe will break, as well.
Do I hear a volunteer to fix it?
regards, tom lane
"Rod Taylor" <rbt@zort.ca> writes:
I think it would be much faster simply to list of the programs that
use Postgresql internals that won't break.
Approximately none, I'm sure :-(. This thread isn't about that, it's
about stirring up the troops to fix everything that must be fixed.
regards, tom lane
Ian Barwick <barwick@gmx.net> writes:
How can I restrict the query to the schemas in the
current search path, i.e. the schema names returned
by SELECT current_schemas() ?
Well, this is the issue open for public discussion.
We could define some function along the lines of
"is_visible_table(oid) returns bool", and then you could use
that as a WHERE clause in your query. But I'm worried about
the performance implications --- is_visible_table() would have
to do several retail probes of the system tables, and I don't
see any way to optimize that across hundreds of table OIDs.
I have a nagging feeling that this could be answered by defining
a view on pg_class that only shows visible tables ... but I don't
quite see how to define that efficiently, either. Ideas anyone?
regards, tom lane
On Wed, May 01, 2002 at 12:03:00AM -0400, Tom Lane wrote:
"Ross J. Reedstrom" <reedstrm@rice.edu> writes:
GNUe will break, as well.
Do I hear a volunteer to fix it?
I'm willing to implement whatever clever solution we all come up with.
I'll have to coordinate w/ the GNUe IRC folks to get it checked in.
Ross
"Ross J. Reedstrom" <reedstrm@rice.edu> writes:
GNUe will break, as well.
I'm willing to implement whatever clever solution we all come up with.
If you need help in inventing a solution, it'd be a good idea to explain
the problem. Personally I'm not familiar with GNUe ...
regards, tom lane
On Wed, May 01, 2002 at 12:56:00AM -0400, Tom Lane wrote:
"Ross J. Reedstrom" <reedstrm@rice.edu> writes:
GNUe will break, as well.
I'm willing to implement whatever clever solution we all come up with.
If you need help in inventing a solution, it'd be a good idea to explain
the problem. Personally I'm not familiar with GNUe ...
I think all the interfaces are having the same fundemental problem: how to
limit the tables 'seen' to a particular list of schema (those in the path).
GNUe is GNU Enterprise System - a somewhat grandiose name for a business
middleware solutions project. It's highly modular, with a common core to
deal with things like DB access. There's a reasonably nice forms designer
to handle quickie 2-tier DB apps (client-server, skip the middleware).
Right now, it's mostly coded in python. I'm taking off on a
business trip for the remainder of the week, starting tomorrow (err
today?!) morning. I'll take the GNUe code along and see what it's db
schema discovery code is actually doing, and think about what sort of
clever things to do. I think for GNUe, we might get away with requiring
the end-user (designer) to select a particular schema to work in, and then
just qualify everything.
Later,
Ross
Tom Lane wrote:
psql's \d command hasn't the foggiest idea that there might now be more
than one pg_class entry with the same relname. It needs to be taught
about that --- but even before that, we need to work out schema-aware
definitions of the wildcard expansion rules for psql's backslash
commands that accept wildcarded names. In the above example, probably
"\d mytab" should have said "no such table" --- because neither foo nor
bar were in my search path, so I should not see them unless I give a
qualified name (eg, "\d foo.mytab" or "\d bar.mytab").
(and also in mail to Bill Cunningham)
My gut feeling is that "\d mytab" should tell you about the same
table that "select * from mytab" would find. Anything else is
probably noise to you --
General consistency with SELECT behaviour sounds right to me.
For commands
that accept wildcard patterns, what should happen --- should "\z my*"
find these tables, if they're not in my search path? Is "\z f*.my*"
sensible to support? I dunno yet.
My digestive organs tell me: an unqualified wildcard pattern should
stick to the search path; the search path should only be overridden
when the user explicitly provides a wildcard pattern for schema names.
This would be consistent with the behaviour of \d etc., i.e.
"\d mytab" should look for 'mytab' in the current search path;
"\dt my*" should look for tables beginning with "my" in the current
search path; "\dt f*.my*" would look for same in all schemas beginning
with "f"; and "\dt *.my*" would look in all schemas.
Problem: "wildcard pattern" is a bit of a misnomer, the relevant
commands take regular expressions, which means the dot in "\z f*.my*"
won't necessarily be the dot in "\z foo.mytab" - it would have to
be written "\z f*\\.my*". Though technically correct this
strikes me as counterintuitive, especially with the double escaping
(once for psql, once for the regex literal).
An alternative solution would be to allow the pattern matching
commands to accept either one ("\z my*") or two ("\z f* my*") regular
expressions; in the latter case the first regex is for the schema name,
the second for the object name. However, doing away with the dot altogether
is also counterintuitive and breaks with the usual schema denotation.
Proposal: in "wildcard" slash commands drop regular expressions and
use LIKE for pattern matching. This would enable commands such as
"\z f%.my%". (Would this mean major breakage? Is there an installed
base of scripts which rely on psql slash commands and regular expressions?)
I can't personally recall ever having needed to use a regular expression
any more complex than the wildcard pattern matching which could be implemented
just as well with LIKE. (Anyone requiring regular expression matching could
still create appropriate views).
