maria-developers team mailing list archive

[Sergey Petrunia <sergey@xxxxxxxxxxx>]

On Tue, Dec 07, 2021 at 07:01:45PM +0300, Sergey Petrunia wrote:
> == Issue #1: ordered index scan is not handled in ha_partition ==

I've hit this again when trying to get range optmizer to work. Please find the
patch below. It follows MySQL-8's approach.

> 
> Testcase:
> 
> create table t10 (a int, b int, key(a desc)) partition by hash(a) partitions 4;
> insert into t10 select seq, seq from seq_0_to_999;
> 
> MariaDB [test]> select * from t10 order by a limit 3;
> +------+------+
> | a    | b    |
> +------+------+
> |    3 |    3 |
> |    7 |    7 |
> |   11 |   11 |
> +------+------+
> 3 rows in set (0.002 sec)
> 
> Correct output:
> 
> MariaDB [test]> select * from t10 use index() order by a limit 3;
> +------+------+
> | a    | b    |
> +------+------+
> |    0 |    0 |
> |    1 |    1 |
> |    2 |    2 |
> +------+------+
> 3 rows in set (0.011 sec)


diff --git a/sql/key.cc b/sql/key.cc
index f2cebfe6d82..c43d3c36d5d 100644
--- a/sql/key.cc
+++ b/sql/key.cc
@@ -495,6 +495,7 @@ int key_cmp(KEY_PART_INFO *key_part, const uchar *key, uint key_length)
   {
     int cmp;
     store_length= key_part->store_length;
+    int sort_order = (key_part->key_part_flag & HA_REVERSE_SORT) ? -1 : 1;
     if (key_part->null_bit)
     {
       /* This key part allows null values; NULL is lower than everything */
@@ -503,19 +504,19 @@ int key_cmp(KEY_PART_INFO *key_part, const uchar *key, uint key_length)
       {
 	/* the range is expecting a null value */
 	if (!field_is_null)
-	  return 1;                             // Found key is > range
+	  return sort_order;                         // Found key is > range
         /* null -- exact match, go to next key part */
 	continue;
       }
       else if (field_is_null)
-	return -1;                              // NULL is less than any value
+	return -sort_order;                     // NULL is less than any value
       key++;					// Skip null byte
       store_length--;
     }
     if ((cmp=key_part->field->key_cmp(key, key_part->length)) < 0)
-      return -1;
+      return -sort_order;
     if (cmp > 0)
-      return 1;
+      return sort_order;
   }
   return 0;                                     // Keys are equal
 }
@@ -574,6 +575,7 @@ int key_rec_cmp(void *key_p, uchar *first_rec, uchar *second_rec)
     do
     {
       field= key_part->field;
+      int sort_order = (key_part->key_part_flag & HA_REVERSE_SORT) ? -1 : 1;
 
       if (key_part->null_bit)
       {
@@ -593,12 +595,12 @@ int key_rec_cmp(void *key_p, uchar *first_rec, uchar *second_rec)
             ; /* Fall through, no NULL fields */
           else
           {
-            DBUG_RETURN(+1);
+            DBUG_RETURN(sort_order);
           }
         }
         else if (!sec_is_null)
         {
-          DBUG_RETURN(-1);
+          DBUG_RETURN(-sort_order);
         }
         else
           goto next_loop; /* Both were NULL */
@@ -612,7 +614,7 @@ int key_rec_cmp(void *key_p, uchar *first_rec, uchar *second_rec)
       */
       if ((result= field->cmp_prefix(field->ptr+first_diff, field->ptr+sec_diff,
                                      key_part->length)))
-        DBUG_RETURN(result);
+        DBUG_RETURN(result * sort_order);
 next_loop:
       key_part++;
       key_part_num++;

BR
 Sergei
-- 
Sergei Petrunia, Software Developer
MariaDB Corporation | Skype: sergefp | Blog: http://petrunia.net