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From:Ole John Aske Date:February 28 2011 10:42am
Subject:bzr commit into mysql-5.1-telco-7.0 branch (ole.john.aske:4234) Bug#11804277
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#At file:///net/fimafeng09/export/home/tmp/oleja/mysql/mysql-5.1-telco-7.0/ based on revid:msabaratnam@stripped

 4234 Ole John Aske	2011-02-28
      Fix for bug#11804277 - INCORRECT INDEX MAY BE SELECTED DUE TO INSUFFICIENT STATISTICS FROM CLUSTER
      
      Add heuristics to ha_ndbcluster::records_in_range()
      which identifies a range as:
      
       - An open bound range  (<column> LT/GT <bound)
       - A closed bound range (<column> BETWEEN <low> AND <HIGH>)
       - A (partial) EQ-range (<column> EQ <bound>)
      
      ... Or a combination of these....
      
      These are handled as follows:
      
      Open bound ranges
      -----------------
      Without a histogram of how the values in the index are
      distributed, we can only assume an equal distrubution.
      A statistically correct estimate for a condition of the form
      '<column> LT/GT <bound>' would then have been to assume it selects
      50% of the rows in the table. However, I have experienced that
      this will cause the range-cost to directly compete with the cost
      of a full table scan. We should therefore be somewhat more
      conservative and estimate 10% of the rows to be returned.
      
      Closed bound range
      ------------------
      We assume this to be somewhat better than an open bounded range
      returning 5% of the rows in the table.
      
      EQ-range
      --------
      An EQ-range will excatly specify a fraction of the first part of
      an index. It is reasonable to assume:
      
        - Specifing a larger fraction of the index will improve the
          selectivity of the EQ-range.
        - Each part of the specified EQ-range will have the same
          selectivity.
      
      We can model this as a Binomial Distribution of the indexed
      values. http://en.wikipedia.org/wiki/Binomial_distrib

    modified:
      mysql-test/suite/ndb/r/ndb_condition_pushdown.result
      mysql-test/suite/ndb/r/ndb_index.result
      mysql-test/suite/ndb/r/ndb_index_unique.result
      mysql-test/suite/ndb/r/ndb_read_multi_range.result
      mysql-test/suite/ndb/r/ndb_statistics.result
      mysql-test/suite/ndb/t/ndb_statistics.test
      sql/ha_ndbcluster.cc
=== modified file 'mysql-test/suite/ndb/r/ndb_condition_pushdown.result'
--- a/mysql-test/suite/ndb/r/ndb_condition_pushdown.result	2011-01-17 13:29:52 +0000
+++ b/mysql-test/suite/ndb/r/ndb_condition_pushdown.result	2011-02-28 10:42:04 +0000
@@ -1910,7 +1910,7 @@ insert into NodeAlias VALUES(null, 8 , '
 12:22:26');
 explain select * from NodeAlias where (aliasKey LIKE '491803%');
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	NodeAlias	range	NodeAlias_KeyIndex	NodeAlias_KeyIndex	48	NULL	10	Using where with pushed condition
+1	SIMPLE	NodeAlias	range	NodeAlias_KeyIndex	NodeAlias_KeyIndex	48	NULL	2	Using where with pushed condition
 select * from NodeAlias where (aliasKey LIKE '491803%') order by id;
 id	nodeId	displayName	aliasKey	objectVersion	changed
 7	8	491803%	491803%	0	2008-03-10 12:22:26
@@ -2225,7 +2225,7 @@ join tx as t2 on tx.a = t2.c and tx.b = 
 where t2.a = 4
 group by t2.c;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	SIMPLE	t2	ref	PRIMARY	PRIMARY	4	const	10	100.00	Using where; Using filesort
+1	SIMPLE	t2	ref	PRIMARY	PRIMARY	4	const	2	100.00	Using where; Using filesort
 1	SIMPLE	tx	eq_ref	PRIMARY	PRIMARY	8	test.t2.c,test.t2.d	1	100.00	
 Warnings:
 Note	1003	select `test`.`t2`.`c` AS `c`,count(distinct `test`.`t2`.`a`) AS `count(distinct t2.a)` from `test`.`tx` join `test`.`tx` `t2` where ((`test`.`tx`.`b` = `test`.`t2`.`d`) and (`test`.`tx`.`a` = `test`.`t2`.`c`) and (`test`.`t2`.`a` = 4)) group by `test`.`t2`.`c`
@@ -2242,7 +2242,7 @@ join tx as t2 on tx.a = t2.c and tx.b = 
 where t2.a = 4
 group by t2.c;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	SIMPLE	t2	ref	PRIMARY	PRIMARY	4	const	10	100.00	Using where; Using filesort
+1	SIMPLE	t2	ref	PRIMARY	PRIMARY	4	const	2	100.00	Using where; Using filesort
 1	SIMPLE	tx	eq_ref	PRIMARY	PRIMARY	8	test.t2.c,test.t2.d	1	100.00	
 Warnings:
 Note	1003	select `test`.`t2`.`c` AS `c`,count(distinct `test`.`t2`.`a`) AS `count(distinct t2.a)` from `test`.`tx` join `test`.`tx` `t2` where ((`test`.`tx`.`b` = `test`.`t2`.`d`) and (`test`.`tx`.`a` = `test`.`t2`.`c`) and (`test`.`t2`.`a` = 4)) group by `test`.`t2`.`c`