Question - which output format is preferable?:
schema_test=# \z
Access privileges for database "schema_test"
Schema | Object | Access privileges
--------+--------+-------------------
public | bar |
foo | bar |
(2 rows)
or
schema_test=# \z
Access privileges for database "schema_test"
Object | Access privileges
------------+-------------------
public.bar |
foo.bar |
(2 rows)
If you've got time to work on fixing frontend code, or even helping
to work out definitional questions like these (...)
Hmm, time for "ask not what your database can do for you but what
you can do for your database". I'm willing to put my keyboard where
my mouth is and take on psql once any outstanding questions are
cleared up, if noone better qualified than me comes
forward and provided someone takes a critical look at anything I do.
Yours
Ian Barwick
On Tue, Apr 30, 2002 at 09:41:47PM +0300, Oleg Bartunov wrote:
I think DBD::Pg driver very much depends on system tables.
Hope, Jeffrey (current maintainer) is online.
These changes may break DBD::Pg. What is the expected
time of this release? I will review my code for impact.
Thanks for the warning,
Jeffrey
On Thu, 2 May 2002, Ian Barwick wrote:
Tom Lane wrote:
[snipped]My gut feeling is that "\d mytab" should tell you about the same
table that "select * from mytab" would find. Anything else is
probably noise to you --General consistency with SELECT behaviour sounds right to me.
I take it temporary tables are going to be included in such a list, since that
would seem sensible from the SELECT behaviour point of view, and may be even
also from the user's point of view.
So, how does one determine the current schema for temporary tables, i.e. what
name would be in search_path if it wasn't implicitly included? (Just throwing
ideas around in my head)
--
Nigel J. Andrews
Director
---
Logictree Systems Limited
Computer Consultants
"Nigel J. Andrews" <nandrews@investsystems.co.uk> writes:
So, how does one determine the current schema for temporary tables,
i.e. what name would be in search_path if it wasn't implicitly included?
The temp schema is pg_temp_nnn where nnn is your BackendId (PROC array
slot number). AFAIK there isn't any exported way to determine your
BackendId from an SQL query. Another problem is that the pg_temp
schema is "lazily evaluated" --- it's not actually attached to and
cleaned out until you first try to create a temp table in a particular
session. This seems a clear win from a performance point of view,
but it makes life even more difficult for queries that are trying to
determine which pg_class entries are visible in one's search path.
I have already had occasion to write subroutines that answer the
question "is this relation (resp. type, function, operator) visible
in the current search path?" --- where visible means not just that
its namespace is in the path, but that this object is the frontmost
entry of its particular name. Perhaps it'd make sense to export these
routines as SQL functions, along the lines of "relation_is_visible(oid)
returns bool". Then one could use queries similar to
select * from pg_class p
where p.relname like 'match_pattern'
and relation_is_visible(p.oid);
to implement a psql command that requires finding tables matching
an (unqualified) relation-name pattern. The tables found would be
only those that you could reference with unqualified table names.
This doesn't yield much insight about cases where the match pattern
includes a (partial?) schema-name specification, though. If I'm
allowed to write something like "\z s*.t*" to find tables beginning
with t in schemas beginning with s, should that include all schemas
beginning with s? Only those in my search path (probably wrong)?
Only those that I have USAGE privilege on? Not sure.
regards, tom lane
On Thu, 2002-05-02 at 05:33, Tom Lane wrote:
"Nigel J. Andrews" <nandrews@investsystems.co.uk> writes:
So, how does one determine the current schema for temporary tables,
i.e. what name would be in search_path if it wasn't implicitly included?The temp schema is pg_temp_nnn where nnn is your BackendId (PROC array
slot number). AFAIK there isn't any exported way to determine your
BackendId from an SQL query.
The non-portable way on Linux RH 7.2 :
create function getpid() returns int as '/lib/libc.so.6','getpid' language 'C';
CREATE
select getpid()
getpid1
---------
31743
(1 row)
I think that useful libc stuff things like this should be put in some
special schema, initially available to superusers only.
perhaps LIBC.GETPID()
----------
Hannu
On Thursday 02 May 2002 05:33, Tom Lane wrote:
[on establishing whether a relation is in the search path]
This doesn't yield much insight about cases where the match pattern
includes a (partial?) schema-name specification, though. If I'm
allowed to write something like "\z s*.t*" to find tables beginning
with t in schemas beginning with s, should that include all schemas
beginning with s? Only those in my search path (probably wrong)?
Only those that I have USAGE privilege on? Not sure.
If namespace privileges are based around the Unix directory/file protection
model (as you stated in another thread, see:
http://geocrawler.com/archives/3/10/2002/4/450/8433871/ ), then
a wildcard search on the schema name should logically include
all visible schemas, not just the ones where the user has USAGE privilege.
Or put it another way, is there any reason to exclude information from
say \z which the user can find out by querying pg_class? At the moment
(at least in CVS from 30.4.02) a user can see permissions on tables in schemas
on which he/she has no USAGE privileges:
template1=# create database schema_test;
CREATE DATABASE
template1=# \c schema_test
You are now connected to database schema_test.
schema_test=# create schema foo;
CREATE
schema_test=# create table foo.bar (pk int, txt text);
CREATE
schema_test=# create schema foo2;
CREATE
schema_test=# create table foo2.bar (pk int, txt text);
CREATE
schema_test=# create user joe;
CREATE USER
schema_test=# grant usage on schema foo to joe;
GRANT
schema_test=# \c - joe
You are now connected as new user joe.
schema_test=> SELECT nspname AS schema,
schema_test-> relname AS object,
schema_test-> relkind AS type,
schema_test-> relacl AS access
schema_test-> FROM pg_class c
schema_test-> INNER JOIN pg_namespace n
schema_test-> ON c.relnamespace=n.oid
schema_test-> WHERE relkind in ('r', 'v', 'S') AND
schema_test-> relname NOT LIKE 'pg$_%%' ESCAPE '$' AND
schema_test-> nspname || '.' || relname LIKE 'f%.b%';
schema | object | type | access
--------+--------+------+--------
foo | bar | r |
foo2 | bar | r |
(2 rows)
i.e. user "joe" can see which objects exist in schema "foo2", even though
he has no USAGE privilege. (Is this behaviour intended?)
