MDEV-415: Back-port of the WL task #1393 from the mysql-5.6 code line.

The task adds a more efficient handling of the queries with 
ORDER BY order LIMIT n, such that n is small enough and
no indexes are used for order.

1 files changed, 30 insertions, 20 deletions

diff --git a/sql/sql_sort.h b/sql/sql_sort.h
index f1a3a2f9d8b..d30ddfb6eec 100644
--- a/sql/sql_sort.h
+++ b/sql/sql_sort.h
@@ -16,6 +16,7 @@
    along with this program; if not, write to the Free Software
    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA */
 
+#include "m_string.h"                           /* memset */
 #include "my_global.h"                          /* uchar */
 #include "my_base.h"                            /* ha_rows */
 #include "my_sys.h"                             /* qsort2_cmp */
@@ -27,7 +28,6 @@ typedef struct st_sort_field SORT_FIELD;
 class Field;
 struct TABLE;
 
-
 /* Defines used by filesort and uniques */
 
 #define MERGEBUFF		7
@@ -65,41 +65,51 @@ struct BUFFPEK_COMPARE_CONTEXT
   void *key_compare_arg;
 };
 
-typedef struct st_sort_param {
-  uint rec_length;          /* Length of sorted records */
-  uint sort_length;			/* Length of sorted columns */
-  uint ref_length;			/* Length of record ref. */
-  uint addon_length;        /* Length of added packed fields */
-  uint res_length;          /* Length of records in final sorted file/buffer */
-  uint keys;				/* Max keys / buffer */
+
+class Sort_param {
+public:
+  uint rec_length;            // Length of sorted records.
+  uint sort_length;           // Length of sorted columns.
+  uint ref_length;            // Length of record ref.
+  uint addon_length;          // Length of added packed fields.
+  uint res_length;            // Length of records in final sorted file/buffer.
+  uint max_keys_per_buffer;   // Max keys / buffer.
   uint min_dupl_count;
-  ha_rows max_rows,examined_rows;
-  TABLE *sort_form;			/* For quicker make_sortkey */
+  ha_rows max_rows;           // Select limit, or HA_POS_ERROR if unlimited.
+  ha_rows examined_rows;      // Number of examined rows.
+  TABLE *sort_form;           // For quicker make_sortkey.
   SORT_FIELD *local_sortorder;
   SORT_FIELD *end;
-  SORT_ADDON_FIELD *addon_field; /* Descriptors for companion fields */
+  SORT_ADDON_FIELD *addon_field; // Descriptors for companion fields.
   uchar *unique_buff;
   bool not_killable;
   char* tmp_buffer;
-  /* The fields below are used only by Unique class */
+  // The fields below are used only by Unique class.
   qsort2_cmp compare;
   BUFFPEK_COMPARE_CONTEXT cmp_context;
-} SORTPARAM;
 
+  Sort_param()
+  {
+    memset(this, 0, sizeof(*this));
+  }
+  void init_for_filesort(uint sortlen, TABLE *table,
+                         ulong max_length_for_sort_data,
+                         ha_rows maxrows, bool sort_positions);
+};
 
-int merge_many_buff(SORTPARAM *param, uchar *sort_buffer,
+
+int merge_many_buff(Sort_param *param, uchar *sort_buffer,
 		    BUFFPEK *buffpek,
 		    uint *maxbuffer, IO_CACHE *t_file);
 uint read_to_buffer(IO_CACHE *fromfile,BUFFPEK *buffpek,
 		    uint sort_length);
-int merge_buffers(SORTPARAM *param,IO_CACHE *from_file,
-		  IO_CACHE *to_file, uchar *sort_buffer,
-		  BUFFPEK *lastbuff,BUFFPEK *Fb,
-		  BUFFPEK *Tb,int flag);
-int merge_index(SORTPARAM *param, uchar *sort_buffer,
+int merge_buffers(Sort_param *param,IO_CACHE *from_file,
+                  IO_CACHE *to_file, uchar *sort_buffer,
+                  BUFFPEK *lastbuff,BUFFPEK *Fb,
+                  BUFFPEK *Tb,int flag);
+int merge_index(Sort_param *param, uchar *sort_buffer,
 		BUFFPEK *buffpek, uint maxbuffer,
 		IO_CACHE *tempfile, IO_CACHE *outfile);
-
 void reuse_freed_buff(QUEUE *queue, BUFFPEK *reuse, uint key_length);
 
 #endif /* SQL_SORT_INCLUDED */