=== modified file 'mysql-test/suite/ndb/r/ndb_index.result'
--- a/mysql-test/suite/ndb/r/ndb_index.result	2010-12-22 11:13:45 +0000
+++ b/mysql-test/suite/ndb/r/ndb_index.result	2011-02-28 10:42:04 +0000
@@ -306,7 +306,7 @@ explain
 select i,vc from t1
 where i>=1 or vc > '0';
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	index_merge	PRIMARY,i1,i2	i1,i2	5,18	NULL	20	Using sort_union(i1,i2); Using where with pushed condition
+1	SIMPLE	t1	index_merge	PRIMARY,i1,i2	i1,i2	5,18	NULL	6	Using sort_union(i1,i2); Using where with pushed condition
 select i,vc from t1
 where i>=1 or vc > '0';
 i	vc
@@ -350,7 +350,7 @@ explain
 select i,vc from t2
 where i>=1 or vc > '0';
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t2	index_merge	i1,i2	i1,i2	5,19	NULL	20	Using sort_union(i1,i2); Using where with pushed condition
+1	SIMPLE	t2	index_merge	i1,i2	i1,i2	5,19	NULL	6	Using sort_union(i1,i2); Using where with pushed condition
 select i,vc from t2
 where i>=1 or vc > '0';
 i	vc

=== modified file 'mysql-test/suite/ndb/r/ndb_index_unique.result'
--- a/mysql-test/suite/ndb/r/ndb_index_unique.result	2011-01-18 07:49:14 +0000
+++ b/mysql-test/suite/ndb/r/ndb_index_unique.result	2011-02-28 10:42:04 +0000
@@ -185,7 +185,7 @@ set @old_ecpd = @@session.engine_conditi
 set engine_condition_pushdown = true;
 explain select * from t2 where (b = 3 OR b = 5) AND c IS NULL AND a < 9 order by a;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t2	range	PRIMARY,b	b	9	NULL	2	Using where with pushed condition; Using filesort
+1	SIMPLE	t2	range	PRIMARY,b	PRIMARY	4	NULL	2	Using where with pushed condition
 select * from t2 where (b = 3 OR b = 5) AND c IS NULL AND a < 9 order by a;
 a	b	c
 3	3	NULL

=== modified file 'mysql-test/suite/ndb/r/ndb_read_multi_range.result'
--- a/mysql-test/suite/ndb/r/ndb_read_multi_range.result	2011-01-18 07:49:14 +0000
+++ b/mysql-test/suite/ndb/r/ndb_read_multi_range.result	2011-02-28 10:42:04 +0000
@@ -605,7 +605,7 @@ SELECT DISTINCT STRAIGHT_JOIN t1.pk FROM
 t1 LEFT JOIN t2 ON t2.a = t1.a AND t2.pk != 6;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	3000	Using temporary
-1	SIMPLE	t2	range	PRIMARY	PRIMARY	4	NULL	20	Using where; Distinct
+1	SIMPLE	t2	range	PRIMARY	PRIMARY	4	NULL	6	Using where; Distinct
 SELECT DISTINCT STRAIGHT_JOIN t1.pk FROM 
 t1 LEFT JOIN t2 ON t2.a = t1.a AND t2.pk != 6;
 drop table t1, t2;