Yours
Ian Barwick
Hannu Krosing <hannu@tm.ee> writes:
On Thu, 2002-05-02 at 05:33, Tom Lane wrote:
The temp schema is pg_temp_nnn where nnn is your BackendId (PROC array
slot number). AFAIK there isn't any exported way to determine your
BackendId from an SQL query.
The non-portable way on Linux RH 7.2 :
create function getpid() returns int as '/lib/libc.so.6','getpid' language 'C';
But PID is not BackendId.
regards, tom lane
On Wed, 1 May 2002, Jeffrey W. Baker wrote:
On Tue, Apr 30, 2002 at 09:41:47PM +0300, Oleg Bartunov wrote:
I think DBD::Pg driver very much depends on system tables.
Hope, Jeffrey (current maintainer) is online.These changes may break DBD::Pg. What is the expected
time of this release? I will review my code for impact.
Jeffrey,
btw, DBD-Pg 1.13 doesn't passed all tests
(Linux 2.4.17, pgsql 7.2.1, DBI-1.21)
t/02prepare.........ok
t/03bind............ok
t/04execute.........FAILED tests 5-7
Failed 3/10 tests, 70.00% okay
t/05fetch...........ok
t/06disconnect......ok
Thanks for the warning,
Jeffrey---------------------------(end of broadcast)---------------------------
TIP 6: Have you searched our list archives?
Regards,
Oleg
_____________________________________________________________
Oleg Bartunov, sci.researcher, hostmaster of AstroNet,
Sternberg Astronomical Institute, Moscow University (Russia)
Internet: oleg@sai.msu.su, http://www.sai.msu.su/~megera/
phone: +007(095)939-16-83, +007(095)939-23-83
Hannu Krosing <hannu@tm.ee> writes:
Is "PROC array slot number" something internal to postgres ?
Yes.
If we used PID then we'd eventually have 64K (or whatever the range of
PIDs is on your platform) different pg_temp_nnn entries cluttering
pg_namespace. But we only need MaxBackends different entries at any one
time. So the correct nnn value is 1..MaxBackends. BackendId meets the
need perfectly.
regards, tom lane
Import Notes
Reply to msg id not found: 1020351642.32039.106.camel@taru.tm.ee
On Wed, 1 May 2002, Jeffrey W. Baker wrote:
These changes may break DBD::Pg. What is the expected
time of this release? I will review my code for impact.
I think the current plan is to go beta in late summer. So there's
no tremendous hurry. I was just sending out a wake-up call ...
regards, tom lane
On Thu, 2002-05-02 at 15:48, Tom Lane wrote:
Hannu Krosing <hannu@tm.ee> writes:
On Thu, 2002-05-02 at 05:33, Tom Lane wrote:
The temp schema is pg_temp_nnn where nnn is your BackendId (PROC array
slot number). AFAIK there isn't any exported way to determine your
BackendId from an SQL query.The non-portable way on Linux RH 7.2 :
create function getpid() returns int as '/lib/libc.so.6','getpid' language 'C';
But PID is not BackendId.
Are you sure ?
I was assuming that BackendId was the process id of current backend
and that's what getpid() returns.
What is the Backend ID then ?
Is "PROC array slot number" something internal to postgres ?
-------------
Hannu
On Thu, May 02, 2002 at 05:28:36PM +0300, Oleg Bartunov wrote:
On Wed, 1 May 2002, Jeffrey W. Baker wrote:
On Tue, Apr 30, 2002 at 09:41:47PM +0300, Oleg Bartunov wrote:
I think DBD::Pg driver very much depends on system tables.
Hope, Jeffrey (current maintainer) is online.These changes may break DBD::Pg. What is the expected
time of this release? I will review my code for impact.Jeffrey,
btw, DBD-Pg 1.13 doesn't passed all tests
(Linux 2.4.17, pgsql 7.2.1, DBI-1.21)t/02prepare.........ok
t/03bind............ok
t/04execute.........FAILED tests 5-7
Failed 3/10 tests, 70.00% okay
t/05fetch...........ok
t/06disconnect......ok
These tests were failing when I inherited the code. I'll fix them
when I rewrite the parser.
-jwb
Ian Barwick <barwick@gmx.de> writes:
i.e. user "joe" can see which objects exist in schema "foo2", even though
he has no USAGE privilege. (Is this behaviour intended?)
It's open for debate I suppose. Historically we have not worried about
preventing people from looking into the system tables, except for cases
such as pg_statistic where this might expose actual user data.
AFAICS we could only prevent this by making selective views on the
system tables and then prohibiting ordinary users from accessing the
underlying tables directly. I'm not in a big hurry to do that myself,
if only for backward-compatibility reasons.
