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diff --git a/src/backend/optimizer/geqo/geqo_eval.c b/src/backend/optimizer/geqo/geqo_eval.c
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+/*------------------------------------------------------------------------
+ *
+ * geqo_eval.c
+ *	  Routines to evaluate query trees
+ *
+ * Portions Copyright (c) 1996-2022, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/backend/optimizer/geqo/geqo_eval.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+/* contributed by:
+   =*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=
+   *  Martin Utesch				 * Institute of Automatic Control	   *
+   =							 = University of Mining and Technology =
+   *  utesch@aut.tu-freiberg.de  * Freiberg, Germany				   *
+   =*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=
+ */
+
+#include "postgres.h"
+
+#include <float.h>
+#include <limits.h>
+#include <math.h>
+
+#include "optimizer/geqo.h"
+#include "optimizer/joininfo.h"
+#include "optimizer/pathnode.h"
+#include "optimizer/paths.h"
+#include "utils/memutils.h"
+
+
+/* A "clump" of already-joined relations within gimme_tree */
+typedef struct
+{
+	RelOptInfo *joinrel;		/* joinrel for the set of relations */
+	int			size;			/* number of input relations in clump */
+} Clump;
+
+static List *merge_clump(PlannerInfo *root, List *clumps, Clump *new_clump,
+						 int num_gene, bool force);
+static bool desirable_join(PlannerInfo *root,
+						   RelOptInfo *outer_rel, RelOptInfo *inner_rel);
+
+
+/*
+ * 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;
+}
+
+/*
+ * gimme_tree
+ *	  Form planner estimates for a join tree constructed in the specified
+ *	  order.
+ *
+ *	 'tour' is the proposed join order, of length 'num_gene'
+ *
+ * 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 and
+ * we can't modify it into a valid order.
+ *
+ * The original implementation of this routine always joined in the specified
+ * order, and so could only build left-sided plans (and right-sided and
+ * mixtures, as a byproduct of the fact that make_join_rel() is symmetric).
+ * It could never produce a "bushy" plan.  This had a couple of big problems,
+ * of which the worst was that there are situations involving join order
+ * restrictions where the only valid plans are bushy.
+ *
+ * The present implementation takes the given tour as a guideline, but
+ * postpones joins that are illegal or seem unsuitable according to some
+ * heuristic rules.  This allows correct bushy plans to be generated at need,
+ * and as a nice side-effect it seems to materially improve the quality of the
+ * generated plans.  Note however that since it's just a heuristic, it can
+ * still fail in some cases.  (In particular, we might clump together
+ * relations that actually mustn't be joined yet due to LATERAL restrictions;
+ * since there's no provision for un-clumping, this must lead to failure.)
+ */
+RelOptInfo *
+gimme_tree(PlannerInfo *root, Gene *tour, int num_gene)
+{
+	GeqoPrivateData *private = (GeqoPrivateData *) root->join_search_private;
+	List	   *clumps;
+	int			rel_count;
+
+	/*
+	 * Sometimes, a relation can't yet be joined to others due to heuristics
+	 * or actual semantic restrictions.  We maintain a list of "clumps" of
+	 * successfully joined relations, with larger clumps at the front. Each
+	 * new relation from the tour is added to the first clump it can be joined
+	 * to; if there is none then it becomes a new clump of its own. When we
+	 * enlarge an existing clump we check to see if it can now be merged with
+	 * any other clumps.  After the tour is all scanned, we forget about the
+	 * heuristics and try to forcibly join any remaining clumps.  If we are
+	 * unable to merge all the clumps into one, fail.
+	 */
+	clumps = NIL;
+
+	for (rel_count = 0; rel_count < num_gene; rel_count++)
+	{
+		int			cur_rel_index;
+		RelOptInfo *cur_rel;
+		Clump	   *cur_clump;
+
+		/* Get the next input relation */
+		cur_rel_index = (int) tour[rel_count];
+		cur_rel = (RelOptInfo *) list_nth(private->initial_rels,
+										  cur_rel_index - 1);
+
+		/* Make it into a single-rel clump */
+		cur_clump = (Clump *) palloc(sizeof(Clump));
+		cur_clump->joinrel = cur_rel;
+		cur_clump->size = 1;
+
+		/* Merge it into the clumps list, using only desirable joins */
+		clumps = merge_clump(root, clumps, cur_clump, num_gene, false);
+	}
+
+	if (list_length(clumps) > 1)
+	{
+		/* Force-join the remaining clumps in some legal order */
+		List	   *fclumps;
+		ListCell   *lc;
+
+		fclumps = NIL;
+		foreach(lc, clumps)
+		{
+			Clump	   *clump = (Clump *) lfirst(lc);
+
+			fclumps = merge_clump(root, fclumps, clump, num_gene, true);
+		}
+		clumps = fclumps;
+	}
+
+	/* Did we succeed in forming a single join relation? */
+	if (list_length(clumps) != 1)
+		return NULL;
+
+	return ((Clump *) linitial(clumps))->joinrel;
+}
+
+/*
+ * Merge a "clump" into the list of existing clumps for gimme_tree.
