MDEV-5846 MySQL Bug #18144 - Cost with FORCE/USE index seems incorrect in some cases.

1 files changed, 12 insertions, 0 deletions

diff --git a/sql/handler.h b/sql/handler.h
index e67e68be931..37c2c86dce8 100644
--- a/sql/handler.h
+++ b/sql/handler.h
@@ -2721,6 +2721,18 @@ public:
   }
   virtual double scan_time()
   { return ulonglong2double(stats.data_file_length) / IO_SIZE + 2; }
+
+  /**
+     The cost of reading a set of ranges from the table using an index
+     to access it.
+     
+     @param index  The index number.
+     @param ranges The number of ranges to be read.
+     @param rows   Total number of rows to be read.
+     
+     This method can be used to calculate the total cost of scanning a table
+     using an index by calling it using read_time(index, 1, table_size).
+  */
   virtual double read_time(uint index, uint ranges, ha_rows rows)
   { return rows2double(ranges+rows); }