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$PostgreSQL: pgsql/doc/src/sgml/spi.sgml,v 1.32 2004/03/05 01:00:45 momjian Exp $
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<chapter id="spi">
 <title>Server Programming Interface</title>

 <indexterm zone="spi">
  <primary>SPI</primary>
 </indexterm>

 <para>
  The <firstterm>Server Programming Interface</firstterm>
  (<acronym>SPI</acronym>) gives writers of user-defined
  <acronym>C</acronym> functions the ability to run
  <acronym>SQL</acronym> commands inside their functions.
  <acronym>SPI</acronym> is a set of
  interface functions to simplify access to the parser, planner,
  optimizer, and executor. <acronym>SPI</acronym> also does some
  memory management.
 </para>

 <note>
  <para>
   The available procedural languages provide various means to
   execute SQL commands from procedures.  Some of these are based on or
   modelled after SPI, so this documentation might be of use for users
   of those languages as well.
  </para>
 </note>

 <para>
  To avoid misunderstanding we'll use the term <quote>function</quote>
  when we speak of <acronym>SPI</acronym> interface functions and
  <quote>procedure</quote> for a user-defined C-function that is
  using <acronym>SPI</acronym>.
 </para>

 <para>
  Note that if during the execution of a procedure the transaction is
  aborted because of an error in a command, then control will not be
  returned to your procedure.  Rather, all work will be rolled back
  and the server will wait for the next command from the client.  A
  related restriction is the inability to execute
  <command>BEGIN</command>, <command>COMMIT</command>, and
  <command>ROLLBACK</command> (transaction control statements) inside
  a procedure.  Both of these restrictions will probably be changed in
  the future.
 </para>

 <para>
  <acronym>SPI</acronym> functions return a nonnegative result on
  success (either via a returned integer value or in the global
  variable <varname>SPI_result</varname>, as described below).  On
  error, a negative result or <symbol>NULL</symbol> will be returned.
 </para>

 <para>
  Source code files that use SPI must include the header file
  <filename>executor/spi.h</filename>.
 </para>


<sect1 id="spi-interface">
 <title>Interface Functions</title>

 <refentry id="spi-spi-connect">
  <refmeta>
   <refentrytitle>SPI_connect</refentrytitle>
  </refmeta>

  <refnamediv>
   <refname>SPI_connect</refname>
   <refpurpose>connect a procedure to the SPI manager</refpurpose>
 </refnamediv>

 <indexterm><primary>SPI_connect</primary></indexterm>

 <refsynopsisdiv>
<synopsis>
int SPI_connect(void)
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   <function>SPI_connect</function> opens a connection from a
   procedure invocation to the SPI manager.  You must call this
   function if you want to execute commands through SPI.  Some utility
   SPI functions may be called from unconnected procedures.
  </para>

  <para>
   If your procedure is already connected,
   <function>SPI_connect</function> will return the error code
   <returnvalue>SPI_ERROR_CONNECT</returnvalue>.  This could happen if
   a procedure that has called <function>SPI_connect</function>
   directly calls another procedure that calls
   <function>SPI_connect</function>.  While recursive calls to the
   <acronym>SPI</acronym> manager are permitted when an SQL command
   called through SPI invokes another function that uses
   <acronym>SPI</acronym>, directly nested calls to
   <function>SPI_connect</function> and
   <function>SPI_finish</function> are forbidden.
  </para>
 </refsect1>

 <refsect1>
  <title>Return Value</title>

  <variablelist>
   <varlistentry>
    <term><symbol>SPI_OK_CONNECT</symbol></term>
    <listitem>
     <para>
      on success
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><symbol>SPI_ERROR_CONNECT</symbol></term>
    <listitem>
     <para>
      on error
     </para>
    </listitem>
   </varlistentry>
  </variablelist>
 </refsect1>
</refentry>

<!-- *********************************************** -->

<refentry id="spi-spi-finish">
 <refmeta>
  <refentrytitle>SPI_finish</refentrytitle>
 </refmeta>

 <refnamediv>
  <refname>SPI_finish</refname>
  <refpurpose>disconnect a procedure from the SPI manager</refpurpose>
 </refnamediv>

 <indexterm><primary>SPI_finish</primary></indexterm>

 <refsynopsisdiv>
<synopsis>
int SPI_finish(void)
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   <function>SPI_finish</function> closes an existing connection to
   the SPI manager.  You must call this function after completing the
   SPI operations needed during your procedure's current invocation.
   You do not need to worry about making this happen, however, if you
   abort the transaction via <literal>elog(ERROR)</literal>.  In that
   case SPI will clean itself up automatically.
  </para>

  <para>
   If <function>SPI_finish</function> is called without having a valid
   connection, it will return <symbol>SPI_ERROR_UNCONNECTED</symbol>.
   There is no fundamental problem with this; it means that the SPI
   manager has nothing to do.
  </para>
 </refsect1>

 <refsect1>
  <title>Return Value</title>

  <variablelist>
   <varlistentry>
    <term><symbol>SPI_OK_FINISH</symbol></term>
    <listitem>
     <para>
      if properly disconnected
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><symbol>SPI_ERROR_UNCONNECTED</symbol></term>
    <listitem>
     <para>
      if called from an unconnected procedure
     </para>
    </listitem>
   </varlistentry>
  </variablelist>
 </refsect1>
</refentry>

<!-- *********************************************** -->

<refentry id="spi-spi-exec">
 <refmeta>
  <refentrytitle>SPI_exec</refentrytitle>
 </refmeta>

 <refnamediv>
  <refname>SPI_exec</refname>
  <refpurpose>execute a command</refpurpose>
 </refnamediv>

 <indexterm><primary>SPI_exec</primary></indexterm>

 <refsynopsisdiv>
<synopsis>
int SPI_exec(const char * <parameter>command</parameter>, int <parameter>count</parameter>)
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   <function>SPI_exec</function> executes the specified SQL command
   for <parameter>count</parameter> rows.
  </para>

  <para>
   This function should only be called from a connected procedure.  If
   <parameter>count</parameter> is zero then it executes the command
   for all rows that it applies to.  If <parameter>count</parameter>
   is greater than 0, then the number of rows for which the command
   will be executed is restricted (much like a
   <literal>LIMIT</literal> clause). For example,
<programlisting>
SPI_exec("INSERT INTO tab SELECT * FROM tab", 5);
</programlisting>
   will allow at most 5 rows to be inserted into the table.
  </para>

  <para>
   You may pass multiple commands in one string, and the command may
   be rewritten by rules. <function>SPI_exec</function> returns the
   result for the command executed last.
  </para>

  <para>
   The actual number of rows for which the (last) command was executed
   is returned in the global variable <varname>SPI_processed</varname>
   (unless the return value of the function is
   <symbol>SPI_OK_UTILITY</symbol>).  If the return value of the
   function is <symbol>SPI_OK_SELECT</symbol> then you may the use
   global pointer <literal>SPITupleTable *SPI_tuptable</literal> to
   access the result rows.
  </para>

  <para>
   The structure <structname>SPITupleTable</structname> is defined
   thus:
<programlisting>
typedef struct
{
    MemoryContext tuptabcxt;    /* memory context of result table */
    uint32      alloced;        /* number of alloced vals */
    uint32      free;           /* number of free vals */
    TupleDesc   tupdesc;        /* row descriptor */
    HeapTuple  *vals;           /* rows */
} SPITupleTable;
</programlisting>
   <structfield>vals</> is an array of pointers to rows.  (The number
   of valid entries is given by <varname>SPI_processed</varname>).
   <structfield>tupdesc</> is a row descriptor which you may pass to
   SPI functions dealing with rows.  <structfield>tuptabcxt</>,
   <structfield>alloced</>, and <structfield>free</> are internal
   fields not intended for use by SPI callers.
  </para>

  <para>
   <function>SPI_finish</function> frees all
   <structname>SPITupleTable</>s allocated during the current
   procedure.  You can free a particular result table earlier, if you
   are done with it, by calling <function>SPI_freetuptable</function>.
  </para>
 </refsect1>

 <refsect1>
  <title>Arguments</title>

  <variablelist>
   <varlistentry>
    <term><literal>const char * <parameter>command</parameter></literal></term>
    <listitem>
     <para>
      string containing command to execute
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>int <parameter>count</parameter></literal></term>
    <listitem>
     <para>
      maximum number of rows to process or return
     </para>
    </listitem>
   </varlistentry>
  </variablelist>
 </refsect1>

