Make EXPLAIN better at displaying MRR/BKA:

- "Using MRR" is no longer shown with range access.
- Instead, both range and BKA accesses will show one of the following:
  = "Rowid-ordered scan"
  = "Key-ordered scan"
  = "Key-ordered Rowid-ordered scan"
depending on whether DS-MRR implementation will do scan keys in order, rowids in order,
or both.
- The patch also introduces a way for other storage engines/MRR implementations to
  pass information to EXPLAIN output about the properties of employed MRR scans.

2 files changed, 9 insertions, 1 deletions

diff --git a/storage/myisam/ha_myisam.cc b/storage/myisam/ha_myisam.cc
index 1edecf5289a..89bdd4597f8 100644
--- a/storage/myisam/ha_myisam.cc
+++ b/storage/myisam/ha_myisam.cc
@@ -2281,6 +2281,13 @@ ha_rows ha_myisam::multi_range_read_info(uint keyno, uint n_ranges, uint keys,
   return ds_mrr.dsmrr_info(keyno, n_ranges, keys, key_parts, bufsz, flags, cost);
 }
 
+
+int ha_myisam::multi_range_read_explain_info(uint mrr_mode, char *str, 
+                                             size_t size)
+{
+  return ds_mrr.dsmrr_explain_info(mrr_mode, str, size);
+}
+
 /* MyISAM MRR implementation ends */
 
 
diff --git a/storage/myisam/ha_myisam.h b/storage/myisam/ha_myisam.h
index 529d31b4a4a..9b9ca5c18d9 100644
--- a/storage/myisam/ha_myisam.h
+++ b/storage/myisam/ha_myisam.h
@@ -170,7 +170,8 @@ public:
   ha_rows multi_range_read_info(uint keyno, uint n_ranges, uint keys,
                                 uint key_parts, uint *bufsz, 
                                 uint *flags, COST_VECT *cost);
-  
+  int multi_range_read_explain_info(uint mrr_mode, char *str, size_t size);
+
   /* Index condition pushdown implementation */
   Item *idx_cond_push(uint keyno, Item* idx_cond);
 private: