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Bug #30584: delete with order by and limit clauses does not

Browse Source 
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()
This commit is contained in:
Gleb Shchepa
2010-06-23 00:32:29 +04:00
parent 21e943e0d1
commit ef4c0f68d1
14 changed files with 2215 additions and 333 deletions
Download Patch File Download Diff File Expand all files Collapse all files

41
sql/sql_update.cc
View File

@@ -203,12 +203,13 @@ int mysql_update(THD *thd,
{
bool using_limit= limit != HA_POS_ERROR;
bool safe_update= test(thd->variables.option_bits & OPTION_SAFE_UPDATES);
bool used_key_is_modified, transactional_table, will_batch;
bool used_key_is_modified= FALSE, transactional_table, will_batch;
bool can_compare_record;
int res;
int error, loc_error;
uint used_index= MAX_KEY, dup_key_found;
uint used_index, dup_key_found;
bool need_sort= TRUE;
bool reverse= FALSE;
#ifndef NO_EMBEDDED_ACCESS_CHECKS
uint want_privilege;
#endif
@@ -358,11 +359,7 @@ int mysql_update(THD *thd,
my_ok(thd); // No matching records
DBUG_RETURN(0);
}
if (!select && limit != HA_POS_ERROR)
{
if ((used_index= get_index_for_order(table, order, limit)) != MAX_KEY)
need_sort= FALSE;
}
/* If running in safe sql mode, don't allow updates without keys */
if (table->quick_keys.is_clear_all())
{
@@ -378,24 +375,20 @@ int mysql_update(THD *thd,
table->mark_columns_needed_for_update();
/* Check if we are modifying a key that we are used to search with */
if (select && select->quick)
{
used_index= select->quick->index;
used_key_is_modified= (!select->quick->unique_key_range() &&
select->quick->is_keys_used(table->write_set));
table->update_const_key_parts(conds);
order= simple_remove_const(order, conds);
used_index= get_index_for_order(order, table, select, limit,
&need_sort, &reverse);
if (need_sort)
{ // Assign table scan index to check below for modified key fields:
used_index= table->file->key_used_on_scan;
}
else
{
used_key_is_modified= 0;
if (used_index == MAX_KEY) // no index for sort order
used_index= table->file->key_used_on_scan;
if (used_index != MAX_KEY)
used_key_is_modified= is_key_used(table, used_index, table->write_set);
if (used_index != MAX_KEY)
{ // Check if we are modifying a key that we are used to search with:
used_key_is_modified= is_key_used(table, used_index, table->write_set);
}
#ifdef WITH_PARTITION_STORAGE_ENGINE
if (used_key_is_modified || order ||
partition_key_modified(table, table->write_set))
@@ -414,7 +407,7 @@ int mysql_update(THD *thd,
table->use_all_columns();
}
/* note: We avoid sorting avoid if we sort on the used index */
/* note: We avoid sorting if we sort on the used index */
if (order && (need_sort || used_key_is_modified))
{
/*
@@ -476,7 +469,7 @@ int mysql_update(THD *thd,
if (used_index == MAX_KEY || (select && select->quick))
init_read_record(&info, thd, table, select, 0, 1, FALSE);
else
init_read_record_idx(&info, thd, table, 1, used_index);
init_read_record_idx(&info, thd, table, 1, used_index, reverse);
thd_proc_info(thd, "Searching rows for update");
ha_rows tmp_limit= limit;