=== modified file 'mysql-test/suite/ndb/r/ndb_statistics.result'
--- a/mysql-test/suite/ndb/r/ndb_statistics.result	2011-01-18 11:49:03 +0000
+++ b/mysql-test/suite/ndb/r/ndb_statistics.result	2011-02-28 10:42:04 +0000
@@ -38,24 +38,124 @@ id	select_type	table	type	possible_keys	
 EXPLAIN
 SELECT * FROM t10000 WHERE k >= 42 and k < 10000;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t10000	range	PRIMARY	PRIMARY	4	NULL	10	Using where with pushed condition
+1	SIMPLE	t10000	range	PRIMARY	PRIMARY	4	NULL	500	Using where with pushed condition
 EXPLAIN
 SELECT * FROM t10000 WHERE k BETWEEN 42 AND 10000;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t10000	range	PRIMARY	PRIMARY	4	NULL	10	Using where with pushed condition
+1	SIMPLE	t10000	range	PRIMARY	PRIMARY	4	NULL	500	Using where with pushed condition
 EXPLAIN
 SELECT * FROM t10000 WHERE k < 42;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t10000	range	PRIMARY	PRIMARY	4	NULL	10	Using where with pushed condition
+1	SIMPLE	t10000	range	PRIMARY	PRIMARY	4	NULL	1000	Using where with pushed condition
 EXPLAIN
 SELECT * FROM t10000 WHERE k > 42;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t10000	range	PRIMARY	PRIMARY	4	NULL	10	Using where with pushed condition
+1	SIMPLE	t10000	range	PRIMARY	PRIMARY	4	NULL	1000	Using where with pushed condition
 EXPLAIN
 SELECT * FROM t10000 AS X JOIN t10000 AS Y
 ON Y.I=X.I AND Y.J = X.I;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	X	ALL	I	NULL	NULL	NULL	10000	
 1	SIMPLE	Y	ref	J,I	I	10	test.X.I,test.X.I	11	Using where
+EXPLAIN
+SELECT * FROM t100 WHERE k < 42;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t100	range	PRIMARY	PRIMARY	4	NULL	10	Using where with pushed condition
+EXPLAIN
+SELECT * FROM t100 WHERE k > 42;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t100	range	PRIMARY	PRIMARY	4	NULL	10	Using where with pushed condition
+EXPLAIN
+SELECT * FROM t10000 WHERE k < 42;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t10000	range	PRIMARY	PRIMARY	4	NULL	1000	Using where with pushed condition
+EXPLAIN
+SELECT * FROM t10000 WHERE k > 42;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t10000	range	PRIMARY	PRIMARY	4	NULL	1000	Using where with pushed condition
+EXPLAIN
+SELECT * FROM t100 WHERE k BETWEEN 42 AND 10000;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t100	range	PRIMARY	PRIMARY	4	NULL	5	Using where with pushed condition
+EXPLAIN
+SELECT * FROM t10000 WHERE k BETWEEN 42 AND 10000;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t10000	range	PRIMARY	PRIMARY	4	NULL	500	Using where with pushed condition
+EXPLAIN
+SELECT * FROM t10000 WHERE I = 0;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t10000	ref	I	I	5	const	200	Using where with pushed condition
+EXPLAIN
+SELECT * FROM t10000 WHERE J = 0;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t10000	ref	J	J	5	const	100	Using where with pushed condition
+EXPLAIN
+SELECT * FROM t10000 WHERE I = 0 AND J = 0;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t10000	ref	J,I	I	10	const,const	4	Using where with pushed condition
+EXPLAIN
+SELECT * FROM t10000 WHERE I = 0;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t10000	ref	I	I	5	const	200	Using where with pushed condition
+EXPLAIN
+SELECT * FROM t10000 WHERE I = 0 AND J > 1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t10000	range	J,I	I	10	NULL	100	Using where with pushed condition
+EXPLAIN
+SELECT * FROM t10000 WHERE I = 0 AND J < 1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t10000	range	J,I	I	10	NULL	50	Using where with pushed condition
+EXPLAIN
+SELECT * FROM t10000 WHERE I = 0 AND J BETWEEN 1 AND 10;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t10000	range	J,I	I	10	NULL	50	Using where with pushed condition
+EXPLAIN
+SELECT * FROM t10000 WHERE I = 0 AND J = 1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t10000	ref	J,I	I	10	const,const	4	Using where with pushed condition
+EXPLAIN
+SELECT * FROM t10000 WHERE J = 0;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t10000	ref	J	J	5	const	100	Using where with pushed condition
+EXPLAIN
+SELECT * FROM t10000 WHERE J = 0 AND K > 1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t10000	range	PRIMARY,J	J	9	NULL	50	Using where with pushed condition
+EXPLAIN
+SELECT * FROM t10000 WHERE J = 0 AND K < 1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t10000	range	PRIMARY,J	J	9	NULL	50	Using where with pushed condition
+EXPLAIN
+SELECT * FROM t10000 WHERE J = 0 AND K BETWEEN 1 AND 10;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t10000	range	PRIMARY,J	J	9	NULL	25	Using where with pushed condition
+EXPLAIN
+SELECT * FROM t10000 WHERE J = 0 AND K = 1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
+EXPLAIN
+SELECT * FROM t10000 WHERE I = 0 AND J <> 1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t10000	range	J,I	I	10	NULL	150	Using where with pushed condition
+EXPLAIN
+SELECT * FROM t10000 WHERE I <> 0 AND J = 1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t10000	ref	J,I	J	5	const	100	Using where with pushed condition
+EXPLAIN
+SELECT * FROM t10000 WHERE I <> 0 AND J <> 1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t10000	range	J,I	J	5	NULL	1500	Using where with pushed condition
+EXPLAIN
+SELECT * FROM t10000 WHERE J <> 1 AND I = 0;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t10000	range	J,I	I	10	NULL	150	Using where with pushed condition
+EXPLAIN
+SELECT * FROM t10000 WHERE J = 1 AND I <> 0;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t10000	ref	J,I	J	5	const	100	Using where with pushed condition
+EXPLAIN
+SELECT * FROM t10000 WHERE J <> 1 AND I <> 0;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t10000	range	J,I	J	5	NULL	1500	Using where with pushed condition
 DROP TABLE t10,t100,t10000;
 End of 5.1 tests

