Clean up cost_sort some more: most callers were double-counting

the cost of reading the source data.

diff --git a/src/backend/optimizer/path/costsize.c b/src/backend/optimizer/path/costsize.c
index 6bf34c6..22eb4d3 100644 (file)
--- a/src/backend/optimizer/path/costsize.c
+++ b/src/backend/optimizer/path/costsize.c
@@ -7,7 +7,7 @@
  *
  *
  * IDENTIFICATION
- *       $Header: /cvsroot/pgsql/src/backend/optimizer/path/costsize.c,v 1.35 1999/04/30 04:01:44 tgl Exp $
+ *       $Header: /cvsroot/pgsql/src/backend/optimizer/path/costsize.c,v 1.36 1999/05/01 19:47:41 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -167,28 +167,23 @@ cost_index(Oid indexid,
 /*
  * cost_sort
  *       Determines and returns the cost of sorting a relation by considering
- *       1. the cost of doing an external sort:        XXX this is probably too low
+ *       the cost of doing an external sort:   XXX this is probably too low
  *                             disk = (p lg p)
  *                             cpu = *CPU-PAGE-WEIGHT* * (t lg t)
- *       2. the cost of reading the sort result into memory (another seqscan)
- *              unless 'noread' is set
  *
  * 'pathkeys' is a list of sort keys
  * 'tuples' is the number of tuples in the relation
  * 'width' is the average tuple width in bytes
- * 'noread' is a flag indicating that the cost of reading the sort
- *                             source data should not be included (i.e., the caller
- *                             will account for it separately).
  *
  * NOTE: some callers currently pass NULL for pathkeys because they
- * can't conveniently supply sort keys.  Since this routine doesn't
+ * can't conveniently supply the sort keys.  Since this routine doesn't
  * currently do anything with pathkeys anyway, that doesn't matter...
+ * but if it ever does, it should react gracefully to lack of key data.
  *
  * Returns a flonum.
- *
  */
 Cost
-cost_sort(List *pathkeys, int tuples, int width, bool noread)
+cost_sort(List *pathkeys, int tuples, int width)
 {
        Cost            temp = 0;
        int                     npages = page_size(tuples, width);
@@ -200,6 +195,8 @@ cost_sort(List *pathkeys, int tuples, int width, bool noread)
        /* We want to be sure the cost of a sort is never estimated as zero,
         * even if passed-in tuple count is zero.  Besides, mustn't do log(0)...
         */
+       if (tuples <= 0)
+               tuples = 1;
        if (npages <= 0)
                npages = 1;
 
@@ -210,13 +207,10 @@ cost_sort(List *pathkeys, int tuples, int width, bool noread)
        temp += npages * log_npages;
 
        /*
-        * could be base_log(pages, NBuffers), but we are only doing 2-way
+        * could be base_log(tuples, NBuffers), but we are only doing 2-way
         * merges
         */
-       temp += _cpu_page_wight_ * tuples * log_npages;
-
-       if (!noread)
-               temp += cost_seqscan(_NONAME_RELATION_ID_, npages, tuples);
+       temp += _cpu_page_wight_ * tuples * base_log((double) tuples, 2.0);
 
        Assert(temp > 0);
 
@@ -282,7 +276,8 @@ cost_nestloop(Cost outercost,
  *       'outercost' and 'innercost' are the (disk+cpu) costs of scanning the
  *                             outer and inner relations
  *       'outersortkeys' and 'innersortkeys' are lists of the keys to be used
- *                             to sort the outer and inner relations
+ *                             to sort the outer and inner relations (or NIL if no explicit
+ *                             sort is needed because the source path is already ordered)
  *       'outertuples' and 'innertuples' are the number of tuples in the outer
  *                             and inner relations
  *       'outerwidth' and 'innerwidth' are the (typical) widths (in bytes)
@@ -309,9 +304,9 @@ cost_mergejoin(Cost outercost,
        temp += outercost;
        temp += innercost;
        if (outersortkeys)                      /* do we need to sort? */
-               temp += cost_sort(outersortkeys, outersize, outerwidth, true);
+               temp += cost_sort(outersortkeys, outersize, outerwidth);
        if (innersortkeys)                      /* do we need to sort? */
-               temp += cost_sort(innersortkeys, innersize, innerwidth, true);
+               temp += cost_sort(innersortkeys, innersize, innerwidth);
        temp += _cpu_page_wight_ * (outersize + innersize);
 
