/*
             * RelationFlushRelation () below will flush relation information
             * from the cache. We must call smgrclose to flush relation
             * information from SMGR & FMGR, too. We assume that for temp
             * relations smgrunlink is already called by heap_destroyr
             * and we skip smgrclose for them.          - vadim 05/22/97
             */
            smgrclose(reln->rd_rel->relsmgr, reln);

 - it avoids memory leaks in SMGR & VFD.

RelationFlushRelation():
   there is no more call FileInvalidate(RelationGetSystemPort(relation));
   - invalid (FileInvalidate() expects File, not SMGR' fd)
   - unuseful anyway.