Re: Optimizer hook

I've applied this patch with revision to put the hook where I thought it
made sense.  Attached is a modification of your dummy.c to show use of
the hook.  I didn't test it heavily, but I did check that it seemed to
work with either order of calling geqo() and standard_join_search().

            regards, tom lane


#include "postgres.h"

#include "fmgr.h"
#include "optimizer/geqo.h"
#include "optimizer/paths.h"
#include "optimizer/pathnode.h"


PG_MODULE_MAGIC;

void    _PG_init(void);
void    _PG_fini(void);

static RelOptInfo *
my_join_search(PlannerInfo *root, int levels_needed, List *initial_rels)
{
    RelOptInfo *dynamic_result, *geqo_result;
    Cost dynamic_cost, geqo_cost;
    List       *dynamic_list, *geqo_list;
    struct HTAB *dynamic_hash, *geqo_hash;
    int            savelength;

    savelength = list_length(root->join_rel_list);

    root->join_rel_hash = NULL;

    elog(LOG, "Starting a join order search \"dynamic\"...");
    dynamic_result = standard_join_search(root, levels_needed, initial_rels);
    dynamic_cost = dynamic_result->cheapest_total_path->total_cost;

    dynamic_list = list_copy(root->join_rel_list);
    dynamic_hash = root->join_rel_hash;

    root->join_rel_list = list_truncate(root->join_rel_list,
                                        savelength);
    root->join_rel_hash = NULL;

    elog(LOG, "Starting a join order search \"geqo\"...");
    geqo_result = geqo(root, levels_needed, initial_rels);
    geqo_cost = geqo_result->cheapest_total_path->total_cost;

    geqo_list = list_copy(root->join_rel_list);
    geqo_hash = root->join_rel_hash;

    fprintf(stderr, "GEQO cost: %f  Dynamic programming cost: %f\n",
            geqo_cost, dynamic_cost);

    if (geqo_cost < dynamic_cost)
    {
        root->join_rel_list = geqo_list;
        root->join_rel_hash = geqo_hash;
        return geqo_result;
    }
    else
    {
        root->join_rel_list = dynamic_list;
        root->join_rel_hash = dynamic_hash;
        return dynamic_result;
    }
}


void
_PG_init(void)
{
    join_search_hook = my_join_search;
}

void
_PG_fini(void)
{
    join_search_hook = NULL;
}