使用占位符时 PDO 缓慢执行（）阶段

Question

我正在制作一些返回计数和按结果分组的 JSON 端点。对于这个端点，我使用 PDO 和命名占位符。使用命名占位符时，PHP 响应在execute 阶段最多需要六秒钟。当执行相同的查询并将值直接放入我的查询中时，响应几乎是瞬间的。

我正在更新仍然使用 mysql_query() 来使用 PDO 语句的旧代码。

    <?php
    header("Access-Control-Allow-Origin: *");
    header("Content-Type: application/json; charset=UTF-8");
    header("Access-Control-Allow-Headers: Content-Type, Access-Control-Allow-Headers, Authorization, X-Requested-With");
    $conn = new PDO('mysql:host=localhost;dbname=nameOfDB', 'username', 'password');
    $conn->setAttribute(PDO::ATTR_EMULATE_PREPARES, false);
    $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    $conn->exec("set names utf8");

    $query_slow = "SELECT t.meta as meta, count(*) as cnt 
    FROM field, repo, t, uplink, link  
    WHERE (
        repo.rp1 = field.id OR 
        repo.rp2 = field.id OR 
        repo.rp3 = field.id OR 
        repo.rp4 = field.id)
    AND repo.combination = t.meta 
    AND t.doc_id = uplink.doc_id 
    AND uplink.written = 1 
    AND uplink.link_id = link.id 
    AND field.id = :field 
    AND t.earliest > :min 
    AND t.latest < :max 
    GROUP BY t.meta 
    ORDER BY cnt desc";

    if($parameters){
        $stmt = $conn->prepare($query_slow);
        $stmt->execute($parameters);
        $data = $stmt->fetchAll(PDO::FETCH_ASSOC);
        echo json_encode($data, JSON_UNESCAPED_UNICODE );
    }

如果我执行var_dump($parameters)，则会返回以下内容：

    $parameters = array(3) {
      [":field"]=>
      int(5)
      [":min"]=>
      int(-1000)
      [":max"]=>
      int(600)
    }

这里是快速查询：

    $query_fast = "SELECT t.meta as meta, count(*) as cnt 
    FROM field, repo, t, uplink, link  
    WHERE (
        repo.rp1 = field.id OR 
        repo.rp2 = field.id OR 
        repo.rp3 = field.id OR 
        repo.rp4 = field.id)
    AND repo.combination = t.meta 
    AND t.doc_id = uplink.doc_id 
    AND uplink.written = 1 
    AND uplink.link_id = link.id 
    AND field.id=5 
    and t.earliest > -1000 
    and t.latest <600  
    GROUP BY t.meta 
    ORDER BY cnt desc";

    if(1==1){
    // I ditched the $parameters, so my execute is empty.
    $stmt = $conn->prepare($query_slow);
    $stmt->execute();
    $data = $stmt->fetchAll(PDO::FETCH_ASSOC);
    echo json_encode($data, JSON_UNESCAPED_UNICODE );
    }

slow_query 最多可能需要 6 秒才能运行。如果我运行相同的查询并填写值和一个空的execute()，我的响应几乎是即时的。我对 PDO 做错了什么？

向execute() 提供数组时，我的页面响应缓慢。使用没有参数的查询时。响应是即时的。

@RiggsFolly 要求的我的计时码：

所以我在那里运行了计时代码：

    if($parameters){
    $time_prepare = microtime(true);
    $stmt = $conn->prepare($querygraph);
    $time_pre_exec = microtime(true);
    $stmt->execute(($parameters));
    //$stmt->execute();
    $time_post_exec = microtime(true);
    $data = $stmt->fetchAll(PDO::FETCH_ASSOC);
    $time_post_fetch = microtime(true);
    echo json_encode($data, JSON_UNESCAPED_UNICODE );
    }

这是使用参数 5、-800 和 800（之前使用的相同）。我的计时码显示：

start:          1563972660.9188      (First line of the script)
prepare:        1563972660.9197        ==$time_prepare
pre execution:  1563972660.9201  ==$time_pre_exec
post execution: 1563972669.0058  ==$time_post_exec ==> 9 seconds!
post fetch:     1563972669.0058 

