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better fix for MySQL bugs

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BUG#26447 prefer a clustered key for an index scan, as secondary index is always slower
  ... which was fixed to cause
BUG#35850 queries take 50% longer
  ... and was reverted

and

BUG#39653 prefer a secondary index for an index scan, as clustered key is always slower
  ... which was fixed to cause
BUG#55656 mysqldump takes six days instead of half an hour
  ... and was amended with a special case workaround


sql/opt_range.cc:
  move get_index_only_read_time() into the handler class
sql/sql_select.cc:
  use cost not an index length when choosing a cheaper index
This commit is contained in:
Sergei Golubchik
2010-10-20 12:58:43 +02:00
parent b56086cbbb
commit 60c15066db
4 changed files with 34 additions and 49 deletions
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7
sql/sql_select.cc
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@ -13367,7 +13367,7 @@ static int test_if_order_by_key(ORDER *order, TABLE *table, uint idx,
uint find_shortest_key(TABLE *table, const key_map *usable_keys)
{
uint min_length= (uint) ~0;
double min_cost= DBL_MAX;
uint best= MAX_KEY;
if (!usable_keys->is_clear_all())
{
@ -13375,9 +13375,10 @@ uint find_shortest_key(TABLE *table, const key_map *usable_keys)
{
if (usable_keys->is_set(nr))
{
if (table->key_info[nr].key_length < min_length)
double cost= table->file->keyread_time(nr, 1, table->file->records());
if (cost < min_cost)
{
min_length=table->key_info[nr].key_length;
min_cost= cost;
best=nr;
}
}