Hi, On 07/09/2015 05:00 PM, Michael Widenius wrote:

Hi!

...

Hi Igor,

I noticed that during Item_cond::fix_fields() and Item_func_between::fix_fields() update these optimizer related SELECT_LEX members:

thd->lex->current_select->cond_count and thd->lex->current_select->between_count

The purpose of these members is to allocate optimizer related buffers in: - update_ref_and_keys() in sql_select.cc and - check_func_dependency() in opt_table_elimination,cc and it seems they have no any other purposes..

Correct.

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From my understanding, this is a dead code and the collected values are never used:

- cond_count and_between_count are later always initialized to 0 before the walk(count_sargable_conds) call in update_ref_and_keys().

And the call to check_func_dependency() is done after this call.

...

- moreover, using the values collected during fix_fields() would not be correct to allocate optimized related buffers, because the code in fix_fields() does not distinguish between different query parts, so the items can be just a part of the SELECT list rather than a part of WHERE/HAVING/ON.

This would note be a problem as the count was supposed to be an upper bound. As it's not normal that you have many IF or BETWEEN in the SELECT part, this was not a problem.

I looked at the patch and it's ok to commit.

Thanks. I created a bug report, for reference: MDEV-8456 Dead code in Item_cond::fix_fields() and Item_func_between::fix_fields() and pushed into 10.1.

Regards, Monty