 <refsect1>
  <title>Return Value</title>

  <para>
   If the execution of the command was successful then one of the
   following (nonnegative) values will be returned:

   <variablelist>
    <varlistentry>
     <term><symbol>SPI_OK_SELECT</symbol></term>
     <listitem>
      <para>
       if a <command>SELECT</command> (but not <command>SELECT
       INTO</>) was executed
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><symbol>SPI_OK_SELINTO</symbol></term>
     <listitem>
      <para>
       if a <command>SELECT INTO</command> was executed
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><symbol>SPI_OK_DELETE</symbol></term>
     <listitem>
      <para>
       if a <command>DELETE</command> was executed
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><symbol>SPI_OK_INSERT</symbol></term>
     <listitem>
      <para>
       if an <command>INSERT</command> was executed
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><symbol>SPI_OK_UPDATE</symbol></term>
     <listitem>
      <para>
       if an <command>UPDATE</command> was executed
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><symbol>SPI_OK_UTILITY</symbol></term>
     <listitem>
      <para>
       if a utility command (e.g., <command>CREATE TABLE</command>)
       was executed
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>

  <para>
   On error, one of the following negative values is returned:

   <variablelist>
    <varlistentry>
     <term><symbol>SPI_ERROR_ARGUMENT</symbol></term>
     <listitem>
      <para>
       if <parameter>command</parameter> is <symbol>NULL</symbol> or
       <parameter>count</parameter> is less than 0
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><symbol>SPI_ERROR_COPY</symbol></term>
     <listitem>
      <para>
       if <command>COPY TO stdout</> or <command>COPY FROM stdin</>
       was attempted
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><symbol>SPI_ERROR_CURSOR</symbol></term>
     <listitem>
      <para>
       if <command>DECLARE</>, <command>CLOSE</>, or <command>FETCH</>
       was attempted
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><symbol>SPI_ERROR_TRANSACTION</symbol></term>
     <listitem>
      <para>
       if <command>BEGIN</>, <command>COMMIT</>, or
       <command>ROLLBACK</> was attempted
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><symbol>SPI_ERROR_OPUNKNOWN</symbol></term>
     <listitem>
      <para>
       if the command type is unknown (shouldn't happen)
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><symbol>SPI_ERROR_UNCONNECTED</symbol></term>
     <listitem>
      <para>
       if called from an unconnected procedure
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>
 </refsect1>

 <refsect1>
  <title>Notes</title>

  <para>
   The functions <function>SPI_exec</function>,
   <function>SPI_execp</function>, and
   <function>SPI_prepare</function> change both
   <varname>SPI_processed</varname> and
   <varname>SPI_tuptable</varname> (just the pointer, not the contents
   of the structure).  Save these two global variables into local
   procedure variables if you need to access the result of
   <function>SPI_exec</function> or <function>SPI_execp</function>
   across later calls.
  </para>
 </refsect1>
</refentry>

<!-- *********************************************** -->

<refentry id="spi-spi-prepare">
 <refmeta>
  <refentrytitle>SPI_prepare</refentrytitle>
 </refmeta>

 <refnamediv>
  <refname>SPI_prepare</refname>
  <refpurpose>prepare a plan for a command, without executing it yet</refpurpose>
 </refnamediv>

 <indexterm><primary>SPI_prepare</primary></indexterm>

 <refsynopsisdiv>
<synopsis>
void * SPI_prepare(const char * <parameter>command</parameter>, int <parameter>nargs</parameter>, Oid * <parameter>argtypes</parameter>)
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   <function>SPI_prepare</function> creates and returns an execution
   plan for the specified command but doesn't execute the command.
   This function should only be called from a connected procedure.
  </para>

  <para>
   When the same or a similar command is to be executed repeatedly, it
   may be advantageous to perform the planning only once.
   <function>SPI_prepare</function> converts a command string into an
   execution plan that can be executed repeatedly using
   <function>SPI_execp</function>.
  </para>

  <para>
   A prepared command can be generalized by writing parameters
   (<literal>$1</>, <literal>$2</>, etc.) in place of what would be
   constants in a normal command.  The actual values of the parameters
   are then specified when <function>SPI_execp</function> is called.
   This allows the prepared command to be used over a wider range of
   situations than would be possible without parameters.
  </para>

  <para>
   The plan returned by <function>SPI_prepare</function> can be used
   only in the current invocation of the procedure since
   <function>SPI_finish</function> frees memory allocated for a plan.
   But a plan can be saved for longer using the function
   <function>SPI_saveplan</function>.
  </para>
 </refsect1>

 <refsect1>
  <title>Arguments</title>

  <variablelist>
   <varlistentry>
    <term><literal>const char * <parameter>command</parameter></literal></term>
    <listitem>
     <para>
      command string
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>int <parameter>nargs</parameter></literal></term>
    <listitem>
     <para>
      number of input parameters (<literal>$1</>, <literal>$2</>, etc.)
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>Oid * <parameter>argtypes</parameter></literal></term>
    <listitem>
     <para>
      pointer to an array containing the <acronym>OID</acronym>s of
      the data types of the parameters
     </para>
    </listitem>
   </varlistentry>
  </variablelist>
 </refsect1>

 <refsect1>
  <title>Return Value</title>

  <para>
   <function>SPI_prepare</function> returns non-null pointer to an
   execution plan.  On error, <symbol>NULL</symbol> will be returned.
   In both cases, <varname>SPI_result</varname> will be set analogous
   to the value returned by <function>SPI_exec</function>, except that
   it is set to <symbol>SPI_ERROR_ARGUMENT</symbol> if
   <parameter>command</parameter> is <symbol>NULL</symbol>, or if
   <parameter>nargs</> is less than 0, or if <parameter>nargs</> is
   greater than 0 and <parameter>argtypes</> is <symbol>NULL</symbol>.
  </para>
 </refsect1>

 <refsect1>
  <title>Notes</title>

  <para>
   There is a disadvantage to using parameters: since the planner does
   not know the values that will be supplied for the parameters, it
   may make worse planning choices than it would make for a normal
   command with all constants visible.
  </para>
 </refsect1>
</refentry>

<!-- *********************************************** -->

<refentry id="spi-spi-getargcount">
 <refmeta>
  <refentrytitle>SPI_getargcount</refentrytitle>
 </refmeta>

 <refnamediv>
  <refname>SPI_getargcount</refname>
  <refpurpose>returns the number of arguments needed when executing a plan
  prepared by <function>SPI_prepare</function></refpurpose>
 </refnamediv>

 <indexterm><primary>SPI_getargcount</primary></indexterm>

 <refsynopsisdiv>
<synopsis>
int SPI_getargcount(void * <parameter>plan</parameter>)
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   <function>SPI_getargcount</function> returns the number of arguments needed
   when executing a plan prepared by <function>SPI_prepare</function>.
  </para>
 </refsect1>

 <refsect1>
  <title>Arguments</title>

  <variablelist>
   <varlistentry>
    <term><literal>void * <parameter>plan</parameter></literal></term>
    <listitem>
     <para>
      execution plan (returned by <function>SPI_prepare</function>)
     </para>
    </listitem>
   </varlistentry>
  </variablelist>
 </refsect1>

 <refsect1>
  <title>Return Value</title>
  <para>
    The expected argument count for the <parameter>plan</parameter> or
    <symbol>SPI_ERROR_ARGUMENT</symbol> if the <parameter>plan
    </parameter> is <symbol>NULL</symbol>
  </para>
 </refsect1>
</refentry>

<!-- *********************************************** -->

<refentry id="spi-spi-getargtypeid">
 <refmeta>
  <refentrytitle>SPI_getargtypeid</refentrytitle>
 </refmeta>

 <refnamediv>
  <refname>SPI_getargtypeid</refname>
  <refpurpose>returns the expected typeid for the specified argument when
  executing a plan prepared by <function>SPI_prepare</function></refpurpose>
 </refnamediv>

 <indexterm><primary>SPI_getargtypeid</primary></indexterm>

 <refsynopsisdiv>
<synopsis>
Oid SPI_getargtypeid(void * <parameter>plan</parameter>, int <parameter>argIndex</parameter>)
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   <function>SPI_getargtypeid</function> returns the Oid representing the type
   id for argument at <parameter>argIndex</parameter> in a plan prepared by
   <function>SPI_prepare</function>. First argument is at index zero.
  </para>
 </refsect1>

