The function JOIN_TAB::choose_best_splitting() did not take into account
that for some tables whose fields were used in the GROUP BY list of
the specification of a splittable materialized derived there might exist
no elements in the array ext_keyuses_for_splitting.
The optimizer erroneously allowed to use join cache when joining a
splittable materialized table together with splitting optimization.
As a consequence in some rare cases the server returned wrong result
sets for queries with materialized derived.
This patch allows to use either join cache without usage of splitting
technique for materialization of a splittable derived table or splitting
without usage of join cache when joining such table. The costs the these
alternatives are compared and the best variant is chosen.
The bug was in the in the code of JOIN::check_for_splittable_materialized()
where the structures describing the fields of a materialized derived
table that potentially could be used in split optimization were build.
As a result of this bug some fields that were not usable for splitting
were detected as usable. This could trigger crashes further in
st_join_table::choose_best_splitting().
t1.pk IS NOT NULL where pk is a PRIMARY KEY
For equalites in the WHERE clause we create a keyuse array that contains the set of all equalities.
For each KEYUSE inside the keyuse array we have a field "null_rejecting"
which tells that the equality will not hold if either the left or right
hand side of the equality is NULL.
If the equality is NULL rejecting then we accordingly add a NOT NULL condition for the field present in
the item val(present in the KEYUSE struct) when we are doing ref access.
For the optimization of splitting with GROUP BY we always set the null_rejecting to TRUE and we are doing ref access on
the GROUP by field. This does create a problem when the equality is NOT NULL rejecting. This happens in this case as
in the equality we have the right hand side as t1.pk where pk is a PRIMARY KEY , hence it is NOT NULLABLE. So we should have
null rejecting set to FALSE for such a case.
The crash happened because JOIN::check_for_splittable_materialized()
called by mistake the function JOIN_TAB::is_inner_table_of_outer_join()
instead of the function TABLE_LIST::is_inner_table_of_outer_join().
The former cannot be called before the call of make_outerjoin_info().
Handle string length as size_t, consistently (almost always:))
Change function prototypes to accept size_t, where in the past
ulong or uint were used. change local/member variables to size_t
when appropriate.
This fix excludes rocksdb, spider,spider, sphinx and connect for now.
in JOIN::inject_best_splitting_cond
The value of SplM_opt_info::last_plan should be set to NULL
before any search for a splitting plan for a splittable
materialized table.
Do not try to apply the splitting optimization to a materialized
derived if it's specified by a select with impossible where
or if all joined tables of this select are constant.
