php多重循环如何提高执行效率

优化基于以下几个原则：

1、尽量以小结果集驱动大结果集（和mysql中join类似）；

2、尽量少在循环中执行sql操作，如果一定要执行sql，尽量批量执行；

3、尽量减少逻辑性代码和调用外部方法，如必要，尽量在在小结果集上处理的；

4、实际应用中发现循环嵌套使用的数据大部分一样，只有小部分不同，果断提取，外部处理;

 

场景1：

<?php

$data = array();
//参数

$kid = []; //数组长度大于300
$dataarray = []; //数组长度大于50

foreach ($dataarray as $k=>$v){

    $starttime = 0;
    $endtime = 0;
    $timearr[$starttime.$endtime]['rid'][] = $k;
    $data = array();
    $i=0;
    foreach ($kid as $kk){

        $data[$i]['k'] = $kk;
        $data[$i]['m'] = $kk;
        $data[$i]['n'] = $kk;
        //必要的赋值操作
        //...

        //各种逻辑判断，并且赋值使用的是上一级嵌套中的变量
        if (!empty($v['a']))
            $data[$i]['a'] =  $v['a'];
        if (!empty($v['a']))
            $data[$i]['a'] = $v['a'].",".$v['a'];

        if (!empty($v['a']))
            $data[$i]['a'] =  $v['a'];
        if (!empty($v['a']))
            $data[$i]['a'] = $v['a'].",".$v['a'];

        if (!empty($v['a']))
            $data[$i]['a'] =  $v['a'];
        if (!empty($v['a']))
            $data[$i]['a'] = $v['a'].",".$v['a'];
        $i++;
    }
    //插入数据
    $allin = $this->model->table('pp')->addALL($data);
}
exit;

 

以上代码实际使用中执行时长大概 20s

 

优化后如下，把必要的逻辑操作，又涉及到上一层循环变量，提取出来，不要放在大结果集中处理，执行时长大概 3秒

<?php

//参数

$kid = [];

$dataarray = [];


foreach ($dataarray as $k=>$v){

    if (!empty($v['a']))
       $a =  $v['a'];
    if (!empty($v['a']))
        $a = $v['a'].",".$v['a'];

    if (!empty($v['a']))
        $a =  $v['a'];
    if (!empty($v['a']))
        $a = $v['a'].",".$v['a'];

    if (!empty($v['a']))
        $a =  $v['a'];
    if (!empty($v['a']))
        $a = $v['a'].",".$v['a'];

    $data = [];
    foreach ($kid as $mm=>$kk){
        $data[$mm]['k'] = $kk;
        $data[$mm]['m'] = $kk;
        $data[$mm]['n'] = $kk;
        //必要的赋值操作
        //...

        $data[$mm]['a'] =  $a;
        $data[$mm]['a'] =  $a;
        $data[$mm]['a'] =  $a;
        $data[$mm]['a'] =  $a;
    }
    //插入数据
    $allin = $this->model->table('pp')->addALL($data);

}

exit;

 

 

场景2：

优化前，执行时间80秒，其中循环时间 62，数据库操作时间 18秒

<?php


//参数

$kid = [];//长度大于300



$dataarray = []; //长度大于50
$stimearr = [];
$etimearr = [];

$countTime = count($stimearr); //长度大于 5

for ($a = 0;$a < $countTime;$a++) { //注意，后面两层嵌套中,除了时间不一样，其他完全一样

    $stime = strtotime($stimearr[$a]);
    $etime = strtotime($etimearr[$a]);


    foreach ($kid as $kk) { // 大结果集
        $data = array();
        $i = 0;
        foreach ($dataarray as $k => $v) { //小结果集合

            $data[$i]['a'] = $kk;
            $data[$i]['a'] = intval($k);
            $data[$i]['a'] = $v['a'];
            $data[$i]['a'] = $v['a'];
            $data[$i]['stime'] = $stime;
            $data[$i]['etime'] = $etime;

            if ($a) {
                $data[$i]['a'] = $k;
                $data[$i]['a'] = $k;
            }
            if ($a) {
                $data[$i]['a'] = $k;
                $data[$i]['a'] = $k;
            }
            $i++;
        }
        //插入数据
        $allin = $this->model->table('pp')->addAll($data);
    }
}
exit;

 

优化后

<?php


//参数

$kid = [];//长度大于300



$dataarray = []; //长度大于50
$stimearr = [];
$etimearr = [];

$countTime = count($stimearr); //长度大于 5


$i = 0;
$data = [];
//提取数据保存
foreach ($dataarray as $k=>$v){ //小结果集

    $a = 'xxx'; //逻辑处理
    $a = 'xxx'; //逻辑处理
    $a = 'xxx'; //逻辑处理
    $a = 'xxx'; //逻辑处理

    foreach ($kid as $mm=>$kk){ //大结果集合
        $data[$i][$mm]['a'] = $kk;
        $data[$i][$mm]['a'] = intval($k);
        $data[$i][$mm]['a'] = $v['a'];
        $data[$i][$mm]['a'] = $v['a'];
        
        $data[$i][$mm]['a'] = $a;
        $data[$i][$mm]['a'] = $a;
        $data[$i][$mm]['a'] = $a;
        
    }
    $i ++;
}

for ($b = 0;$b < $countTime;$a++) {
    $stime = strtotime($stimearr[$b]);
    $etime = strtotime($etimearr[$b]);
    foreach ($data as $k=>$v){
        foreach ($v as $kk=>$vv){
            $data[$k][$kk] = array_merge($data[$k][$kk],['starttime'=>$stime,'endtime'=>$etime]);
        }
        //插入数据
        $allin = $this->model->table('pp')->addALL($data[$k]);
    }
}