OSDN Git Service

Refactor hint application mechamism
[pghintplan/pg_hint_plan.git] / pg_hint_plan.c
index 9e0d15c..0fa0303 100644 (file)
@@ -374,9 +374,6 @@ static void pg_hint_plan_ProcessUtility(Node *parsetree,
                                                        DestReceiver *dest, char *completionTag);
 static PlannedStmt *pg_hint_plan_planner(Query *parse, int cursorOptions,
                                                                                 ParamListInfo boundParams);
-static void pg_hint_plan_get_relation_info(PlannerInfo *root,
-                                                                                  Oid relationObjectId,
-                                                                                  bool inhparent, RelOptInfo *rel);
 static RelOptInfo *pg_hint_plan_join_search(PlannerInfo *root,
                                                                                        int levels_needed,
                                                                                        List *initial_rels);
@@ -456,6 +453,8 @@ static void make_rels_by_clauseless_joins(PlannerInfo *root,
                                                                                  RelOptInfo *old_rel,
                                                                                  ListCell *other_rels);
 static bool has_join_restriction(PlannerInfo *root, RelOptInfo *rel);
+static void set_plain_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
+                                                                  RangeTblEntry *rte);
 static void set_append_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
                                                                        Index rti, RangeTblEntry *rte);
 static void generate_mergeappend_paths(PlannerInfo *root, RelOptInfo *rel,
@@ -537,7 +536,6 @@ static const struct config_enum_entry parse_debug_level_options[] = {
 /* Saved hook values in case of unload */
 static ProcessUtility_hook_type prev_ProcessUtility = NULL;
 static planner_hook_type prev_planner = NULL;
-static get_relation_info_hook_type prev_get_relation_info = NULL;
 static join_search_hook_type prev_join_search = NULL;
 static set_rel_pathlist_hook_type prev_set_rel_pathlist = NULL;
 
@@ -671,8 +669,6 @@ _PG_init(void)
        ProcessUtility_hook = pg_hint_plan_ProcessUtility;
        prev_planner = planner_hook;
        planner_hook = pg_hint_plan_planner;
-       prev_get_relation_info = get_relation_info_hook;
-       get_relation_info_hook = pg_hint_plan_get_relation_info;
        prev_join_search = join_search_hook;
        join_search_hook = pg_hint_plan_join_search;
        prev_set_rel_pathlist = set_rel_pathlist_hook;
@@ -697,7 +693,6 @@ _PG_fini(void)
        /* Uninstall hooks. */
        ProcessUtility_hook = prev_ProcessUtility;
        planner_hook = prev_planner;
-       get_relation_info_hook = prev_get_relation_info;
        join_search_hook = prev_join_search;
        set_rel_pathlist_hook = prev_set_rel_pathlist;
 
@@ -2528,7 +2523,7 @@ setup_guc_enforcement(SetHint **options, int noptions, GucContext context)
  * If hint is not NULL, set up using it, elsewise reset to initial environment.
  */
 static void
-setup_parallel_plan_enfocement(ParallelHint *hint, HintState *state)
+setup_parallel_plan_enforcement(ParallelHint *hint, HintState *state)
 {
        if (hint)
        {
@@ -3041,9 +3036,9 @@ find_parallel_hint(PlannerInfo *root, Index relid, RelOptInfo *rel)
         *   - not a base relation and inheritance children
         *   - not an ordinary relation (such as join and subquery)
         */
-       if (rel && ((rel->reloptkind != RELOPT_BASEREL &&
-                                rel->reloptkind != RELOPT_OTHER_MEMBER_REL) ||
-                               rel->rtekind != RTE_RELATION))
+       if (!rel || rel->rtekind != RTE_RELATION ||
+               (rel->reloptkind != RELOPT_BASEREL &&
+                rel->reloptkind != RELOPT_OTHER_MEMBER_REL))
                return NULL;
 
        rte = root->simple_rte_array[relid];
@@ -3095,13 +3090,18 @@ regexpeq(const char *s1, const char *s2)
        return DatumGetBool(result);
 }
 
