Statements affected by this bug are delete statements that have all
these conditions
1) single table delete syntax
2) and in (sub-query) predicate
3) semi-join optimization enabled
4) an order by clause.
Semijoin optimization on an innocent looking query, such as
DELETE FROM t1 WHERE c1 IN (select c2 from t2) ORDER BY c1;
turns it from a single table delete to a multi-table delete.
During multi_delete::initialize_tables for the top level join object, a
table is initialized missing a keep_current_rowid flag, needed to
position a handler for removal of the correct row after the filesort
structure has been built.
Fix provided by Monty (monty@mariadb.com)
OK'd in slack:#askmonty 2023-12-01
applicable to 11.1 on
MDEV-32441 SENT_ROWS shows random wrong values when stored function
is selected.
MDEV-32281 EXAMINED_ROWS is not populated in
information_schema.processlist upon SELECT.
Added ROWS_SENT to information_schema.processlist
This is to have the same information as Percona server (SENT_ROWS)
To ensure that information_schema.processlist has correct values for
sent_rows and examined_rows I introduced two new variables to hold the
total counts so far. This was needed as stored functions and stored
procedures will reset the normal counters to be able to count rows for
each statement individually for slow query log.
Other things:
- Selects with functions shows in processlist the total examined_rows
and sent_rows by the main statement and all functions.
- Stored procedures shows in processlist examined_rows and sent_rows
per stored procedure statement.
- Fixed some double accounting for sent_rows and examined_rows.
- HANDLER operations now also supports send_rows and examined_rows.
- Display sizes for MEMORY_USED, MAX_MEMORY_USED, EXAMINED_ROWS and
QUERY_ID in information_schema.processlist changed to 10 characters.
- EXAMINED_ROWS and SENT_ROWS changed to bigint.
- INSERT RETURNING and DELETE RETURNING now updates SENT_ROWS.
- As thd is always up to date with examined_rows, we do not need
to handle examined row counting for unions or filesort.
- I renamed SORT_INFO::examined_rows to m_examined_rows to ensure that
we don't get bugs in merges that tries to use examined_rows.
- Removed calls of type "thd->set_examined_row_count(0)" as they are
not needed anymore.
- Removed JOIN::join_examined_rows
- Removed not used functions:
THD::set_examined_row_count()
- Made inline some functions that where called for each row.
The ROWNUM() function is for SELECT mapped to JOIN->accepted_rows, which is
incremented for each accepted rows.
For Filesort, update, insert, delete and load data, we map ROWNUM() to
internal variables incremented when the table is changed.
The connection between the row counter and Item_func_rownum is done
in sql_select.cc::fix_items_after_optimize() and
sql_insert.cc::fix_rownum_pointers()
When ROWNUM() is used anywhere in query, the optimization to ignore ORDER
BY in sub queries are disabled. This was done to get the following common
Oracle query to work:
select * from (select * from t1 order by a desc) as t where rownum() <= 2;
MDEV-3926 "Wrong result with GROUP BY ... WITH ROLLUP" contains a discussion
about this topic.
LIMIT optimization is enabled when in a top level WHERE clause comparing
ROWNUM() with a numerical constant using any of the following expressions:
- ROWNUM() < #
- ROWNUM() <= #
- ROWNUM() = 1
ROWNUM() can be also be the right argument to the comparison function.
LIMIT optimization is done in two cases:
- For the current sub query when the ROWNUM comparison is done on the top
level:
SELECT * from t1 WHERE rownum() <= 2 AND t1.a > 0
- For an inner sub query, when the upper level has only a ROWNUM comparison
in the WHERE clause:
SELECT * from (select * from t1) as t WHERE rownum() <= 2
In Oracle mode, one can also use ROWNUM without parentheses.
Other things:
- Fixed bug where the optimizer tries to optimize away sub queries
with RAND_TABLE_BIT set (non-deterministic queries). Now these
sub queries will not be converted to joins. This bug fix was also
needed to get rownum() working inside subqueries.
- In remove_const() remove setting simple_order to FALSE if ROLLUP is
USED. This code was disable a long time ago because of wrong assignment
in the following code. Instead we set simple_order to false if
RAND_TABLE_BIT was used in the SELECT list. This ensures that
we don't delete ORDER BY if the result set is not deterministic, like
in 'SELECT RAND() AS 'r' FROM t1 ORDER BY r';
- Updated parameters for Sort_param::init_for_filesort() to be able
to provide filesort with information where the number of accepted
rows should be stored
- Reordered fields in class Filesort to optimize storage layout
- Added new error messsage to tell that a function can't be used in HAVING
- Added field 'with_rownum' to THD to mark that ROWNUM() is used in the
query.
Co-author: Oleksandr Byelkin <sanja@mariadb.com>
LIMIT optimization for sub query
For the case when the SJM scan table is the first table in the join order,
then if we want to do the sorting on the SJM scan table, then we need to
make sure that we unpack the values to base table fields in two cases:
1) Reading the SJM table and writing the sort-keys inside the sort-buffer
2) Reading the sorted data from the sort file
This task deals with packing the sort key inside the sort buffer, which would
lead to efficient usage of the memory allocated for the sort buffer.
The changes brought by this feature are
1) Sort buffers would have sort keys of variable length
2) The format for sort keys inside the sort buffer would look like
|<sort_length><null_byte><key_part1><null_byte><key_part2>.......|
sort_length is the extra bytes that are required to store the variable
length of a sort key.
3) When packing of sort key is done we store the ORIGINAL VALUES inside
the sort buffer and not the STRXFRM form (mem-comparable sort keys).
4) Special comparison function packed_keys_comparison() is introduced
to compare 2 sort keys.
This patch also contains contributions from Sergei Petrunia.
This task deals with packing the non-sorted fields (or addon fields).
This would lead to efficient usage of the memory allocated for the sort buffer.
The changes brought by this feature are
1) Sort buffers would have records of variable length
2) Each record in the sort buffer would be stored like
<sort_key1><sort_key2>....<addon_length><null_bytes><field1><field2>....
addon_length is the extra bytes that are required to store the variable
length of addon field across different records.
3) Changes in rr_unpack_from_buffer and rr_from_tempfile to take into account
the variable length of records.
Ported WL#1509 Pack values of non-sorted fields in the sort buffer from
MySQL by Tor Didriksen
filesort and init_read_record() for the same table.
This will simplify code for WINDOW FUNCTIONS (MDEV-6115)
- Filesort_info renamed to SORT_INFO and moved to filesort.h
- filesort now returns SORT_INFO
- init_read_record() now takes a SORT_INFO parameter.
- unique declaration is moved to uniques.h
- subselect caching of buffers is now more explicit than before
- filesort_buffer is now reusable even if rec_length has changed.
- filsort_free_buffers() and free_io_cache() calls are removed
- Remove one malloc() when using get_addon_fields()
Other things:
- Added --debug-assert-on-not-freed-memory option to make it easier to
debug some not-freed-memory issues.
"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.
sql/sql_insert.cc:
CREATE ... IF NOT EXISTS may do nothing, but
it is still not a failure. don't forget to my_ok it.
******
CREATE ... IF NOT EXISTS may do nothing, but
it is still not a failure. don't forget to my_ok it.
sql/sql_table.cc:
small cleanup
******
small cleanup
This patch:
- Moves all definitions from the mysql_priv.h file into
header files for the component where the variable is
defined
- Creates header files if the component lacks one
- Eliminates all include directives from mysql_priv.h
- Eliminates all circular include cycles
- Rename time.cc to sql_time.cc
- Rename mysql_priv.h to sql_priv.h
