We need every instruction to have its own arena, because we want to
track instruction's state (INITIALIZED_FOR_SP -> EXECUTED). Because of
`if' statements and other conditional instructions used in stored
procedures, not every instruction of a stored procedure gets executed
during the first (or even subsequent) execution of the procedure.
So it's better if we track the execution state of every instruction
independently.
All instructions of a given procedure now also share sp_head's
mem_root, but keep their own free_list.
This simplifies juggling with free Item lists in sp_head::execute.
- free_items() moved to be a member of Query_arena.
- logic of 'backup_arena' debug member of Query_arena has been
changed to support
multi-backups. Until now, TRUE 'backup_arena' meant that there is
exactly one active backup of the THD arena. Now it means simply that
the arena is used for backup, so that we can't accidentally overwrite an
existing backup. This allows doing multiple backups, e.g. in
sp_head::execute and Cursor::fetch, when THD arena is already backed up
but we want to set yet another arena (usually the 'permanent' arena,
to save permanent transformations/optimizations of a parsed tree).
The source of the problem is in Field_longlong::cmp. If 'this' is
an unsigned number, the method casts both the current value, and
the constant that we compare with to an unsigned number. As a
result if the constant we compare with is a negative number, it
wraps to some unsigned number, and the comparison is incorrect.
When the optimizer chooses the "range" access method, this problem
causes handler::read_range_next to reject the current key when the
upper bound key is a negative number because handler::compare_key
incorrectly considers the positive and negative keys to be equal.
The current patch does not correct the source of the problem in
Field_longlong::cmp because it is not easy to propagate sign
information about the constant at query execution time. Instead
the patch changes the range optimizer so that it never compares
unsiged fields with negative constants. As an added benefit,
queries that do such comparisons will execute faster because
the range optimizer replaces conditions like:
(a) (unsigned_int [< | <=] negative_constant) == FALSE
(b) (unsigned_int [> | >=] negative_constant) == TRUE
with the corresponding constants.
In some cases this may even result in constant time execution.
Fixed buf #11487.
Added a call of QUICK_RANGE_SELECT::init to the
QUICK_RANGE_SELECT::reset method. Without it the second
evaluation of a subquery employing the range access failed.
subselect.result, subselect.test:
Added a test case for bug #11487.
The source of the problem is in Field_longlong::cmp. If 'this' is
an unsigned number, the method casts both the current value, and
the constant that we compare with to an unsigned number. As a
result if the constant we compare with is a negative number, it
wraps to some unsigned number, and the comparison is incorrect.
When the optimizer chooses the "range" access method, this problem
causes handler::read_range_next to reject the current key when the
upper bound key is a negative number because handler::compare_key
incorrectly considers the positive and negative keys to be equal.
The current patch does not correct the source of the problem in
Field_longlong::cmp because it is not easy to propagate sign
information about the constant at query execution time. Instead
the patch changes the range optimizer so that it never compares
unsiged fields with negative constants. As an added benefit,
queries that do such comparisons will execute faster because
the range optimizer replaces conditions like:
(a) (unsigned_int [< | <=] negative_constant) == FALSE
(b) (unsigned_int [> | >=] negative_constant) == TRUE
with the corresponding constants.
In some cases this may even result in constant time execution.
