From ef4c0f68d12ac8d86f57550599a1be24aa9c6bfe Mon Sep 17 00:00:00 2001 From: Gleb Shchepa Date: Wed, 23 Jun 2010 00:32:29 +0400 Subject: Bug #30584: delete with order by and limit clauses does not use limit efficiently Bug #36569: UPDATE ... WHERE ... ORDER BY... always does a filesort even if not required Also two bugs reported after QA review (before the commit of bugs above to public trees, no documentation needed): Bug #53737: Performance regressions after applying patch for bug 36569 Bug #53742: UPDATEs have no effect after applying patch for bug 36569 Execution of single-table UPDATE and DELETE statements did not use the same optimizer as was used in the compilation of SELECT statements. Instead, it had an optimizer of its own that did not take into account that you can omit sorting by retrieving rows using an index. Extra optimization has been added: when applicable, single-table UPDATE/DELETE statements use an existing index instead of filesort. A corresponding SELECT query would do the former. Also handling of the DESC ordering expression has been added when reverse index scan is applicable. From now on most single table UPDATE and DELETE statements show the same disk access patterns as the corresponding SELECT query. We verify this by comparing the result of SHOW STATUS LIKE 'Sort% Currently the get_index_for_order function a) checks quick select index (if any) for compatibility with the ORDER expression list or b) chooses the cheapest available compatible index, but only if the index scan is cheaper than filesort. Second way is implemented by the new test_if_cheaper_ordering function (extracted part the test_if_skip_sort_order()). mysql-test/r/log_state.result: Updated result for optimized query, bug #36569. mysql-test/r/single_delete_update.result: Test case for bug #30584, bug #36569 and bug #53742. mysql-test/r/update.result: Updated result for optimized query, bug #30584. Note: "Handler_read_last 1" omitted, see bug 52312: lost Handler_read_last status variable. mysql-test/t/single_delete_update.test: Test case for bug #30584, bug #36569 and bug #53742. sql/opt_range.cc: Bug #30584, bug #36569: UPDATE/DELETE ... WHERE ... ORDER BY... always does a filesort even if not required * get_index_for_order() has been rewritten entirely and moved to sql_select.cc New QUICK_RANGE_SELECT::make_reverse method has been added. sql/opt_range.h: Bug #30584, bug #36569: UPDATE/DELETE ... WHERE ... ORDER BY... always does a filesort even if not required * get_index_for_order() has been rewritten entirely and moved to sql_select.cc New functions: * QUICK_SELECT_I::make_reverse() * SQL_SELECT::set_quick() sql/records.cc: Bug #30584, bug #36569: UPDATE/DELETE ... WHERE ... ORDER BY... always does a filesort even if not required * init_read_record_idx() has been modified to allow reverse index scan New functions: * rr_index_last() * rr_index_desc() sql/records.h: Bug #30584, bug #36569: UPDATE/DELETE ... WHERE ... ORDER BY... always does a filesort even if not required init_read_record_idx() has been modified to allow reverse index scan sql/sql_delete.cc: Bug #30584, bug #36569: UPDATE/DELETE ... WHERE ... ORDER BY... always does a filesort even if not required mysql_delete: an optimization has been added to skip unnecessary sorting with ORDER BY clause where select result ordering is acceptable. sql/sql_select.cc: Bug #30584, bug #36569, bug #53737, bug #53742: UPDATE/DELETE ... WHERE ... ORDER BY... always does a filesort even if not required The const_expression_in_where function has been modified to accept both Item and Field pointers. New functions: * get_index_for_order() * test_if_cheaper_ordering() has been extracted from test_if_skip_sort_order() to share with get_index_for_order() * simple_remove_const() sql/sql_select.h: Bug #30584, bug #36569: UPDATE/DELETE ... WHERE ... ORDER BY... always does a filesort even if not required New functions: * test_if_cheaper_ordering() * simple_remove_const() * get_index_for_order() sql/sql_update.cc: Bug #30584, bug #36569: UPDATE/DELETE ... WHERE ... ORDER BY... always does a filesort even if not required mysql_update: an optimization has been added to skip unnecessary sorting with ORDER BY clause where a select result ordering is acceptable. sql/table.cc: Bug #30584, bug #36569: UPDATE/DELETE ... WHERE ... ORDER BY... always does a filesort even if not required New functions: * TABLE::update_const_key_parts() * is_simple_order() sql/table.h: Bug #30584, bug #36569: UPDATE/DELETE ... WHERE ... ORDER BY... always does a filesort even if not required New functions: * TABLE::update_const_key_parts() * is_simple_order() --- mysql-test/r/update.result | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'mysql-test/r/update.result') diff --git a/mysql-test/r/update.result b/mysql-test/r/update.result index 006eaba4e69..6c3f54fca38 100644 --- a/mysql-test/r/update.result +++ b/mysql-test/r/update.result @@ -306,8 +306,8 @@ Handler_read_first 0 Handler_read_key 0 Handler_read_next 0 Handler_read_prev 0 -Handler_read_rnd 1 -Handler_read_rnd_next 9 +Handler_read_rnd 0 +Handler_read_rnd_next 0 alter table t1 disable keys; flush status; delete from t1 order by a limit 1; -- cgit v1.2.1