Hi, Zardosht!
On Jun 18, Zardosht Kasheff wrote:
>
> What I am trying to figure out is what changes need to be done to the
> query optimizer to properly support this feature.
...
> Here is my failed attempt at answer the question:
> I looked at places where handler::primary_key_is_clustered is called.
> I figured that if there are locations where the optimizer needs to
> know if the primary key is clustered, they may also be places where
> the optimizer needs to know if another key is clustered. I only saw
> one potential location where this might be necessary:
>
> in sql_select.cc, in function test_if_skip_sort_order,
> we have : bool is_covering= table->covering_keys.is_set(nr) ||
> nr == table->s->primary_key &&
> table->file->primary_key_is_clustered();
>
> I figure that this will also need to take into account if the key is
> clustered, correct?
Yes. I'd generalize the above as
bool is_covering= table->covering_keys.is_set(nr) ||
table->file->index_flags(nr) & HA_CLUSTERED_KEY;
alternatively, we could simply initialize table->covering_keys bitmap to
include all clustered keys. This should be even better, I suppose - it
will cover more code paths in the optimizer, not only
test_if_skip_sort_order().
> So, in conclusion, given everything above, I have one general question
> and one specific question.
> The general question: can anyone think of any other place where the
> optimizer needs to be tweaked to be aware of clustered keys?
I think yes.
In partitioning, in mrr (DsMrr_impl::choose_mrr_impl), in many places in
the range optimizer.
Simple grep for the word 'clustered' returns lots of matches :(
> The specific question: does any tweaking need to happen in
> test_if_skip_sort_order.
Yes, see above.
Regards / Mit vielen Grüßen,
Sergei
--
__ ___ ___ ____ __
/ |/ /_ __/ __/ __ \/ / Sergei Golubchik <serg@stripped>
/ /|_/ / // /\ \/ /_/ / /__ Principal Software Engineer/Server Architect
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