We still do have the option of separate databases, and I'd be inclined
to tell people to use those if they want airtight separation between
users.
regards, tom lane
Hannu Krosing <hannu@tm.ee> writes:
On Thu, 2002-05-02 at 16:52, Tom Lane wrote:
If we used PID then we'd eventually have 64K (or whatever the range of
PIDs is on your platform) different pg_temp_nnn entries cluttering
pg_namespace.
Should they not be cleaned up at backend exit even when they are in
range 1..MaxBackends ?
Hm. We currently remove the schema contents (ie the temp tables) but
not the pg_namespace entry itself. Seems like deleting that only to
have to recreate it would be a waste of cycles.
regards, tom lane
Import Notes
Reply to msg id not found: 1020440376.1517.1.camel@taru.tm.ee
On Thu, 2002-05-02 at 16:52, Tom Lane wrote:
Hannu Krosing <hannu@tm.ee> writes:
Is "PROC array slot number" something internal to postgres ?
Yes.
If we used PID then we'd eventually have 64K (or whatever the range of
PIDs is on your platform) different pg_temp_nnn entries cluttering
pg_namespace.
Should they not be cleaned up at backend exit even when they are in
range 1..MaxBackends ?
But we only need MaxBackends different entries at any one
time. So the correct nnn value is 1..MaxBackends. BackendId meets the
need perfectly.
----------
Hannu
Re: BackendID and the schema search path
Coming back to this subject if I may but only briefly, I hope. How about making
a slight change to current_schemas() and including an optional argument such
that something like:
current_schemas(1)
returns the complete list of schemas in the search path including the implicit
temporary space and the pg_catalog (if not already listed obviously), while
current_schemas() and current_schemas(0) behave as now.
An alternative is to provide a get_backend_id() call but I don't think there's
really appropiate and then means the client has to know how to construct the
name of the temporary schema, which isn't a good idea.
Having something like this would enable client's like PgAccess to determine the
complete list of visible objects. Without it it's difficult to see how it is
possible to include temporary objects in a list of tables and such. In such
a circumstance I'm inclined to say temporary objects are intermediate items and
so of no interest to the PgAccess user.
--
Nigel J. Andrews
Director
---
Logictree Systems Limited
Computer Consultants
"Nigel J. Andrews" <nandrews@investsystems.co.uk> writes:
Coming back to this subject if I may but only briefly, I hope. How
about making a slight change to current_schemas() and including an
optional argument such that something like:
current_schemas(1)
returns the complete list of schemas in the search path including the
implicit temporary space and the pg_catalog (if not already listed
obviously), while current_schemas() and current_schemas(0) behave as
now.
I don't really care for that syntax, but certainly we could talk about
providing a version of current_schemas that tells the Whole Truth.
Having something like this would enable client's like PgAccess to
determine the complete list of visible objects.
Well, no, it wouldn't. Say there are multiple tables named foo in
different namespaces in your search path (eg, a temp table hiding a
permanent table of the same name). A test like "where current_schemas
*= relnamespace" won't reflect this correctly.
I'm suspecting that what we really need is some kind of
"is_visible_table()" test function, and then you'd do
select * from pg_class where is_visible_table(oid);
At least I've not been able to think of a better idea than that.
regards, tom lane
On Mon, 6 May 2002, Tom Lane wrote:
"Nigel J. Andrews" <nandrews@investsystems.co.uk> writes:
Coming back to this subject if I may but only briefly, I hope. How
about making a slight change to current_schemas() and including an
optional argument such that something like:
current_schemas(1)
returns the complete list of schemas in the search path including the
implicit temporary space and the pg_catalog (if not already listed
obviously), while current_schemas() and current_schemas(0) behave as
now.I don't really care for that syntax, but certainly we could talk about
providing a version of current_schemas that tells the Whole Truth.Having something like this would enable client's like PgAccess to
determine the complete list of visible objects.Well, no, it wouldn't. Say there are multiple tables named foo in
different namespaces in your search path (eg, a temp table hiding a
permanent table of the same name). A test like "where current_schemas
*= relnamespace" won't reflect this correctly.I'm suspecting that what we really need is some kind of
"is_visible_table()" test function, and then you'd do
select * from pg_class where is_visible_table(oid);
At least I've not been able to think of a better idea than that.
Ok, where I was coming from was the idea of the client, I'm most interested in
PgAccess at the moment, retrieving the search path and cross referencing that
against the results of the queries for tables etc.
I seemed to remember mention of an is_visible() function earlier in the thread
but that for some reason this would mean a performance hit across the board, or
at least in many places. However, reviewing my emails I see not such comment
about performance. Tom originally suggested relation_is_visible(oid) as the
function.
I also got it wrong about when the temporary space is emptied. I had been
thinking it was when the connection terminated. However, I see from the same
old message that this happens when the first temporary item is created in a
session. Therefore, my way would be invalid anyway; or would it?
--
Nigel J. Andrews
Director
---
Logictree Systems Limited
Computer Consultants
"Nigel J. Andrews" <nandrews@investsystems.co.uk> writes:
I also got it wrong about when the temporary space is emptied. I had been
thinking it was when the connection terminated. However, I see from the same
old message that this happens when the first temporary item is created in a
session. Therefore, my way would be invalid anyway; or would it?
It would work as long as the variant form of current_schemas() truly
reflects the effective search path --- because until you create a
temporary item, there is no temp schema in the effective path.