+
+/* Remove indexes instructed not to use by hint. */
 static void
-delete_indexes(ScanMethodHint *hint, RelOptInfo *rel, Oid relationObjectId)
+restrict_indexes(PlannerInfo *root, ScanMethodHint *hint, RelOptInfo *rel,
+                          bool using_parent_hint)
 {
        ListCell           *cell;
        ListCell           *prev;
        ListCell           *next;
        StringInfoData  buf;
+       RangeTblEntry  *rte = root->simple_rte_array[rel->relid];
+       Oid                             relationObjectId = rte->relid;
 
        /*
         * We delete all the IndexOptInfo list and prevent you from being usable by
@@ -3164,10 +3164,11 @@ delete_indexes(ScanMethodHint *hint, RelOptInfo *rel, Oid relationObjectId)
                }
 
                /*
-                * to make the index a candidate when definition of this index is
-                * matched with the index's definition of current_hint_state.
+                * Apply index restriction of parent hint to children. Since index
+                * inheritance is not explicitly described we should search for an
+                * children's index with the same definition to that of the parent.
                 */
-               if (OidIsValid(relationObjectId) && !use_index)
+               if (using_parent_hint && !use_index)
                {
                        foreach(l, current_hint_state->parent_index_infos)
                        {
@@ -3175,71 +3176,61 @@ delete_indexes(ScanMethodHint *hint, RelOptInfo *rel, Oid relationObjectId)
                                HeapTuple                       ht_idx;
                                ParentIndexInfo    *p_info = (ParentIndexInfo *)lfirst(l);
 
-                               /* check to match the parameter of unique */
-                               if (p_info->indisunique != info->unique)
-                                       continue;
-
-                               /* check to match the parameter of index's method */
-                               if (p_info->method != info->relam)
-                                       continue;
-
-                               /* to check to match the indexkey's configuration */
-                               if ((list_length(p_info->column_names)) !=
-                                        info->ncolumns)
+                               /*
+                                * we check the 'same' index by comparing uniqueness, access
+                                * method and index key columns.
+                                */
+                               if (p_info->indisunique != info->unique ||
+                                       p_info->method != info->relam ||
+                                       list_length(p_info->column_names) != info->ncolumns)
                                        continue;
 
-                               /* check to match the indexkey's configuration */
+                               /* Check if index key columns match */
                                for (i = 0; i < info->ncolumns; i++)
                                {
                                        char       *c_attname = NULL;
                                        char       *p_attname = NULL;
 
-                                       p_attname =
-                                               list_nth(p_info->column_names, i);
+                                       p_attname = list_nth(p_info->column_names, i);
 
-                                       /* both are expressions */
+                                       /*
+                                        * if both of the key of the same position are expressions,
+                                        * ignore them for now and check later.
+                                        */
                                        if (info->indexkeys[i] == 0 && !p_attname)
                                                continue;
 
-                                       /* one's column is expression, the other is not */
+                                       /* deny if one is expression while another is not */
                                        if (info->indexkeys[i] == 0 || !p_attname)
                                                break;
 
                                        c_attname = get_attname(relationObjectId,
                                                                                                info->indexkeys[i]);
 
-                                       if (strcmp(p_attname, c_attname) != 0)
-                                               break;
-
-                                       if (p_info->indcollation[i] != info->indexcollations[i])
-                                               break;
-
-                                       if (p_info->opclass[i] != info->opcintype[i])
-                                               break;
-
-                                       if (((p_info->indoption[i] & INDOPTION_DESC) != 0) !=
-                                               info->reverse_sort[i])
+                                       /* deny if any of column attributes don't match */
+                                       if (strcmp(p_attname, c_attname) != 0 ||
+                                               p_info->indcollation[i] != info->indexcollations[i] ||
+                                               p_info->opclass[i] != info->opcintype[i]||
+                                               ((p_info->indoption[i] & INDOPTION_DESC) != 0)
+                                               != info->reverse_sort[i] ||
+                                               ((p_info->indoption[i] & INDOPTION_NULLS_FIRST) != 0)
+                                               != info->nulls_first[i])
                                                break;
-
-                                       if (((p_info->indoption[i] & INDOPTION_NULLS_FIRST) != 0) !=
-                                               info->nulls_first[i])
-                                               break;
-
                                }
 
