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-From pgsql-hackers-owner+M8916@postgresql.org Thu May 17 11:51:45 2001
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- for <pgsql-hackers@postgreSQL.org>; Thu, 17 May 2001 17:22:16 +0200
-Subject: [HACKERS] possible DOMAIN implementation
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-Date: Thu, 17 May 2001 17:22:05 +0200
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-Thread-Topic: possible DOMAIN implementation
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-From: =?iso-8859-2?Q?Hor=E1k_Daniel?= <horak@sit.plzen-city.cz>
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-Hello,
-
-I have spend some thinking about implementation of DOMAIN capability.
-Here are my ideas.
-
-What is a domain? It is an alias for a type with size, constraints and
-default values. It is like one column of a table. And this is the main
-idea of my "implementation". It should be possible to implement it using
-existing system tables.
-
-New rules for grammar can be easily created from already existing pieces
-(column definition of a table).
-
-How to store information about a domain in system tables?
-When a new domain is created it will:
-- put a record into pg_type with typnam = domain name, new code for
-typtype = 'd' and typrelid = oid of a new record in pg_class (next line)
-- put a record into pg_class to create a fictional table with a new
-relkind ('d'?), relnatts = 1, relname can be system generated
-(pg_d_<domainname>)
-- put a records into pg_attribute and pg_attrdef with "column
-(attribute) definition" - real type, size, default value etc., owner
-will the fictional table from the previous step
-
-Then it will be required to modify functions that works with types. When
-typtype of a retrieved type is 'd' then it will perform lookups into
-pg_class, pg_attribute and pg_attrdef to find the real definition of the
-domain. These additional lookups will also create a performace penalty
-of using domains. But every feature has its costs. I know this paragraph
-about the real implementation is very short, but I think there are
-people that know the "type mechanism" better then I know. And can easier
-tell if it is possible to go this way.
-
-I hope you understand my explanation. It is also possible that I don't
-know some aspects of the backend code that makes my idea wrong.
-
- Dan
-
-----------------------------------------------
-Ing. Daniel Horak
-network and system administrator
-e-mail: horak@sit.plzen-city.cz
-privat e-mail: dan.horak@email.cz ICQ:36448176
-----------------------------------------------
-
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-From pgsql-hackers-owner+M8925@postgresql.org Thu May 17 14:04:29 2001
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-To: =?iso-8859-2?Q?Hor=E1k_Daniel?= <horak@sit.plzen-city.cz>
-cc: pgsql-hackers@postgresql.org
-Subject: Re: [HACKERS] possible DOMAIN implementation
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-Comments: In-reply-to =?iso-8859-2?Q?Hor=E1k_Daniel?= <horak@sit.plzen-city.cz>
- message dated "Thu, 17 May 2001 17:22:05 +0200"
-Date: Thu, 17 May 2001 13:58:45 -0400
-Message-ID: <12167.990122325@sss.pgh.pa.us>
-From: Tom Lane <tgl@sss.pgh.pa.us>
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-
-=?iso-8859-2?Q?Hor=E1k_Daniel?= <horak@sit.plzen-city.cz> writes:
-> When a new domain is created it will:
-> - put a record into pg_type with typnam = domain name, new code for
-> typtype = 'd' and typrelid = oid of a new record in pg_class (next line)
-> - put a record into pg_class to create a fictional table with a new
-> relkind ('d'?), relnatts = 1, relname can be system generated
-> (pg_d_<domainname>)
-
-Ugh. Don't overload pg_class with things that are not tables. I see no
-reason that either pg_class or pg_attribute should be involved in the
-definition of a domain. Make new system tables if you need to, but
-don't confuse the semantics of critical tables.
-
-> - put a records into pg_attribute and pg_attrdef with "column
-> (attribute) definition" - real type, size, default value etc., owner
-> will the fictional table from the previous step
-
-> Then it will be required to modify functions that works with types. When
-> typtype of a retrieved type is 'd' then it will perform lookups into
-> pg_class, pg_attribute and pg_attrdef to find the real definition of the
-> domain. These additional lookups will also create a performace penalty
-> of using domains.
-
-Why shouldn't this info be directly available from the pg_type row?
-
- regards, tom lane
-
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