2021-10-17

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删除wp_posts-revisions能提高性能吗

长期以来我一直没有删过 wp_posts 里的 revisions 条目，今天我尝试了一下，把所有 revisions 全部删掉：

删除以后，表 wp_posts 占用空间降了85%，但 页面平均生成时间 并没有任何改善。原因是：即使在删掉 revisions 之前，我的 wp_posts 占用空间都还没有MariaDB设置的 innodb-buffer-pool-size 大。

所以我又把 revisions 给加回去了。

Merge sort

快速理解

图解：🔗 [图解排序算法(四)之归并排序 - dreamcatcher-cx - 博客园] https://www.cnblogs.com/chengxiao/p/6194356.html

python merge sort

附带了python代码的解释：🔗 [python归并排序--递归实现 - 简书] https://www.jianshu.com/p/3ad5373465fd

代码，使用了递归：（特别要注意第21, 22行的代码：经常在这个地方把逻辑写复杂了）

def mergesort(arr):
    if len(arr) <= 1:
        return arr
    middle = len(arr) // 2
    left = mergesort(arr[:middle])
    right = mergesort(arr[middle:])
    return merge(left, right)


def merge(left, right):
    C = []
    li = 0
    ri = 0
    while (li < len(left) and ri < len(right)):
        if left[li] < right[ri]:
            C.append(left[li])
            li += 1
        else:
            C.append(right[ri])
            ri += 1
    C += left[li:]
    C += right[ri:]
    return C


if __name__ == '__main__':
    A = [5, 3, 6, 1, 2, 8, 2, 0, 10, 3, 4]
    print(mergesort(A))

代码，不使用递归：

def mergesort(arr):
    B = []
    for i in range(0, len(arr)):
        B.append([])
        B[i].append(arr[i])
    j = len(B)
    while j > 1:
        k = 0
        B = B[:j]
        for l in range(0, len(B) - 1, 2):
            B[k] = merge(B[l], B[l + 1])
            k += 1
        if len(B) % 2 != 0:
            B[k] = B[-1]
            j = j // 2 + 1
        else:
            j = j // 2
    return B[0]


def merge(left, right):
    C = []
    li = 0
    ri = 0
    while (li < len(left) and ri < len(right)):
        if left[li] < right[ri]:
            C.append(left[li])
            li += 1
        else:
            C.append(right[ri])
            ri += 1
    C += left[li:]
    C += right[ri:]
    return C


if __name__ == '__main__':
    A = [5, 3, 6, 1, 2, 8, 2, 0, 10, 3, 11]
    print(mergesort(A))

python radix sort

见中文算法导论p100

python代码和讲解参考：🔗 [基数排序python实现 - sfencs - 博客园] https://www.cnblogs.com/sfencs-hcy/p/10616446.html

A = [125, 126, 642, 363, 10, 99, 512, 578, 999, 850, 193, 736, 74]
j = len(str(max(A)))
i = 0
while i <= j:
    bucket = [[] for _ in range(0, 10)]
    for item in A:
        bucket[(item // (10 ** i)) % 10].append(item)
    A.clear()
    for x in bucket:
        for v in x:
            A.append(v)
    i += 1
print(A)