doc/src/sgml/ref/create_extension.sgml

   1 <!--
   2 doc/src/sgml/ref/create_extension.sgml
   3 PostgreSQL documentation
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   5
   6 <refentry id="sql-createextension">
   7  <indexterm zone="sql-createextension">
   8   <primary>CREATE EXTENSION</primary>
   9  </indexterm>
  10
  11  <refmeta>
  12   <refentrytitle>CREATE EXTENSION</refentrytitle>
  13   <manvolnum>7</manvolnum>
  14   <refmiscinfo>SQL - Language Statements</refmiscinfo>
  15  </refmeta>
  16
  17  <refnamediv>
  18   <refname>CREATE EXTENSION</refname>
  19   <refpurpose>install an extension</refpurpose>
  20  </refnamediv>
  21
  22  <refsynopsisdiv>
  23 <synopsis>
  24 CREATE EXTENSION [ IF NOT EXISTS ] <replaceable class="parameter">extension_name</replaceable>
  25     [ WITH ] [ SCHEMA <replaceable class="parameter">schema_name</replaceable> ]
  26              [ VERSION <replaceable class="parameter">version</replaceable> ]
  27              [ CASCADE ]
  28 </synopsis>
  29  </refsynopsisdiv>
  30
  31  <refsect1>
  32   <title>Description</title>
  33
  34   <para>
  35    <command>CREATE EXTENSION</command> loads a new extension into the current
  36    database.  There must not be an extension of the same name already loaded.
  37   </para>
  38
  39   <para>
  40    Loading an extension essentially amounts to running the extension's script
  41    file.  The script will typically create new <acronym>SQL</acronym> objects such as
  42    functions, data types, operators and index support methods.
  43    <command>CREATE EXTENSION</command> additionally records the identities
  44    of all the created objects, so that they can be dropped again if
  45    <command>DROP EXTENSION</command> is issued.
  46   </para>
  47
  48   <para>
  49    The user who runs <command>CREATE EXTENSION</command> becomes the
  50    owner of the extension for purposes of later privilege checks, and
  51    normally also becomes the owner of any objects created by the
  52    extension's script.
  53   </para>
  54
  55   <para>
  56    Loading an extension ordinarily requires the same privileges that would
  57    be required to create its component objects.  For many extensions this
  58    means superuser privileges are needed.
  59    However, if the extension is marked <firstterm>trusted</firstterm> in
  60    its control file, then it can be installed by any user who has
  61    <literal>CREATE</literal> privilege on the current database.
  62    In this case the extension object itself will be owned by the calling
  63    user, but the contained objects will be owned by the bootstrap superuser
  64    (unless the extension's script explicitly assigns them to the calling
  65    user).  This configuration gives the calling user the right to drop the
  66    extension, but not to modify individual objects within it.
  67   </para>
  68
  69  </refsect1>
  70
  71  <refsect1>
  72   <title>Parameters</title>
  73
  74     <variablelist>
  75      <varlistentry>
  76       <term><literal>IF NOT EXISTS</literal></term>
  77       <listitem>
  78        <para>
  79         Do not throw an error if an extension with the same name already
  80         exists.  A notice is issued in this case.  Note that there is no
  81         guarantee that the existing extension is anything like the one that
  82         would have been created from the currently-available script file.
  83        </para>
  84       </listitem>
  85      </varlistentry>
  86
  87      <varlistentry>
  88       <term><replaceable class="parameter">extension_name</replaceable></term>
  89       <listitem>
  90        <para>
  91         The name of the extension to be
  92         installed. <productname>PostgreSQL</productname> will create the
  93         extension using details from the file
  94         <literal>SHAREDIR/extension/</literal><replaceable class="parameter">extension_name</replaceable><literal>.control</literal>.
  95        </para>
  96       </listitem>
  97      </varlistentry>
  98
  99      <varlistentry>
 100       <term><replaceable class="parameter">schema_name</replaceable></term>
 101       <listitem>
 102        <para>
 103         The name of the schema in which to install the extension's
 104         objects, given that the extension allows its contents to be
 105         relocated.  The named schema must already exist.
 106         If not specified, and the extension's control file does not specify a
 107         schema either, the current default object creation schema is used.
 108        </para>
 109
 110        <para>
 111         If the extension specifies a <literal>schema</literal> parameter in its
 112         control file, then that schema cannot be overridden with
 113         a <literal>SCHEMA</literal> clause.  Normally, an error will be raised if
 114         a <literal>SCHEMA</literal> clause is given and it conflicts with the
 115         extension's <literal>schema</literal> parameter.  However, if
 116         the <literal>CASCADE</literal> clause is also given,
 117         then <replaceable class="parameter">schema_name</replaceable> is
 118         ignored when it conflicts.  The
 119         given <replaceable class="parameter">schema_name</replaceable> will be
 120         used for installation of any needed extensions that do not
 121         specify <literal>schema</literal> in their control files.