        Assert(temp >= 0);

diff --git a/src/backend/optimizer/path/joinpath.c b/src/backend/optimizer/path/joinpath.c
index 5edfed6..8b2f513 100644 (file)
--- a/src/backend/optimizer/path/joinpath.c
+++ b/src/backend/optimizer/path/joinpath.c
@@ -7,7 +7,7 @@
  *
  *
  * IDENTIFICATION
- *       $Header: /cvsroot/pgsql/src/backend/optimizer/path/joinpath.c,v 1.33 1999/04/03 00:18:28 tgl Exp $
+ *       $Header: /cvsroot/pgsql/src/backend/optimizer/path/joinpath.c,v 1.34 1999/05/01 19:47:42 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -348,7 +348,7 @@ match_unsorted_outer(RelOptInfo *joinrel,
                                (mergeinnerpath->path_cost <
                                 (cheapest_inner->path_cost +
                                  cost_sort(matchedJoinKeys, innerrel->size,
-                                                       innerrel->width, false))));
+                                                       innerrel->width))));
                        if (!path_is_cheaper_than_sort)
                        {
                                varkeys = make_pathkeys_from_joinkeys(matchedJoinKeys,
@@ -464,8 +464,7 @@ match_unsorted_inner(RelOptInfo *joinrel,
                if (clauses && matchedJoinKeys)
                {
                        temp1 = outerrel->cheapestpath->path_cost +
-                               cost_sort(matchedJoinKeys, outerrel->size, outerrel->width,
-                                                 false);
+                               cost_sort(matchedJoinKeys, outerrel->size, outerrel->width);
 
                        temp2 = (bool) (FLOAT_IS_ZERO(innerpath->outerjoincost)
                                                        || (innerpath->outerjoincost > temp1));

diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
index 095f0ec..0370889 100644 (file)
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -7,7 +7,7 @@
  *
  *
  * IDENTIFICATION
- *       $Header: /cvsroot/pgsql/src/backend/optimizer/plan/createplan.c,v 1.51 1999/04/30 04:04:27 tgl Exp $
+ *       $Header: /cvsroot/pgsql/src/backend/optimizer/plan/createplan.c,v 1.52 1999/05/01 19:47:40 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1106,7 +1106,7 @@ make_sort(List *tlist, Oid nonameid, Plan *lefttree, int keycount)
        Plan       *plan = &node->plan;
 
        copy_costsize(plan, lefttree);
-       plan->cost += cost_sort(NULL, plan->plan_size, plan->plan_width, true);
+       plan->cost += cost_sort(NULL, plan->plan_size, plan->plan_width);
        plan->state = (EState *) NULL;
        plan->targetlist = tlist;
        plan->qual = NIL;

diff --git a/src/include/optimizer/cost.h b/src/include/optimizer/cost.h
index fdaf17d..2b75271 100644 (file)
--- a/src/include/optimizer/cost.h
+++ b/src/include/optimizer/cost.h
@@ -6,7 +6,7 @@
  *
  * Copyright (c) 1994, Regents of the University of California
  *
- * $Id: cost.h,v 1.17 1999/02/13 23:21:43 momjian Exp $
+ * $Id: cost.h,v 1.18 1999/05/01 19:47:39 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -34,7 +34,7 @@ extern Cost cost_seqscan(int relid, int relpages, int reltuples);
 extern Cost cost_index(Oid indexid, int expected_indexpages, Cost selec,
                   int relpages, int reltuples, int indexpages,
                   int indextuples, bool is_injoin);
-extern Cost cost_sort(List *pathkeys, int tuples, int width, bool noread);
+extern Cost cost_sort(List *pathkeys, int tuples, int width);
 extern Cost cost_nestloop(Cost outercost, Cost innercost, int outertuples,
                          int innertuples, int outerpages, bool is_indexjoin);
 extern Cost cost_mergejoin(Cost outercost, Cost innercost,