/*
* geqo_eval
*
* Returns cost of a query tree as an individual of the population.
*
* If no legal join order can be extracted from the proposed tour,
* returns DBL_MAX.
*/
Cost
geqo_eval(PlannerInfo *root, Gene *tour, int num_gene)
{
MemoryContext mycontext;
MemoryContext oldcxt;
RelOptInfo *joinrel;
Cost fitness;
int savelength;
struct HTAB *savehash;
/*
* Create a private memory context that will hold all temp storage
* allocated inside gimme_tree().
*
* Since geqo_eval() will be called many times, we can't afford to let all
* that memory go unreclaimed until end of statement. Note we make the
* temp context a child of the planner's normal context, so that it will
* be freed even if we abort via ereport(ERROR).
*/
mycontext = AllocSetContextCreate(CurrentMemoryContext,
"GEQO",
ALLOCSET_DEFAULT_SIZES);
oldcxt = MemoryContextSwitchTo(mycontext);
/*
* gimme_tree will add entries to root->join_rel_list, which may or may
* not already contain some entries. The newly added entries will be
* recycled by the MemoryContextDelete below, so we must ensure that the
* list is restored to its former state before exiting. We can do this by
* truncating the list to its original length. NOTE this assumes that any
* added entries are appended at the end!
*
* We also must take care not to mess up the outer join_rel_hash, if there
* is one. We can do this by just temporarily setting the link to NULL.
* (If we are dealing with enough join rels, which we very likely are, a
* new hash table will get built and used locally.)
*
* join_rel_level[] shouldn't be in use, so just Assert it isn't.
*/
savelength = list_length(root->join_rel_list);
savehash = root->join_rel_hash;
Assert(root->join_rel_level == NULL);
root->join_rel_hash = NULL;
/* construct the best path for the given combination of relations */
joinrel = gimme_tree(root, tour, num_gene);
/*
* compute fitness, if we found a valid join
*
* XXX geqo does not currently support optimization for partial result
* retrieval, nor do we take any cognizance of possible use of
* parameterized paths --- how to fix?
*/
if (joinrel)
{
Path *best_path = joinrel->cheapest_total_path;
fitness = best_path->total_cost;
}
else
fitness = DBL_MAX;
/*
* Restore join_rel_list to its former state, and put back original
* hashtable if any.
*/
root->join_rel_list = list_truncate(root->join_rel_list,
savelength);
root->join_rel_hash = savehash;
/* release all the memory acquired within gimme_tree */
MemoryContextSwitchTo(oldcxt);
MemoryContextDelete(mycontext);
return fitness;
}
/*
* geqo_eval
*
* Returns cost of a query tree as an individual of the population.
*/
Cost
geqo_eval(Gene *tour, int num_gene, GeqoEvalData *evaldata)
{
MemoryContext mycontext;
MemoryContext oldcxt;
RelOptInfo *joinrel;
Cost fitness;
int savelength;
struct HTAB *savehash;
/*
* Because gimme_tree considers both left- and right-sided trees, there is
* no difference between a tour (a,b,c,d,...) and a tour (b,a,c,d,...) ---
* the same join orders will be considered. To avoid redundant cost
* calculations, we simply reject tours where tour[0] > tour[1], assigning
* them an artificially bad fitness.
*
* init_tour() is aware of this rule and so we should never reject a tour
* during the initial filling of the pool. It seems difficult to persuade
* the recombination logic never to break the rule, however.
*/
if (num_gene >= 2 && tour[0] > tour[1])
return DBL_MAX;
/*
* Create a private memory context that will hold all temp storage
* allocated inside gimme_tree().
*
* Since geqo_eval() will be called many times, we can't afford to let all
* that memory go unreclaimed until end of statement. Note we make the
* temp context a child of the planner's normal context, so that it will
* be freed even if we abort via ereport(ERROR).
*/
mycontext = AllocSetContextCreate(CurrentMemoryContext,
"GEQO",
ALLOCSET_DEFAULT_MINSIZE,
ALLOCSET_DEFAULT_INITSIZE,
ALLOCSET_DEFAULT_MAXSIZE);
oldcxt = MemoryContextSwitchTo(mycontext);
/*
* gimme_tree will add entries to root->join_rel_list, which may or may
* not already contain some entries. The newly added entries will be
* recycled by the MemoryContextDelete below, so we must ensure that the
* list is restored to its former state before exiting. We can do this by
* truncating the list to its original length. NOTE this assumes that any
* added entries are appended at the end!
*
* We also must take care not to mess up the outer join_rel_hash, if there
* is one. We can do this by just temporarily setting the link to NULL.
* (If we are dealing with enough join rels, which we very likely are, a
* new hash table will get built and used locally.)
*/
savelength = list_length(evaldata->root->join_rel_list);
savehash = evaldata->root->join_rel_hash;
evaldata->root->join_rel_hash = NULL;
/* construct the best path for the given combination of relations */
joinrel = gimme_tree(tour, num_gene, evaldata);
/*
* compute fitness
*
* XXX geqo does not currently support optimization for partial result
* retrieval --- how to fix?
*/
if (joinrel)
fitness = joinrel->cheapest_total_path->total_cost;
else
fitness = DBL_MAX;
/*
* Restore join_rel_list to its former state, and put back original
* hashtable if any.
*/
evaldata->root->join_rel_list = list_truncate(evaldata->root->join_rel_list,
savelength);
evaldata->root->join_rel_hash = savehash;
/* release all the memory acquired within gimme_tree */
MemoryContextSwitchTo(oldcxt);
MemoryContextDelete(mycontext);
return fitness;
}
