Tweak collation setup for GIN index comparison functions.

Honor index column's collation spec if there is one, don't go to the
expense of calling get_typcollation when we can reasonably assume that
all GIN storage types will use default collation, and be sure to set
a collation for the comparePartialFn too.

src/backend/access/gin/ginutil.c

@@ -16,13 +16,13 @@
 
 #include "access/gin_private.h"
 #include "access/reloptions.h"
+#include "catalog/pg_collation.h"
 #include "catalog/pg_type.h"
 #include "miscadmin.h"
 #include "storage/bufmgr.h"
 #include "storage/freespace.h"
 #include "storage/indexfsm.h"
 #include "storage/lmgr.h"
-#include "utils/lsyscache.h"
 
 
 /*
@@ -63,8 +63,23 @@ initGinState(GinState *state, Relation index)
 		fmgr_info_copy(&(state->compareFn[i]),
 					   index_getprocinfo(index, i + 1, GIN_COMPARE_PROC),
 					   CurrentMemoryContext);
-		fmgr_info_set_collation(get_typcollation(index->rd_att->attrs[i]->atttypid),
-							&(state->compareFn[i]));
+
+		/*
+		 * If the index column has a specified collation, index_getprocinfo
+		 * will have installed it into the fmgr info, and we should honor it.
+		 * However, we may have a collatable storage type for a noncollatable
+		 * indexed data type (for instance, hstore uses text index entries).
+		 * If there's no index collation then specify default collation in
+		 * case the comparison function needs one.  This is harmless if the
+		 * comparison function doesn't care about collation, so we just do it
+		 * unconditionally.  (We could alternatively call get_typcollation,
+		 * but that seems like expensive overkill --- there aren't going to be
+		 * any cases where a GIN storage type has a nondefault collation.)
+		 */
+		if (!OidIsValid(state->compareFn[i].fn_collation))
+			fmgr_info_set_collation(DEFAULT_COLLATION_OID,
+									&(state->compareFn[i]));
+
 		fmgr_info_copy(&(state->extractValueFn[i]),
 					   index_getprocinfo(index, i + 1, GIN_EXTRACTVALUE_PROC),
 					   CurrentMemoryContext);
@@ -84,6 +99,11 @@ initGinState(GinState *state, Relation index)
 				   index_getprocinfo(index, i + 1, GIN_COMPARE_PARTIAL_PROC),
 						   CurrentMemoryContext);
 
+			/* As above, install collation spec in case compare fn needs it */
+			if (!OidIsValid(state->comparePartialFn[i].fn_collation))
+				fmgr_info_set_collation(DEFAULT_COLLATION_OID,
+										&(state->comparePartialFn[i]));
+
 			state->canPartialMatch[i] = true;
 		}
 		else