Hi!
I have a quick question on some code I am thinking of removing that
I'd like to get some opinions on. At the moment, there are 2 functions
in the optimizer in Drizzle for searching for an optimal query plan:
- find_best
- greedy_search
The method that is used is determined by the optimizer_search_depth
parameter. We can see this from the following code:
if (search_depth == MAX_TABLES+2)
{ /*
TODO: 'MAX_TABLES+2' denotes the old implementation of find_best before
the greedy version. Will be removed when greedy_search is approved.
*/
join->best_read= DBL_MAX;
if (find_best(join, join_tables, join->const_tables, 1.0, 0.0))
return(true);
}
else
{
if (search_depth == 0)
/* Automatically determine a reasonable value for 'search_depth' */
search_depth= determine_search_depth(join);
if (greedy_search(join, join_tables, search_depth, prune_level))
return(true);
}
Currently, in drizzle, optimizer_search_depth is set to 62 by default
so we never actually use the find_best method for searching for an
optimal plan. Thus, I'm wondering if anyone has any objections to
removing the find_best method? That way, we only have 1 method for
searching through query plans.
From looking at the comments in the optimizer source code, it seems
that find_best will be removed from the MySQL source in the future
also (if it has not already?)
-Padraig
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