Implement operator class parameters

PostgreSQL provides set of template index access methods, where opclasses have
much freedom in the semantics of indexing.  These index AMs are GiST, GIN,
SP-GiST and BRIN.  There opclasses define representation of keys, operations on
them and supported search strategies.  So, it's natural that opclasses may be
faced some tradeoffs, which require user-side decision.  This commit implements
opclass parameters allowing users to set some values, which tell opclass how to
index the particular dataset.

This commit doesn't introduce new storage in system catalog.  Instead it uses
pg_attribute.attoptions, which is used for table column storage options but
unused for index attributes.

In order to evade changing signature of each opclass support function, we
implement unified way to pass options to opclass support functions.  Options
are set to fn_expr as the constant bytea expression.  It's possible due to the
fact that opclass support functions are executed outside of expressions, so
fn_expr is unused for them.

This commit comes with some examples of opclass options usage.  We parametrize
signature length in GiST.  That applies to multiple opclasses: tsvector_ops,
gist__intbig_ops, gist_ltree_ops, gist__ltree_ops, gist_trgm_ops and
gist_hstore_ops.  Also we parametrize maximum number of integer ranges for
gist__int_ops.  However, the main future usage of this feature is expected
to be json, where users would be able to specify which way to index particular
json parts.

Catversion is bumped.

Discussion: https://postgr.es/m/d22c3a18-31c7-1879-fc11-4c1ce2f5e5af%40postgrespro.ru
Author: Nikita Glukhov, revised by me
Reviwed-by: Nikolay Shaplov, Robert Haas, Tom Lane, Tomas Vondra, Alvaro Herrera

4 files changed, 6 insertions, 0 deletions

diff --git a/src/include/utils/lsyscache.h b/src/include/utils/lsyscache.h
index 4e646c55e90..374f57fb43a 100644
--- a/src/include/utils/lsyscache.h
+++ b/src/include/utils/lsyscache.h
@@ -90,6 +90,7 @@ extern char get_attgenerated(Oid relid, AttrNumber attnum);
 extern Oid	get_atttype(Oid relid, AttrNumber attnum);
 extern void get_atttypetypmodcoll(Oid relid, AttrNumber attnum,
 								  Oid *typid, int32 *typmod, Oid *collid);
+extern Datum get_attoptions(Oid relid, int16 attnum);
 extern Oid	get_cast_oid(Oid sourcetypeid, Oid targettypeid, bool missing_ok);
 extern char *get_collation_name(Oid colloid);
 extern bool get_collation_isdeterministic(Oid colloid);
diff --git a/src/include/utils/rel.h b/src/include/utils/rel.h
index 2a13d8aad0c..74106b37314 100644
--- a/src/include/utils/rel.h
+++ b/src/include/utils/rel.h
@@ -177,6 +177,7 @@ typedef struct RelationData
 	Oid		   *rd_exclprocs;	/* OIDs of exclusion ops' procs, if any */
 	uint16	   *rd_exclstrats;	/* exclusion ops' strategy numbers, if any */
 	Oid		   *rd_indcollation;	/* OIDs of index collations */
+	bytea	  **rd_opcoptions;	/* parsed opclass-specific options */
 
 	/*
 	 * rd_amcache is available for index and table AMs to cache private data
diff --git a/src/include/utils/relcache.h b/src/include/utils/relcache.h
index d77f5beec68..d596c210b10 100644
--- a/src/include/utils/relcache.h
+++ b/src/include/utils/relcache.h
@@ -14,6 +14,7 @@
 #ifndef RELCACHE_H
 #define RELCACHE_H
 
+#include "postgres.h"
 #include "access/tupdesc.h"
 #include "nodes/bitmapset.h"
 
@@ -50,6 +51,8 @@ extern Oid	RelationGetReplicaIndex(Relation relation);
 extern List *RelationGetIndexExpressions(Relation relation);
 extern List *RelationGetDummyIndexExpressions(Relation relation);
 extern List *RelationGetIndexPredicate(Relation relation);
+extern Datum *RelationGetIndexRawAttOptions(Relation relation);
+extern bytea **RelationGetIndexAttOptions(Relation relation, bool copy);
 
 typedef enum IndexAttrBitmapKind
 {
diff --git a/src/include/utils/ruleutils.h b/src/include/utils/ruleutils.h
index abd9a4dfa0b..8306c760a9a 100644
--- a/src/include/utils/ruleutils.h
+++ b/src/include/utils/ruleutils.h
@@ -38,6 +38,7 @@ extern List *set_deparse_context_plan(List *dpcontext,
 extern List *select_rtable_names_for_explain(List *rtable,
 											 Bitmapset *rels_used);
 extern char *generate_collation_name(Oid collid);
+extern char *generate_opclass_name(Oid opclass);
 extern char *get_range_partbound_string(List *bound_datums);
 
 #endif							/* RULEUTILS_H */