 <refsect1>
  <title>Arguments</title>

  <variablelist>
   <varlistentry>
    <term><literal>void * <parameter>plan</parameter></literal></term>
    <listitem>
     <para>
      execution plan (returned by <function>SPI_prepare</function>)
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>int <parameter>argIndex</parameter></literal></term>
    <listitem>
     <para>
      zero based index of the argument
     </para>
    </listitem>
   </varlistentry>
  </variablelist>
 </refsect1>

 <refsect1>
  <title>Return Value</title>
  <para>
    The type id of the argument at the given index or <symbol>
    SPI_ERROR_ARGUMENT</symbol> if the <parameter>plan</parameter> is
    <symbol>NULL</symbol> or <parameter>argIndex</parameter> is less than 0 or
    not less than the number of arguments declared for the <parameter>plan
    </parameter>
  </para>
 </refsect1>
</refentry>

<!-- *********************************************** -->

<refentry id="spi-spi-is-cursor-plan">
 <refmeta>
  <refentrytitle>SPI_is_cursor_plan</refentrytitle>
 </refmeta>

 <refnamediv>
  <refname>SPI_is_cursor_plan</refname>
  <refpurpose>returns <symbol>true</symbol> if a plan
  prepared by <function>SPI_prepare</function> can be passed
  as an argument to <function>SPI_cursor_open</function></refpurpose>
 </refnamediv>

 <indexterm><primary>SPI_is_cursor_plan</primary></indexterm>

 <refsynopsisdiv>
<synopsis>
bool SPI_is_cursor_plan(void * <parameter>plan</parameter>)
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   <function>SPI_is_cursor_plan</function> returns <symbol>true</symbol>
   if a plan prepared by <function>SPI_prepare</function> can be passed
   as an argument to <function>SPI_cursor_open</function> and <symbol>
   false</symbol> if that is not the case. The criteria is that the
   <parameter>plan</parameter> represents one single command and that this
   command is a <command>SELECT</command> without an <command>INTO</command>
   clause.
  </para>
 </refsect1>

 <refsect1>
  <title>Arguments</title>

  <variablelist>
   <varlistentry>
    <term><literal>void * <parameter>plan</parameter></literal></term>
    <listitem>
     <para>
      execution plan (returned by <function>SPI_prepare</function>)
     </para>
    </listitem>
   </varlistentry>
  </variablelist>
 </refsect1>

 <refsect1>
  <title>Return Value</title>
  <para>
    <symbol>true</symbol> or <symbol>false</symbol> to indicate if the
    <parameter>plan</parameter> can produce a cursor or not, or
    <symbol>SPI_ERROR_ARGUMENT</symbol> if the <parameter>plan</parameter>
    is <symbol>NULL</symbol>
  </para>
 </refsect1>
</refentry>

<!-- *********************************************** -->

<refentry id="spi-spi-execp">
 <refmeta>
  <refentrytitle>SPI_execp</refentrytitle>
 </refmeta>

 <refnamediv>
  <refname>SPI_execp</refname>
  <refpurpose>executes a plan prepared by <function>SPI_prepare</function></refpurpose>
 </refnamediv>

 <indexterm><primary>SPI_execp</primary></indexterm>

 <refsynopsisdiv>
<synopsis>
int SPI_execp(void * <parameter>plan</parameter>, Datum * <parameter>values</parameter>, const char * <parameter>nulls</parameter>, int <parameter>count</parameter>)
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   <function>SPI_execp</function> executes a plan prepared by
   <function>SPI_prepare</function>.  <parameter>tcount</parameter>
   has the same interpretation as in <function>SPI_exec</function>.
  </para>
 </refsect1>

 <refsect1>
  <title>Arguments</title>

  <variablelist>
   <varlistentry>
    <term><literal>void * <parameter>plan</parameter></literal></term>
    <listitem>
     <para>
      execution plan (returned by <function>SPI_prepare</function>)
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>Datum *<parameter>values</parameter></literal></term>
    <listitem>
     <para>
      actual parameter values
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>const char * <parameter>nulls</parameter></literal></term>
    <listitem>
     <para>
      An array describing which parameters are null.
      <literal>n</literal> indicates a null value (entry in
      <parameter>values</> will be ignored); a space indicates a
      nonnull value (entry in <parameter>values</> is valid).
     </para>

     <para>
      If <parameter>nulls</parameter> is <symbol>NULL</symbol> then
      <function>SPI_execp</function> assumes that no parameters are
      null.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>int <parameter>count</parameter></literal></term>
    <listitem>
     <para>
      number of row for which plan is to be executed
     </para>
    </listitem>
   </varlistentry>
  </variablelist>
 </refsect1>

 <refsect1>
  <title>Return Value</title>

  <para>
   The return value is the same as for <function>SPI_exec</function>
   or one of the following:

   <variablelist>
    <varlistentry>
     <term><symbol>SPI_ERROR_ARGUMENT</symbol></term>
     <listitem>
      <para>
       if <parameter>plan</parameter> is <symbol>NULL</symbol> or
       <parameter>count</parameter> is less than 0
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><symbol>SPI_ERROR_PARAM</symbol></term>
     <listitem>
      <para>
       if <parameter>values</parameter> is <symbol>NULL</symbol> and
       <parameter>plan</parameter> was prepared with some parameters
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>

  <para>
   <varname>SPI_processed</varname> and
   <varname>SPI_tuptable</varname> are set as in
   <function>SPI_exec</function> if successful.
  </para>
 </refsect1>

 <refsect1>
  <title>Notes</title>

  <para>
   If one of the objects (a table, function, etc.) referenced by the
   prepared plan is dropped during the session then the result of
   <function>SPI_execp</function> for this plan will be unpredictable.
  </para>
 </refsect1>
</refentry>

<!-- *********************************************** -->

<refentry id="spi-spi-cursor-open">
 <refmeta>
  <refentrytitle>SPI_cursor_open</refentrytitle>
 </refmeta>

 <refnamediv>
  <refname>SPI_cursor_open</refname>
  <refpurpose>set up a cursor using a plan created with <function>SPI_prepare</function></refpurpose>
 </refnamediv>

 <indexterm><primary>SPI_cursor_open</primary></indexterm>

 <refsynopsisdiv>
<synopsis>
Portal SPI_cursor_open(const char * <parameter>name</parameter>, void * <parameter>plan</parameter>, Datum * <parameter>values</parameter>, const char * <parameter>nulls</parameter>)
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   <function>SPI_cursor_open</function> sets up a cursor (internally,
   a portal) that will execute a plan prepared by
   <function>SPI_prepare</function>.
  </para>

  <para>
   Using a cursor instead of executing the plan directly has two
   benefits.  First, the result rows can be retrieved a few at a time,
   avoiding memory overrun for queries that return many rows.  Second,
   a portal can outlive the current procedure (it can, in fact, live
   to the end of the current transaction).  Returning the portal name
   to the procedure's caller provides a way of returning a row set as
   result.
  </para>
 </refsect1>

 <refsect1>
  <title>Arguments</title>

  <variablelist>
   <varlistentry>
    <term><literal>const char * <parameter>name</parameter></literal></term>
    <listitem>
     <para>
      name for portal, or <symbol>NULL</symbol> to let the system
      select a name
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>void * <parameter>plan</parameter></literal></term>
    <listitem>
     <para>
      execution plan (returned by <function>SPI_prepare</function>)
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>Datum * <parameter>values</parameter></literal></term>
    <listitem>
     <para>
      actual parameter values
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>const char *<parameter>nulls</parameter></literal></term>
    <listitem>
     <para>
      An array describing which parameters are null values.
      <literal>n</literal> indicates a null value (entry in
      <parameter>values</> will be ignored); a space indicates a
      nonnull value (entry in <parameter>values</> is valid).  If
      <parameter>nulls</parameter> is <symbol>NULL</> then
      <function>SPI_cursor_open</function> assumes that no parameters
      are null.
     </para>
    </listitem>
   </varlistentry>
  </variablelist>
 </refsect1>

 <refsect1>
  <title>Return Value</title>

  <para>
   pointer to portal containing the cursor, or <symbol>NULL</symbol>
   on error
  </para>
 </refsect1>
</refentry>

<!-- *********************************************** -->

<refentry id="spi-spi-cursor-find">
 <refmeta>
  <refentrytitle>SPI_cursor_find</refentrytitle>
 </refmeta>