 122        </para>
 123
 124        <para>
 125         Remember that the extension itself is not considered to be within any
 126         schema: extensions have unqualified names that must be unique
 127         database-wide.  But objects belonging to the extension can be within
 128         schemas.
 129        </para>
 130       </listitem>
 131      </varlistentry>
 132
 133      <varlistentry>
 134       <term><replaceable class="parameter">version</replaceable></term>
 135       <listitem>
 136        <para>
 137         The version of the extension to install.  This can be written as
 138         either an identifier or a string literal.  The default version is
 139         whatever is specified in the extension's control file.
 140        </para>
 141       </listitem>
 142      </varlistentry>
 143
 144      <varlistentry>
 145       <term><literal>CASCADE</literal></term>
 146       <listitem>
 147        <para>
 148         Automatically install any extensions that this extension depends on
 149         that are not already installed.  Their dependencies are likewise
 150         automatically installed, recursively.  The <literal>SCHEMA</literal> clause,
 151         if given, applies to all extensions that get installed this way.
 152         Other options of the statement are not applied to
 153         automatically-installed extensions; in particular, their default
 154         versions are always selected.
 155        </para>
 156       </listitem>
 157      </varlistentry>
 158   </variablelist>
 159  </refsect1>
 160
 161  <refsect1>
 162   <title>Notes</title>
 163
 164   <para>
 165    Before you can use <command>CREATE EXTENSION</command> to load an extension
 166    into a database, the extension's supporting files must be installed.
 167    Information about installing the extensions supplied with
 168    <productname>PostgreSQL</productname> can be found in
 169    <link linkend="contrib">Additional Supplied Modules</link>.
 170   </para>
 171
 172   <para>
 173    The extensions currently available for loading can be identified from the
 174    <link linkend="view-pg-available-extensions"><structname>pg_available_extensions</structname></link>
 175    or
 176    <link linkend="view-pg-available-extension-versions"><structname>pg_available_extension_versions</structname></link>
 177    system views.
 178   </para>
 179
 180   <caution>
 181    <para>
 182     Installing an extension as superuser requires trusting that the
 183     extension's author wrote the extension installation script in a secure
 184     fashion.  It is not terribly difficult for a malicious user to create
 185     trojan-horse objects that will compromise later execution of a
 186     carelessly-written extension script, allowing that user to acquire
 187     superuser privileges.  However, trojan-horse objects are only hazardous
 188     if they are in the <varname>search_path</varname> during script
 189     execution, meaning that they are in the extension's installation target
 190     schema or in the schema of some extension it depends on.  Therefore, a
 191     good rule of thumb when dealing with extensions whose scripts have not
 192     been carefully vetted is to install them only into schemas for which
 193     CREATE privilege has not been and will not be granted to any untrusted
 194     users.  Likewise for any extensions they depend on.
 195    </para>
 196
 197    <para>
 198     The extensions supplied with <productname>PostgreSQL</productname> are
 199     believed to be secure against installation-time attacks of this sort,
 200     except for a few that depend on other extensions.  As stated in the
 201     documentation for those extensions, they should be installed into secure
 202     schemas, or installed into the same schemas as the extensions they
 203     depend on, or both.
 204    </para>
 205   </caution>
 206
 207   <para>
 208    For information about writing new extensions, see
 209    <xref linkend="extend-extensions"/>.
 210   </para>
 211  </refsect1>
 212
 213  <refsect1>
 214   <title>Examples</title>
 215
 216   <para>
 217    Install the <link linkend="hstore">hstore</link> extension into the
 218    current database, placing its objects in schema <literal>addons</literal>:
 219 <programlisting>
 220 CREATE EXTENSION hstore SCHEMA addons;
 221 </programlisting>
 222    Another way to accomplish the same thing:
 223 <programlisting>
 224 SET search_path = addons;
 225 CREATE EXTENSION hstore;
 226 </programlisting></para>
 227  </refsect1>
 228
 229  <refsect1>
 230   <title>Compatibility</title>
 231
 232   <para>
 233    <command>CREATE EXTENSION</command> is a <productname>PostgreSQL</productname>
 234    extension.
 235   </para>
 236  </refsect1>
 237
 238  <refsect1>
 239   <title>See Also</title>
 240
 241   <simplelist type="inline">
 242    <member><xref linkend="sql-alterextension"/></member>
 243    <member><xref linkend="sql-dropextension"/></member>
 244   </simplelist>
 245  </refsect1>
 246
 247 </refentry>