src/common/backend/parser/parse_oper.cpp

@@ -135,6 +135,7 @@ Oid LookupOperNameTypeNames(
 {
     Oid leftoid, rightoid;
 
+    /* fetch type's OID by given TypeNames */
     if (oprleft == NULL)
         leftoid = InvalidOid;
     else
@@ -174,9 +175,9 @@ void get_sort_group_operators(
 {
     TypeCacheEntry* typentry = NULL;
     int cache_flags;
-    Oid lt_opr;	// Oid of '<' 
-    Oid eq_opr;	// Oid of '=' 
-    Oid gt_opr;	// Oid of '>' 
+    Oid lt_opr;	//  '<' 
+    Oid eq_opr;	//  '=' 
+    Oid gt_opr;	//  '>' 
     bool hashable = false;
 
     /*
@@ -218,7 +219,11 @@ void get_sort_group_operators(
         *isHashable = hashable;
 }
 
-/* given operator tuple, return the operator OID */
+/* 
+ * given operator tuple, return the operator OID. 
+ * 
+ * This is a wrapper of HeapTupleGetOid().
+ */
 Oid oprid(Operator op)
 {
     return HeapTupleGetOid(op);
@@ -508,9 +513,13 @@ Oid compatible_oper_opid(List* op, Oid arg1, Oid arg2, bool noError)
     Operator optup;
     Oid result;
 
+    /* given binary opname and OIDs of its args, find the operator tuple. */
     optup = compatible_oper(NULL, op, arg1, arg2, noError, -1);
     if (optup != NULL) {
+        /* given operator tuple, return the operator OID.  */
         result = oprid(optup);
+
+        /* release the unit of optup in SysCache. */
         ReleaseSysCache(optup);
         return result;
     }