 <refnamediv>
  <refname>SPI_cursor_find</refname>
  <refpurpose>find an existing cursor by name</refpurpose>
 </refnamediv>

 <indexterm><primary>SPI_cursor_find</primary></indexterm>

 <refsynopsisdiv>
<synopsis>
Portal SPI_cursor_find(const char * <parameter>name</parameter>)
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   <function>SPI_cursor_find</function> finds an existing portal by
   name.  This is primarily useful to resolve a cursor name returned
   as text by some other function.
  </para>
 </refsect1>

 <refsect1>
  <title>Arguments</title>

  <variablelist>
   <varlistentry>
    <term><literal>const char * <parameter>name</parameter></literal></term>
    <listitem>
     <para>
      name of the portal
     </para>
    </listitem>
   </varlistentry>
  </variablelist>
 </refsect1>

 <refsect1>
  <title>Return Value</title>

  <para>
   pointer to the portal with the specified name, or
   <symbol>NULL</symbol> if none was found
  </para>
 </refsect1>
</refentry>

<!-- *********************************************** -->

<refentry id="spi-spi-cursor-fetch">
 <refmeta>
  <refentrytitle>SPI_cursor_fetch</refentrytitle>
 </refmeta>

 <refnamediv>
  <refname>SPI_cursor_fetch</refname>
  <refpurpose>fetch some rows from a cursor</refpurpose>
 </refnamediv>

 <indexterm><primary>SPI_cursor_fetch</primary></indexterm>

 <refsynopsisdiv>
<synopsis>
void SPI_cursor_fetch(Portal <parameter>portal</parameter>, bool <parameter>forward</parameter>, int <parameter>count</parameter>)
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   <function>SPI_cursor_fetch</function> fetches some rows from a
   cursor.  This is equivalent to the SQL command <command>FETCH</>.
  </para>
 </refsect1>

 <refsect1>
  <title>Arguments</title>

  <variablelist>
   <varlistentry>
    <term><literal>Portal <parameter>portal</parameter></literal></term>
    <listitem>
     <para>
      portal containing the cursor
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>bool <parameter>forward</parameter></literal></term>
    <listitem>
     <para>
      true for fetch forward, false for fetch backward
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>int <parameter>count</parameter></literal></term>
    <listitem>
     <para>
      maximum number of rows to fetch
     </para>
    </listitem>
   </varlistentry>
  </variablelist>
 </refsect1>

 <refsect1>
  <title>Return Value</title>

  <para>
   <varname>SPI_processed</varname> and
   <varname>SPI_tuptable</varname> are set as in
   <function>SPI_exec</function> if successful.
  </para>
 </refsect1>
</refentry>

<!-- *********************************************** -->

<refentry id="spi-spi-cursor-move">
 <refmeta>
  <refentrytitle>SPI_cursor_move</refentrytitle>
 </refmeta>

 <refnamediv>
  <refname>SPI_cursor_move</refname>
  <refpurpose>move a cursor</refpurpose>
 </refnamediv>

 <indexterm><primary>SPI_cursor_move</primary></indexterm>

 <refsynopsisdiv>
<synopsis>
void SPI_cursor_move(Portal <parameter>portal</parameter>, bool <parameter>forward</parameter>, int <parameter>count</parameter>)
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   <function>SPI_cursor_move</function> skips over some number of rows
   in a cursor.  This is equivalent to the SQL command
   <command>MOVE</>.
  </para>
 </refsect1>

 <refsect1>
  <title>Arguments</title>

  <variablelist>
   <varlistentry>
    <term><literal>Portal <parameter>portal</parameter></literal></term>
    <listitem>
     <para>
      portal containing the cursor
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>bool <parameter>forward</parameter></literal></term>
    <listitem>
     <para>
      true for move forward, false for move backward
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>int <parameter>count</parameter></literal></term>
    <listitem>
     <para>
      maximum number of rows to move
     </para>
    </listitem>
   </varlistentry>
  </variablelist>
 </refsect1>
</refentry>

<!-- *********************************************** -->

<refentry id="spi-spi-cursor-close">
 <refmeta>
  <refentrytitle>SPI_cursor_close</refentrytitle>
 </refmeta>

 <refnamediv>
  <refname>SPI_cursor_close</refname>
  <refpurpose>close a cursor</refpurpose>
 </refnamediv>

 <indexterm><primary>SPI_cursor_close</primary></indexterm>

 <refsynopsisdiv>
<synopsis>
void SPI_cursor_close(Portal <parameter>portal</parameter>)
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   <function>SPI_cursor_close</function> closes a previously created
   cursor and releases its portal storage.
  </para>

  <para>
   All open cursors are closed automatically at the end of a
   transaction.  <function>SPI_cursor_close</function> need only be
   invoked if it is desirable to release resources sooner.
  </para>
 </refsect1>

 <refsect1>
  <title>Arguments</title>

  <variablelist>
   <varlistentry>
    <term><literal>Portal <parameter>portal</parameter></literal></term>
    <listitem>
     <para>
      portal containing the cursor
     </para>
    </listitem>
   </varlistentry>
  </variablelist>
 </refsect1>
</refentry>

<!-- *********************************************** -->

<refentry id="spi-spi-saveplan">
 <refmeta>
  <refentrytitle>SPI_saveplan</refentrytitle>
 </refmeta>

 <refnamediv>
  <refname>SPI_saveplan</refname>
  <refpurpose>save a plan</refpurpose>
 </refnamediv>

 <indexterm><primary>SPI_saveplan</primary></indexterm>

 <refsynopsisdiv>
<synopsis>
void * SPI_saveplan(void * <parameter>plan</parameter>)
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   <function>SPI_saveplan</function> saves a passed plan (prepared by
   <function>SPI_prepare</function>) in memory protected from freeing
   by <function>SPI_finish</function> and by the transaction manager
   and returns a pointer to the saved plan.  This gives you the
   ability to reuse prepared plans in the subsequent invocations of
   your procedure in the current session.  You may save the pointer
   returned in a local variable.  Always check if this pointer is
   <symbol>NULL</symbol> or not either when preparing a plan or using
   an already prepared plan in <function>SPI_execp</function>.
  </para>
 </refsect1>

 <refsect1>
  <title>Arguments</title>

  <variablelist>
   <varlistentry>
    <term><literal>void * <parameter>plan</parameter></literal></term>
    <listitem>
     <para>
      the plan to be saved
     </para>
    </listitem>
   </varlistentry>
  </variablelist>
 </refsect1>

 <refsect1>
  <title>Return Value</title>

  <para>
   Pointer to the saved plan; <symbol>NULL</symbol> if unsuccessful.
   On error, <varname>SPI_result</varname> is set thus:

   <variablelist>
    <varlistentry>
     <term><symbol>SPI_ERROR_ARGUMENT</symbol></term>
     <listitem>
      <para>
       if <parameter>plan</parameter> is <symbol>NULL</symbol>
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><symbol>SPI_ERROR_UNCONNECTED</symbol></term>
     <listitem>
      <para>
       if called from an unconnected procedure
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>
 </refsect1>

 <refsect1>
  <title>Notes</title>

  <para>
   If one of the objects (a table, function, etc.) referenced by the
   prepared plan is dropped during the session then the results of
   <function>SPI_execp</function> for this plan will be unpredictable.
  </para>
 </refsect1>
</refentry>

</sect1>

<sect1 id="spi-interface-support">
 <title>Interface Support Functions</title>

 <para>
  The functions described here provide an interface for extracting
  information from result sets returned by <function>SPI_exec</> and
  other SPI functions.
 </para>

 <para>
  All functions described in this section may be used by both
  connected and unconnected procedures.
 </para>

<!-- *********************************************** -->

<refentry id="spi-spi-fname">
 <refmeta>
  <refentrytitle>SPI_fname</refentrytitle>
 </refmeta>

 <refnamediv>
  <refname>SPI_fname</refname>
  <refpurpose>determine the column name for the specified column number</refpurpose>
 </refnamediv>

 <indexterm><primary>SPI_fname</primary></indexterm>

 <refsynopsisdiv>
<synopsis>
char * SPI_fname(TupleDesc <parameter>rowdesc</parameter>, int <parameter>colnumber</parameter>)
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   <function>SPI_fname</function> returns the column name of the
   specified column.  (You can use <function>pfree</function> to
   release the copy of the name when you don't need it anymore.)
  </para>
 </refsect1>