+                               /* deny this if any difference found */
                                if (i != info->ncolumns)
                                        continue;
 
+                               /* check on key expressions  */
                                if ((p_info->expression_str && (info->indexprs != NIL)) ||
                                        (p_info->indpred_str && (info->indpred != NIL)))
                                {
-                                       /*
-                                        * Fetch the pg_index tuple by the Oid of the index
-                                        */
+                                       /* fetch the index of this child */
                                        ht_idx = SearchSysCache1(INDEXRELID,
                                                                                         ObjectIdGetDatum(info->indexoid));
 
-                                       /* check to match the expression's parameter of index */
+                                       /* check expressions if both expressions are available */
                                        if (p_info->expression_str &&
                                                !heap_attisnull(ht_idx, Anum_pg_index_indexprs))
                                        {
@@ -3260,17 +3251,17 @@ delete_indexes(ScanMethodHint *hint, RelOptInfo *rel, Oid relationObjectId)
                                                                                                         ObjectIdGetDatum(
                                                                                                                 relationObjectId));
 
+                                               /* deny if expressions don't match */
                                                if (strcmp(p_info->expression_str,
                                                                   text_to_cstring(DatumGetTextP(result))) != 0)
                                                {
                                                        /* Clean up */
                                                        ReleaseSysCache(ht_idx);
-
                                                        continue;
                                                }
                                        }
 
-                                       /* Check to match the predicate's parameter of index */
+                                       /* compare index predicates  */
                                        if (p_info->indpred_str &&
                                                !heap_attisnull(ht_idx, Anum_pg_index_indpred))
                                        {
@@ -3278,10 +3269,6 @@ delete_indexes(ScanMethodHint *hint, RelOptInfo *rel, Oid relationObjectId)
                                                bool        isnull;
                                                Datum       result;
 
-                                               /*
-                                                * to change the predicate's parameter of child's
-                                                * index to strings
-                                                */
                                                predDatum = SysCacheGetAttr(INDEXRELID, ht_idx,
                                                                                                         Anum_pg_index_indpred,
                                                                                                         &isnull);
@@ -3296,7 +3283,6 @@ delete_indexes(ScanMethodHint *hint, RelOptInfo *rel, Oid relationObjectId)
                                                {
                                                        /* Clean up */
                                                        ReleaseSysCache(ht_idx);
-
                                                        continue;
                                                }
                                        }
@@ -3332,16 +3318,21 @@ delete_indexes(ScanMethodHint *hint, RelOptInfo *rel, Oid relationObjectId)
 
        if (debug_level == 1)
        {
-               char   *relname;
                StringInfoData  rel_buf;
+               char *disprelname = "";
 
-               if (OidIsValid(relationObjectId))
-                       relname = get_rel_name(relationObjectId);
+               /*
+                * If this hint targetted the parent, use the real name of this
+                * child. Otherwise use hint specification.
+                */
+               if (using_parent_hint)
+                       disprelname = get_rel_name(rte->relid);
                else
-                       relname = hint->relname;
+                       disprelname = hint->relname;
+                       
 
                initStringInfo(&rel_buf);
-               quote_value(&rel_buf, relname);
+               quote_value(&rel_buf, disprelname);
 
                ereport(LOG,
                                (errmsg("available indexes for %s(%s):%s",
@@ -3433,15 +3424,27 @@ get_parent_index_info(Oid indexoid, Oid relid)
 }
 
