Add equalimage B-Tree support functions.

Invent the concept of a B-Tree equalimage ("equality implies image
equality") support function, registered as support function 4.  This
indicates whether it is safe (or not safe) to apply optimizations that
assume that any two datums considered equal by an operator class's order
method must be interchangeable without any loss of semantic information.
This is static information about an operator class and a collation.

Register an equalimage routine for almost all of the existing B-Tree
opclasses.  We only need two trivial routines for all of the opclasses
that are included with the core distribution.  There is one routine for
opclasses that index non-collatable types (which returns 'true'
unconditionally), plus another routine for collatable types (which
returns 'true' when the collation is a deterministic collation).

This patch is infrastructure for an upcoming patch that adds B-Tree
deduplication.

Author: Peter Geoghegan, Anastasia Lubennikova
Discussion: https://postgr.es/m/CAH2-Wzn3Ee49Gmxb7V1VJ3-AC8fWn-Fr8pfWQebHe8rYRxt5OQ@mail.gmail.com

1 files changed, 14 insertions, 4 deletions

diff --git a/doc/src/sgml/xindex.sgml b/doc/src/sgml/xindex.sgml
index ffb5164aaa0..2e06ad01bf5 100644
--- a/doc/src/sgml/xindex.sgml
+++ b/doc/src/sgml/xindex.sgml
@@ -402,7 +402,7 @@
 
   <para>
    B-trees require a comparison support function,
-   and allow two additional support functions to be
+   and allow three additional support functions to be
    supplied at the operator class author's option, as shown in <xref
    linkend="xindex-btree-support-table"/>.
    The requirements for these support functions are explained further in
@@ -441,6 +441,13 @@
        </entry>
        <entry>3</entry>
       </row>
+      <row>
+       <entry>
+        Determine if it is safe for indexes that use the operator
+        class to apply the btree deduplication optimization (optional)
+       </entry>
+       <entry>4</entry>
+      </row>
      </tbody>
     </tgroup>
    </table>
@@ -980,7 +987,8 @@ DEFAULT FOR TYPE int8 USING btree FAMILY integer_ops AS
   OPERATOR 5 > ,
   FUNCTION 1 btint8cmp(int8, int8) ,
   FUNCTION 2 btint8sortsupport(internal) ,
-  FUNCTION 3 in_range(int8, int8, int8, boolean, boolean) ;
+  FUNCTION 3 in_range(int8, int8, int8, boolean, boolean) ,
+  FUNCTION 4 btequalimage(oid) ;
 
 CREATE OPERATOR CLASS int4_ops
 DEFAULT FOR TYPE int4 USING btree FAMILY integer_ops AS
@@ -992,7 +1000,8 @@ DEFAULT FOR TYPE int4 USING btree FAMILY integer_ops AS
   OPERATOR 5 > ,
   FUNCTION 1 btint4cmp(int4, int4) ,
   FUNCTION 2 btint4sortsupport(internal) ,
-  FUNCTION 3 in_range(int4, int4, int4, boolean, boolean) ;
+  FUNCTION 3 in_range(int4, int4, int4, boolean, boolean) ,
+  FUNCTION 4 btequalimage(oid) ;
 
 CREATE OPERATOR CLASS int2_ops
 DEFAULT FOR TYPE int2 USING btree FAMILY integer_ops AS
@@ -1004,7 +1013,8 @@ DEFAULT FOR TYPE int2 USING btree FAMILY integer_ops AS
   OPERATOR 5 > ,
   FUNCTION 1 btint2cmp(int2, int2) ,
   FUNCTION 2 btint2sortsupport(internal) ,
-  FUNCTION 3 in_range(int2, int2, int2, boolean, boolean) ;
+  FUNCTION 3 in_range(int2, int2, int2, boolean, boolean) ,
+  FUNCTION 4 btequalimage(oid) ;
 
 ALTER OPERATOR FAMILY integer_ops USING btree ADD
   -- cross-type comparisons int8 vs int2