Still, the issue of hiding seems to be a good reason not to code
clients that way.
regards, tom lane
On Mon, 6 May 2002, Nigel J. Andrews wrote:
On Mon, 6 May 2002, Tom Lane wrote:
"Nigel J. Andrews" <nandrews@investsystems.co.uk> writes:
Coming back to this subject if I may but only briefly, I hope. How
about making a slight change to current_schemas() and including an
optional argument such that something like:
current_schemas(1)
returns the complete list of schemas in the search path including the
implicit temporary space and the pg_catalog (if not already listed
obviously), while current_schemas() and current_schemas(0) behave as
now.I don't really care for that syntax, but certainly we could talk about
providing a version of current_schemas that tells the Whole Truth.
Wouldn't such a function just be based on
backend/catalog/namespace.c:RelnameGetRelid(const char *relname) ?
I'm suspecting that what we really need is some kind of
"is_visible_table()" test function, and then you'd do
select * from pg_class where is_visible_table(oid);
At least I've not been able to think of a better idea than that.[snip]
For this if we look once again at RelnameGetRelid(relname) in
backend/catalog/namespace.c wouldn't this is_visible() function simply be a
wrapper around it? Obviously the parameter [probably] wouldn't be an OID but
rather a name.
If I knew which file would be most appropiate for this (utils/adt/name.c?) I'd
have had a go at making a patch.
--
Nigel J. Andrews
Director
---
Logictree Systems Limited
Computer Consultants
"Nigel J. Andrews" <nandrews@investsystems.co.uk> writes:
For this if we look once again at RelnameGetRelid(relname) in
backend/catalog/namespace.c wouldn't this is_visible() function simply be a
wrapper around it?
Sort of. It's there already, see RelationIsVisible.
regards, tom lane
On Mon, 6 May 2002, Tom Lane wrote:
"Nigel J. Andrews" <nandrews@investsystems.co.uk> writes:
For this if we look once again at RelnameGetRelid(relname) in
backend/catalog/namespace.c wouldn't this is_visible() function simply be a
wrapper around it?Sort of. It's there already, see RelationIsVisible.
Doh. Next function down.
I see there are routines doing similar things but for functions and others. I'm
right in saying that OID isn't unique in a database (necessarily) and so we
couldn't have a general object_is_visible(oid) function that did the appropiate
from the type of object refered to?
It just seems that if we're interested in showing tables according to
visibility then shouldn't we be doing the same for these other things?
--
Nigel J. Andrews
Director
---
Logictree Systems Limited
Computer Consultants
"Nigel J. Andrews" <nandrews@investsystems.co.uk> writes:
I see there are routines doing similar things but for functions and
others. I'm right in saying that OID isn't unique in a database
(necessarily) and so we couldn't have a general object_is_visible(oid)
function that did the appropiate from the type of object refered to?
Not in the current structure. Even if OID were guaranteed unique across
the database, how would you determine which kind of object a given OID
referred to? Seems like it would take expensive probing of a lot of
different tables until you found a match --- which is a bit silly when
the calling query generally knows darn well where it got the OID from.
I suppose we could define an object_is_visible(tableoid, oid) function,
but I'm not sure if it has any real usefulness.
It just seems that if we're interested in showing tables according to
visibility then shouldn't we be doing the same for these other things?
Sure; if we go this routine then all five of the FooIsVisible routines
will need to be exported as SQL functions.
regards, tom lane
Tom Lane wrote:
bar were in my search path, so I should not see them unless I give a
qualified name (eg, "\d foo.mytab" or "\d bar.mytab"). For commands
that accept wildcard patterns, what should happen --- should "\z my*"
find these tables, if they're not in my search path? Is "\z f*.my*"
sensible to support? I dunno yet.
I am still reading the thread, but I thought \z mytab should show only
the first match, like SELECT * from mytab, and \z *.mytab should show
all matching tables in the schema search path. This does make '.' a
special character in the psql wildcard character set, but as no one uses
'.' in a table name, I think it is OK.
--
Bruce Momjian | http://candle.pha.pa.us
pgman@candle.pha.pa.us | (610) 853-3000
+ If your life is a hard drive, | 830 Blythe Avenue
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026On Wednesday 01 May 2002 06:38, Tom Lane wrote:
Ian Barwick <barwick@gmx.net> writes:
How can I restrict the query to the schemas in the
current search path, i.e. the schema names returned
by SELECT current_schemas() ?Well, this is the issue open for public discussion.
We could define some function along the lines of
"is_visible_table(oid) returns bool", and then you could use
that as a WHERE clause in your query. But I'm worried about
the performance implications --- is_visible_table() would have
to do several retail probes of the system tables, and I don't
see any way to optimize that across hundreds of table OIDs.I have a nagging feeling that this could be answered by defining
a view on pg_class that only shows visible tables ... but I don't
quite see how to define that efficiently, either. Ideas anyone?
(time passes...)
How about a function such as the one attached: "select_schemas_setof()"
which returns the OIDs of the schemas in the current search path as
a set. (Note: "select_schemas_setof()" as shown is a userspace C function.)