 /*
- * Set planner guc parameters according to corresponding scan hints.
+ * cancel hint enforcement
  */
 static void
-setup_hint_enforcement(PlannerInfo *root, Oid relationObjectId,
-                                          bool inhparent, RelOptInfo *rel)
+reset_hint_enforcement()
 {
-       Index new_parent_relid = 0;
+       setup_scan_method_enforcement(NULL, current_hint_state);
+       setup_parallel_plan_enforcement(NULL, current_hint_state);
+}
+
+/*
+ * Set planner guc parameters according to corresponding scan hints.
+ */
+static bool
+setup_hint_enforcement(PlannerInfo *root, RelOptInfo *rel)
+{
+       Index   new_parent_relid = 0;
        ListCell *l;
-       ScanMethodHint *scanhint = NULL;
+       ScanMethodHint *shint = NULL;
+       ParallelHint   *phint = NULL;
+       bool                    inhparent = root->simple_rte_array[rel->relid]->inh;
+       Oid             relationObjectId = root->simple_rte_array[rel->relid]->relid;
 
        /*
         * We could register the parent relation of the following children here
@@ -3455,13 +3458,13 @@ setup_hint_enforcement(PlannerInfo *root, Oid relationObjectId,
                if (debug_level > 1)
                        ereport(pg_hint_plan_message_level,
                                        (errhidestmt(true),
-                                        errmsg ("pg_hint_plan%s: get_relation_info"
+                                        errmsg ("pg_hint_plan%s: setup_hint_enforcement"
                                                         " skipping inh parent: relation=%u(%s), inhparent=%d,"
                                                         " current_hint_state=%p, hint_inhibit_level=%d",
                                                         qnostr, relationObjectId,
                                                         get_rel_name(relationObjectId),
                                                         inhparent, current_hint_state, hint_inhibit_level)));
-               return;
+               return false;
        }
 
        /* Find the parent for this relation other than the registered parent */
@@ -3492,28 +3495,27 @@ setup_hint_enforcement(PlannerInfo *root, Oid relationObjectId,
                 * hint to other childrens of this parent so remember it * to avoid
                 * hinthintredundant setup cost.
                 */
-               ScanMethodHint *parent_scan_hint = NULL;
-               ParallelHint   *parent_parallel_hint = NULL;
-
                current_hint_state->parent_relid = new_parent_relid;
                                
                /* Find hints for the parent */
-               current_hint_state->parent_scan_hint = parent_scan_hint = 
+               current_hint_state->parent_scan_hint =
                        find_scan_hint(root, current_hint_state->parent_relid, NULL);
 
-               current_hint_state->parent_parallel_hint = parent_parallel_hint = 
+               current_hint_state->parent_parallel_hint =
                        find_parallel_hint(root, current_hint_state->parent_relid, NULL);
 
-               if (parent_scan_hint)
+               /*
+                * If hint is found for the parent, apply it for this child instead
+                * of its own.
+                */
+               if (current_hint_state->parent_scan_hint)
                {
-                       /*
-                        * If hint is found for the parent, apply it for this child instead
-                        * of its own.
-                        */
-                       parent_scan_hint->base.state = HINT_STATE_USED;
+                       ScanMethodHint * pshint = current_hint_state->parent_scan_hint;
+
+                       pshint->base.state = HINT_STATE_USED;
 
                        /* Apply index mask in the same manner to the parent. */
-                       if (parent_scan_hint->indexnames)
+                       if (pshint->indexnames)
                        {
                                Oid                     parentrel_oid;
                                Relation        parent_rel;
@@ -3530,7 +3532,7 @@ setup_hint_enforcement(PlannerInfo *root, Oid relationObjectId,
                                        ListCell   *lc;
                                        ParentIndexInfo *parent_index_info;
 
-                                       foreach(lc, parent_scan_hint->indexnames)
+                                       foreach(lc, pshint->indexnames)
                                        {
                                                if (RelnameCmp(&indexname, &lfirst(lc)) == 0)
                                                        break;
@@ -3541,106 +3543,82 @@ setup_hint_enforcement(PlannerInfo *root, Oid relationObjectId,
                                        parent_index_info =
                                                get_parent_index_info(indexoid, parentrel_oid);
                                        current_hint_state->parent_index_infos =
-                                               lappend(current_hint_state->parent_index_infos, parent_index_info);
+                                               lappend(current_hint_state->parent_index_infos,
+                                                               parent_index_info);
                                }
                                heap_close(parent_rel, NoLock);
                        }
                }
-
-               /* Setup planner environment */
-               setup_scan_method_enforcement(parent_scan_hint, current_hint_state);
-               setup_parallel_plan_enfocement(
-                       find_parallel_hint(root, rel->relid, rel), current_hint_state);
        }
 
