From: Jürgen Purtz <juergen@purtz.de>
To: pgsql-docs@lists.postgresql.org
To: daelhithe@hotmail.com
Subject: Re: Documentation - chapter 52, system catalogs
Date: Tue, 5 May 2020 12:20:44 +0200
Message-ID: <aecbf4cf-9717-f83c-744e-4ed074989037@purtz.de> (raw)
In-Reply-To: <158860579891.671.9854443057028888145@wrigleys.postgresql.org>
References: <158860579891.671.9854443057028888145@wrigleys.postgresql.org>
On 04.05.20 17:23, PG Doc comments form wrote:
> The following documentation comment has been logged on the website:
>
> Page: https://www.postgresql.org/docs/11/catalogs-overview.html
> Description:
>
> The documentation for chapter 52 does not clearly identify the schema
> associated with the system catalogs in either the chapter header or overview
> sections; had I not stumbled across a reference in the documentation for the
> postgres_fdw to the pg_catalog search path, I would have been unable to
> reference the content in those catalogs via foreign data wrappers, and
> although the majority of the content has been exposed via the
> information_schema views and tables, there remain a few elements of interest
> that appear to only exist in the pg_catalog qualified content.
I think that the topic "fdw" is only a symptom, not the real reason for
the confusion. We can improve the chapters "System Catalog" and
"Information Schema" in general by centralizing some already existing
paragraphs in the "Overview" chapter and adding some more explanations.
The attached patch contains:
- for "System Catalog": moving paragraphs from bottom of 51. to top of
51.1. (in PG 11 it is chapter 52); explanation that "System Catalog" is
a synonym for a concrete schema and its tables.
- for "Information Schema": moving paragraphs from bottom of 36. to
middle of 36.1. ; an explanation that it relies on the system catalog;
change the title of 36.1. to "Overview" in correlation with "System
Catalog".
--
Jürgen Purtz
Attachments:0001-catalog.patch (text/x-patch, 6.0K) downloaddiff --git a/doc/src/sgml/catalogs.sgml b/doc/src/sgml/catalogs.sgmlindex ce33df9e58..8854bda05f 100644--- a/doc/src/sgml/catalogs.sgml+++ b/doc/src/sgml/catalogs.sgml@@ -6,6 +6,23 @@
<chapter id="catalogs">
<title>System Catalogs</title>
+ <sect1 id="catalogs-overview">+ <title>Overview</title>++ <para>+ The term <firstterm>system catalog</firstterm> is a widely used+ synonym for the schema <firstterm>pg_catalog</firstterm> and+ its tables. They are listed in <xref linkend="catalog-table"/>+ with links to more detailed documentation.+ </para>++ <para>+ Most system catalogs are copied from the template database during+ database creation and are thereafter database-specific. A few+ catalogs are physically shared across all databases in a cluster;+ these are noted in the descriptions of the individual catalogs.+ </para>+
<para>
The system catalogs are the place where a relational database
management system stores schema metadata, such as information about
@@ -23,21 +40,6 @@
of the system catalogs is ever decreasing.
</para>
- <sect1 id="catalogs-overview">- <title>Overview</title>-- <para>- <xref linkend="catalog-table"/> lists the system catalogs.- More detailed documentation of each catalog follows below.- </para>-- <para>- Most system catalogs are copied from the template database during- database creation and are thereafter database-specific. A few- catalogs are physically shared across all databases in a cluster;- these are noted in the descriptions of the individual catalogs.- </para>-
<table id="catalog-table">
<title>System Catalogs</title>
diff --git a/doc/src/sgml/information_schema.sgml b/doc/src/sgml/information_schema.sgmlindex 7a995a1b64..ea8561d9e5 100644--- a/doc/src/sgml/information_schema.sgml+++ b/doc/src/sgml/information_schema.sgml@@ -7,46 +7,8 @@
<primary>information schema</primary>
</indexterm>
- <para>- The information schema consists of a set of views that contain- information about the objects defined in the current database. The- information schema is defined in the SQL standard and can therefore- be expected to be portable and remain stable — unlike the system- catalogs, which are specific to- <productname>PostgreSQL</productname> and are modeled after- implementation concerns. The information schema views do not,- however, contain information about- <productname>PostgreSQL</productname>-specific features; to inquire- about those you need to query the system catalogs or other- <productname>PostgreSQL</productname>-specific views.- </para>-- <note>- <para>- When querying the database for constraint information, it is possible- for a standard-compliant query that expects to return one row to- return several. This is because the SQL standard requires constraint- names to be unique within a schema, but- <productname>PostgreSQL</productname> does not enforce this- restriction. <productname>PostgreSQL</productname>- automatically-generated constraint names avoid duplicates in the- same schema, but users can specify such duplicate names.- </para>-- <para>- This problem can appear when querying information schema views such- as <literal>check_constraint_routine_usage</literal>,- <literal>check_constraints</literal>, <literal>domain_constraints</literal>, and- <literal>referential_constraints</literal>. Some other views have similar- issues but contain the table name to help distinguish duplicate- rows, e.g., <literal>constraint_column_usage</literal>,- <literal>constraint_table_usage</literal>, <literal>table_constraints</literal>.- </para>- </note>--
<sect1 id="infoschema-schema">
- <title>The Schema</title>+ <title>Overview</title>
<para>
The information schema itself is a schema named
@@ -57,6 +19,44 @@
the space savings achieved by that are minuscule).
</para>
+ <para>+ The information schema consists of a set of views to tables+ in the schema <firstterm>pg_catalog</firstterm>, so it contains+ information about the objects defined in the current database. The+ information schema is defined in the SQL standard and can therefore+ be expected to be portable and remain stable — unlike the system+ catalogs, which are specific to+ <productname>PostgreSQL</productname> and are modeled after+ implementation concerns. The information schema views do not,+ however, contain information about+ <productname>PostgreSQL</productname>-specific features; to inquire+ about those you need to query the system catalogs or other+ <productname>PostgreSQL</productname>-specific views.+ </para>++ <note>+ <para>+ When querying the database for constraint information, it is possible+ for a standard-compliant query that expects to return one row to+ return several. This is because the SQL standard requires constraint+ names to be unique within a schema, but+ <productname>PostgreSQL</productname> does not enforce this+ restriction. <productname>PostgreSQL</productname>+ automatically-generated constraint names avoid duplicates in the+ same schema, but users can specify such duplicate names.+ </para>++ <para>+ This problem can appear when querying information schema views such+ as <literal>check_constraint_routine_usage</literal>,+ <literal>check_constraints</literal>, <literal>domain_constraints</literal>, and+ <literal>referential_constraints</literal>. Some other views have similar+ issues but contain the table name to help distinguish duplicate+ rows, e.g., <literal>constraint_column_usage</literal>,+ <literal>constraint_table_usage</literal>, <literal>table_constraints</literal>.+ </para>+ </note>+
<para>
By default, the information schema is not in the schema search
path, so you need to access all objects in it through qualified
@@ -65,6 +65,7 @@
should be careful if you want to put the information schema in the
path.
</para>
+
</sect1>
<sect1 id="infoschema-datatypes">
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To: pgsql-docs@postgresql.org
Cc: juergen@purtz.de, pgsql-docs@lists.postgresql.org, daelhithe@hotmail.com
Subject: Re: Documentation - chapter 52, system catalogs
In-Reply-To: <aecbf4cf-9717-f83c-744e-4ed074989037@purtz.de>
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