in EXPLAIN as select_type==MATERIALIZED.
Before, we had select_type==SUBQUERY and it was difficult to tell materialized
subqueries from uncorrelated scalar-context subqueries.
If has been decided that the first match strategy is to be used to join table T
from a semi-join nest while no buffer can be employed to join this table
then no join buffer can be used to join any table in the join sequence between
the first one belonging to the semi-join nest and table T.
The tables from the same semi-join or outer join nest cannot use
join buffers if in the join sequence of the query execution plan
they are separated by a table that is planned to be joined without
usage of a join buffer.
Analysis:
lp:894397 was a consequence of a prior incorrect fix of lp:833777
which didn't take into account that even when all tables are
constant there may be correlated conditions, and the where clause
is not equivalent to the constant conditions.
Solution:
When there are constant tables only, evaluate only the conditions
that reference outer fields, because the constant conditions are
already checked, and the where clause doesn't have other conditions
than constant ones, and outer referencing ones. The fix for
lp:894397 also fixes lp:833777.
- Make EXPLAIN display "Start temporary" at the start of the fanout (it used to display
at the first table whose rowid gets into temp. table which is not that useful for
the user)
- Updated test results (all checked)
- Break down POSITION/advance_sj_state() into four classes
representing potential semi-join strategies.
- Treat all strategies uniformly (before, DuplicateWeedout
was special as it was the catch-all strategy. Now, we're
still relying on it to be the catch-all, but are able to
function,e.g. with firstmatch=on,duplicate_weedout=off.
- Update test results (checked)
Analysis:
The optimizer distinguishes two kinds of 'constant' conditions:
expensive ones, and non-expensive ones. The non-expensive conditions
are evaluated inside make_join_select(), and if false, already the
optimizer detects empty query results.
In order to avoid arbitrarily expensive optimization, the evaluation of
expensive constant conditions is delayed until execution. These conditions
are attached to JOIN::exec_const_cond and evaluated in the beginning of
JOIN::exec. The relevant execution logic is:
JOIN::exec()
{
if (! join->exec_const_cond->val_int())
{
produce an empty result;
stop execution
}
continue execution
execute the original WHERE clause (that contains exec_const_cond)
...
}
As a result, when an expensive constant condition is
TRUE, it is evaluated twice - once through
JOIN::exec_const_cond, and once through JOIN::cond.
When the expensive constant condition is a subquery,
predicate, the subquery is evaluated twice. If we have
many levels of subqueries, this logic results in a chain
of recursive subquery executions that walk a perfect
binary tree. The result is that for subquries with depth N,
JOIN::exec is executed O(2^N) times.
Solution:
Notice that the second execution of the constant conditions
happens inside do_select(), in the branch:
if (join->table_count == join->const_tables) { ... }
In this case exec_const_cond is equivalent to the whole WHERE
clause, therefore the WHERE clause has already been checked in
the beginnig of JOIN::exec, and has been found to be true.
The bug is addressed by not evaluating the WHERE clause if there
was exec_const_conds, and it was TRUE.
If the optimizer switch 'semijoin_with_cache' is set to 'off' then
join cache cannot be used to join inner tables of a semijoin.
Also fixed a bug in the function check_join_cache_usage() that led
to wrong output of the EXPLAIN commands for some test cases.
mysql-test/r/select.result:
Test case for lp:780425
mysql-test/r/select_pkeycache.result:
lp:780425
mysql-test/t/select.test:
lp:780425
sql/sql_select.cc:
Added DBUG_ASSERT to be prove some logic and later be able to simplify the code
Set implicit_grouping if we delete a GROUP BY to signal do_select() that a grouping needs to be done.
In MariaDB, when running in ONLY_FULL_GROUP_BY mode,
the server produced in incorrect error message that there
is an aggregate function without GROUP BY, for artificially
created MIN/MAX functions during subquery MIN/MAX optimization.
The fix introduces a way to distinguish between artifially
created MIN/MAX functions as a result of a rewrite, and normal
ones present in the query. The test for ONLY_FULL_GROUP_BY violation
now tests in addition if a MIN/MAX function was part of a MIN/MAX
subquery rewrite.
In order to be able to distinguish these MIN/MAX functions, the
patch introduces an additional flag in Item_in_subselect::in_strategy -
SUBS_STRATEGY_CHOSEN. This flag is set when the optimizer makes its
final choice of a subuqery strategy. In order to make the choice
consistent, access to Item_in_subselect::in_strategy is provided
via new class methods.
******
Fix MySQL BUG#12329653
In MariaDB, when running in ONLY_FULL_GROUP_BY mode,
the server produced in incorrect error message that there
is an aggregate function without GROUP BY, for artificially
created MIN/MAX functions during subquery MIN/MAX optimization.
The fix introduces a way to distinguish between artifially
created MIN/MAX functions as a result of a rewrite, and normal
ones present in the query. The test for ONLY_FULL_GROUP_BY violation
now tests in addition if a MIN/MAX function was part of a MIN/MAX
subquery rewrite.
