Lightrun还可以这样用？

class="prettyprint hljs sql" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">SELECT 
    p.id as id1_1_1_,
    p.name as name2_1_1_, 
    p.birth_date as birth_da3_1_1_, 
    p.owner_id as owner_id4_1_1_, 
    p.type_id as type_id5_1_1_, 
    o.id as id1_0_0_, 
    o.first_name as first_na2_0_0_, 
    o.last_name as last_nam3_0_0_, 
    o.address as address4_0_0_, 
    o.city as city5_0_0_, 
    o.telephone as telephon6_0_0_
FROM 
    pets p 
JOIN 
    owners o ON o.id = p.owner_id 
WHERE 
    p.id IN (3, 6)
 
SELECT 
    pt.id as id1_3_0_, 
    pt.name as name2_3_0_ 
FROM 
    types pt 
WHERE 
    pt.id = 3
 
SELECT 
    pt.id as id1_3_0_, 
    pt.name as name2_3_0_ 
FROM 
    types pt 
WHERE 
    pt.id = 6

那么，为什么会有3个查询被执行，而不是只有一个？这就是臭名昭著的N+1查询问题。

使用Lightrun进行Java性能调优

虽然你可以使用集成测试来检测N+1查询问题，但有时你不能这样做，因为你被雇来分析的系统已经部署到生产中，而你还没有看到源代码。

在这种情况下，像Lightrun这样的工具就变得非常方便，因为你可以简单地动态注入一个运行时快照，这个快照只有在满足特定条件时才会被记录。

第一步是在 DefaultLoadEventListener Hibernate类的 loadFromDatasource 方法中添加一个运行时快照。

注意，快照只记录相关的 LoadEvent 的 isAssociationFetch() 方法返回 true 。这个条件允许我们捕获N+1查询问题所执行的二次查询。

现在，当加载所有姓戴维斯的宠物主人时，PetClinic应用程序会执行以下SQL查询。

class="prettyprint hljs sql" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">SELECT DISTINCT 
    o.id AS id1_0_0_,
    p.id AS id1_1_1_,
    o.first_name AS first_na2_0_0_,
    o.last_name AS last_nam3_0_0_,
    o.address AS address4_0_0_,
    o.city AS city5_0_0_,
    o.telephone AS telephon6_0_0_,
    p.name AS name2_1_1_,
    p.birth_date AS birth_da3_1_1_,
    p.owner_id AS owner_id4_1_1_,
    p.type_id AS type_id5_1_1_,
    p.owner_id AS owner_id4_1_0__,
    p.id AS id1_1_0__
FROM 
    owners o
LEFT OUTER JOIN 
    pets p ON o.id=p.owner_id
WHERE 
    o.last_name LIKE 'Davis%'
 
SELECT 
    pt.id as id1_3_0_, 
    pt.name as name2_3_0_ 
FROM 
    types pt 
WHERE 
    pt.id = 6
 
SELECT 
    pt.id as id1_3_0_, 
    pt.name as name2_3_0_ 
FROM 
    types pt 
WHERE 
    pt.id = 3
 

而在检查Lightrun快照控制台时，我们可以看到有两条记录被注册。

第一个快照看起来如下。

而第二个快照看起来是这样的。

请注意，由于大量使用了 FetchType.EAGER 策略，这两个快照对应于Spring Petclinic应用程序执行的二级查询。

结论

虽然你可以在测试过程中使用JPA关联获取验证器来检测这些N+1查询问题，但如果你的任务是分析一个你从未见过的运行时系统，那么Lightrun就是一个发现各种问题及其发生原因的伟大工具。