在没有占位符的查询上使用相同的参数时，我使用相同的查询和一个空的 execute()。我用我在准备好的语句中使用的相同值替换了占位符。时序如下：

prepare:        1563973120.2965
pre execution:  1563973120.2969      //before execution()
post execution: 1563973120.312      //after executeion()
post fetch:     1563973120.3121

Answer 1

对于那些有类似问题的人； @YourCommonSense 的建议解决了这个问题。

我必须明确使用 bindValue();现在整个执行 - 从开始到结束 - 大约需要 0.02 秒，这比我希望的要好得多。对于动态生成的查询，我将代码更改为：

$conditions = [];           //values to be inserted by type on placeholder
$parameters = [];           //kind of thing to execute in the query with the placeholder (substring of a query with a named placeholder)
$bindTypes=[];              //the type expected to be for a placeholder (the function takes this as third argument. It should be a long type (strings give errors, hence the if/else if block))
$placeholders=[];           //contains only the :placeholders. Use this to tell the bindvalue() function that you want to bind a value X to placeholder :X 

if(isset($_GET["min"])){
    $mindate = (int)$_GET["min"];
    if($mindate != ""){
        $conditions[] = 't.earliest>= :mindate';
        $parameters[] = $mindate;
        $bindTypes[] = 'int';
        $placeholders[] = ':mindate';
    }
}
if(isset($_GET["max"])){
    $maxdate= (int)$_GET["max"];
    if($maxdate!= ""){
        $conditions[] = 't.latest>= :maxdate';
        $parameters[] = $maxdate;
        $bindTypes[] = 'int';
        $placeholders[] = ':maxdate';
    }
}

if($parameters){
    $stmt = $conn->prepare($querygraph);
    for ($i=0; $i<count($placeholders); $i++) {

        if($bindTypes[$i]=='str'){// it's better to use integers as comparison 
            $stmt->bindValue($placeholders[$i], $parameters[$i], PDO::PARAM_STR);
        } else if($bindTypes[$i]=='int'){
            echo $placeholders[$i];
            $stmt->bindValue($placeholders[$i], $parameters[$i], PDO::PARAM_INT);
        }

    } 
    $stmt->execute();
    $data = $stmt->fetchAll(PDO::FETCH_ASSOC);
    echo json_encode($data, JSON_UNESCAPED_UNICODE );
}

Answer 2

绑定值并不会真正影响性能（准备好的语句确实会两次往返数据库，但性能差异确实可以忽略不计）。我宁愿建议您改用 JOIN 查询 - 这也将简化您的 WHERE 子句，可能会影响性能。

您也可以直接指定连接对象的字符集，而不必理会SET NAMES 查询。

如果查询很慢，您应该查看表的索引 - 您是否正确使用了表上的任何主键？如果是，您仍然可以向您加入的字段添加一些索引。例如，field 表的 ID 和 uplink 表的 doc_id 都应该是主键。

<?php
header("Access-Control-Allow-Origin: *");
header("Content-Type: application/json; charset=UTF-8");
header("Access-Control-Allow-Headers: Content-Type, Access-Control-Allow-Headers, Authorization, X-Requested-With");

$conn = new PDO('mysql:host=localhost;dbname=nameOfDB;charset=utf8', 'username', 'password');
$conn->setAttribute(PDO::ATTR_EMULATE_PREPARES, false);
$conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

$query = "SELECT t.meta, COUNT(*) as cnt 
          FROM field AS f 
          JOIN rep AS r
              ON f.id IN (r.rp1, r.rp2, r.rp3, r.rp4)
          JOIN t 
              ON t.meta = r.combination
          JOIN uplink AS u 
              ON u.doc_id = t.doc_id
          JOIN link AS l 
              ON l.id = u.link_id
          WHERE u.written = 1
            AND f.id = :field 
            AND t.earliest > :min 
            AND t.latest < :max 
          GROUP BY t.meta 
          ORDER BY cnt DESC 
          ");

if ($parameters) {
    $stmt = $conn->prepare($query);
    $stmt->execute($parameters);
    $data = $stmt->fetchAll(PDO::FETCH_ASSOC);
    echo json_encode($data, JSON_UNESCAPED_UNICODE);
}