It works like this:
template1=# CREATE DATABASE schema_test;
CREATE DATABASE
template1=# \c schema_test
You are now connected to database schema_test.
schema_test=# CREATE OR REPLACE FUNCTION current_schemas_setof()
schema_test-# RETURNS setof OID
schema_test-# as '/path/to/current_schemas_setof.so'
schema_test-# LANGUAGE 'C';
CREATE FUNCTION
I can then do this:
schema_test=# CREATE SCHEMA foo;
CREATE SCHEMA
schema_test=# CREATE TABLE foo.mytab(col1 int, col2 text);
CREATE TABLE
schema_test=# CREATE SCHEMA bar;
CREATE SCHEMA
schema_test=# CREATE TABLE bar.mytab(col1 int, col2 text);
CREATE TABLE
schema_test=# SET search_path = public, foo, bar;
SET
schema_test=# SELECT current_schemas();
current_schemas
------------------
{public,foo,bar}
(1 row)
schema_test=# SELECT current_schemas_setof, n.nspname
schema_test-# FROM public.current_schemas_setof() cs, pg_namespace n
schema_test-# WHERE cs.current_schemas_setof = n.oid;
current_schemas_setof | nspname
----------------------+------------
16563 | pg_temp_1
11 | pg_catalog
2200 | public
24828 | foo
24835 | bar
(3 rows)
With the function in place I can then create an SQL function like this:
CREATE OR REPLACE FUNCTION public.first_visible_namespace(name)
RETURNS oid
AS
'SELECT n.oid
FROM pg_namespace n, pg_class c, public.current_schemas_setof() cs
WHERE c.relname= $1
AND c.relnamespace=n.oid
AND n.oid= cs.current_schemas_setof
LIMIT 1'
LANGUAGE 'sql';
which can be used like this:
schema_test=# select public.first_visible_namespace('mytab');
first_visible_namespace
-------------------------
24828
(1 row)
i.e. finds the first visible schema containing an unqualified relation name.
24828 corresponds to the OID of schema "foo".
The following VIEW:
CREATE VIEW public.desc_table_view AS
SELECT n.nspname AS "Schema",
c.relname AS "Table",
a.attname AS "Column",
format_type (a.atttypid, a.atttypmod) AS "Type"
FROM pg_class c, pg_attribute a, pg_namespace n
WHERE a.attnum > 0
AND c.relkind IN ('r', 'v', 'S')
AND a.attrelid = c.oid
AND c.relnamespace=n.oid
AND n.oid IN (SELECT first_visible_namespace(c.relname))
ORDER BY a.attnum;
then provides a simplified simulation of psql's slash command \d [NAME] for
unqualified relation names, e.g.:
schema_test=# SELECT * FROM public.desc_table_view WHERE "Table" = 'mytab';
Schema | Table | Column | Type
--------+-------+--------+---------
foo | mytab | col1 | integer
foo | mytab | col2 | text
(2 rows)
schema_test=# SET search_path= bar, foo, public;
SET
schema_test=# SELECT * FROM public.desc_table_view WHERE "Table" = 'mytab';
Schema | Table | Column | Type
--------+-------+--------+---------
bar | mytab | col1 | integer
bar | mytab | col2 | text
(2 rows)
schema_test=# SET search_path= public;
SET
schema_test=# SELECT * FROM public.desc_table_view WHERE "Table" = 'mytab';
Schema | Table | Column | Type
--------+-------+--------+------
(0 rows)
which I think is the desired behaviour. Currently \d [NAME] produces this:
schema_test=# SET search_path= bar, foo, public;
SET
schema_test=# \d mytab
Table "mytab"
Column | Type | Modifiers
--------+---------+-----------
col1 | integer |
col1 | integer |
col2 | text |
col2 | text |
i.e. finds and describes "foo.mytab" and "bar.mytab".
(Note: "SELECT * FROM public.desc_table_view" will just dump an unordered
list of all columns for the first visible instance of each table name).
Assuming "current_schemas_setof()" can be implemented as an internal function,
(I haven't managed it myself yet :-( ), I suspect it is a more efficient
alternative to a putative "is_visible_table(oid)" and could be used in psql
(and elsewhere) to resolve the schemas of unqualified relation names.
Thoughts? (Or am I barking up the wrong tree?)
BTW is anyone working on schema support in psql? If the various definition
issues raised by Tom Lane at the start of this thread are resolved (discussion
seems to have trailed off without a consensus), I have some free time in June
and would be willing to take it on.
Ian Barwick
Attachments:
Ian Barwick <barwick@gmx.net> writes:
CREATE OR REPLACE FUNCTION public.first_visible_namespace(name)
RETURNS oid
AS
'SELECT n.oid
FROM pg_namespace n, pg_class c, public.current_schemas_setof() cs
WHERE c.relname=3D $1
AND c.relnamespace=3Dn.oid
AND n.oid=3D cs.current_schemas_setof
LIMIT 1'
LANGUAGE 'sql';
I don't believe this is correct. The LIMIT clause will ensure you
get at most one answer, but it'd be pure luck whether it is the right
answer, when there are multiple tables of the same name in the
namespaces of the search path.
The following VIEW:
CREATE VIEW public.desc_table_view AS
SELECT n.nspname AS "Schema",
c.relname AS "Table",
a.attname AS "Column",
format_type=09(a.atttypid, a.atttypmod) AS "Type"
FROM pg_class c, pg_attribute a, pg_namespace n
WHERE a.attnum > 0
AND c.relkind IN ('r', 'v', 'S')
AND a.attrelid =3D c.oid
AND c.relnamespace=3Dn.oid
AND n.oid IN (SELECT first_visible_namespace(c.relname))
ORDER BY a.attnum;
I was hoping to find something more efficient than that --- quite aside
from the speed or correctness of first_visible_namespace(), a query
depending on an IN is not going to be fast.
regards, tom lane
Tom Lane wrote:
If you don't create schemas then you get backwards-compatible behavior
(all the users end up sharing the "public" schema as their current
schema).
