Hi,
Approved.
I have one nit-pick: While I generally agree that the ? operator might
make assignments clearer than if statements, I do not think this is
particularly readable:
> + /*
> + Cannot use join buffering if either
> + 1. Join buffering is disabled by the user, or
> + 2. Outer joined table, and join buffering disabled for outer join, or
> + 3. Semi-joined table, and join buffering disabled for semi-join, or
> + 4. Unlinked cache is forced and there are multiple inner tables of
> + this outer join.
> + */
> + tab->use_join_cache=
> + (thd->variables.optimizer_join_cache_level == 0 || // 1
> + ((tab->table->map& join->outer_join)&&
> // 2
> + thd->variables.optimizer_join_cache_level<= 2) || // 2
> + (tab->emb_sj_nest != NULL&& //
> 3
> + thd->variables.optimizer_join_cache_level<= 2) || // 3
> + (force_unlinked_cache&& // 4
> + tl->in_outer_join_nest()&& //
> 4
> + tl->embedding->nested_join->join_list.elements> 1)) ?
> // 4
> + JOIN_CACHE::ALG_NONE : // Indicates that join buffering cannot be used
> + JOIN_CACHE::ALG_BNL | JOIN_CACHE::ALG_BKA | JOIN_CACHE::ALG_BKA_UNIQUE;
When if-statements are that complex this becomes a bit difficult to
read, IMHO.
Also, I urge you to in some way document the deficiencies in the cost
model that we discussed in relation to this bug.
--
Øystein
