MySQL性能不佳

Question

我的应用程序的一部分存在一个大问题。我使用的是SQLAlchemy和MySQL的组合，并且大部分的工作都很好，但是有一个痒会持续加载，有时甚至5-6分钟，载入客户列表。该表大约有3000行，这对于数据库标准来说应该是相当小的，并且我在一个稍大的表格（25k行）上有一个简单的连接。

在SQL炼金术查询如下：

last_inv = db.session.query(Sales.id).order_by(Sales.invoice_date.desc()).filter(Customer.email == Sales.email).limit(1).correlate(Customer) 
results = db.session.query(Customer, last_inv.as_scalar()).filter_by(archive=0) 

原始SQL看起来是这样的：

SELECT customer.id AS customer_id 
    , customer.first_name AS customer_first_name 
    , customer.middle_name AS customer_middle_name 
    , customer.last_name AS customer_last_name 
    , customer.email AS customer_email 
    , customer.password AS customer_password 
    , customer.address1 AS customer_address1 
    , customer.address2 AS customer_address2 
    , customer.city AS customer_city 
    , customer.state AS customer_state 
    , customer.zip AS customer_zip 
    , customer.country AS customer_country 
    , customer.phone AS customer_phone 
    , customer.cell_phone AS customer_cell_phone 
    , customer.current_plan AS customer_current_plan 
    , customer.minutes_current_plan AS customer_minutes_current_plan 
    , customer.orig_sales_id AS customer_orig_sales_id 
    , customer.sales_id AS customer_sales_id 
    , customer.team_id AS customer_team_id 
    , customer.refill_date AS customer_refill_date 
    , customer.minutes_refill_date AS customer_minutes_refill_date 
    , customer.active AS customer_active 
    , customer.archive AS customer_archive 
    , customer.imported AS customer_imported 
    , customer.ipaddress AS customer_ipaddress 
    , customer.auto_renewal AS customer_auto_renewal 
    , customer.signup_date AS customer_signup_date 
    , customer.esn AS customer_esn 
    , customer.last_update_date AS customer_last_update_date 
    , customer.last_update_by AS customer_last_update_by 
    , customer.notes AS customer_notes 
    , customer.current_pin AS customer_current_pin 
    , customer.minutes_current_pin AS customer_minutes_current_pin 
    , customer.security_pin AS customer_security_pin 
    , (SELECT sales.id 
      FROM sales 
     WHERE customer.email = sales.email 
     ORDER 
      BY sales.invoice_date DESC LIMIT 1) AS anon_1 
    FROM customer 
WHERE customer.team_id = 1 
    AND customer.archive = 0 

我已经试过无数的事情，但这是真的开始让我感到绝望。这一切都在亚马逊上运行，并且htop在运行时显示100％的MySQL使用率。 Profiler对phpmyadmin进行查询时，HeidiSQL显示它在不到两秒的时间内完成（当不在cahce中查找时），所以它不是实际的查询造成的（正如我理解的那样）。

这是EXPLAIN显示：

从phpmyadmin的

id select_type table type possible_keys key key_len ref rows Extra 
1 PRIMARY customer ALL NULL NULL NULL NULL 3621 Using where 
2 DEPENDENT SUBQUERY sales ALL NULL NULL NULL NULL 22619 Using where; Using filesort 

Profiler是here和视觉表现here。

我在EC2上运行一个m1.small实例，内存为1650MB。

我也运行了一个mysqlprofiler，以下是结果before和after我所做的优化。我的my.cnf文件是here。

我已经尝试在表上运行OPTIMIZE，但由于某种原因未优化的表的数量总是98，所以我想我做错了什么。我使用this脚本，以及phpmyadmin中的原始sql，但没有成功。

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Answer 1

尝试创建这个多列索引，这应该加快查询更多：

CREATE INDEX sales_eml_invdat ON sales(email, invoice_date); 

上三列

CREATE INDEX sales_eml_invdat_id ON sales(email, invoice_date, id); 

但只有在一个情况下

甚至当id不是主键柱。
如果id是主键，那么前一个索引就足够了。

---- ------编辑

我很抱歉，我忘了MySQL是没有那么聪明的人DBMS。
它不能自己检测到这种情况，必须明确告诉他如何去做。
请rewrtite子查询到：

SELECT sales.id 
FROM sales 
WHERE customer.email = sales.email 
ORDER BY sales.email DESC, sales.invoice_date DESC 
LIMIT 1 

这种变化使MySQL使用(email, invoice_date)指数跳过文件排序，请试试吧。