The sort length is extracted similarly to how sortlength() function does
it. The function makes use of filesort_use_addons function to compute
the length of addon fields. Finally, by calling compute_sort_costs we
get the fastest_sort possible.
Other changes:
* Sort_param::using_addon_fields() assumes addon fields are already
allocated. This makes the use of Sort_param unusable for
compute_sort_costs *if* we don't want to allocate addon fields.
As a preliminary fix, pass "with_addon_fields" as bool value to
compute_sort_costs() and make the internal functions use that value
instead of Sort_param::using_addon_fields() method.
The ideal fix would be to define a "leaner" struct with only the
necessary members, but this can be done as a separate commit.
* Remove unnecessary fields from Sort_costs::costs array.
As we do not yet differentiate between merge sort with fixed length vs
dynamic length fields, eliminate that differentiation from enum sort_type.
It can be added at a later date when we indeed have a cost
differentiation.
No logic changes.
Extract some of init_for_filesort logic into a separate function:
* Sort_param::setup_lengths_and_limit can be used to fill in the various
xxx_length members of Sort_param, without having to allocate any of the other
buffers.
One effect of this change in the test suite is that tests with very few
rows changed to use sub queries instead of materialization. This is
correct and expected as for these the materialization overhead is too high.
A lot of tests where fixed to still use materialization by adding a
few rows to the tables (most tests has only 2-3 rows and are thus easily
affected when cost computations are changed).
Other things:
- Added more variables to TMPTABLE_COSTS for better cost calculation
- Added cost of copying rows to TMPTABLE_COSTS lookup and write
- Added THD::optimizer_cache_hit_ratio for easier cost calculations
- Added DISK_FAST_READ_SIZE to be used when calculating costs when
reading big blocks from a disk
This cleans up the interface for choose_plan() as it is not depending
on setting join->emb_sj_nest.
choose_plan() now sets up join->emb_sj_nest and join->allowed_tables before
calling optimize_straight_join() and best_extension_by_limited_search().
Other things:
- Removed "& ~join->const_table_map" as the constant tables should never
be in sj_innert_tables.
- Converted some 'if' to DBUG_ASSERT() as these should always be true.
- Calculate 'allowed_tables' in choose_plan() as this never changes in
the childs.
- Added assert to check that next_emb->nested_join->n_tables doesn't
get to a wrong value.
