diff options
Diffstat (limited to 'sql/sql_select.cc')
| -rw-r--r-- | sql/sql_select.cc | 18 |
1 files changed, 16 insertions, 2 deletions
diff --git a/sql/sql_select.cc b/sql/sql_select.cc index 2aeddf2415d..e0f560f0b3a 100644 --- a/sql/sql_select.cc +++ b/sql/sql_select.cc @@ -9736,10 +9736,24 @@ make_join_select(JOIN *join,SQL_SELECT *select,COND *cond) if (!sel->quick_keys.is_subset(tab->checked_keys) || !sel->needed_reg.is_subset(tab->checked_keys)) { + /* + "Range checked for each record" is a "last resort" access method + that should only be used when the other option is a cross-product + join. + + We use the following condition (it's approximate): + 1. There are potential keys for (sel->needed_reg) + 2. There were no possible ways to construct a quick select, or + the quick select would be more expensive than the full table + scan. + */ tab->use_quick= (!sel->needed_reg.is_clear_all() && (sel->quick_keys.is_clear_all() || - (sel->quick && - (sel->quick->records >= 100L)))) ? + (sel->quick && + sel->quick->read_time > + tab->table->file->scan_time() + + tab->table->file->stats.records/TIME_FOR_COMPARE + ))) ? 2 : 1; sel->read_tables= used_tables & ~current_map; sel->quick_keys.clear_all(); |