=== modified file 'mysql-test/suite/ndb/t/ndb_statistics.test'
--- a/mysql-test/suite/ndb/t/ndb_statistics.test	2011-01-18 11:49:03 +0000
+++ b/mysql-test/suite/ndb/t/ndb_statistics.test	2011-02-28 10:42:04 +0000
@@ -62,6 +62,82 @@ EXPLAIN
 SELECT * FROM t10000 AS X JOIN t10000 AS Y
   ON Y.I=X.I AND Y.J = X.I;
 
+#
+# Bug #11804277: INCORRECT INDEX MAY BE SELECTED DUE TO INSUFFICIENT 
+#                STATISTICS FROM CLUSTER
+#
+
+# Open bounded range should return 10% of #rows in table
+EXPLAIN
+SELECT * FROM t100 WHERE k < 42;
+EXPLAIN
+SELECT * FROM t100 WHERE k > 42;
+EXPLAIN
+SELECT * FROM t10000 WHERE k < 42;
+EXPLAIN
+SELECT * FROM t10000 WHERE k > 42;
+
+#Closed bounded range should return 5% of #rows in table
+EXPLAIN
+SELECT * FROM t100 WHERE k BETWEEN 42 AND 10000;
+EXPLAIN
+SELECT * FROM t10000 WHERE k BETWEEN 42 AND 10000;
+
+#EQ-range selectivity depends on
+#  - key length specified
+#  - #rows in table.
+#  - unique/non-unique index
+#  - min 2% selectivity
+#
+#  Possibly combined with open/closed ranges as
+#  above which further improves selectivity
+#
+EXPLAIN
+SELECT * FROM t10000 WHERE I = 0;
+EXPLAIN
+SELECT * FROM t10000 WHERE J = 0;
+
+EXPLAIN
+SELECT * FROM t10000 WHERE I = 0 AND J = 0;
+
+EXPLAIN
+SELECT * FROM t10000 WHERE I = 0;
+EXPLAIN
+SELECT * FROM t10000 WHERE I = 0 AND J > 1;
+EXPLAIN
+SELECT * FROM t10000 WHERE I = 0 AND J < 1;
+EXPLAIN
+SELECT * FROM t10000 WHERE I = 0 AND J BETWEEN 1 AND 10;
+EXPLAIN
+SELECT * FROM t10000 WHERE I = 0 AND J = 1;
+
+EXPLAIN
+SELECT * FROM t10000 WHERE J = 0;
+EXPLAIN
+SELECT * FROM t10000 WHERE J = 0 AND K > 1;
+EXPLAIN
+SELECT * FROM t10000 WHERE J = 0 AND K < 1;
+EXPLAIN
+SELECT * FROM t10000 WHERE J = 0 AND K BETWEEN 1 AND 10;
+EXPLAIN
+SELECT * FROM t10000 WHERE J = 0 AND K = 1;
+
+## Verify selection of 'best' index
+## (The one of index I/J being EQ)
+EXPLAIN
+SELECT * FROM t10000 WHERE I = 0 AND J <> 1;
+EXPLAIN
+SELECT * FROM t10000 WHERE I <> 0 AND J = 1;
+EXPLAIN
+SELECT * FROM t10000 WHERE I <> 0 AND J <> 1;
+
+EXPLAIN
+SELECT * FROM t10000 WHERE J <> 1 AND I = 0;
+EXPLAIN
+SELECT * FROM t10000 WHERE J = 1 AND I <> 0;
+EXPLAIN
+SELECT * FROM t10000 WHERE J <> 1 AND I <> 0;
+
 
