If we don't have any stats for a boolean column, assume

the disbursion is 0.5, not something small.

diff --git a/src/backend/utils/cache/lsyscache.c b/src/backend/utils/cache/lsyscache.c
index 90969744c9d92b75808a8f7ed5d2cd16717e8df1..688740e32da4d605737d881cb1e6b09db5e70920 100644 (file)
--- a/src/backend/utils/cache/lsyscache.c
+++ b/src/backend/utils/cache/lsyscache.c
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *   $Header: /cvsroot/pgsql/src/backend/utils/cache/lsyscache.c,v 1.39 2000/01/26 05:57:17 momjian Exp $
+ *   $Header: /cvsroot/pgsql/src/backend/utils/cache/lsyscache.c,v 1.40 2000/02/16 01:00:23 tgl Exp $
  *
  * NOTES
  *   Eventually, the index information should go through here, too.
@@ -183,6 +183,7 @@ double
 get_attdisbursion(Oid relid, AttrNumber attnum, double min_estimate)
 {
    HeapTuple   atp;
+   Form_pg_attribute att_tup;
    double      disbursion;
    int32       ntuples;
 
@@ -197,10 +198,21 @@ get_attdisbursion(Oid relid, AttrNumber attnum, double min_estimate)
             relid, attnum);
        return min_estimate;
    }
+   att_tup = (Form_pg_attribute) GETSTRUCT(atp);
 
-   disbursion = ((Form_pg_attribute) GETSTRUCT(atp))->attdisbursion;
+   disbursion = att_tup->attdisbursion;
    if (disbursion > 0.0)
-       return disbursion;      /* we have a specific estimate */
+       return disbursion;      /* we have a specific estimate from VACUUM */
+
+   /*
+    * Special-case boolean columns: the disbursion of a boolean is highly
+    * unlikely to be anywhere near 1/numtuples, instead it's probably more
+    * like 0.5.
+    *
+    * Are there any other cases we should wire in special estimates for?
+    */
+   if (att_tup->atttypid == BOOLOID)
+       return 0.5;
 
    /*
     * Disbursion is either 0 (no data available) or -1 (disbursion