-       /* Process index restriction hint inheritance */
-       if (current_hint_state->parent_scan_hint != 0)
-       {
-               delete_indexes(current_hint_state->parent_scan_hint, rel,
-                                          relationObjectId);
-
-               /* Scan fixation status is the same to the parent. */
-               if (debug_level > 1)
-                       ereport(pg_hint_plan_message_level,
-                                       (errhidestmt(true),
-                                        errmsg("pg_hint_plan%s: get_relation_info:"
-                                                       " index deletion by parent hint: "
-                                                       "relation=%u(%s), inhparent=%d, current_hint_state=%p,"
-                                                       " hint_inhibit_level=%d",
-                                                       qnostr, relationObjectId,
-                                                       get_rel_name(relationObjectId),
-                                                       inhparent, current_hint_state, hint_inhibit_level)));
-               return;
-       }
+       if (current_hint_state->parent_scan_hint)
+               shint = current_hint_state->parent_scan_hint;
+       else
+               shint = find_scan_hint(root, rel->relid, rel);
 
-       /* This table doesn't have a parent hint. Apply its own hint if any. */
-       if ((scanhint = find_scan_hint(root, rel->relid, rel)) != NULL)
+       if (shint)
        {
-               setup_scan_method_enforcement(scanhint, current_hint_state);
+               bool using_parent_hint =
+                       (shint == current_hint_state->parent_scan_hint);
 
-               delete_indexes(scanhint, rel, InvalidOid);
+               /* Setup scan enforcement environment */
+               setup_scan_method_enforcement(shint, current_hint_state);
+
+               /* restrict unwanted inexes */
+               restrict_indexes(root, shint, rel, using_parent_hint);
 
                if (debug_level > 1)
+               {
+                       char *additional_message = "";
+
+                       if (shint == current_hint_state->parent_scan_hint)
+                               additional_message = " by parent hint";
+
                        ereport(pg_hint_plan_message_level,
                                        (errhidestmt(true),
-                                        errmsg ("pg_hint_plan%s: get_relation_info"
-                                                        " index deletion:"
-                                                        " relation=%u(%s), inhparent=%d, current_hint=%p,"
+                                        errmsg ("pg_hint_plan%s: setup_hint_enforcement"
+                                                        " index deletion%s:"
+                                                        " relation=%u(%s), inhparent=%d, "
+                                                        "current_hint_state=%p,"
                                                         " hint_inhibit_level=%d, scanmask=0x%x",
-                                                        qnostr, relationObjectId,
+                                                        qnostr, additional_message,
+                                                        relationObjectId,
                                                         get_rel_name(relationObjectId),
-                                                        inhparent, current_hint_state, hint_inhibit_level,
-                                                        scanhint->enforce_mask)));
-               return;
+                                                        inhparent, current_hint_state,
+                                                        hint_inhibit_level,
+                                                        shint->enforce_mask)));
+               }
        }
 
        /* Do the same for parallel plan enforcement */
-       setup_parallel_plan_enfocement(find_parallel_hint(root, rel->relid, rel),
-                                                                  current_hint_state);
-
-       /* Nothing to apply. Reset the scan mask to intial state */
-       if (debug_level > 1)
-               ereport(pg_hint_plan_message_level,
-                               (errhidestmt (true),
-                                errmsg ("pg_hint_plan%s: get_relation_info"
-                                                " no hint applied:"
-                                                " relation=%u(%s), inhparent=%d, current_hint=%p,"
-                                                " hint_inhibit_level=%d, scanmask=0x%x",
-                                                qnostr, relationObjectId,
-                                                get_rel_name(relationObjectId),
-                                                inhparent, current_hint_state, hint_inhibit_level,
-                                                current_hint_state->init_scan_mask)));
-       setup_scan_method_enforcement(NULL,     current_hint_state);
-}
+       if (current_hint_state->parent_parallel_hint)
+               phint = current_hint_state->parent_parallel_hint;
+       else
+               phint = find_parallel_hint(root, rel->relid, rel);
 
