From: Ole John Aske
Date: February 28 2011 11:38am
Subject: bzr push into mysql-5.1-telco-7.0 branch (ole.john.aske:4234 to 4235)
List-Archive: http://lists.mysql.com/commits/132103
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 4235 Ole John Aske	2011-02-28
      Fixed compiler warnings introduced by last push.

    modified:
      sql/ha_ndbcluster.cc
 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 'sql/ha_ndbcluster.cc'
--- a/sql/ha_ndbcluster.cc	2011-02-28 10:42:04 +0000
+++ b/sql/ha_ndbcluster.cc	2011-02-28 11:38:19 +0000
@@ -11256,7 +11256,7 @@ ha_ndbcluster::records_in_range(uint inx
         if (eq_fraction >= 1.0)        // Exact match -> 1 row
           DBUG_RETURN(1);
 
-        rows = (Uint64)(table_rows / pow(table_rows, eq_fraction));
+        rows = (Uint64)((double)table_rows / pow(table_rows, eq_fraction));
         if (rows > (table_rows/50))    // EQ-range: Max 2% of rows
           rows= (table_rows/50);
 

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