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diff --git a/src/include/lib/binaryheap.h b/src/include/lib/binaryheap.h
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+/*
+ * binaryheap.h
+ *
+ * A simple binary heap implementation
+ *
+ * Portions Copyright (c) 2012-2021, PostgreSQL Global Development Group
+ *
+ * src/include/lib/binaryheap.h
+ */
+
+#ifndef BINARYHEAP_H
+#define BINARYHEAP_H
+
+/*
+ * For a max-heap, the comparator must return <0 iff a < b, 0 iff a == b,
+ * and >0 iff a > b.  For a min-heap, the conditions are reversed.
+ */
+typedef int (*binaryheap_comparator) (Datum a, Datum b, void *arg);
+
+/*
+ * binaryheap
+ *
+ *		bh_size			how many nodes are currently in "nodes"
+ *		bh_space		how many nodes can be stored in "nodes"
+ *		bh_has_heap_property	no unordered operations since last heap build
+ *		bh_compare		comparison function to define the heap property
+ *		bh_arg			user data for comparison function
+ *		bh_nodes		variable-length array of "space" nodes
+ */
+typedef struct binaryheap
+{
+	int			bh_size;
+	int			bh_space;
+	bool		bh_has_heap_property;	/* debugging cross-check */
+	binaryheap_comparator bh_compare;
+	void	   *bh_arg;
+	Datum		bh_nodes[FLEXIBLE_ARRAY_MEMBER];
+} binaryheap;
+
+extern binaryheap *binaryheap_allocate(int capacity,
+									   binaryheap_comparator compare,
+									   void *arg);
+extern void binaryheap_reset(binaryheap *heap);
+extern void binaryheap_free(binaryheap *heap);
+extern void binaryheap_add_unordered(binaryheap *heap, Datum d);
+extern void binaryheap_build(binaryheap *heap);
+extern void binaryheap_add(binaryheap *heap, Datum d);
+extern Datum binaryheap_first(binaryheap *heap);
+extern Datum binaryheap_remove_first(binaryheap *heap);
+extern void binaryheap_replace_first(binaryheap *heap, Datum d);
+
+#define binaryheap_empty(h)			((h)->bh_size == 0)
+
+#endif							/* BINARYHEAP_H */