 <refsect1>
  <title>Arguments</title>

  <variablelist>
   <varlistentry>
    <term><literal>TupleDesc <parameter>rowdesc</parameter></literal></term>
    <listitem>
     <para>
      input row description
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>int <parameter>colnumber</parameter></literal></term>
    <listitem>
     <para>
      column number (count starts at 1)
     </para>
    </listitem>
   </varlistentry>
  </variablelist>
 </refsect1>

 <refsect1>
  <title>Return Value</title>

  <para>
   The column name; <symbol>NULL</symbol> if
   <parameter>colnumber</parameter> is out of range.
   <varname>SPI_result</varname> set to
   <symbol>SPI_ERROR_NOATTRIBUTE</symbol> on error.
  </para>
 </refsect1>
</refentry>

<!-- *********************************************** -->

<refentry id="spi-spi-fnumber">
 <refmeta>
  <refentrytitle>SPI_fnumber</refentrytitle>
 </refmeta>

 <refnamediv>
  <refname>SPI_fnumber</refname>
  <refpurpose>determine the column number for the specified column name</refpurpose>
 </refnamediv>

 <indexterm><primary>SPI_fnumber</primary></indexterm>

 <refsynopsisdiv>
<synopsis>
int SPI_fnumber(TupleDesc <parameter>rowdesc</parameter>, const char * <parameter>colname</parameter>)
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   <function>SPI_fnumber</function> returns the column number for the
   column with the specified name.
  </para>

  <para>
   If <parameter>colname</parameter> refers to a system column (e.g.,
   <literal>oid</>) then the appropriate negative column number will
   be returned.  The caller should be careful to test the return value
   for exact equality to <symbol>SPI_ERROR_NOATTRIBUTE</symbol> to
   detect an error; testing the result for less than or equal to 0 is
   not correct unless system columns should be rejected.
  </para>
 </refsect1>

 <refsect1>
  <title>Arguments</title>

  <variablelist>
   <varlistentry>
    <term><literal>TupleDesc <parameter>rowdesc</parameter></literal></term>
    <listitem>
     <para>
      input row description
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>const char * <parameter>colname</parameter></literal></term>
    <listitem>
     <para>
      column name
     </para>
    </listitem>
   </varlistentry>
  </variablelist>
 </refsect1>

 <refsect1>
  <title>Return Value</title>

  <para>
   Column number (count starts at 1), or
   <symbol>SPI_ERROR_NOATTRIBUTE</symbol> if the named column was not
   found.
  </para>
 </refsect1>
</refentry>

<!-- *********************************************** -->

<refentry id="spi-spi-getvalue">
 <refmeta>
  <refentrytitle>SPI_getvalue</refentrytitle>
 </refmeta>

 <refnamediv>
  <refname>SPI_getvalue</refname>
  <refpurpose>return the string value of the specified column</refpurpose>
 </refnamediv>

 <indexterm><primary>SPI_getvalue</primary></indexterm>

 <refsynopsisdiv>
<synopsis>
char * SPI_getvalue(HeapTuple <parameter>row</parameter>, TupleDesc <parameter>rowdesc</parameter>, int <parameter>colnumber</parameter>)
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   <function>SPI_getvalue</function> returns the string representation
   of the value of the specified column.
  </para>

  <para>
   The result is returned in memory allocated using
   <function>palloc</function>.  (You can use
   <function>pfree</function> to release the memory when you don't
   need it anymore.)
  </para>
 </refsect1>

 <refsect1>
  <title>Arguments</title>

  <variablelist>
   <varlistentry>
    <term><literal>HeapTuple <parameter>row</parameter></literal></term>
    <listitem>
     <para>
      input row to be examined
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>TupleDesc <parameter>rowdesc</parameter></literal></term>
    <listitem>
     <para>
      input row description
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>int <parameter>colnumber</parameter></literal></term>
    <listitem>
     <para>
      column number (count starts at 1)
     </para>
    </listitem>
   </varlistentry>
  </variablelist>
 </refsect1>

 <refsect1>
  <title>Return Value</title>

  <para>
   Column value, or <symbol>NULL</symbol> if the column is null,
   <parameter>colnumber</parameter> is out of range
   (<varname>SPI_result</varname> is set to
   <symbol>SPI_ERROR_NOATTRIBUTE</symbol>), or no no output function
   available (<varname>SPI_result</varname> is set to
   <symbol>SPI_ERROR_NOOUTFUNC</symbol>).
  </para>
 </refsect1>
</refentry>

<!-- *********************************************** -->

<refentry id="spi-spi-getbinval">
 <refmeta>
  <refentrytitle>SPI_getbinval</refentrytitle>
 </refmeta>

 <refnamediv>
  <refname>SPI_getbinval</refname>
  <refpurpose>return the binary value of the specified column</refpurpose>
 </refnamediv>

 <indexterm><primary>SPI_getbinval</primary></indexterm>

 <refsynopsisdiv>
<synopsis>
Datum SPI_getbinval(HeapTuple <parameter>row</parameter>, TupleDesc <parameter>rowdesc</parameter>, int <parameter>colnumber</parameter>, bool * <parameter>isnull</parameter>)
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   <function>SPI_getbinval</function> returns the value of the
   specified column in the internal form (as type <type>Datum</type>).
  </para>

  <para>
   This function does not allocate new space for the datum.  In the
   case of a pass-by-reference data type, the return value will be a
   pointer into the passed row.
  </para>
 </refsect1>

 <refsect1>
  <title>Arguments</title>

  <variablelist>
   <varlistentry>
    <term><literal>HeapTuple <parameter>row</parameter></literal></term>
    <listitem>
     <para>
      input row to be examined
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>TupleDesc <parameter>rowdesc</parameter></literal></term>
    <listitem>
     <para>
      input row description
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>int <parameter>rownumber</parameter></literal></term>
    <listitem>
     <para>
      column number (count starts at 1)
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>bool * <parameter>isnull</parameter></literal></term>
    <listitem>
     <para>
      flag for a null value in the column
     </para>
    </listitem>
   </varlistentry>
  </variablelist>
 </refsect1>

 <refsect1>
  <title>Return Value</title>

  <para>
   The binary value of the column is returned.  The variable pointed
   to by <parameter>isnull</parameter> is set to true if the column is
   null, else to false.
  </para>

  <para>
   <varname>SPI_result</varname> is set to
   <symbol>SPI_ERROR_NOATTRIBUTE</symbol> on error.
  </para>
 </refsect1>
</refentry>

<!-- *********************************************** -->

<refentry id="spi-spi-gettype">
 <refmeta>
  <refentrytitle>SPI_gettype</refentrytitle>
 </refmeta>

 <refnamediv>
  <refname>SPI_gettype</refname>
  <refpurpose>return the data type name of the specified column</refpurpose>
 </refnamediv>

 <indexterm><primary>SPI_gettype</primary></indexterm>

 <refsynopsisdiv>
<synopsis>
char * SPI_gettype(TupleDesc <parameter>rowdesc</parameter>, int <parameter>colnumber</parameter>)
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   <function>SPI_gettype</function> returns the data type name of the
   specified column.  (You can use <function>pfree</function> to
   release the copy of the name when you don't need it anymore.)
  </para>
 </refsect1>

 <refsect1>
  <title>Arguments</title>

  <variablelist>
   <varlistentry>
    <term><literal>TupleDesc <parameter>rowdesc</parameter></literal></term>
    <listitem>
     <para>
      input row description
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>int <parameter>colnumber</parameter></literal></term>
    <listitem>
     <para>
      column number (count starts at 1)
     </para>
    </listitem>
   </varlistentry>
  </variablelist>
 </refsect1>

 <refsect1>
  <title>Return Value</title>

  <para>
   The data type name of the specified column, or
   <symbol>NULL</symbol> on error.  <varname>SPI_result</varname> is
   set to <symbol>SPI_ERROR_NOATTRIBUTE</symbol> on error.
  </para>
 </refsect1>
</refentry>

<!-- *********************************************** -->

<refentry id="spi-spi-gettypeid">
 <refmeta>
  <refentrytitle>SPI_gettypeid</refentrytitle>
 </refmeta>

 <refnamediv>
  <refname>SPI_gettypeid</refname>
  <refpurpose>return the data type <acronym>OID</acronym> of the specified column</refpurpose>
 </refnamediv>

