Fix potential overflow problems when relation size exceeds

2gig.  Fix failure to reliably put the smaller relation on the inside of
a hashjoin.

diff --git a/src/backend/optimizer/path/costsize.c b/src/backend/optimizer/path/costsize.c
index cb30dec42cc152c2545151dce6e53adae726142b..c00a9684dba615774e685e683b3e1ee1b44742dc 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 1.33 1999/02/15 03:22:04 momjian Exp $
+ *   $Header: /cvsroot/pgsql/src/backend/optimizer/path/costsize.c,v 1.34 1999/04/05 02:07:07 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -37,6 +37,7 @@
 extern int NBuffers;
 
 static int compute_attribute_width(TargetEntry *tlistentry);
+static double relation_byte_size (int tuples, int width);
 static double base_log(double x, double b);
 static int compute_targetlist_width(List *targetlist);
 
@@ -323,27 +324,35 @@ cost_hashjoin(Cost outercost,
    Cost        temp = 0;
    int         outerpages = page_size(outersize, outerwidth);
    int         innerpages = page_size(innersize, innerwidth);
-   int         nrun = ceil((double) outerpages / (double) NBuffers);
 
-   if (outerpages < innerpages)
-       return _disable_cost_;
    if (!_enable_hashjoin_)
        temp += _disable_cost_;
 
-   /*
-    * temp += outercost + (nrun + 1) * innercost;
-    *
-    * the innercost shouldn't be used it.  Instead the cost of hashing the
-    * innerpath should be used
-    *
-    * ASSUME innercost is 1 for now -- a horrible hack - jolly temp +=
-    * outercost + (nrun + 1);
+   /* Bias against putting larger relation on inside.
     *
-    * But we must add innercost to result.     - vadim 04/24/97
+    * Code used to use "outerpages < innerpages" but that has
+    * poor resolution when both relations are small.
     */
-   temp += outercost + innercost + (nrun + 1);
+   if (relation_byte_size(outersize, outerwidth) <
+       relation_byte_size(innersize, innerwidth))
+       temp += _disable_cost_;
+
+   /* cost of source data */
+   temp += outercost + innercost;
+
+   /* cost of computing hash function: must do it once per tuple */
+   temp += _cpu_page_wight_ * (outersize + innersize);
+
+   /* cost of main-memory hashtable */
+   temp += (innerpages < NBuffers) ? innerpages : NBuffers;
+
+   /* if inner relation is too big then we will need to "batch" the join,
+    * which implies writing and reading most of the tuples to disk an
+    * extra time.
+    */
+   if (innerpages > NBuffers)
+       temp += 2 * (outerpages + innerpages);
 
-   temp += _cpu_page_wight_ * (outersize + nrun * innersize);
    Assert(temp >= 0);
 
    return temp;
@@ -458,6 +467,19 @@ compute_joinrel_size(JoinPath *joinpath)
    return temp1;
 }
 
+/*
+ * relation_byte_size
+ *    Estimate the storage space in bytes for a given number of tuples
+ *    of a given width (size in bytes).
+ *    To avoid overflow with big relations, result is a double.
+ */
+
+static double
+relation_byte_size (int tuples, int width)
+{
+   return ((double) tuples) * ((double) (width + sizeof(HeapTupleData)));
+}
+
 /*
  * page_size
  *   Returns an estimate of the number of pages covered by a given
@@ -466,10 +488,9 @@ compute_joinrel_size(JoinPath *joinpath)
 int
 page_size(int tuples, int width)
 {
-   int         temp = 0;
+   int         temp;
 
-   temp = ceil((double) (tuples * (width + sizeof(HeapTupleData)))
-               / BLCKSZ);
+   temp = (int) ceil(relation_byte_size(tuples, width) / BLCKSZ);
    Assert(temp >= 0);
    return temp;
 }