BUG #17336: logtape sort performance and overflow

The following bug has been logged on the website:

Bug reference: 17336
Logged by: ma liangzhu
Email address: ma100(at)hotmail(dot)com
PostgreSQL version: 14.1
Operating system: centos7
Description:

In logtape.c,

* Each `swap_nodes` will execute assignment statement three times, while
we only need execute once like in tuplesort.c

* right_offset(unsigned i) parameter i seemed should be `unsigned long`

Here's a patch

-------------------------------------
```diff
diff --git a/src/backend/utils/sort/logtape.c
b/src/backend/utils/sort/logtape.c
index 48baccd..c96d1ca 100644
--- a/src/backend/utils/sort/logtape.c
+++ b/src/backend/utils/sort/logtape.c
@@ -340,16 +340,6 @@ ltsReadFillBuffer(LogicalTape *lt)
return (lt->nbytes > 0);
}

-static inline void
-swap_nodes(long *heap, unsigned long a, unsigned long b)
-{
- unsigned long swap;
-
- swap = heap[a];
- heap[a] = heap[b];
- heap[b] = swap;
-}
-
static inline unsigned long
left_offset(unsigned long i)
{
@@ -357,7 +347,7 @@ left_offset(unsigned long i)
}

static inline unsigned long
-right_offset(unsigned i)
+right_offset(unsigned long i)
{
return 2 * i + 2;
}
@@ -411,6 +401,8 @@ ltsGetFreeBlock(LogicalTapeSet *lts)
/* sift down */
pos = 0;
heapsize = lts->nFreeBlocks;
+ long t = heap[pos];
+
while (true)
{
unsigned long left = left_offset(pos);
@@ -426,12 +418,13 @@ ltsGetFreeBlock(LogicalTapeSet *lts)
else
break;

- if (heap[min_child] >= heap[pos])
+ if (heap[min_child] >= t)
break;

- swap_nodes(heap, min_child, pos);
+ heap[pos] = heap[min_child];
pos = min_child;
}
+ heap[pos] = t;

return blocknum;
}
@@ -514,18 +507,20 @@ ltsReleaseBlock(LogicalTapeSet *lts, long blocknum)
/* place entry at end of minheap array */
heap[pos] = blocknum;
lts->nFreeBlocks++;
+ long t = heap[pos];

/* sift up */
while (pos != 0)
{
unsigned long parent = parent_offset(pos);

- if (heap[parent] < heap[pos])
+ if (heap[parent] < t)
break;

- swap_nodes(heap, parent, pos);
+ heap[pos] = heap[parent];
pos = parent;
}
+ heap[pos] = t;
}

/*
```