-static void
-pg_hint_plan_get_relation_info(PlannerInfo *root, Oid relationObjectId,
-                                                          bool inhparent, RelOptInfo *rel)
-{
-       if (prev_get_relation_info)
-               (*prev_get_relation_info) (root, relationObjectId, inhparent, rel);
+       setup_parallel_plan_enforcement(phint, current_hint_state);
 
-       /* 
-        * Do nothing if we don't have a valid hint in this context or current
-        * nesting depth is at SPI calls.
-        */
-       if (!current_hint_state || hint_inhibit_level > 0)
+       /* Nothing to apply. Reset the scan mask to intial state */
+       if (!shint && ! phint)
        {
                if (debug_level > 1)
                        ereport(pg_hint_plan_message_level,
                                        (errhidestmt (true),
                                         errmsg ("pg_hint_plan%s: get_relation_info"
-                                                        " no hint to apply: relation=%u(%s), inhparent=%d,"
-                                                        " current_hint_state=%p, hint_inhibit_level=%d",
+                                                        " no hint applied:"
+                                                        " relation=%u(%s), inhparent=%d, current_hint=%p,"
+                                                        " hint_inhibit_level=%d, scanmask=0x%x",
                                                         qnostr, relationObjectId,
                                                         get_rel_name(relationObjectId),
-                                                        inhparent, current_hint_state, hint_inhibit_level)));
-               return;
-       }
+                                                        inhparent, current_hint_state, hint_inhibit_level,
+                                                        current_hint_state->init_scan_mask)));
 
-       setup_hint_enforcement(root, relationObjectId, inhparent, rel);
+               setup_scan_method_enforcement(NULL,     current_hint_state);
 
-       return;
+               return false;
+       }
+
+       return true;
 }
 
 /*
@@ -4086,150 +4064,6 @@ transform_join_hints(HintState *hstate, PlannerInfo *root, int nbaserel,
 }
 