 <indexterm><primary>SPI_gettypeid</primary></indexterm>

 <refsynopsisdiv>
<synopsis>
Oid SPI_gettypeid(TupleDesc <parameter>rowdesc</parameter>, int <parameter>colnumber</parameter>)
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   <function>SPI_gettypeid</function> returns the
   <acronym>OID</acronym> of the data type of the specified column.
  </para>
 </refsect1>

 <refsect1>
  <title>Arguments</title>

  <variablelist>
   <varlistentry>
    <term><literal>TupleDesc <parameter>rowdesc</parameter></literal></term>
    <listitem>
     <para>
      input row description
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>int <parameter>colnumber</parameter></literal></term>
    <listitem>
     <para>
      column number (count starts at 1)
     </para>
    </listitem>
   </varlistentry>
  </variablelist>
 </refsect1>

 <refsect1>
  <title>Return Value</title>

  <para>
   The <acronym>OID</acronym> of the data type of the specified column
   or <symbol>InvalidOid</symbol> on error.  On error,
   <varname>SPI_result</varname> is set to
   <symbol>SPI_ERROR_NOATTRIBUTE</symbol>.
  </para>
 </refsect1>
</refentry>

<!-- *********************************************** -->

<refentry id="spi-spi-getrelname">
 <refmeta>
  <refentrytitle>SPI_getrelname</refentrytitle>
 </refmeta>

 <refnamediv>
  <refname>SPI_getrelname</refname>
  <refpurpose>return the name of the specified relation</refpurpose>
 </refnamediv>

 <indexterm><primary>SPI_getrelname</primary></indexterm>

 <refsynopsisdiv>
<synopsis>
char * SPI_getrelname(Relation <parameter>rel</parameter>)
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   <function>SPI_getrelname</function> returns the name of the
   specified relation.  (You can use <function>pfree</function> to
   release the copy of the name when you don't need it anymore.)
  </para>
 </refsect1>

 <refsect1>
  <title>Arguments</title>

  <variablelist>
   <varlistentry>
    <term><literal>Relation <parameter>rel</parameter></literal></term>
    <listitem>
     <para>
      input relation
     </para>
    </listitem>
   </varlistentry>
  </variablelist>
 </refsect1>

 <refsect1>
  <title>Return Value</title>

  <para>
   The name of the specified relation.
  </para>
 </refsect1>
</refentry>

 </sect1>

 <sect1 id="spi-memory">
  <title>Memory Management</title>

  <para>
   <productname>PostgreSQL</productname> allocates memory within
   <firstterm>memory contexts</firstterm><indexterm><primary>memory
   context</primary><secondary>in SPI</secondary></indexterm>, which provide a convenient method of
   managing allocations made in many different places that need to
   live for differing amounts of time.  Destroying a context releases
   all the memory that was allocated in it.  Thus, it is not necessary
   to keep track of individual objects to avoid memory leaks; instead
   only a relatively small number of contexts have to be managed.
   <function>palloc</function> and related functions allocate memory
   from the <quote>current</> context.
  </para>

  <para>
   <function>SPI_connect</function> creates a new memory context and
   makes it current.  <function>SPI_finish</function> restores the
   previous current memory context and destroys the context created by
   <function>SPI_connect</function>.  These actions ensure that
   transient memory allocations made inside your procedure are
   reclaimed at procedure exit, avoiding memory leakage.
  </para>

  <para>
   However, if your procedure needs to return an object in allocated
   memory (such as a value of a pass-by-reference data type), you
   cannot allocate that memory using <function>palloc</function>, at
   least not while you are connected to SPI.  If you try, the object
   will be deallocated by <function>SPI_finish</function>, and your
   procedure will not work reliably.  To solve this problem, use
   <function>SPI_palloc</function> to allocate memory for your return
   object.  <function>SPI_palloc</function> allocates memory in the
   <quote>upper executor context</quote>, that is, the memory context
   that was current when <function>SPI_connect</function> was called,
   which is precisely the right context for return a value from your
   procedure.
  </para>

  <para>
   If <function>SPI_palloc</function> is called while the procedure is
   not connected to SPI, then it acts the same as a normal
   <function>palloc</function>.  Before a procedure connects to the
   SPI manager, the current memory context is the upper executor
   context, so all allocations made by the procedure via
   <function>palloc</function> or by SPI utility functions are made in
   this context.
  </para>

  <para>
   When <function>SPI_connect</function> is called, the private
   context of the procedure, which is created by
   <function>SPI_connect</function>, is made the current context.  All
   allocations made by <function>palloc</function>,
   <function>repalloc</function>, or SPI utility functions (except for
   <function>SPI_copytuple</function>,
   <function>SPI_copytupledesc</function>,
   <function>SPI_copytupleintoslot</function>,
   <function>SPI_modifytuple</function>, and
   <function>SPI_palloc</function>) are made in this context.  When a
   procedure disconnects from the SPI manager (via
   <function>SPI_finish</function>) the current context is restored to
   the upper executor context, and all allocations made in the
   procedure memory context are freed and cannot be used any more.
  </para>

  <para>
   All functions described in this section may be used by both
   connected and unconnected procedures.  In an unconnected procedure,
   they act the same as the underlying ordinary server functions
   (<function>palloc</>, etc.).
  </para>

<!-- *********************************************** -->

<refentry id="spi-spi-palloc">
 <refmeta>
  <refentrytitle>SPI_palloc</refentrytitle>
 </refmeta>

 <refnamediv>
  <refname>SPI_palloc</refname>
  <refpurpose>allocate memory in the upper executor context</refpurpose>
 </refnamediv>

 <indexterm><primary>SPI_palloc</primary></indexterm>

 <refsynopsisdiv>
<synopsis>
void * SPI_palloc(Size <parameter>size</parameter>)
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   <function>SPI_palloc</function> allocates memory in the upper
   executor context.
  </para>
 </refsect1>

 <refsect1>
  <title>Arguments</title>

  <variablelist>
   <varlistentry>
    <term><literal>Size <parameter>size</parameter></literal></term>
    <listitem>
     <para>
      size in bytes of storage to allocate
     </para>
    </listitem>
   </varlistentry>
  </variablelist>
 </refsect1>

 <refsect1>
  <title>Return Value</title>

  <para>
   pointer to new storage space of the specified size
  </para>
 </refsect1>
</refentry>

<!-- *********************************************** -->

<refentry id="spi-realloc">
 <refmeta>
  <refentrytitle>SPI_repalloc</refentrytitle>
 </refmeta>

 <refnamediv>
  <refname>SPI_repalloc</refname>
  <refpurpose>reallocate memory in the upper executor context</refpurpose>
 </refnamediv>

 <indexterm><primary>SPI_repalloc</primary></indexterm>

 <refsynopsisdiv>
<synopsis>
void * SPI_repalloc(void * <parameter>pointer</parameter>, Size <parameter>size</parameter>)
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   <function>SPI_repalloc</function> changes the size of a memory
   segment previously allocated using <function>SPI_palloc</function>.
  </para>

  <para>
   This function is no longer different from plain
   <function>repalloc</function>.  It's kept just for backward
   compatibility of existing code.
  </para>
 </refsect1>

 <refsect1>
  <title>Arguments</title>

  <variablelist>
   <varlistentry>
    <term><literal>void * <parameter>pointer</parameter></literal></term>
    <listitem>
     <para>
      pointer to existing storage to change
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>Size <parameter>size</parameter></literal></term>
    <listitem>
     <para>
      size in bytes of storage to allocate
     </para>
    </listitem>
   </varlistentry>
  </variablelist>
 </refsect1>

 <refsect1>
  <title>Return Value</title>

  <para>
   pointer to new storage space of specified size with the contents
   copied from the existing area
  </para>
 </refsect1>
</refentry>

<!-- *********************************************** -->

<refentry id="spi-spi-pfree">
 <refmeta>
  <refentrytitle>SPI_pfree</refentrytitle>
 </refmeta>

 <refnamediv>
  <refname>SPI_pfree</refname>
  <refpurpose>free memory in the upper executor context</refpurpose>
 </refnamediv>

 <indexterm><primary>SPI_pfree</primary></indexterm>

 <refsynopsisdiv>
<synopsis>
void SPI_pfree(void * <parameter>pointer</parameter>)
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   <function>SPI_pfree</function> frees memory previously allocated
   using <function>SPI_palloc</function> or
   <function>SPI_repalloc</function>.
  </para>