I am a little uncomfortable about this. It means that CREATE TABLE will
create a table in 'public' if the user doesn't have a schema of their
own, and in their private schema if it exists. I seems strange to have
such a distinction based on whether a private schema exists. Is this OK?
--
Bruce Momjian | http://candle.pha.pa.us
pgman@candle.pha.pa.us | (610) 853-3000
+ If your life is a hard drive, | 830 Blythe Avenue
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026Bruce Momjian <pgman@candle.pha.pa.us> writes:
I am a little uncomfortable about this. It means that CREATE TABLE will
create a table in 'public' if the user doesn't have a schema of their
own, and in their private schema if it exists. I seems strange to have
such a distinction based on whether a private schema exists. Is this OK?
You have a better idea?
Given that we want to support both backwards-compatible and SQL-spec-
compatible behavior, I think some such ugliness is inevitable.
regards, tom lane
Tom Lane wrote:
Bruce Momjian <pgman@candle.pha.pa.us> writes:
I am a little uncomfortable about this. It means that CREATE TABLE will
create a table in 'public' if the user doesn't have a schema of their
own, and in their private schema if it exists. I seems strange to have
such a distinction based on whether a private schema exists. Is this OK?You have a better idea?
Given that we want to support both backwards-compatible and SQL-spec-
compatible behavior, I think some such ugliness is inevitable.
I don't have a better idea, but I am wondering how this will work. If I
create a schema with my name, does it get added to the front of my
schema schema search path automatically, or do I set it with SET,
perhaps in my per-user startup SET column?
If I want to prevent some users from creating tables in my database, do
I remove CREATE on the schema using REVOKE SCHEMA, then create a schema
for every user using the database?
--
Bruce Momjian | http://candle.pha.pa.us
pgman@candle.pha.pa.us | (610) 853-3000
+ If your life is a hard drive, | 830 Blythe Avenue
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026Bruce Momjian <pgman@candle.pha.pa.us> writes:
I don't have a better idea, but I am wondering how this will work. If I
create a schema with my name, does it get added to the front of my
schema schema search path automatically,
Yes (unless you've futzed with the standard value of search_path).
If I want to prevent some users from creating tables in my database, do
I remove CREATE on the schema using REVOKE SCHEMA, then create a schema
for every user using the database?
Well, you revoke world create access on the public schema (or maybe even
delete the public schema, if you don't need it). I don't see why you'd
give people their own schemas if the intent is to keep them from
creating tables.
regards, tom lane
Tom Lane wrote:
Bruce Momjian <pgman@candle.pha.pa.us> writes:
I don't have a better idea, but I am wondering how this will work. If I
create a schema with my name, does it get added to the front of my
schema schema search path automatically,Yes (unless you've futzed with the standard value of search_path).
If I want to prevent some users from creating tables in my database, do
I remove CREATE on the schema using REVOKE SCHEMA, then create a schema
for every user using the database?Well, you revoke world create access on the public schema (or maybe even
delete the public schema, if you don't need it). I don't see why you'd
give people their own schemas if the intent is to keep them from
creating tables.
No, I was saying you would have to create schemas for the people who you
_want_ to be able to create tables.
With the old NOCREATE patch, you could just remove create permission
from a user. With schemas, you have to remove all permission for table
creation, then grant it to those you want by creating schemas for them.
This is similar to handling of Unix permissions. If you want to
restrict access to a file or directory, you remove public permission,
and add group permission, then add the people who you want access to
that group.
There are no _negative_ permissions, as there are no negative
permissions in the unix file system. I just wanted to be clear that
restricting access will be multi-step process.
If I remove public create access to public, can the super user or db
owner still create tables?
--
Bruce Momjian | http://candle.pha.pa.us
pgman@candle.pha.pa.us | (610) 853-3000
+ If your life is a hard drive, | 830 Blythe Avenue
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026Bruce Momjian <pgman@candle.pha.pa.us> writes:
If I remove public create access to public, can the super user or db
owner still create tables?
Superusers can always do whatever they want.
The DB owner (assume he's not a superuser) has no special privileges
w.r.t. the public schema at the moment. We could perhaps put in a
kluge to change this, but it would definitely be a kluge --- I don't
see any clean way to make the behavior different.
One possible approach would be for a superuser to change the ownership
of public to be the DB owner.
regards, tom lane
There was discussion of how template1's "public" schema should behave.
I think the only solution is to make template1's public schema writable
only by the super-user. This way, we can allow utility commands to
connect to template1, but they can't change anything or add their own
tables.
As part of createdb, the new database will have to have it's public
schema changed to world-writable.
--
Bruce Momjian | http://candle.pha.pa.us
pgman@candle.pha.pa.us | (610) 853-3000
+ If your life is a hard drive, | 830 Blythe Avenue
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026
As part of createdb, the new database will have to have it's public
schema changed to world-writable.
I have to admit that much of the schema related discussion has been over my
head, but I think what I understand you to be saying here is that the
default would be to allow anybody to create tables in any database that they
connect to, in the same way that they currently can (with pg <= 7.2.1).
