Add documentation for opclass options

911e7020770 added opclass options and adjusted documentation for each
particular affected opclass.  However, documentation for extendability was
not adjusted.  This commit adjusts documentation for interfaces of index AMs
and opclasses.

Discussion: https://postgr.es/m/CAH2-WzmQnW6%2Bz5F9AW%2BSz%2BzEcEvXofTwh_A9J3%3D_WA-FBP0wYg%40mail.gmail.com
Author: Alexander Korotkov
Reported-by: Peter Geoghegan
Reviewed-by: Peter Geoghegan

1 files changed, 159 insertions, 2 deletions

diff --git a/doc/src/sgml/gist.sgml b/doc/src/sgml/gist.sgml
index a7eec1e9497..31c28fdb61c 100644
--- a/doc/src/sgml/gist.sgml
+++ b/doc/src/sgml/gist.sgml
@@ -269,7 +269,7 @@ CREATE INDEX ON my_table USING GIST (my_inet_column inet_ops);
 
  <para>
    There are five methods that an index operator class for
-   <acronym>GiST</acronym> must provide, and four that are optional.
+   <acronym>GiST</acronym> must provide, and five that are optional.
    Correctness of the index is ensured
    by proper implementation of the <function>same</function>, <function>consistent</function>
    and <function>union</function> methods, while efficiency (size and speed) of the
@@ -287,7 +287,9 @@ CREATE INDEX ON my_table USING GIST (my_inet_column inet_ops);
    if the operator class wishes to support ordered scans (nearest-neighbor
    searches). The optional ninth method <function>fetch</function> is needed if the
    operator class wishes to support index-only scans, except when the
-   <function>compress</function> method is omitted.
+   <function>compress</function> method is omitted. The optional tenth method
+   <function>options</function> is needed if the operator class provides
+   the user-specified parameters.
  </para>
 
  <variablelist>
@@ -939,6 +941,161 @@ my_fetch(PG_FUNCTION_ARGS)
 
      </listitem>
     </varlistentry>
+
+    <varlistentry>
+     <term><function>options</function></term>
+     <listitem>
+      <para>
+       Allows defintion of user-visible parameters that control operator
+       class behavior.
+      </para>
+
+      <para>
+        The <acronym>SQL</acronym> declaration of the function must look like this:
+
+<programlisting>
+CREATE OR REPLACE FUNCTION my_options(internal)
+RETURNS void
+AS 'MODULE_PATHNAME'
+LANGUAGE C STRICT;
+</programlisting>
+      </para>
+
+      <para>
+       The function has given pointer to <replaceable>local_relopts</replaceable>
+       struct, which needs to be filled with a set of operator class
+       specific options.  The options can be accessed from other support
+       functions using <literal>PG_HAS_OPCLASS_OPTIONS()</literal> and
+       <literal>PG_GET_OPCLASS_OPTIONS()</literal> macros.
+      </para>
+
+       <para>
+        The sample implementation of my_option() and parameters usage
+        in the another support function are given below:
+
+<programlisting>
+typedef enum MyEnumType
+{
+    MY_ENUM_ON,
+    MY_ENUM_OFF,
+    MY_ENUM_AUTO
+} MyEnumType;
+
+typedef struct
+{
+    int32   vl_len_;    /* varlena header (do not touch directly!) */
+    int     int_param;  /* integer parameter */
+    double  real_param; /* real parameter */
+    MyEnumType enum_param; /* enum parameter */
+    int     str_param;  /* string parameter */
+} MyOptionsStruct;
+
+/* String representations for enum values */
+static relopt_enum_elt_def myEnumValues[] =
+{
+    {"on", MY_ENUM_ON},
+    {"off", MY_ENUM_OFF},
+    {"auto", MY_ENUM_AUTO},
+    {(const char *) NULL}   /* list terminator */
+};
+
+static char *str_param_default = "default";
+
+/*
+ * Sample validatior: checks that string is not longer than 8 bytes.
+ */
+static void 
+validate_my_string_relopt(const char *value)
+{
+    if (strlen(value) > 8)
+        ereport(ERROR,
+                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+                 errmsg("str_param must be at most 8 bytes")));
+}
+
+/*
+ * Sample filler: switches characters to lower case.
+ */
+static Size 
+fill_my_string_relopt(const char *value, void *ptr)
+{
+    char   *tmp = str_tolower(value, strlen(value), DEFAULT_COLLATION_OID);
+    int     len = strlen(tmp);
+
+    if (ptr)
+        strcpy((char *) ptr, tmp);
+
+    pfree(tmp);
+    return len + 1;
+}
+
+PG_FUNCTION_INFO_V1(my_options);
+
+Datum
+my_options(PG_FUNCTION_ARGS)
+{
+    local_relopts *relopts = (local_relopts *) PG_GETARG_POINTER(0);
+
+    init_local_reloptions(relopts, sizeof(MyOptionsStruct));
+    add_local_int_reloption(relopts, "int_param", "integer parameter",
+                            100, 0, 1000000,
+                            offsetof(MyOptionsStruct, int_param));
+    add_local_real_reloption(relopts, "real_param", "real parameter",
+                             1.0, 0.0, 1000000.0,
+                             offsetof(MyOptionsStruct, real_param));
+    add_local_enum_reloption(relopts, "enum_param", "enum parameter",
+                             myEnumValues, MY_ENUM_ON,
+                             "Valid values are: \"on\", \"off\" and \"auto\".",
+                             offsetof(MyOptionsStruct, enum_param));
+    add_local_string_reloption(relopts, "str_param", "string parameter",
+                               str_param_default,
+                               &amp;validate_my_string_relopt,
+                               &amp;fill_my_string_relopt,
+                               offsetof(MyOptionsStruct, str_param));
+
+    PG_RETURN_VOID();
+}
+
+PG_FUNCTION_INFO_V1(my_compress);
+
+Datum
+my_compress(PG_FUNCTION_ARGS)
+{
+    int     int_param = 100;
+    double  real_param = 1.0;
+    MyEnumType enum_param = MY_ENUM_ON;
+    char   *str_param = str_param_default;
+
+    /*
+     * Normally, when opclass contains 'options' method, then options are always
+     * passed to support functions.  However, if you add 'options' method to
+     * existing opclass, previously defined indexes have no options, so the
+     * check is required.
+     */
+    if (PG_HAS_OPCLASS_OPTIONS())
+    {
+        MyOptionsStruct *options = (MyOptionsStruct *) PG_GET_OPCLASS_OPTIONS();
+
+        int_param = options->int_param;
+        real_param = options->real_param;
+        enum_param = options->enum_param;
+        str_param = GET_STRING_RELOPTION(options, str_param);
+    }
+
+    /* the rest implementation of support function */
+}
+
+</programlisting>
+      </para>
+
+      <para>
+       Since the representation of the key in <acronym>GiST</acronym> is
+       flexible, it may depends on user-specified parameters.  For instace,
+       the length of key signature may be such parameter.  See
+       <literal>gtsvector_options()</literal> for example.
+      </para>
+     </listitem>
+    </varlistentry>
   </variablelist>
 
   <para>