  <para>
   This function is no longer different from plain
   <function>pfree</function>.  It's kept just for backward
   compatibility of existing code.
  </para>
 </refsect1>

 <refsect1>
  <title>Arguments</title>

  <variablelist>
   <varlistentry>
    <term><literal>void * <parameter>pointer</parameter></literal></term>
    <listitem>
     <para>
      pointer to existing storage to free
     </para>
    </listitem>
   </varlistentry>
  </variablelist>
 </refsect1>
</refentry>

<!-- *********************************************** -->

<refentry id="spi-spi-copytuple">
 <refmeta>
  <refentrytitle>SPI_copytuple</refentrytitle>
 </refmeta>

 <refnamediv>
  <refname>SPI_copytuple</refname>
  <refpurpose>make a copy of a row in the upper executor context</refpurpose>
 </refnamediv>

 <indexterm><primary>SPI_copytuple</primary></indexterm>

 <refsynopsisdiv>
<synopsis>
HeapTuple SPI_copytuple(HeapTuple <parameter>row</parameter>)
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   <function>SPI_copytuple</function> makes a copy of a row in the
   upper executor context.
  </para>
 </refsect1>

 <refsect1>
  <title>Arguments</title>

  <variablelist>
   <varlistentry>
    <term><literal>HeapTuple <parameter>row</parameter></literal></term>
    <listitem>
     <para>
      row to be copied
     </para>
    </listitem>
   </varlistentry>
  </variablelist>
 </refsect1>

 <refsect1>
  <title>Return Value</title>

  <para>
   the copied row; <symbol>NULL</symbol> only if
   <parameter>tuple</parameter> is <symbol>NULL</symbol>
  </para>
 </refsect1>
</refentry>

<!-- *********************************************** -->

<refentry id="spi-spi-copytupledesc">
 <refmeta>
  <refentrytitle>SPI_copytupledesc</refentrytitle>
 </refmeta>

 <refnamediv>
  <refname>SPI_copytupledesc</refname>
  <refpurpose>make a copy of a row descriptor in the upper executor context</refpurpose>
 </refnamediv>

 <indexterm><primary>SPI_copytupledesc</primary></indexterm>

 <refsynopsisdiv>
<synopsis>
TupleDesc SPI_copytupledesc(TupleDesc <parameter>tupdesc</parameter>)
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   <function>SPI_copytupledesc</function> makes a copy of a row
   descriptor in the upper executor context.
  </para>
 </refsect1>

 <refsect1>
  <title>Arguments</title>

  <variablelist>
   <varlistentry>
    <term><literal>TupleDesc <parameter>tupdesc</parameter></literal></term>
    <listitem>
     <para>
      row descriptor to be copied
     </para>
    </listitem>
   </varlistentry>
  </variablelist>
 </refsect1>

 <refsect1>
  <title>Return Value</title>

  <para>
   the copied row descriptor; <symbol>NULL</symbol> only if
   <parameter>tupdesc</parameter> is <symbol>NULL</symbol>
  </para>
 </refsect1>
</refentry>

<!-- *********************************************** -->

<refentry id="spi-spi-copytupleintoslot">
 <refmeta>
  <refentrytitle>SPI_copytupleintoslot</refentrytitle>
 </refmeta>

 <refnamediv>
  <refname>SPI_copytupleintoslot</refname>
  <refpurpose>make a copy of a row and descriptor in the upper executor context</refpurpose>
 </refnamediv>

 <indexterm><primary>SPI_copytupleintoslot</primary></indexterm>

 <refsynopsisdiv>
<synopsis>
TupleTableSlot * SPI_copytupleintoslot(HeapTuple <parameter>row</parameter>, TupleDesc <parameter>rowdesc</parameter>)
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   <function>SPI_copytupleintoslot</function> makes a copy of a row in
   the upper executor context, returning it in the form of a filled-in
   <type>TupleTableSlot</type> structure.
  </para>
 </refsect1>

 <refsect1>
  <title>Arguments</title>

  <variablelist>
   <varlistentry>
    <term><literal>HeapTuple <parameter>row</parameter></literal></term>
    <listitem>
     <para>
      row to be copied
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>TupleDesc <parameter>rowdesc</parameter></literal></term>
    <listitem>
     <para>
      row descriptor to be copied
     </para>
    </listitem>
   </varlistentry>
  </variablelist>
 </refsect1>

 <refsect1>
  <title>Return Value</title>

  <para>
   <type>TupleTableSlot</type> containing the copied row and
   descriptor; <symbol>NULL</symbol> only if
   <parameter>row</parameter> or <parameter>rowdesc</parameter> are
   <symbol>NULL</symbol>
  </para>
 </refsect1>
</refentry>

<!-- *********************************************** -->

<refentry id="spi-spi-modifytuple">
 <refmeta>
  <refentrytitle>SPI_modifytuple</refentrytitle>
 </refmeta>

 <refnamediv>
  <refname>SPI_modifytuple</refname>
  <refpurpose>create a row by replacing selected fields of a given row</refpurpose>
 </refnamediv>

 <indexterm><primary>SPI_modifytuple</primary></indexterm>

 <refsynopsisdiv>
<synopsis>
HeapTuple SPI_modifytuple(Relation <parameter>rel</parameter>, HeapTuple <parameter>row</parameter>, <parameter>ncols</parameter>, <parameter>colnum</parameter>, Datum * <parameter>values</parameter>, const char * <parameter>nulls</parameter>)
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   <function>SPI_modifytuple</function> creates a new row by
   substituting new values for selected columns, copying the original
   row's columns at other positions.  The input row is not modified.
  </para>
 </refsect1>

 <refsect1>
  <title>Arguments</title>

  <variablelist>
   <varlistentry>
    <term><literal>Relation <parameter>rel</parameter></literal></term>
    <listitem>
     <para>
      Used only as the source of the row descriptor for the row.
      (Passing a relation rather than a row descriptor is a
      misfeature.)
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>HeapTuple <parameter>row</parameter></literal></term>
    <listitem>
     <para>
      row to be modified
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>int <parameter>ncols</parameter></literal></term>
    <listitem>
     <para>
      number of column numbers in the array
      <parameter>colnum</parameter>
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>int * <parameter>colnum</parameter></literal></term>
    <listitem>
     <para>
      array of the numbers of the columns that are to be changed
      (count starts at 1)
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>Datum * <parameter>values</parameter></literal></term>
    <listitem>
     <para>
      new values for the specified columns
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>const char * <parameter>Nulls</parameter></literal></term>
    <listitem>
     <para>
      which new values are null, if any (see <function>SPI_execp</function> for the format)
     </para>
    </listitem>
   </varlistentry>
  </variablelist>
 </refsect1>

 <refsect1>
  <title>Return Value</title>

  <para>
   new row with modifications, allocated in the upper executor
   context; <symbol>NULL</symbol> only if <parameter>row</parameter>
   is <symbol>NULL</symbol>
  </para>

  <para>
   On error, <varname>SPI_result</varname> is set as follows:
   <variablelist>
    <varlistentry>
     <term><symbol>SPI_ERROR_ARGUMENT</symbol></term>
     <listitem>
      <para>
       if <parameter>rel</> is <symbol>NULL</>, or if
       <parameter>row</> is <symbol>NULL</>, or if <parameter>ncols</>
       is less than or equal to 0, or if <parameter>colnum</> is
       <symbol>NULL</>, or if <parameter>values</> is <symbol>NULL</>.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><symbol>SPI_ERROR_NOATTRIBUTE</symbol></term>
     <listitem>
      <para>
       if <parameter>colnum</> contains an invalid column number (less
       than or equal to 0 or greater than the number of column in
       <parameter>row</>)
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>
 </refsect1>
</refentry>

<!-- *********************************************** -->

<refentry id="spi-spi-freetuple">
 <refmeta>
  <refentrytitle>SPI_freetuple</refentrytitle>
 </refmeta>

 <refnamediv>
  <refname>SPI_freetuple</refname>
  <refpurpose>frees a row allocated in the upper executor context</refpurpose>
 </refnamediv>

 <indexterm><primary>SPI_freetuple</primary></indexterm>

 <refsynopsisdiv>
<synopsis>
void SPI_freetuple(HeapTuple <parameter>row</parameter>)
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   <function>SPI_freetuple</function> frees a row previously allocated
   in the upper executor context.
  </para>

