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 6bf34c6a25ac1cfb4e1d8dcdca0ef0c5e95ba6fe..22eb4d3e53d8715619cbf311bef40049a32f07ca 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 5edfed65b0e9039a39a32afcfbebfa2723565c00..8b2f5139ecdfafdb8a1ae4196e67364cda8e4f31 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 095f0ec2755f17d3bdb4da513a1951dea4a9ac65..03708897b7a002b725b5df42c0f131d13e8bb174 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 fdaf17d91ffb8b989dd786cf79017d2d1322fca4..2b752711a68d08a33c421ed1a15211309f82f8a0 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,