php - MongoDB $lookup 的结果非常慢

Question

我正在使用 PHP 与 MongoDB 交互，最近我在 5 个集合上使用了 $lookup ，我的查询开始需要大约 20-25 秒才能获得结果。我所有的收藏都有测试数据，不超过30-40条。我还使用了分析，但收到消息:“查询未记录(太大)”

我正在分享我的 PHP 文件中的代码。我还尝试在字段上创建索引，该索引在集合之间创建联接，但得到了相同的结果。请告诉我创建集合结构和从 MongoDB 检索数据的最佳方法。

提前致谢。

    $collection = new MongoCollection($db, 'col_main');
    $condition = array();
    $condition[] = array(
            '$lookup' => array(
                "from" => "col_a",
                "localField" => "a",
                "foreignField" => "_id",
                "as" => "col_a"
            )
        );
    $condition[] = array(
            '$lookup' => array(
                "from" => "col_b",
                "localField" => "b",
                "foreignField" => "_id",
                "as" => "col_b"
            )
        );

    $condition[] = array(
            '$lookup' => array(
                "from" => "col_c",
                "localField" => "c",
                "foreignField" => "_id",
                "as" => "col_c"
            )
        );

    $condition[] = array(
            '$lookup' => array(
                "from" => "col_e",
                "localField" => "e",
                "foreignField" => "_id",
                "as" => "col_e"
            )
        );

    $condition[] = array(
            '$lookup' => array(
                "from" => "col_f",
                "localField" => "f",
                "foreignField" => "_id",
                "as" => "col_f"
            )
        );      

    $condition[]  = array(
            '$project' => $projection
        );

    $condition[] = array ( 
                    '$unwind' => '$col_a'

                );

    $condition[] = array (
                    '$unwind' => '$col_a.translation'

                );      

    $condition[] = array ( 
                    '$unwind' => '$col_b'

                );

    $condition[] = array (
                    '$unwind' => '$col_b.translation'

                );

    $condition[] = array ( 
                    '$unwind' => '$col_c'

                );

    $condition[] = array (
                    '$unwind' => '$col_c.translation'

                );

    $condition[] = array ( 
                    '$unwind' => '$col_e'

                );

    $condition[] = array (
                    '$unwind' => '$col_e.staff_name'

                );

    $condition[] = array (
                    '$unwind' => '$col_e.staff_surname'

                );          

    $condition[] = array ( 
                    '$unwind' => '$col_f'

                );

    $condition[] = array (
                    '$unwind' => '$col_f.translation'

                );      


    //Some More conditions

        $condition[] = array(
                    '$match' => array( 'col_b.translation.language' => $val )
                );
            $condition[] = array(
                    '$match' => array( 'col_a.translation.language' => $val )
                );
            $condition[] = array(
                    '$match' => array( 'col_c.translation.language' => $val )
                );  

            $condition[] = array(
                    '$match' => array( 'col_f.translation.language' => $val )
                );              


    return  $collection->aggregate($condition);         

Answer 1

当您使用许多展开操作来乘以对象时，这可能会产生大量数据，每个 $unwind muliplayes documnet 集，因此可能会产生巨大的内存消耗，甚至交换。

如果我们有 3 个数组，每个数组有 3 个元素，那么我们将对 a、b、c 执行展开我们将得到:

• 第一步后有 3 个文档，
• 第 2 步后有 9 个文档
• 最后一步后有 27 个文档..