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Optimization of key usage (ORDER BY) (SCRUM)

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This commit is contained in:
ram@mysql.r18.ru
2003-01-04 14:59:52 +04:00
parent 259b79beac
commit a7ef436bc4
3 changed files with 139 additions and 0 deletions
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84
sql/sql_select.cc
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@ -5933,6 +5933,69 @@ static uint find_shortest_key(TABLE *table, key_map usable_keys)
return best;
}
/*
SYNOPSIS
is_subkey()
key_part - first key parts
ref_key_part - second key parts
ref_key_part_end - last+1 part of the second key
DESCRIPTION
Test if a second key is the subkey of the first one.
NOTE
Second key MUST be shorter than the first one.
RETURN
1 - is the subkey
0 - otherwise
*/
inline bool
is_subkey(KEY_PART_INFO *key_part, KEY_PART_INFO *ref_key_part,
KEY_PART_INFO *ref_key_part_end)
{
for (; ref_key_part < ref_key_part_end; key_part++, ref_key_part++)
if (!key_part->field->eq(ref_key_part->field))
return 0;
return 1;
}
/*
SYNOPSIS
test_if_subkey()
ref - number of key, used for WHERE clause
usable_keys - keys for testing
DESCRIPTION
Test if we can use one of the 'usable_keys' instead of 'ref' key.
RETURN
MAX_KEY - if we can't use other key
the number of found key - otherwise
*/
static uint
test_if_subkey(ORDER *order, TABLE *table, uint ref, key_map usable_keys)
{
uint nr;
uint min_length= (uint) ~0;
uint best= MAX_KEY;
uint not_used;
KEY_PART_INFO *ref_key_part= table->key_info[ref].key_part;
uint ref_key_parts= table->key_info[ref].key_parts;
KEY_PART_INFO *ref_key_part_end= ref_key_part + ref_key_parts;
for (nr= 0; usable_keys; usable_keys>>= 1, nr++)
{
if ((usable_keys & 1) &&
table->key_info[nr].key_length < min_length &&
table->key_info[nr].key_parts >= ref_key_parts &&
is_subkey(table->key_info[nr].key_part, ref_key_part,
ref_key_part_end) &&
test_if_order_by_key(order, table, nr, &not_used))
{
min_length= table->key_info[nr].key_length;
best= nr;
}
}
return best;
}
/*
Test if we can skip the ORDER BY by using an index.
@ -5980,6 +6043,27 @@ test_if_skip_sort_order(JOIN_TAB *tab,ORDER *order,ha_rows select_limit,
*/
int order_direction;
uint used_key_parts;
if (!(usable_keys & ((key_map) 1 << ref_key)))
{
/*
We come here when ref_key is not among usable_keys
*/
uint a;
if ((a= test_if_subkey(order, table, ref_key, usable_keys)) < MAX_KEY)
{
if (tab->ref.key >= 0)
{
tab->ref.key= a;
table->file->index_init(a);
}
else
{
select->quick->index= a;
select->quick->init();
}
ref_key= a;
}
}
/* Check if we get the rows in requested sorted order by using the key */
if ((usable_keys & ((key_map) 1 << ref_key)) &&
(order_direction = test_if_order_by_key(order,table,ref_key,