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Bug #36259 (Optimizing with ORDER BY) and bug#45828 (Optimizer won't

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use partial primary key if another index can prevent filesort

The fix for bug #28404 causes the covering ordering indexes to be 
preferred unconditionally over non-covering and ref indexes.

Fixed by comparing the cost of using a covering index to the cost of
using a ref index even for covering ordering indexes.
Added an assertion to clarify the condition the local variables should
be in.
This commit is contained in:
Georgi Kodinov
2009-07-07 15:52:34 +03:00
parent b12a166d64
commit d9e82ba86c
4 changed files with 166 additions and 6 deletions
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10
sql/sql_select.cc
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@ -13132,9 +13132,17 @@ test_if_skip_sort_order(JOIN_TAB *tab,ORDER *order,ha_rows select_limit,
for (nr=0; nr < table->s->keys ; nr++)
{
int direction;
if (keys.is_set(nr) &&
(direction= test_if_order_by_key(order, table, nr, &used_key_parts)))
{
/*
At this point we are sure that ref_key is a non-ordering
key (where "ordering key" is a key that will return rows
in the order required by ORDER BY).
*/
DBUG_ASSERT (ref_key != (int) nr);
bool is_covering= table->covering_keys.is_set(nr) ||
(nr == table->s->primary_key &&
table->file->primary_key_is_clustered());
@ -13215,7 +13223,7 @@ test_if_skip_sort_order(JOIN_TAB *tab,ORDER *order,ha_rows select_limit,
*/
index_scan_time= select_limit/rec_per_key *
min(rec_per_key, table->file->scan_time());
if (is_covering ||
if ((ref_key < 0 && is_covering) ||
(ref_key < 0 && (group || table->force_index)) ||
index_scan_time < read_time)
{