+ *
+ * We try to merge the clump into some existing clump, and repeat if
+ * successful.  When no more merging is possible, insert the clump
+ * into the list, preserving the list ordering rule (namely, that
+ * clumps of larger size appear earlier).
+ *
+ * If force is true, merge anywhere a join is legal, even if it causes
+ * a cartesian join to be performed.  When force is false, do only
+ * "desirable" joins.
+ */
+static List *
+merge_clump(PlannerInfo *root, List *clumps, Clump *new_clump, int num_gene,
+			bool force)
+{
+	ListCell   *lc;
+	int			pos;
+
+	/* Look for a clump that new_clump can join to */
+	foreach(lc, clumps)
+	{
+		Clump	   *old_clump = (Clump *) lfirst(lc);
+
+		if (force ||
+			desirable_join(root, old_clump->joinrel, new_clump->joinrel))
+		{
+			RelOptInfo *joinrel;
+
+			/*
+			 * Construct a RelOptInfo representing the join of these two input
+			 * relations.  Note that we expect the joinrel not to exist in
+			 * root->join_rel_list yet, and so the paths constructed for it
+			 * will only include the ones we want.
+			 */
+			joinrel = make_join_rel(root,
+									old_clump->joinrel,
+									new_clump->joinrel);
+
+			/* Keep searching if join order is not valid */
+			if (joinrel)
+			{
+				/* Create paths for partitionwise joins. */
+				generate_partitionwise_join_paths(root, joinrel);
+
+				/*
+				 * Except for the topmost scan/join rel, consider gathering
+				 * partial paths.  We'll do the same for the topmost scan/join
+				 * rel once we know the final targetlist (see
+				 * grouping_planner).
+				 */
+				if (!bms_equal(joinrel->relids, root->all_baserels))
+					generate_useful_gather_paths(root, joinrel, false);
+
+				/* Find and save the cheapest paths for this joinrel */
+				set_cheapest(joinrel);
+
+				/* Absorb new clump into old */
+				old_clump->joinrel = joinrel;
+				old_clump->size += new_clump->size;
+				pfree(new_clump);
+
+				/* Remove old_clump from list */
+				clumps = foreach_delete_current(clumps, lc);
+
+				/*
+				 * Recursively try to merge the enlarged old_clump with
+				 * others.  When no further merge is possible, we'll reinsert
+				 * it into the list.
+				 */
+				return merge_clump(root, clumps, old_clump, num_gene, force);
+			}
+		}
+	}
+
+	/*
+	 * No merging is possible, so add new_clump as an independent clump, in
+	 * proper order according to size.  We can be fast for the common case
+	 * where it has size 1 --- it should always go at the end.
+	 */
+	if (clumps == NIL || new_clump->size == 1)
+		return lappend(clumps, new_clump);
+
+	/* Else search for the place to insert it */
+	for (pos = 0; pos < list_length(clumps); pos++)
+	{
+		Clump	   *old_clump = (Clump *) list_nth(clumps, pos);
+
+		if (new_clump->size > old_clump->size)
+			break;				/* new_clump belongs before old_clump */
+	}
+	clumps = list_insert_nth(clumps, pos, new_clump);
+
+	return clumps;
+}
+
+/*
+ * Heuristics for gimme_tree: do we want to join these two relations?
+ */
+static bool
+desirable_join(PlannerInfo *root,
+			   RelOptInfo *outer_rel, RelOptInfo *inner_rel)
+{
+	/*
+	 * Join if there is an applicable join clause, or if there is a join order
+	 * restriction forcing these rels to be joined.
+	 */
+	if (have_relevant_joinclause(root, outer_rel, inner_rel) ||
+		have_join_order_restriction(root, outer_rel, inner_rel))
+		return true;
+
+	/* Otherwise postpone the join till later. */
+	return false;
+}