  <para>
   This function is no longer different from plain
   <function>heap_freetuple</function>.  It's kept just for backward
   compatibility of existing code.
  </para>
 </refsect1>

 <refsect1>
  <title>Arguments</title>

  <variablelist>
   <varlistentry>
    <term><literal>HeapTuple <parameter>row</parameter></literal></term>
    <listitem>
     <para>
      row to free
     </para>
    </listitem>
   </varlistentry>
  </variablelist>
 </refsect1>
</refentry>

<!-- *********************************************** -->

<refentry id="spi-spi-freetupletable">
 <refmeta>
  <refentrytitle>SPI_freetuptable</refentrytitle>
 </refmeta>

 <refnamediv>
  <refname>SPI_freetuptable</refname>
  <refpurpose>free a row set created by <function>SPI_exec</> or a similar function</refpurpose>
 </refnamediv>

 <indexterm><primary>SPI_freetuptable</primary></indexterm>

 <refsynopsisdiv>
<synopsis>
void SPI_freetuptable(SPITupleTable * <parameter>tuptable</parameter>)
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   <function>SPI_freetuptable</function> frees a row set created by a
   prior SPI command execution function, such as
   <function>SPI_exec</>.  Therefore, this function is usually called
   with the global variable <varname>SPI_tupletable</varname> as
   argument.
  </para>

  <para>
   This function is useful if a SPI procedure needs to execute
   multiple commands and does not want to keep the results of earlier
   commands around until it ends.  Note that any unfreed row sets will
   be freed anyway at <function>SPI_finish</>.
  </para>
 </refsect1>

 <refsect1>
  <title>Arguments</title>

  <variablelist>
   <varlistentry>
    <term><literal>SPITupleTable * <parameter>tuptable</parameter></literal></term>
    <listitem>
     <para>
      pointer to row set to free
     </para>
    </listitem>
   </varlistentry>
  </variablelist>
 </refsect1>
</refentry>

<!-- *********************************************** -->

<refentry id="spi-spi-freeplan">
 <refmeta>
  <refentrytitle>SPI_freeplan</refentrytitle>
 </refmeta>

 <refnamediv>
  <refname>SPI_freeplan</refname>
  <refpurpose>free a previously saved plan</refpurpose>
 </refnamediv>

 <indexterm><primary>SPI_freeplan</primary></indexterm>

 <refsynopsisdiv>
<synopsis>
int SPI_freeplan(void *<parameter>plan</parameter>)
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   <function>SPI_freeplan</function> releases a command execution plan
   previously returned by <function>SPI_prepare</function> or saved by
   <function>SPI_saveplan</function>.
  </para>
 </refsect1>

 <refsect1>
  <title>Arguments</title>

  <variablelist>
   <varlistentry>
    <term><literal>void * <parameter>plan</parameter></literal></term>
    <listitem>
     <para>
      pointer to plan to free
     </para>
    </listitem>
   </varlistentry>
  </variablelist>
 </refsect1>

 <refsect1>
  <title>Return Value</title>

  <para>
   <symbol>SPI_ERROR_ARGUMENT</symbol> if <parameter>plan</parameter>
   is <symbol>NULL</symbol>.
  </para>
 </refsect1>
</refentry>

 </sect1>

 <sect1 id="spi-visibility">
  <title>Visibility of Data Changes</title>

  <para>
   The following two rules govern the visibility of data changes in
   functions that use SPI (or any other C function):

   <itemizedlist>
    <listitem>
     <para>
      During the execution of an SQL command, any data changes made by
      the command (or by function called by the command, including
      trigger functions) are invisible to the command.  For
      example, in command
<programlisting>
INSERT INTO a SELECT * FROM a;
</programlisting>
      the inserted rows are invisible to the <command>SELECT</command>
      part.
     </para>
    </listitem>

    <listitem>
     <para>
      Changes made by a command C are visible to all commands that are
      started after C, no matter whether they are started inside C
      (during the execution of C) or after C is done.
     </para>
    </listitem>
   </itemizedlist>
  </para>

  <para>
   The next section contains an example that illustrates the
   application of these rules.
  </para>
 </sect1>

 <sect1 id="spi-examples">
  <title>Examples</title>

  <para>
   This section contains a very simple example of SPI usage. The
   procedure <function>execq</function> takes an SQL command as its
   first argument and a row count as its second, executes the command
   using <function>SPI_exec</function> and returns the number of rows
   that were processed by the command.  You can find more complex
   examples for SPI in the source tree in
   <filename>src/test/regress/regress.c</filename> and in
   <filename>contrib/spi</filename>.
  </para>

<programlisting>
#include "executor/spi.h"

int execq(text *sql, int cnt);

int
execq(text *sql, int cnt)
{
    char *command;
    int ret;
    int proc;

    /* Convert given text object to a C string */
    command = DatumGetCString(DirectFunctionCall1(textout,
                                                  PointerGetDatum(sql)));

    SPI_connect();
    
    ret = SPI_exec(command, cnt);
    
    proc = SPI_processed;
    /*
     * If this is a SELECT and some rows were fetched,
     * then the rows are printed via elog(INFO).
     */
    if (ret == SPI_OK_SELECT && SPI_processed > 0)
    {
        TupleDesc tupdesc = SPI_tuptable->tupdesc;
        SPITupleTable *tuptable = SPI_tuptable;
        char buf[8192];
        int i, j;
        
        for (j = 0; j < proc; j++)
        {
            HeapTuple tuple = tuptable->vals[j];
            
            for (i = 1, buf[0] = 0; i <= tupdesc->natts; i++)
                snprintf(buf + strlen (buf), sizeof(buf) - strlen(buf), " %s%s",
                        SPI_getvalue(tuple, tupdesc, i),
                        (i == tupdesc->natts) ? " " : " |");
            elog (INFO, "EXECQ: %s", buf);
        }
    }

    SPI_finish();
    pfree(command);

    return (proc);
}
</programlisting>

  <para>
   (This function uses call convention version 0, to make the example
   easier to understand.  In real applications you should user the new
   version 1 interface.)
  </para>

  <para>
   This is how you declare the function after having compiled it into
   a shared library:

<programlisting>
CREATE FUNCTION execq(text, integer) RETURNS integer
    AS '<replaceable>filename</replaceable>'
    LANGUAGE C;
</programlisting>
  </para>

  <para>
   Here is a sample session:

<programlisting>
=> SELECT execq('CREATE TABLE a (x integer)', 0);
 execq
-------
     0
(1 row)

=> INSERT INTO a VALUES (execq('INSERT INTO a VALUES (0)', 0));
INSERT 167631 1
=> SELECT execq('SELECT * FROM a', 0);
INFO:  EXECQ:  0    -- inserted by execq
INFO:  EXECQ:  1    -- returned by execq and inserted by upper INSERT

 execq
-------
     2
(1 row)

=> SELECT execq('INSERT INTO a SELECT x + 2 FROM a', 1);
 execq
-------
     1
(1 row)

=> SELECT execq('SELECT * FROM a', 10);
INFO:  EXECQ:  0
INFO:  EXECQ:  1
INFO:  EXECQ:  2    -- 0 + 2, only one row inserted - as specified

 execq
-------
     3              -- 10 is the max value only, 3 is the real number of rows
(1 row)

=> DELETE FROM a;
DELETE 3
=> INSERT INTO a VALUES (execq('SELECT * FROM a', 0) + 1);
INSERT 167712 1
=> SELECT * FROM a;
 x
---
 1                  -- no rows in a (0) + 1
(1 row)

=> INSERT INTO a VALUES (execq('SELECT * FROM a', 0) + 1);
INFO:  EXECQ:  0
INSERT 167713 1
=> SELECT * FROM a;
 x
---
 1
 2                  -- there was one row in a + 1
(2 rows)

-- This demonstrates the data changes visibility rule:

=> INSERT INTO a SELECT execq('SELECT * FROM a', 0) * x FROM a;
INFO:  EXECQ:  1
INFO:  EXECQ:  2
INFO:  EXECQ:  1
INFO:  EXECQ:  2
INFO:  EXECQ:  2
INSERT 0 2
=> SELECT * FROM a;
 x
---
 1
 2
 2                  -- 2 rows * 1 (x in first row)
 6                  -- 3 rows (2 + 1 just inserted) * 2 (x in second row)
(4 rows)               ^^^^^^ 
                       rows visible to execq() in different invocations
</programlisting>
  </para>
 </sect1>
</chapter>
