php笔记之：有规律大文件的读取与写入的分析_PHP
这几天在做一个东西.研究PHP读取行数较多的文件(大概上百万行).考虑到效率问题.进行了简单的研究.总结如下
第一条.file()函数的效率问题.
file()函数的效率很底下 如果是有规律的文件.比如每行一条相应数据.那么尽量不要是用file()函数
可以使用file_get_contents()然后用explode切割.这样效率会快三分之一
举个例子:
文件样式如下:
11111\n
22222\n
33333\n
44444\n
55555\n
.....\n
nnnnnnnnnnn\n
如果用file($file)读入的话.耗时很长.
可以用如下方法explode("\n",file_get_contents($file));效率会快很多.
第二条,数组的遍历方式.
数据已经被读入数组了.下面就是遍历了.
我所需要的是确定数组中有无一个值的存在,比如说44444是否在数组中.首先想到的是in_array()
不过实验了下发现效率很低下.于是参考别人的代码想到一个办法.把数组翻转过来.变成所有值都为1.原来的值变成了索引.那么只要我在if里写($arr[索引]==1)去判断.果然效率高出很多.
在数组的遍历过程中.如果数组个头非常大,并且数组中的数据并不是全能用到的话,最好把用来遍历的数组抽出来.这样会提高很多效率.
第三条,数组的存储.
把计算过后的数据保存起来.存在一个文件中.考虑了三种方法.一种是直接写成php文件.一种是serialize,一种是json串.
第一种方式
直接写入文件保存成PHP
需要的时候直接require进来.
第二种方式.把变量serialize然后file_put_contents()进入文件.使用的时候unserialize就ok.
第三种方式和第二种类似.只不过写成了json串.
经过测试.发现第二种效率最高.第三种其次.和第二种效率不相上下.第一种最慢.和我预想的差距很大.真是大跌眼镜.
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