 /*
- * set_plain_rel_pathlist
- *       Build access paths for a plain relation (no subquery, no inheritance)
- *
- * This function was copied and edited from set_plain_rel_pathlist() in
- * src/backend/optimizer/path/allpaths.c
- *
- * - removed parallel stuff.
- */
-static void
-set_plain_rel_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
-{
-       Relids          required_outer;
-
-       /*
-        * We don't support pushing join clauses into the quals of a seqscan, but
-        * it could still have required parameterization due to LATERAL refs in
-        * its tlist.
-        */
-       required_outer = rel->lateral_relids;
-
-       /* Consider sequential scan */
-       add_path(rel, create_seqscan_path(root, rel, required_outer, 0));
-
-       /* If appropriate, consider parallel sequential scan */
-       if (rel->consider_parallel && required_outer == NULL)
-       {
-               ParallelHint *phint = find_parallel_hint(root, rel->relid, rel);
-
-               /* Consider parallel paths only if not inhibited by hint */
-               if (!phint || phint->nworkers > 0)
-                       create_plain_partial_paths(root, rel);
-
-               /*
-                * Overwirte parallel_workers if requested. partial_pathlist seems to
-                * have up to one path but looping over all possible paths don't harm.
-                */
-               if (phint && phint->nworkers > 0 && phint->force_parallel)
-               {
-                       ListCell *l;
-                       foreach (l, rel->partial_pathlist)
-                       {
-                               Path *ppath = (Path *) lfirst(l);
-                               
-                               Assert(ppath->parallel_workers > 0);
-                               ppath->parallel_workers = phint->nworkers;
-                       }
-               }                       
-       }
-
-       /* Consider index scans */
-       create_index_paths(root, rel);
-
-       /* Consider TID scans */
-       create_tidscan_paths(root, rel);
-}
-
-/*
- * Clear exiting access paths and create new ones applying hints.
- * This does the similar to set_rel_pathlist
- */
-static void
-rebuild_scan_path(HintState *hstate, PlannerInfo *root, int level,
-                                 List *initial_rels)
-{
-       ListCell   *l;
-
-       foreach(l, initial_rels)
-       {
-               RelOptInfo         *rel = (RelOptInfo *) lfirst(l);
-               RangeTblEntry  *rte;
-
-               /* Skip relations which we can't choose scan method. */
-               if (rel->reloptkind != RELOPT_BASEREL || rel->rtekind != RTE_RELATION)
-                       continue;
-
-               rte = root->simple_rte_array[rel->relid];
-
-               /* We can't force scan method of foreign tables */
-               if (rte->relkind == RELKIND_FOREIGN_TABLE)
-                       continue;
-
-               /*
-                * Create scan paths with GUC parameters which are at the beginning of
-                * planner if scan method hint is not specified, otherwise use
-                * specified hints and mark the hint as used.
-                */
-               setup_scan_method_enforcement(find_scan_hint(root, rel->relid, rel),
-                                                                         hstate);
-
-               /* Setup parallel environment according to the hint */
-               setup_parallel_plan_enfocement(
-                       find_parallel_hint(root, rel->relid, rel), current_hint_state);
-
-               /* remove existing partial paths from this baserel */
-               list_free_deep(rel->partial_pathlist);
-               rel->partial_pathlist = NIL;
-
-               /* remove existing paths from this baserel */
-               list_free_deep(rel->pathlist);
-               rel->pathlist = NIL;
-
-               if (rte->inh)
-               {
-                       ListCell *l;
-
-                       /* remove partial paths from all chlidren */
-                       foreach (l, root->append_rel_list)
-                       {
-                               AppendRelInfo  *appinfo = (AppendRelInfo *) lfirst(l);
-                               RelOptInfo         *childrel;
-
-                               if (appinfo->parent_relid != rel->relid)
-                                       continue;
-
-                               childrel = root->simple_rel_array[appinfo->child_relid];
-                               list_free_deep(childrel->partial_pathlist);
-                               childrel->partial_pathlist = NIL;
-                       }
-                       /* It's an "append relation", process accordingly */
-                       set_append_rel_pathlist(root, rel, rel->relid, rte);
-               }
-               else
-               {
-                       set_plain_rel_pathlist(root, rel, rte);
-               }
-
-               /*
-                * If this is a baserel, consider gathering any partial paths we may
-                * hinthave created for it.
-                */
-               if (rel->reloptkind == RELOPT_BASEREL)
-                       generate_gather_paths(root, rel);
-
-               /* Now find the cheapest of the paths for this rel */
-               set_cheapest(rel);
-       }
-
-       /*
-        * Restore the GUC variables we set above.
-        */
-       setup_scan_method_enforcement(NULL, hstate);
-}
-
-/*
  * wrapper of make_join_rel()
  *
  * call make_join_rel() after changing enable_* parameters according to given
@@ -4380,9 +4214,6 @@ pg_hint_plan_join_search(PlannerInfo *root, int levels_needed,
                        return standard_join_search(root, levels_needed, initial_rels);
        }
 
-       /* apply scan method hint rebuild scan path. */
-       rebuild_scan_path(current_hint_state, root, levels_needed, initial_rels);
-
        /*
         * In the case using GEQO, only scan method hints and Set hints have
         * effect.  Join method and join order is not controllable by hints.
@@ -4428,55 +4259,94 @@ pg_hint_plan_set_rel_pathlist(PlannerInfo * root, RelOptInfo *rel,
                                                          Index rti, RangeTblEntry *rte)
 {
        ParallelHint   *phint;
-       List               *oldpathlist;
        ListCell           *l;
-       bool                    regenerate = false;
 
-       /* Hint has not been parsed yet, or this is not a parallel'able relation */
-       if (current_hint_state == NULL || rel->partial_pathlist == NIL)
+       /* call the previous hook */
+       if (prev_set_rel_pathlist)
+               prev_set_rel_pathlist(root, rel, rti, rte);
+
+       /* Nothing to do when hint has not been parsed yet */
+       if (current_hint_state == NULL)
                return;
 
