DS-MRR support improvements (MWL#123, MWL#124, MWL#125)

- Lots of TODO comments
- add mrr_sort_keys flag to @@optimizer_switch
- [from Igor] SQL layer part passes HA_MRR_MATERIALIZED_KEYS flag
- Don't call rnd_pos() many times in a row if sorted rowid buffer
  has the same rowid value for multiple consequive (rowid, range_id) pairs.

sql/handler.h

@@ -1322,6 +1322,12 @@ void get_sweep_read_cost(TABLE *table, ha_rows nrows, bool interrupted,
 */
 #define HA_MRR_NO_NULL_ENDPOINTS 128
 
+/*
+  The MRR user has materialized range keys somewhere in the user's buffer.
+  This can be used for optimization of the procedure that sorts these keys
+  since in this case key values don't have to be copied into the MRR buffer.
+*/
+#define HA_MRR_MATERIALIZED_KEYS 256
 
 
 /*

sql/multi_range_read.h

@@ -114,6 +114,8 @@ private:
   uchar *mrr_buf_last;  /* When reading: end of used buffer space */
   uchar *mrr_buf_end;   /* End of the buffer */
 
+  uchar *mrr_buf_next_identical;
+
   bool dsmrr_eof; /* TRUE <=> We have reached EOF when reading index tuples */
 
   /* TRUE <=> need range association, buffer holds {rowid, range_id} pairs */
@@ -143,8 +145,8 @@ private:
                                uint *buffer_size, COST_VECT *cost);
   bool check_cpk_scan(uint keyno, uint mrr_flags);
   static int key_tuple_cmp(void* arg, uchar* key1, uchar* key2);
-  int dsmrr_fill_buffer();
-  void dsmrr_fill_buffer_cpk();
+  int dsmrr_fill_rowid_buffer();
+  void dsmrr_fill_key_buffer();
   int dsmrr_next_cpk(char **range_info);
 };
 

sql/mysql_priv.h

@@ -571,12 +571,13 @@ protected:
 #define OPTIMIZER_SWITCH_PARTIAL_MATCH_ROWID_MERGE 512
 #define OPTIMIZER_SWITCH_PARTIAL_MATCH_TABLE_SCAN 1024
 #define OPTIMIZER_SWITCH_SUBQUERY_CACHE (1<<11)
+#define OPTIMIZER_SWITCH_MRR_SORT_KEYS (1<<12)
 
 #ifdef DBUG_OFF
-#  define OPTIMIZER_SWITCH_LAST (1<<12)
-#else
-#  define OPTIMIZER_SWITCH_TABLE_ELIMINATION (1<<12)
 #  define OPTIMIZER_SWITCH_LAST (1<<13)
+#else
+#  define OPTIMIZER_SWITCH_TABLE_ELIMINATION (1<<13)
+#  define OPTIMIZER_SWITCH_LAST (1<<14)
 #endif
 
 #ifdef DBUG_OFF 
@@ -592,7 +593,8 @@ protected:
                                     OPTIMIZER_SWITCH_SEMIJOIN | \
                                     OPTIMIZER_SWITCH_PARTIAL_MATCH_ROWID_MERGE|\
                                     OPTIMIZER_SWITCH_PARTIAL_MATCH_TABLE_SCAN|\
-                                    OPTIMIZER_SWITCH_SUBQUERY_CACHE)
+                                    OPTIMIZER_SWITCH_SUBQUERY_CACHE|\
+                                    OPTIMIZER_SWITCH_MRR_SORT_KEYS)
 #else
 #  define OPTIMIZER_SWITCH_DEFAULT (OPTIMIZER_SWITCH_INDEX_MERGE | \
                                     OPTIMIZER_SWITCH_INDEX_MERGE_UNION | \
@@ -606,7 +608,8 @@ protected:
                                     OPTIMIZER_SWITCH_SEMIJOIN | \
                                     OPTIMIZER_SWITCH_PARTIAL_MATCH_ROWID_MERGE|\
                                     OPTIMIZER_SWITCH_PARTIAL_MATCH_TABLE_SCAN|\
-                                    OPTIMIZER_SWITCH_SUBQUERY_CACHE)
+                                    OPTIMIZER_SWITCH_SUBQUERY_CACHE|\
+                                    OPTIMIZER_SWITCH_MRR_SORT_KEYS)
 #endif
 
 /*

sql/mysqld.cc

@@ -308,6 +308,7 @@ static const char *optimizer_switch_names[]=
   "partial_match_rowid_merge",
   "partial_match_table_scan",
   "subquery_cache",
+  "mrr_sort_keys",
 #ifndef DBUG_OFF
   "table_elimination",
 #endif
@@ -329,6 +330,7 @@ static const unsigned int optimizer_switch_names_len[]=
   sizeof("partial_match_rowid_merge") - 1,
   sizeof("partial_match_table_scan") - 1,
   sizeof("subquery_cache") - 1,
+  sizeof("mrr_sort_keys") - 1,
 #ifndef DBUG_OFF
   sizeof("table_elimination") - 1,
 #endif
@@ -415,7 +417,8 @@ static const char *optimizer_switch_str="index_merge=on,index_merge_union=on,"
                                         "semijoin=on,"
                                         "partial_match_rowid_merge=on,"
                                         "partial_match_table_scan=on,"
-                                        "subquery_cache=on"
+                                        "subquery_cache=on,"
+                                        "mrr_sort_keys=on"
 #ifndef DBUG_OFF
                                         ",table_elimination=on";
 #else

sql/sql_join_cache.cc

@@ -651,6 +651,9 @@ int JOIN_CACHE_BKA::init()
 
   use_emb_key= check_emb_key_usage();
 
+  if (use_emb_key)
+    mrr_mode|= HA_MRR_MATERIALIZED_KEYS;
+
   create_remaining_fields(FALSE);
 
   set_constants();
@@ -2631,6 +2634,8 @@ int JOIN_CACHE_BKA_UNIQUE::init()
       data_fields_offset+= copy->length;
   } 
 
+  mrr_mode|= HA_MRR_MATERIALIZED_KEYS;
+
   DBUG_RETURN(rc);
 }