In order to be able to distinguish these MIN/MAX functions, the
patch introduces an additional flag in Item_in_subselect::in_strategy -
SUBS_STRATEGY_CHOSEN. This flag is set when the optimizer makes its
final choice of a subuqery strategy. In order to make the choice
consistent, access to Item_in_subselect::in_strategy is provided
via new class methods.
The function add_ref_to_table_cond missed updating the value of
join_tab->pre_idx_push_select_cond after having updated the value
of join_tab->select->pre_idx_push_select_cond.
The bug happened because in some cases the function JOIN::exec
did not save the value of TABLE::pre_idx_push_select_cond in
TABLE::select->pre_idx_push_select_cond for the sort table.
Noticed and fixed a bug in the function make_cond_remainder
that builds the remainder condition after extraction of an index
pushdown condition from the where condition. The code
erroneously assumed that the function make_cond_for_table left
the value of ICP_COND_USES_INDEX_ONLY in sub-condition markers.
Adjusted many result files from the regression test suite
after this fix .
The call of the virtual function cancel_pushed_idx_cond in the code of
the function test_if_skip_sort_order was misplaced when backporting the
fix for bug 58816.
- The bug was caused by the following scenario:
= a quick select is created with get_quick_select_for_ref. The quick
select refers to temporary (derived) table. It saves table->file, which
refers to a ha_heap object.
= When temp table is populated, ha_heap reaches max. size and is converted
to a ha_myisam. However, quick->file remains pointing to where ha_heap
was.
= Attempt to use the quick select causes crash.
- Fixed by introducing QUICK_SELECT_I::replace_handler(). Note that it will
not work for index_merge quick selects. Which is fine, because these
quick selects are never created for derived tables.
- The problem was that the value of READ_RECORD::file was not updated when the underlying table
was temporary and was converted from heap to myisam. Resolved by eliminating READ_RECORD::file,
always use READ_RECORD::table->file
Honor unique/not unique when creating keys for internal tempory tables.
Added new variables to be used to limit how keys are created for internal temporary tables.
include/maria.h:
Added maria_max_key_length() and maria_max_key_segments()
include/myisam.h:
Added myisam_max_key_length() and myisam_max_key_segments()
mysql-test/r/mysql.result:
Drop all used tables
mysql-test/r/subselect4.result:
Added test case for lp:879939
mysql-test/t/mysql.test:
Drop all used tables
mysql-test/t/subselect4.test:
Added test case for lp:879939
sql/mysql_priv.h:
Added internal_tmp_table_max_key_length and internal_tmp_table_max_key_segments to be used to limit how keys for derived tables are created.
sql/mysqld.cc:
Added internal_tmp_table_max_key_length and internal_tmp_table_max_key_segments to be used to limit how keys for derived tables are created.
sql/share/errmsg.txt:
Added new error message for internal errors
sql/sql_select.cc:
Give error if we try to create a wrong key (this error should never happen)
Honor unique/not unique when creating keys for internal tempory tables.
storage/maria/ha_maria.cc:
Added change_table_ptr() to ensure that external_ref points always to the correct table.
(Not having this caused an assert in the included test)
storage/maria/ha_maria.h:
Added change_table_ptr() to ensure that external_ref points always to the correct table.
storage/maria/ma_check.c:
Fixed bug in Duplicate key error printing (now row position is printed correctly)
storage/maria/ma_create.c:
maria_max_key_length() -> _ma_max_key_length()
storage/maria/ma_info.c:
Added extern function maria_max_key_length() to calculate the max key length based on current block size.
storage/maria/ma_open.c:
maria_max_key_length() -> _ma_max_key_length()
storage/maria/maria_def.h:
maria_max_key_length() -> _ma_max_key_length()
storage/myisam/ha_myisam.cc:
Added change_table_ptr() to ensure that external_ref points always to the correct table.
(Not having this caused an assert in the included test)
storage/myisam/ha_myisam.h:
Added change_table_ptr() to ensure that external_ref points always to the correct table.
- when create_ref_for_key() is constructing a ref access for
a table that's inside a SJ-Materialization nest, it may not
use references to fields of tables that are unside the nest (because
these fields will not yet have values when ref access will be used)
The check was performed in the first of create_ref_for_key's loops (the
one which counts how many key parts are usable) but not in the second
(the one which actually fills the TABLE_REF structure).
The function JOIN::drop_unused_derived_keys could erroneously set
the value of REF::key to 0 for a joined materialized view/derived table
in the case when no REF access to the table was used by the query
execution plan. This could cause a crash of the server.
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 bug manifested itself with queries containing non-correlated
IN subqueries over materialized views/derived tables.
The bug happened because the code of the function generate_derived_keys did
not take into account that the function could be called twice when the
optimizer was deciding whether in-exist transformation should be applied.
- in make_join_select(), use the correct condition to check whether the current table is a SJM nest (the previous
condition used to be correct before, but then sj-materialization temp table creation was moved to happen before
make_join_select was called)
