Properly change the state of parallel hints.

[pghintplan/pg_hint_plan.git] / core.c

diff --git a/core.c b/core.c
index 333d420..a90828f 100644 (file)
--- a/core.c
+++ b/core.c
@@ -575,6 +575,83 @@ standard_join_search(PlannerInfo *root, int levels_needed, List *initial_rels)
 }
 
 /*
+ * create_plain_partial_paths
+ *       Build partial access paths for parallel scan of a plain relation
+ */
+static void
+create_plain_partial_paths(PlannerInfo *root, RelOptInfo *rel)
+{
+       int                     parallel_workers;
+
+       parallel_workers = compute_parallel_worker(rel, rel->pages);
+
+       /* If any limit was set to zero, the user doesn't want a parallel scan. */
+       if (parallel_workers <= 0)
+               return;
+
+       /* Add an unordered partial path based on a parallel sequential scan. */
+       add_partial_path(rel, create_seqscan_path(root, rel, NULL, parallel_workers));
+}
+
+/*
+ * Compute the number of parallel workers that should be used to scan a
+ * relation.  "pages" is the number of pages from the relation that we
+ * expect to scan.
+ */
+static int
+compute_parallel_worker(RelOptInfo *rel, BlockNumber pages)
+{
+       int                     parallel_workers;
+
+       /*
+        * If the user has set the parallel_workers reloption, use that; otherwise
+        * select a default number of workers.
+        */
+       if (rel->rel_parallel_workers != -1)
+               parallel_workers = rel->rel_parallel_workers;
+       else
+       {
+               int                     parallel_threshold;
+
+               /*
+                * If this relation is too small to be worth a parallel scan, just
+                * return without doing anything ... unless it's an inheritance child.
+                * In that case, we want to generate a parallel path here anyway.  It
+                * might not be worthwhile just for this relation, but when combined
+                * with all of its inheritance siblings it may well pay off.
+                */
+               if (pages < (BlockNumber) min_parallel_relation_size &&
+                       rel->reloptkind == RELOPT_BASEREL)
+                       return 0;
+
+               /*
+                * Select the number of workers based on the log of the size of the
+                * relation.  This probably needs to be a good deal more
+                * sophisticated, but we need something here for now.  Note that the
+                * upper limit of the min_parallel_relation_size GUC is chosen to
+                * prevent overflow here.
+                */
+               parallel_workers = 1;
+               parallel_threshold = Max(min_parallel_relation_size, 1);
+               while (pages >= (BlockNumber) (parallel_threshold * 3))
+               {
+                       parallel_workers++;
+                       parallel_threshold *= 3;
+                       if (parallel_threshold > INT_MAX / 3)
+                               break;                  /* avoid overflow */
+               }
+       }
+
+       /*
+        * In no case use more than max_parallel_workers_per_gather workers.
+        */
+       parallel_workers = Min(parallel_workers, max_parallel_workers_per_gather);
+
+       return parallel_workers;
+}
+
+
+/*
  * join_search_one_level
  *       Consider ways to produce join relations containing exactly 'level'
  *       jointree items.  (This is one step of the dynamic-programming method