(If that's not the case, you can ignore the rest of the message.)
What value do users get from being able to create temp tables in any
database?
Don't _most_ people expect databases (from any vendor) to be writable only
by the owner? I have to confess that I was surprised when I discovered that
others could create tables in my PG database (although I don't have much
exposure to other flavors of databases).
ISTM that the best default is to have it not world writable, but that will
tend to cause some consternation when people transition to 7.3 and discover
(as I did) that the current pg_restore may hit snags on a non-world writable
DB in certain circumstances.
If I put data into a database and want to allow anybody to read it and don't
want to worry about administering accounts for hundreds of users, I might
create an account that anybody can use to connect. I would be unhappy if
someone was able to expand that permission into something like creating
tables and filling them so much that it causes problems for me.
(As I said, this is all predicated on my understanding at the beginning, so
if I've misunderstood this issue then perhaps this wouldn't be a problem for
me.)
-ron
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Ron Snyder wrote:
As part of createdb, the new database will have to have it's public
schema changed to world-writable.I have to admit that much of the schema related discussion has been over my
head, but I think what I understand you to be saying here is that the
default would be to allow anybody to create tables in any database that they
connect to, in the same way that they currently can (with pg <= 7.2.1).(If that's not the case, you can ignore the rest of the message.)
The issue I was raising is the creation of tables in the default
'public' schema, which is the one used by users who don't have a schema
matching their name. I was saying that template1 should prevent
creation of tables by anyone but the superuser.
As far as temp tables, I think we should enable that for all
non-template1 databases.
(In fact, what happens if you create a database while a temp table
exists in template1. Seems it would not be cleaned up in the new
database.)
--
Bruce Momjian | http://candle.pha.pa.us
pgman@candle.pha.pa.us | (610) 853-3000
+ If your life is a hard drive, | 830 Blythe Avenue
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026Bruce Momjian <pgman@candle.pha.pa.us> writes:
As part of createdb, the new database will have to have it's public
schema changed to world-writable.
That ain't gonna happen, unfortunately. CREATE DATABASE runs in some
database other than the target one, so it's essentially impossible for
the newly-created DB to contain any internal state that's different
from the template DB. Next idea please?
regards, tom lane
Tom Lane wrote:
Bruce Momjian <pgman@candle.pha.pa.us> writes:
As part of createdb, the new database will have to have it's public
schema changed to world-writable.That ain't gonna happen, unfortunately. CREATE DATABASE runs in some
database other than the target one, so it's essentially impossible for
the newly-created DB to contain any internal state that's different
from the template DB. Next idea please?
Yes, there was an even bigger problem with my argument. If someone
wanted to make public no-write, and have all created databases inherit
from that, it wouldn't work because it would clear that on creation.
How about if we hard-wire template1 as being no-write to public
somewhere in the code, rather than in the db tables?
--
Bruce Momjian | http://candle.pha.pa.us
pgman@candle.pha.pa.us | (610) 853-3000
+ If your life is a hard drive, | 830 Blythe Avenue
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026Bruce Momjian <pgman@candle.pha.pa.us> writes:
How about if we hard-wire template1 as being no-write to public
somewhere in the code, rather than in the db tables?
Seems pretty icky :-(
It occurs to me that maybe we don't need to worry. The main reason why
we've offered the advice "don't fill template1 with junk" in the past
is that it was so hard to clear out the junk without zapping built-in
entries. But now, you really have to work hard at it to shoot yourself
in the foot that way. If you created junk in template1.public, no
sweat:
\c template1 postgres
DROP SCHEMA public;
CREATE SCHEMA public;
-- don't forget to set its permissions appropriately
(This assumes we get DROP SCHEMA implemented in time for 7.3, but
I think we can build that based on Rod's pg_depend stuff.) (Which
I really really gotta review and apply soon.)
I'm of the opinion that template1 and public are not very special
at the moment; the C-level code doesn't think either of them are
special, which is why you can drop and recreate them if you have to.
We should try not to re-introduce any low-level specialness.
regards, tom lane
Tom Lane wrote:
Bruce Momjian <pgman@candle.pha.pa.us> writes:
How about if we hard-wire template1 as being no-write to public
somewhere in the code, rather than in the db tables?Seems pretty icky :-(
It occurs to me that maybe we don't need to worry. The main reason why
we've offered the advice "don't fill template1 with junk" in the past
is that it was so hard to clear out the junk without zapping built-in
entries. But now, you really have to work hard at it to shoot yourself
in the foot that way. If you created junk in template1.public, no
sweat:
\c template1 postgres
DROP SCHEMA public;
CREATE SCHEMA public;
-- don't forget to set its permissions appropriately
(This assumes we get DROP SCHEMA implemented in time for 7.3, but
I think we can build that based on Rod's pg_depend stuff.) (Which
I really really gotta review and apply soon.)I'm of the opinion that template1 and public are not very special
at the moment; the C-level code doesn't think either of them are
special, which is why you can drop and recreate them if you have to.
We should try not to re-introduce any low-level specialness.
It is strange we have to allow template1 open just for client stuff. I
would really like to lock it down read-only. I guess we can tell admins
to lock down public in template1, and all newly created databases will
be the same.
--
Bruce Momjian | http://candle.pha.pa.us
pgman@candle.pha.pa.us | (610) 853-3000
+ If your life is a hard drive, | 830 Blythe Avenue
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026