1 files changed, 29 insertions, 4 deletions

diff --git a/sql/handler.cc b/sql/handler.cc
index 4d53c3e8424..02753f24812 100644
--- a/sql/handler.cc
+++ b/sql/handler.cc
@@ -3208,20 +3208,45 @@ LEX_CSTRING *handler::engine_name()
   by index 'keyno' of one range containing 'rows' key entries.
   If ranges == 0 then the function returns only the cost of copying
   those key entries into the engine buffers.
+
+ This function doesn't take in account into copying the key to record
+ (INDEX_COPY_COST) or comparing the key to the where clause (TIME_FOR_COMPARE)
 */
 
 double handler::keyread_time(uint index, uint ranges, ha_rows rows)
 {
+  size_t len;
+  double cost;
   DBUG_ASSERT(ranges == 0 || ranges == 1);
-  size_t len= table->key_info[index].key_length + ref_length;
+  len= table->key_info[index].key_length + ref_length;
   if (table->file->is_clustering_key(index))
     len= table->s->stored_rec_length;
-  double cost= (double)rows*len/(stats.block_size+1)*IDX_BLOCK_COPY_COST;
+
+  cost= ((double)rows*len/(stats.block_size+1)*INDEX_BLOCK_COPY_COST);
+  /*
+    We divide the cost with optimizer_cache_cost as ha_keyread_time()
+    and ha_key_scan_time() will multiply the result value with
+    optimizer_cache_cost and we want to keep the above 'memory operation'
+    cost unaffected by this multiplication.
+  */
+  cost/= optimizer_cache_cost;
   if (ranges)
   {
     uint keys_per_block= (uint) (stats.block_size*3/4/len+1);
-    ulonglong blocks= (rows+ keys_per_block- 1)/keys_per_block;
-    cost+= blocks;
+    /*
+      We let the cost grow slowly in proportion to number of rows to
+      promote indexes with less rows.
+      We do not calculate exact number of block reads as then index
+      only reads will be more costly than normal reads, especially
+      compared to InnoDB clustered keys.
+
+      INDEX_LOOKUP_COST is the cost of finding the first key in the
+      range.  Finding the next key is usually a fast operation so we
+      don't count it here, it is taken into account in
+      ha_keyread_and_copy_time()
+    */
+    cost+= (((double) (rows / keys_per_block) + INDEX_LOOKUP_COST) *
+            avg_io_cost());
   }
   return cost;
 }