-       phint = find_parallel_hint(root, rel->relid, rel);
+       /* Don't touch dummy rel */
+       if (IS_DUMMY_REL(rel))
+               return;
 
-       if (phint == NULL || !phint->force_parallel)
+       /* We cannot handle if this requires an outer */
+       if (rel->lateral_relids)
                return;
 
-       /*
-        * This relation contains gather paths previously created and they prevent
-        * adding new gahter path with same cost. Remove them.
-        */
-       oldpathlist = rel->pathlist;
-       rel->pathlist = NIL;
-       foreach (l, oldpathlist)
+       if (!setup_hint_enforcement(root, rel))
        {
-               Path *path = (Path *) lfirst(l);
+               /*
+                * No enforcement requested, but we might have to generate gather
+                * path on this relation
+                */
 
-               if (IsA(path, GatherPath) &&
-                       path->parallel_workers != phint->nworkers)
+               /* If no need of a gather path, just return */
+               if (rel->reloptkind != RELOPT_BASEREL || max_hint_nworkers < 1 ||
+                       rel->partial_pathlist == NIL)
+                       return;
+
+               /* Lower the priorities of existing paths, then add a new path */
+               foreach (l, rel->pathlist)
                {
-                       pfree(path);
-                       regenerate = true;
+                       Path *path = (Path *) lfirst(l);
+
+                       if (path->startup_cost < disable_cost)
+                       {
+                               path->startup_cost += disable_cost;
+                               path->total_cost += disable_cost;
+                       }
                }
-               else
-                       rel->pathlist = lappend(rel->pathlist, path);
+
+               generate_gather_paths(root, rel);
+               return;
        }
-       list_free(oldpathlist);
 
-       if (regenerate)
+       /* Here, we regenerate paths with the current hint restriction */
+
+       /* Remove prviously paths except dummy rels */
+       list_free_deep(rel->pathlist);
+       rel->pathlist = NIL;
+
+       /* Rebuild access paths */
+       set_plain_rel_pathlist(root, rel, rte);
+
+       /*
+        * create_plain_partial_paths creates partial paths with reasonably
+        * estimated number of workers. Force the requested number of workers if
+        * hard mode.
+        */
+       phint = find_parallel_hint(root, rel->relid, rel);
+
+       if (phint)
        {
-               foreach (l, rel->partial_pathlist)
+               /* if inhibiting parallel, remove existing partial paths  */
+               if (phint->nworkers == 0 && rel->partial_pathlist)
                {
-                       Path *ppath = (Path *) lfirst(l);
-                       
-                       if (phint && phint->nworkers > 0 && phint->force_parallel)
+                       list_free_deep(rel->partial_pathlist);
+                       rel->partial_pathlist = NIL;
+               }
+
+               /* enforce number of workers if requested */
+               if (rel->partial_pathlist && phint->force_parallel)
+               {
+                       foreach (l, rel->partial_pathlist)
                        {
-                               Assert(ppath->parallel_workers > 0);
+                               Path *ppath = (Path *) lfirst(l);
+
                                ppath->parallel_workers = phint->nworkers;
-                       }                       
+                       }
                }
-               
-               generate_gather_paths(root, rel);
+
+               /* Generate gather paths for base rels */
+               if (rel->reloptkind == RELOPT_BASEREL)
+                       generate_gather_paths(root, rel);
        }
+
+       reset_hint_enforcement();
 }
 
 /*
@@ -4484,7 +4354,8 @@ pg_hint_plan_set_rel_pathlist(PlannerInfo * root, RelOptInfo *rel,
  *       Build access paths for a base relation
  *
  * This function was copied and edited from set_rel_pathlist() in
- * src/backend/optimizer/path/allpaths.c
+ * src/backend/optimizer/path/allpaths.c in order not to copy other static
+ * functions not required here.
  */
 static void
 set_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,