Re: On disable_cost - Mailing list pgsql-hackers

BTW, getting off the question of EXPLAIN output for a moment,
I don't understand why disable_cost is still a thing.  The
one remaining usage seems trivial to replace, as attached.

            regards, tom lane

diff --git a/src/backend/optimizer/path/costsize.c b/src/backend/optimizer/path/costsize.c
index e1523d15df..a676ed2ef6 100644
--- a/src/backend/optimizer/path/costsize.c
+++ b/src/backend/optimizer/path/costsize.c
@@ -137,9 +137,6 @@ double        parallel_setup_cost = DEFAULT_PARALLEL_SETUP_COST;
 double        recursive_worktable_factor = DEFAULT_RECURSIVE_WORKTABLE_FACTOR;

 int            effective_cache_size = DEFAULT_EFFECTIVE_CACHE_SIZE;
-
-Cost        disable_cost = 1.0e10;
-
 int            max_parallel_workers_per_gather = 2;

 bool        enable_seqscan = true;
@@ -4355,15 +4352,15 @@ final_cost_hashjoin(PlannerInfo *root, HashPath *path,

     /*
      * If the bucket holding the inner MCV would exceed hash_mem, we don't
-     * want to hash unless there is really no other alternative, so apply
-     * disable_cost.  (The executor normally copes with excessive memory usage
+     * want to hash unless there is really no other alternative, so mark path
+     * as disabled.  (The executor normally copes with excessive memory usage
      * by splitting batches, but obviously it cannot separate equal values
      * that way, so it will be unable to drive the batch size below hash_mem
      * when this is true.)
      */
     if (relation_byte_size(clamp_row_est(inner_path_rows * innermcvfreq),
                            inner_path->pathtarget->width) > get_hash_memory_limit())
-        startup_cost += disable_cost;
+        path->jpath.path.disabled_nodes++;

     /*
      * Compute cost of the hashquals and qpquals (other restriction clauses)
diff --git a/src/include/optimizer/cost.h b/src/include/optimizer/cost.h
index 854a782944..ebd0e93f5e 100644
--- a/src/include/optimizer/cost.h
+++ b/src/include/optimizer/cost.h
@@ -47,7 +47,6 @@ typedef enum
  */

 /* parameter variables and flags (see also optimizer.h) */
-extern PGDLLIMPORT Cost disable_cost;
 extern PGDLLIMPORT int max_parallel_workers_per_gather;
 extern PGDLLIMPORT bool enable_seqscan;
 extern PGDLLIMPORT bool enable_indexscan;