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Documentation of the system catalogs, directed toward PostgreSQL developers

$PostgreSQL: pgsql/doc/src/sgml/catalogs.sgml,v 2.106 2005/06/28 05:08:50 tgl Exp $

$PostgreSQL: pgsql/doc/src/sgml/catalogs.sgml,v 2.107 2005/07/07 20:39:56 tgl Exp $

-->

<chapter id="catalogs">

<entry>query rewrite rules</entry>

</row>

<row>

<entry><link linkend="catalog-pg-shdepend"><structname>pg_shdepend</structname></link></entry>

<entry>dependencies on shared objects</entry>

</row>

<row>

<entry><link linkend="catalog-pg-statistic"><structname>pg_statistic</structname></link></entry>

<entry>planner statistics</entry>

RESTRICT</> case.

</para>

<para>

See also <link linkend="catalog-pg-shdepend"><structname>pg_shdepend</structname></link>,

which performs a similar function for dependencies involving objects

that are shared across a database cluster.

</para>

<table>

<title><structname>pg_depend</> Columns</title>

<row>

<entry><structfield>proargmodes</structfield></entry>

<entry><type>"char"[]</type></entry>

<entry><type>char[]</type></entry>

<entry></entry>

<entry>

An array with the modes of the function arguments, encoded as

</sect1>

<sect1 id="catalog-pg-shdepend">

<title><structname>pg_shdepend</structname></title>

<indexterm zone="catalog-pg-shdepend">

<primary>pg_shdepend</primary>

</indexterm>

<para>

The catalog <structname>pg_shdepend</structname> records the

dependency relationships between database objects and shared objects,

such as roles. This information allows

<productname>PostgreSQL</productname> to ensure that those objects are

unreferenced before attempting to delete them.

</para>

<para>

See also <link linkend="catalog-pg-depend"><structname>pg_depend</structname></link>,

which performs a similar function for dependencies involving objects

within a single database.

</para>

<para>

Unlike most system catalogs, <structname>pg_shdepend</structname>

is shared across all databases of a cluster: there is only one

copy of <structname>pg_shdepend</structname> per cluster, not

one per database.

</para>

<table>

<title><structname>pg_shdepend</> Columns</title>

<tgroup cols=4>

<thead>

<row>

<entry>Name</entry>

<entry>Type</entry>

<entry>References</entry>

<entry>Description</entry>

</row>

</thead>

<tbody>

<row>

<entry><structfield>dbid</structfield></entry>

<entry><type>oid</type></entry>

<entry><literal><link linkend="catalog-pg-database"><structname>pg_database</structname></link>.oid</literal></entry>

<entry>The OID of the database the dependent object is in,

or zero for a shared object</entry>

</row>

<row>

<entry><structfield>classid</structfield></entry>

<entry><type>oid</type></entry>

<entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>

<entry>The OID of the system catalog the dependent object is in</entry>

</row>

<row>

<entry><structfield>objid</structfield></entry>

<entry><type>oid</type></entry>

<entry>any OID column</entry>

<entry>The OID of the specific dependent object</entry>

</row>

<row>

<entry><structfield>refclassid</structfield></entry>

<entry><type>oid</type></entry>

<entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>

<entry>The OID of the system catalog the referenced object is in

(must be a shared catalog)</entry>

</row>

<row>

<entry><structfield>refobjid</structfield></entry>

<entry><type>oid</type></entry>

<entry>any OID column</entry>

<entry>The OID of the specific referenced object</entry>

</row>

<row>

<entry><structfield>deptype</structfield></entry>

<entry><type>char</type></entry>

<entry></entry>

<entry>

A code defining the specific semantics of this dependency relationship; see text.

</entry>

</row>

</tbody>

</tgroup>

</table>

<para>

In all cases, a <structname>pg_shdepend</structname> entry indicates that

the referenced object may not be dropped without also dropping the dependent

object. However, there are several subflavors identified by

<structfield>deptype</>:

<variablelist>

<varlistentry>

<term><symbol>SHARED_DEPENDENCY_OWNER</> (<literal>o</>)</term>

<listitem>

<para>

The referenced object (which must be a role) is the owner of the

dependent object.

</para>

</listitem>

</varlistentry>

<varlistentry>

<term><symbol>SHARED_DEPENDENCY_ACL</> (<literal>a</>)</term>

<listitem>

<para>

The referenced object (which must be a role) is mentioned in the

ACL (access control list, i.e., privileges list) of the

dependent object. (A <symbol>SHARED_DEPENDENCY_ACL</> entry is

not made for the owner of the object, since the owner will have

a <symbol>SHARED_DEPENDENCY_OWNER</> entry anyway.)

</para>

</listitem>

</varlistentry>

<varlistentry>

<term><symbol>SHARED_DEPENDENCY_PIN</> (<literal>p</>)</term>

<listitem>

<para>

There is no dependent object; this type of entry is a signal

that the system itself depends on the referenced object, and so

that object must never be deleted. Entries of this type are

created only by <command>initdb</command>. The columns for the

dependent object contain zeroes.

</para>

</listitem>

</varlistentry>

</variablelist>

Other dependency flavors may be needed in future. Note in particular

that the current definition only supports roles as referenced objects.

</para>

</sect1>

<sect1 id="catalog-pg-statistic">

<title><structname>pg_statistic</structname></title>

<entry><literal><link linkend="catalog-pg-database"><structname>pg_database</structname></link>.oid</literal></entry>

<entry>

OID of the database in which the object exists, or

zero if the object is aglobally-shared object, or

zero if the object is a shared object, or

NULL if the object is a transaction ID

</entry>

</row>

OBJS = catalog.o dependency.o heap.o index.o indexing.o namespace.o aclchk.o\

pg_aggregate.o pg_constraint.o pg_conversion.o pg_depend.o\

pg_largeobject.o pg_namespace.o pg_operator.o pg_proc.o pg_type.o

pg_largeobject.o pg_namespace.o pg_operator.o pg_proc.o pg_shdepend.o\

pg_type.o

BKIFILES = postgres.bki postgres.description