Improve page split in rtree emulation. Now if splitted result has

big misalignement, then it tries to split page basing on distribution
of boxe's centers.

Per report from  Dolafi, Tom 

 Backpatch is needed, change doesn't affect on-disk storage.

diff --git a/src/backend/access/gist/gistproc.c b/src/backend/access/gist/gistproc.c
index 19868a127e71e26fdbc92a1cc6bc9ad082abd9e1..590be9133fbc5b04c13c7c443087f0e5a149afb2 100644 (file)
--- a/src/backend/access/gist/gistproc.c
+++ b/src/backend/access/gist/gistproc.c
@@ -10,7 +10,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- * $PostgreSQL: pgsql/src/backend/access/gist/gistproc.c,v 1.10 2007/01/05 22:19:22 momjian Exp $
+ * $PostgreSQL: pgsql/src/backend/access/gist/gistproc.c,v 1.11 2007/09/07 17:04:26 teodor Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -21,13 +21,6 @@
 #include "utils/geo_decls.h"
 
 
-typedef struct
-{
-   BOX        *key;
-   int         pos;
-} KBsort;
-
-static int compare_KB(const void *a, const void *b);
 static bool gist_box_leaf_consistent(BOX *key, BOX *query,
                         StrategyNumber strategy);
 static double size_box(Datum dbox);
@@ -194,22 +187,6 @@ gist_box_penalty(PG_FUNCTION_ARGS)
    PG_RETURN_POINTER(result);
 }
 
-/*
- * qsort comparator for box areas
- */
-static int
-compare_KB(const void *a, const void *b)
-{
-   BOX        *abox = ((const KBsort *) a)->key;
-   BOX        *bbox = ((const KBsort *) b)->key;
-   double      sa = (abox->high.x - abox->low.x) * (abox->high.y - abox->low.y);
-   double      sb = (bbox->high.x - bbox->low.x) * (bbox->high.y - bbox->low.y);
-
-   if (sa == sb)
-       return 0;
-   return (sa > sb) ? 1 : -1;
-}
-
 static void
 chooseLR(GIST_SPLITVEC *v,
         OffsetNumber *list1, int nlist1, BOX *union1,
@@ -417,44 +394,56 @@ gist_box_picksplit(PG_FUNCTION_ARGS)
            ADDLIST(listT, unionT, posT, i);
    }
 
-   /* bad disposition, sort by ascending and resplit */
-   if ((posR == 0 || posL == 0) && (posT == 0 || posB == 0))
+#define LIMIT_RATIO    0.1
+#define _IS_BADRATIO(x,y)  ( (y) == 0 || (float)(x)/(float)(y) < LIMIT_RATIO )
+#define IS_BADRATIO(x,y) ( _IS_BADRATIO((x),(y)) || _IS_BADRATIO((y),(x)) )
+   /* bad disposition, try to split by centers of boxes  */
+   if ( IS_BADRATIO(posR, posL) && IS_BADRATIO(posT, posB) )
    {
-       KBsort     *arr = (KBsort *) palloc(sizeof(KBsort) * maxoff);
+       double  avgCenterX=0.0, avgCenterY=0.0;
+       double  CenterX, CenterY;
 
-       posL = posR = posB = posT = 0;
        for (i = FirstOffsetNumber; i <= maxoff; i = OffsetNumberNext(i))
        {
-           arr[i - 1].key = DatumGetBoxP(entryvec->vector[i].key);
-           arr[i - 1].pos = i;
+           cur = DatumGetBoxP(entryvec->vector[i].key);
+           avgCenterX +=  ((double)cur->high.x + (double)cur->low.x)/2.0;
+           avgCenterY +=  ((double)cur->high.y + (double)cur->low.y)/2.0;
        }
-       qsort(arr, maxoff, sizeof(KBsort), compare_KB);
+
+       avgCenterX /= maxoff;
+       avgCenterY /= maxoff;
+
+       posL = posR = posB = posT = 0;
        for (i = FirstOffsetNumber; i <= maxoff; i = OffsetNumberNext(i))
        {
-           cur = arr[i - 1].key;
-           if (cur->low.x - pageunion.low.x < pageunion.high.x - cur->high.x)
-               ADDLIST(listL, unionL, posL, arr[i - 1].pos);
-           else if (cur->low.x - pageunion.low.x == pageunion.high.x - cur->high.x)
+           cur = DatumGetBoxP(entryvec->vector[i].key);
+           
+           CenterX =  ((double)cur->high.x + (double)cur->low.x)/2.0;
+           CenterY =  ((double)cur->high.y + (double)cur->low.y)/2.0;
+
+           if (CenterX < avgCenterX) 
+               ADDLIST(listL, unionL, posL, i);
+           else if (CenterX == avgCenterX)
            {
                if (posL > posR)
-                   ADDLIST(listR, unionR, posR, arr[i - 1].pos);
+                   ADDLIST(listR, unionR, posR, i);
                else
-                   ADDLIST(listL, unionL, posL, arr[i - 1].pos);
+                   ADDLIST(listL, unionL, posL, i);
            }
            else
-               ADDLIST(listR, unionR, posR, arr[i - 1].pos);
+               ADDLIST(listR, unionR, posR, i);
 
-           if (cur->low.y - pageunion.low.y < pageunion.high.y - cur->high.y)
-               ADDLIST(listB, unionB, posB, arr[i - 1].pos);
-           else if (cur->low.y - pageunion.low.y == pageunion.high.y - cur->high.y)
+           if (CenterY < avgCenterY)
+               ADDLIST(listB, unionB, posB, i);
+           else if (CenterY == avgCenterY)
            {
                if (posB > posT)
-                   ADDLIST(listT, unionT, posT, arr[i - 1].pos);
+                   ADDLIST(listT, unionT, posT, i);
                else
-                   ADDLIST(listB, unionB, posB, arr[i - 1].pos);
+                   ADDLIST(listB, unionB, posB, i);
            }
-           else
-               ADDLIST(listT, unionT, posT, arr[i - 1].pos);
+           else 
+               ADDLIST(listT, unionT, posT, i);
        }
    }