 DROP TABLE t10,t100,t10000;
 

=== modified file 'sql/ha_ndbcluster.cc'
--- a/sql/ha_ndbcluster.cc	2011-02-24 09:46:11 +0000
+++ b/sql/ha_ndbcluster.cc	2011-02-28 10:42:04 +0000
@@ -11182,7 +11182,100 @@ ha_ndbcluster::records_in_range(uint inx
     DBUG_RETURN(rows);
   }
 
-  DBUG_RETURN(10); /* Good guess when you don't know anything */
+  /* Use simple heuristics to estimate fraction
+     of 'stats.record' returned from range.
+  */
+  do
+  {
+    if (stats.records == ~(ha_rows)0 || stats.records == 0)
+    {
+      /* Refresh statistics, only read from datanodes if 'use_exact_count' */
+      THD *thd= current_thd;
+      if (update_stats(thd, THDVAR(thd, use_exact_count)))
+        break;
+    }
+
+    Uint64 rows;
+    Uint64 table_rows= stats.records;
+    size_t eq_bound_len= 0;
+    size_t min_key_length= (min_key) ? min_key->length : 0;
+    size_t max_key_length= (max_key) ? max_key->length : 0; 
+
+    // Might have an closed/open range bound:
+    // Low range open
+    if (!min_key_length)
+    {
+      rows= (!max_key_length) 
+           ? table_rows             // No range was specified
+           : table_rows/10;         // -oo .. <high range> -> 10% selectivity
+    }
+    // High range open
+    else if (!max_key_length)
+    {
+      rows= table_rows/10;          // <low range>..oo -> 10% selectivity
+    }
+    else
+    {
+      size_t bounds_len= min(min_key_length,max_key_length);
+      uint eq_bound_len= 0;
+      uint eq_bound_offs= 0;
+
+      KEY_PART_INFO* key_part= key_info->key_part;
+      KEY_PART_INFO* end= key_part+key_info->key_parts;
+      for (; key_part != end; key_part++) 
+      {
+        uint part_length= key_part->store_length;
+        if (eq_bound_offs+part_length > bounds_len ||
+            memcmp(&min_key->key[eq_bound_offs],
+                   &max_key->key[eq_bound_offs],
+                   part_length))
+        {
+          break;
+        }
+        eq_bound_len+= key_part->length;
+        eq_bound_offs+= part_length;
+      }
+
+      if (!eq_bound_len)
+      {
+        rows= table_rows/20;        // <low range>..<high range> -> 5% 
+      }
+      else
+      {
+        // Has an equality range on a leading part of 'key_length':
+        // - Null indicator, and HA_KEY_BLOB_LENGTH bytes in
+        //   'extra_length' are removed from key_fraction calculations.
+        // - Assume reduced selectivity for non-unique indexes
+        //   by decreasing 'eq_fraction' by 20%
+        // - Assume equal selectivity for all eq_parts in key.
+
+        double eq_fraction = (double)(eq_bound_len) / 
+                                     (key_length - key_info->extra_length);
+        if (idx_type == ORDERED_INDEX) // Non-unique index -> less selectivity
+          eq_fraction/= 1.20;
+        if (eq_fraction >= 1.0)        // Exact match -> 1 row
+          DBUG_RETURN(1);
+
+        rows = (Uint64)(table_rows / pow(table_rows, eq_fraction));
+        if (rows > (table_rows/50))    // EQ-range: Max 2% of rows
+          rows= (table_rows/50);
+
+        if (min_key_length > eq_bound_offs)
+          rows/= 2;
+        if (max_key_length > eq_bound_offs)
+          rows/= 2;
+      }
+    }
+
+    // Make sure that EQ is preferred even if row-count is low
+    if (eq_bound_len && rows < 2)      // At least 2 rows as not exact
+      rows= 2;
+    else if (rows < 3)
+      rows= 3;
+    DBUG_RETURN(min(rows,table_rows));
+  } while (0);
+
+  DBUG_RETURN(10); /* Poor guess when you don't know anything */
 }
 
 ulonglong ha_ndbcluster::table_flags(void) const


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bzr commit into mysql-5.1-telco-7.0 branch (ole.john.aske:4234) Bug#11804277Ole John Aske28 Feb