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authorNathan Bossart2023-09-18 21:06:08 +0000
committerNathan Bossart2023-09-18 21:06:08 +0000
commitc103d073819a2189d849c0a93d51c726be524c48 (patch)
treec590a7adbbc8de211687517da7fca32dfcffe2d9
parent83223f5f714482dd44883c68ecac2ae8c2d838e8 (diff)
Add function for removing arbitrary nodes in binaryheap.
This commit introduces binaryheap_remove_node(), which can be used to remove any node from a binary heap. The implementation is straightforward. The target node is replaced with the last node in the heap, and then we sift as needed to preserve the heap property. This new function is intended for use in a follow-up commit that will improve the performance of pg_restore. Reviewed-by: Tom Lane Discussion: https://postgr.es/m/3612876.1689443232%40sss.pgh.pa.us
-rw-r--r--src/common/binaryheap.c29
-rw-r--r--src/include/lib/binaryheap.h3
2 files changed, 32 insertions, 0 deletions
diff --git a/src/common/binaryheap.c b/src/common/binaryheap.c
index 39a8243a6d..19e095f1fb 100644
--- a/src/common/binaryheap.c
+++ b/src/common/binaryheap.c
@@ -216,6 +216,35 @@ binaryheap_remove_first(binaryheap *heap)
}
/*
+ * binaryheap_remove_node
+ *
+ * Removes the nth (zero based) node from the heap. The caller must ensure
+ * that there are at least (n + 1) nodes in the heap. O(log n) worst case.
+ */
+void
+binaryheap_remove_node(binaryheap *heap, int n)
+{
+ int cmp;
+
+ Assert(!binaryheap_empty(heap) && heap->bh_has_heap_property);
+ Assert(n >= 0 && n < heap->bh_size);
+
+ /* compare last node to the one that is being removed */
+ cmp = heap->bh_compare(heap->bh_nodes[--heap->bh_size],
+ heap->bh_nodes[n],
+ heap->bh_arg);
+
+ /* remove the last node, placing it in the vacated entry */
+ heap->bh_nodes[n] = heap->bh_nodes[heap->bh_size];
+
+ /* sift as needed to preserve the heap property */
+ if (cmp > 0)
+ sift_up(heap, n);
+ else if (cmp < 0)
+ sift_down(heap, n);
+}
+
+/*
* binaryheap_replace_first
*
* Replace the topmost element of a non-empty heap, preserving the heap
diff --git a/src/include/lib/binaryheap.h b/src/include/lib/binaryheap.h
index 3647aeae65..9525dcaec4 100644
--- a/src/include/lib/binaryheap.h
+++ b/src/include/lib/binaryheap.h
@@ -59,8 +59,11 @@ extern void binaryheap_build(binaryheap *heap);
extern void binaryheap_add(binaryheap *heap, bh_node_type d);
extern bh_node_type binaryheap_first(binaryheap *heap);
extern bh_node_type binaryheap_remove_first(binaryheap *heap);
+extern void binaryheap_remove_node(binaryheap *heap, int n);
extern void binaryheap_replace_first(binaryheap *heap, bh_node_type d);
#define binaryheap_empty(h) ((h)->bh_size == 0)
+#define binaryheap_size(h) ((h)->bh_size)
+#define binaryheap_get_node(h, n) ((h)->bh_nodes[n])
#endif /* BINARYHEAP_H */