Question

我在Galera集群（3台服务器）中有一个MariaDB-tabel subject_message_new，用于注册用户已阅读邮件。我们有31000个用户和数百万条消息，因此该表非常大（现在高达150万条记录）。如果更新了消息，则必须删除所有带有$id_message的读取内容。

用户还可以将邮件复制到其他主题，以便邮件（$id_message）引用原始邮件（id_message_org），同时还必须删除该连接的原始邮件中的the-read-entry 。

这是我的MySQL表：

Kolom   Type    Commentaar
id  bigint(20) Auto nummering    
id_message  int(11)  
id_subject  int(11) NULL     
nr_user int(11)  
datetime    datetime     

Indexen
PRIMARY id
INDEX   nr_user
INDEX   id_message
INDEX   id_subject

Foreign keys
id_message  subject_message(id_message) CASCADE CASCADE
nr_user users(nr_user)  CASCADE CASCADE
id_subject  subject(id_subject) CASCADE CASCADE

我有一个PHP函数，在消息发生更改后调用

function message_new($id_message,$id_subject){
 global $conn;
 mysqli_query($conn,"DELETE FROM subject_message_new WHERE (id_message='$id_message' AND id_subject='$id_subject') OR id_message IN(SELECT id_message FROM subject_message WHERE id_message_org='$id_message')");
}

如果我将子查询拆分为2 x DELETE - 查询需要2 x 6-12秒......

此功能（查询）在制作中花费的时间长达6-12秒。有人可以告诉我如何调整这个吗？还是让它更好用？

Answer 1

问题在于删除方法中的子查询。将单个语句拆分为两个查询显然会提高性能。

DELETE FROM subject_message_new WHERE id_message ='$ id_message'AND_subject ='$ id_subject';

从subject_message_new删除smn INNER JOIN subject_message sm on smn.id_message = sm.id_message_org;

注意：我们应该尝试在执行选择，更新或删除操作
时更喜欢JOIN而不是子查询

然后在subject_message_new表的id_message和id_subject列中添加索引。并在subject_message中为列id_message_org添加索引。这肯定可以解决问题。

Answer 2

也许使用多表UPDATE/DELETE语法重写查询会有所帮助，它会是这样的：

DELETE  subject_message_new.* FROM subject_message_new
    LEFT JOIN subject_message
    ON (subject_message_new.id_message = subject_message.id_message)
    WHERE (subject_message_new.id_message='$id_message'
    AND subject_message_new.id_subject='$id_subject')
    OR  id_message.id_message_org='$id_message';

删除 - 查询花费了太多时间

2 个答案: