Disable the code that attempts to group window functions together
by their PARTITION BY / ORDER BY clauses, because
1. It doesn't work: when I issue a query with just one window function,
and no indexes on the table, filesort is not invoked at all.
2. It is not possible to check that it works currently.
Add my own code that does invoke filesort() for each window function.
- Hopefully the sort criteria is right
- Debugging shows that filesort operates on {sort_key, rowid} pairs (OK)
- We can read the filesort rowid result in order.
"Re-factor the code for post-join operations".
The patch mainly contains the code ported from mysql-5.6 and
created for two essential architectural changes:
1. WL#5558: Resolve ORDER BY execution method at the optimization stage
2. WL#6071: Inline tmp tables into the nested loops algorithm
The first task was implemented for mysql-5.6 by Ole John Aske.
It allows to make all decisions on ORDER BY operation at the optimization
stage.
The second task implemented for mysql-5.6 by Evgeny Potemkin adds JOIN_TAB
nodes for post-join operations that require temporary tables. It allows
to execute these operations within the nested loops algorithm that used to
be used before this task only for join queries. Besides these task moves
all planning on the execution of these operations from the execution phase
to the optimization phase.
Some other re-factoring changes of mysql-5.6 were pulled in, mainly because
it was easier to pull them in than roll them back. In particular all
changes concerning Ref_ptr_array were incorporated.
The port required some changes in the MariaDB code that concerned the
functionality of EXPLAIN and ANALYZE. This was done mainly by Sergey
Petrunia.
This task is to allow storage engines that can execute GROUP BY or
summary queries efficiently to intercept a full query or sub query from
MariaDB and deliver the result either to the client or to a temporary
table for further processing.
- Added code in sql_select.cc to intercept GROUP BY queries.
Creation of group_by_handler is done after all optimizations to allow
storage engine to benefit of an optimized WHERE clause and suggested
indexes to use.
- Added group by handler to sequence engine and a group_by test suite as
a way to test the new interface.
- Intercept EXPLAIN with a message "Storage engine handles GROUP BY"
libmysqld/CMakeLists.txt:
Added new group_by_handler files
sql/CMakeLists.txt:
Added new group_by_handler files
sql/group_by_handler.cc:
Implementation of group_by_handler functions
sql/group_by_handler.h:
Definition of group_by_handler class
sql/handler.h:
Added handlerton function to create a group_by_handler, if the storage
engine can intercept the query.
sql/item_cmpfunc.cc:
Allow one to evaluate item_equal any time.
sql/sql_select.cc:
Added code to intercept GROUP BY queries
- If all tables are from the same storage engine and the query is
using sum functions, call create_group_by() to check if the storage
engine can intercept the query.
- If yes:
- create a temporary table to hold a GROUP_BY row or result
- In do_select() intercept normal query execution by instead
calling the group_by_handler to get the result
- Intercept EXPLAIN
sql/sql_select.h:
Added handling of group_by_handler
Added caching of the original join tab (needed for cleanup after
group_by handler)
storage/sequence/mysql-test/sequence/group_by.result:
Test group_by_handler interface
storage/sequence/mysql-test/sequence/group_by.test:
Test group_by_handler interface
storage/sequence/sequence.cc:
Added simple group_by_engine for handling COUNT(*) and
SUM(primary_key). This was done as a test of the group_by_handler
interface
- Added mem_root to all calls to new Item
- Added private method operator new(size_t size) to Item to ensure that
we always use a mem_root when creating an item.
This saves use once call to current_thd per Item creation
Added mandatory thd parameter to Item (and all derivative classes) constructor.
Added thd parameter to all routines that may create items.
Also removed "current_thd" from Item::Item. This reduced number of
pthread_getspecific() calls from 290 to 177 per OLTP RO transaction.
- Make semi-join optimizer not to choose LooseScan
when 1) the index is not covered and 2) full index
scan will be required.
- Make sure that the code in make_join_select() that may change
full index scan into a range scan is not invoked when the table
uses full scan.
- Changed ER(ER_...) to ER_THD(thd, ER_...) when thd was known or if there was many calls to current_thd in the same function.
- Changed ER(ER_..) to ER_THD_OR_DEFAULT(current_thd, ER...) in some places where current_thd is not necessary defined.
- Removing calls to current_thd when we have access to thd
Part of this is optimization (not calling current_thd when not needed),
but part is bug fixing for error condition when current_thd is not defined
(For example on startup and end of mysqld)
Notable renames done as otherwise a lot of functions would have to be changed:
- In JOIN structure renamed:
examined_rows -> join_examined_rows
record_count -> join_record_count
- In Field, renamed new_field() to make_new_field()
Other things:
- Added DBUG_ASSERT(thd == tmp_thd) in Item_singlerow_subselect() just to be safe.
- Removed old 'tab' prefix in JOIN_TAB::save_explain_data() and use members directly
- Added 'thd' as argument to a few functions to avoid calling current_thd.
Fixed several optimizer issues relatied to GROUP BY:
a) Refering to a SELECT column in HAVING sometimes calculated it twice, which caused problems with non determinstic functions
b) Removing duplicate fields and constants from GROUP BY was done too late for "using index for group by" optimization to work
c) EXPLAIN SELECT ... GROUP BY did wrongly show 'Using filesort' in some cases involving "Using index for group-by"
a) was fixed by:
- Changed last argument to Item::split_sum_func2() from bool to int to allow more flags
- Added flag argument to Item::split_sum_func() to allow on to specify if the item was in the SELECT part
- Mark all split_sum_func() calls from SELECT with SPLIT_SUM_SELECT
- Changed split_sum_func2() to do nothing if called with an argument that is not a sum function and doesn't include sum functions, if we are not an argument to SELECT.
This ensures that in a case like
select a*sum(b) as f1 from t1 where a=1 group by c having f1 <= 10;
That 'a' in the SELECT part is stored as a reference in the temporary table togeher with sum(b) while the 'a' in having isn't (not needed as 'a' is already a reference to a column in the result)
b) was fixed by:
- Added an extra remove_const() pass for GROUP BY arguments before make_join_statistics() in case of one table SELECT.
This allowes get_best_group_min_max() to optimize things better.
c) was fixed by:
- Added test for group by optimization in JOIN::exec_inner for
select->quick->get_type() == QUICK_SELECT_I::QS_TYPE_GROUP_MIN_MAX
item.cc:
- Simplifed Item::split_sum_func2()
- Split test to make them faster and easier to read
- Changed last argument to Item::split_sum_func2() from bool to int to allow more flags
- Added flag argument to Item::split_sum_func() to allow on to specify if the item was in the SELECT part
- Changed split_sum_func2() to do nothing if called with an argument that is not a sum function and doesn't include sum functions, if we are not an argument to SELECT.
opt_range.cc:
- Simplified get_best_group_min_max() by calcuating first how many group_by elements.
- Use join->group instead of join->group_list to test if group by, as join->group_list may be NULL if everything was optimized away.
sql_select.cc:
- Added an extra remove_const() pass for GROUP BY arguments before make_join_statistics() in case of one table SELECT.
- Use group instead of group_list to test if group by, as group_list may be NULL if everything was optimized away.
- Moved printing of "Error in remove_const" to remove_const() instead of having it in caller.
- Simplified some if tests by re-ordering code.
- update_depend_map_for_order() and remove_const() fixed to handle the case where make_join_statistics() has not yet been called (join->join_tab is 0 in this case)
This is MDEV-7601, including it's sub tasks MDEV-7594, MDEV-7555, MDEV-7590, MDEV-7581, MDEV-7589
The problem was that select_lex->non_agg_fields was not properly reset for re-execution and this caused an overwrite of a random memory position.
The fix was move non_agg_fields from select_lext to JOIN, which is properly reset.
Split first_breadth_first_tab() into
JOIN::first_breadth_first_optimization_tab() and
JOIN::first_breadth_first_execution_tab().
This allows to eliminate function call and one condition. Adjusted callers
accordingly.
Overhead change:
first_breadth_first_tab() 0.07% -> out of radar
next_breadth_first_tab() 0.04% -> 0.04%
JOIN::cleanup() 0.15% -> 0.11%
JOIN::save_explain_data_intern() 0.28% -> 0.24%
Step#5: changing the function remove_eq_conds() into a virtual method in Item.
It removes 6 virtual calls for Item_func::type(), and adds only 2
virtual calls for Item***::remove_eq_conds().
sql_alloc() has additional costs compared to direct mem_root allocation:
- function call: it is defined in a separate translation unit and can't be
inlined
- it needs to call pthread_getspecific() to get THD::mem_root
It is called dozens of times implicitely at least by:
- List<>::push_back()
- List<>::push_front()
- new (for Sql_alloc derived classes)
- sql_memdup()
Replaced lots of implicit sql_alloc() calls with direct mem_root allocation,
passing through THD pointer whenever it is needed.
Number of sql_alloc() calls reduced 345 -> 41 per OLTP RO transaction.
pthread_getspecific() overhead dropped 0.76 -> 0.59
sql_alloc() overhed dropped 0.25 -> 0.06
- Remove ANALYZE's timing code off the the execution path of regular
SELECTs.
- Improve the tracker that tracks counts/execution times of SELECTs or
DML statements:
= regular execution just increments counters
= ANALYZE will also collect timings.
JOIN::cur_dups_producing_tables was not maintained correctly in
the cases of greedy optimization (search_depth < n_tables).
Moved it to POSITION structure where it will be maintained automatically.
Removed POSITION::prefix_dups_producing_tables since its value can now
be calculated.
Show total execution time (r_total_time_ms) for various parts of the
query:
1. time spent in SELECTs
2. time spent reading rows from storage engines
#2 currently gets the data from P_S.
Temporary table count fix. The number of temporary tables was increased
when the table is not actually created. (when do_not_open was passed
as TRUE to create_tmp_table).
Join_plan_state performs out-of-API initialization of DYNAMIC_ARRAY. This is
done to postpone actual array initialization till first use, whilst retaining
the right to call delete_dynamic().
Since delete_dynamic() now checks DYNAMIC_ARRAY::malloc_flags it should be
initialized it as well.
- Changed 0x%lx -> %p
array.c:
- Static (preallocated) buffer can now be anywhere
my_sys.h
- Define MY_INIT_BUFFER_USED
sql_delete.cc & sql_lex.cc
- Use memroot when allocating classes (avoids call to current_thd)
sql_explain.h:
- Use preallocated buffers
sql_explain.cc:
- Use preallocated buffers and memroot
sql_select.cc:
- Use multi_alloc_root() instead of many alloc_root()
- Update calls to Explain
- When traversing JOIN_TABs with first_linear_tab/next_linear_tab(), don't forget
to enter the semi-join nest when it is the first table in the join order.
Failure to do so could cause e.g. I_S tables not to be filled.
