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;
 }