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Make GEQO's planning deterministic by having it start from a predictable

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random number seed each time.  This is how it used to work years ago, but
we got rid of the seed reset because it was resetting the main random()
sequence and thus having undesirable effects on the rest of the system.
To fix, establish a private random number state for each execution of
geqo(), and initialize the state using the new GUC variable geqo_seed.
People who want to experiment with different random searches can do so
by changing geqo_seed, but you'll always get the same plan for the same
value of geqo_seed (if holding all other planner inputs constant, of course).

The new state is kept in PlannerInfo by adding a "void *" field reserved
for use by join_search hooks.  Most of the rather bulky code changes in
this commit are just arranging to pass PlannerInfo around to all the GEQO
functions (many of which formerly didn't receive it).

Andres Freund, with some editorialization by Tom
This commit is contained in:
Tom Lane
2009-07-16 20:55:44 +00:00
parent c43feefa80
commit f5bc74192d
27 changed files with 305 additions and 202 deletions
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28
src/backend/optimizer/geqo/geqo_eval.c
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@@ -6,7 +6,7 @@
* Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $PostgreSQL: pgsql/src/backend/optimizer/geqo/geqo_eval.c,v 1.88 2009/01/01 17:23:43 momjian Exp $
* $PostgreSQL: pgsql/src/backend/optimizer/geqo/geqo_eval.c,v 1.89 2009/07/16 20:55:44 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -42,7 +42,7 @@ static bool desirable_join(PlannerInfo *root,
* Returns cost of a query tree as an individual of the population.
*/
Cost
geqo_eval(Gene *tour, int num_gene, GeqoEvalData *evaldata)
geqo_eval(PlannerInfo *root, Gene *tour, int num_gene)
{
MemoryContext mycontext;
MemoryContext oldcxt;
@@ -94,13 +94,13 @@ geqo_eval(Gene *tour, int num_gene, GeqoEvalData *evaldata)
* (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;
savelength = list_length(root->join_rel_list);
savehash = root->join_rel_hash;
evaldata->root->join_rel_hash = NULL;
root->join_rel_hash = NULL;
/* construct the best path for the given combination of relations */
joinrel = gimme_tree(tour, num_gene, evaldata);
joinrel = gimme_tree(root, tour, num_gene);
/*
* compute fitness
@@ -117,9 +117,9 @@ geqo_eval(Gene *tour, int num_gene, GeqoEvalData *evaldata)
* 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;
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);
@@ -134,7 +134,6 @@ geqo_eval(Gene *tour, int num_gene, GeqoEvalData *evaldata)
* order.
*
* 'tour' is the proposed join order, of length 'num_gene'
* 'evaldata' contains the context we need
*
* Returns a new join relation whose cheapest path is the best plan for
* this join order. NB: will return NULL if join order is invalid.
@@ -153,8 +152,9 @@ geqo_eval(Gene *tour, int num_gene, GeqoEvalData *evaldata)
* plans.
*/
RelOptInfo *
gimme_tree(Gene *tour, int num_gene, GeqoEvalData *evaldata)
gimme_tree(PlannerInfo *root, Gene *tour, int num_gene)
{
GeqoPrivateData *private = (GeqoPrivateData *) root->join_search_private;
RelOptInfo **stack;
int stack_depth;
RelOptInfo *joinrel;
@@ -193,7 +193,7 @@ gimme_tree(Gene *tour, int num_gene, GeqoEvalData *evaldata)
/* Get the next input relation and push it */
cur_rel_index = (int) tour[rel_count];
stack[stack_depth] = (RelOptInfo *) list_nth(evaldata->initial_rels,
stack[stack_depth] = (RelOptInfo *) list_nth(private->initial_rels,
cur_rel_index - 1);
stack_depth++;
@@ -211,7 +211,7 @@ gimme_tree(Gene *tour, int num_gene, GeqoEvalData *evaldata)
* have exhausted the input, the heuristics can't prevent popping.
*/
if (rel_count < num_gene - 1 &&
!desirable_join(evaldata->root, outer_rel, inner_rel))
!desirable_join(root, outer_rel, inner_rel))
break;
/*
@@ -220,7 +220,7 @@ gimme_tree(Gene *tour, int num_gene, GeqoEvalData *evaldata)
* root->join_rel_list yet, and so the paths constructed for it
* will only include the ones we want.
*/
joinrel = make_join_rel(evaldata->root, outer_rel, inner_rel);
joinrel = make_join_rel(root, outer_rel, inner_rel);
/* Can't pop stack here if join order is not valid */
if (!joinrel)