From 303cd18beaaf4a4133a0988d71bfea0bd2b4444b Mon Sep 17 00:00:00 2001 From: Nathan Bossart Date: Thu, 20 Jul 2023 09:52:20 -0700 Subject: [PATCH v10 2/4] 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 --- src/common/binaryheap.c | 29 +++++++++++++++++++++++++++++ src/include/lib/binaryheap.h | 3 +++ 2 files changed, 32 insertions(+) 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 @@ -215,6 +215,35 @@ binaryheap_remove_first(binaryheap *heap) return result; } +/* + * 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 * 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 */ -- 2.25.1