在使用lepus3.7监控MySQL数据库的时候，碰到了以下几个问题，本博客给出了这些问题产生的原因，以及相应的解决办法。
1. 问题1：php页面无法连接数据库
直接使用php程序执行php文件，可以连接mysql，但是在httpd中同样的php页面无法连接mysql。
lepus的web程序(PHP代码)无法连接数据库时，web界面上什么操作也无法继续。
为此编写了最简单的PDO连接测试代码：
php代码如下：
[linuxidc@linuxidc lepus]$ cat mysql.php
<?php
try{
#$dsn="mysql:host=127.0.0.1;dbname=lepus;";
$dsn="mysql:host=11.1.1.11;dbname=lepus;";
$user="coe2coe";
$pwd="XXXXXXXXXX";
$sql="select now() as a";
$dbh=new PDO($dsn,$user,$pwd);
$stmt=$dbh->prepare($sql);
$stmt->execute();
$row=$stmt->fetch(PDO::FETCH_ASSOC);
echo "result:".$row['a'];
}
catch(PDOException $e) {
echo "FAILED:".$e->getMessage();
}
?>
php程序直接执行php文件：
[linuxidc@linuxidc lepus]$ php mysql.php
result:2018-09-27 00:03:44
通过浏览器访问这个页面：
FAILED:SQLSTATE[HY000] [2003] Can't connect to MySQL server on '11.1.1.11' (13)
lepus的web程序给出的错误提示信息更加模糊。
原因：
通过一番baidu之后，终于看到了一个比较靠谱的分析。
Linux(CentOS7)的selinux安全机制禁止了httpd中的模块访问网络。
[linuxidc@linuxidc lepus]$ sudo getsebool -a |grep httpd
httpd_anon_write --> off
httpd_builtin_scripting --> on
httpd_can_check_spam --> off
httpd_can_connect_ftp --> off
httpd_can_connect_ldap --> off
httpd_can_connect_mythtv --> off
httpd_can_connect_zabbix --> off
httpd_can_network_connect --> off
httpd_can_network_connect_cobbler --> off
httpd_can_network_connect_db --> off
httpd_can_network_memcache --> off
httpd_can_network_relay --> off
httpd_can_sendmail --> off
httpd_dbus_avahi --> off
httpd_dbus_sssd --> off
httpd_dontaudit_search_dirs --> off
httpd_enable_cgi --> on
httpd_enable_ftp_server --> off
httpd_enable_homedirs --> off
httpd_execmem --> off
httpd_graceful_shutdown --> on
httpd_manage_ipa --> off
httpd_mod_auth_ntlm_winbind --> off
httpd_mod_auth_pam --> off
httpd_read_user_content --> off
httpd_run_ipa --> off
httpd_run_preupgrade --> off
httpd_run_stickshift --> off
httpd_serve_cobbler_files --> off
httpd_setrlimit --> off
httpd_ssi_exec --> off
httpd_sys_script_anon_write --> off
httpd_tmp_exec --> off
httpd_tty_comm --> off
httpd_unified --> off
httpd_use_cifs --> off
httpd_use_fusefs --> off
httpd_use_gpg --> off
httpd_use_nfs --> off
httpd_use_openstack --> off
httpd_use_sasl --> off
httpd_verify_dns --> off
解决办法：
临时办法：临时禁用SELINUX。
[linuxidc@linuxidc lepus]$ sudo setenforce 0
永久办法：修改selinux配置文件，禁用SELINUX。
[linuxidc@linuxidc lepus]$ cat /etc/selinux/config
# This file controls the state of SELinux on the system.
# SELINUX= can take one of these three values:
# enforcing - SELinux security policy is enforced.
# permissive - SELinux prints warnings instead of enforcing.
# disabled - No SELinux policy is loaded.
#SELINUX=enforcing
SELINUX=disabled
# SELINUXTYPE= can take one of three two values:
# targeted - Targeted processes are protected,
# minimum - Modification of targeted policy. Only selected processes are protected.
# mls - Multi Level Security protection.
SELINUXTYPE=targeted
验证：
再次在浏览器中访问这个php页面：
result:2018-09-27 00:09:26
2. 问题2：lepus日志中出现group by警告。
2018-09-27 01:12:41 [WARNING] check mysql 11.1.1.11:3408 failure: 1055 Expression #2 of SELECT list is not in GROUP BY clause and contains nonaggregated column 'information_schema.processlist.USER' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by
原因：
这是lepus后端监控程序写的log。
默认情况下sql_mode包含ONLY_FULL_GROUP_BY。
mysql> select @@sql_mode;
+-------------------------------------------------------------------------------------------------------------------------------------------+
| @@sql_mode |
+-------------------------------------------------------------------------------------------------------------------------------------------+
| ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION |
+-------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.01 sec)
解决办法：
去掉ONLY_FULL_GROUP_BY。
sql_mode=STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION
3. 问题3：复制监控查询不到数据。
没有查询到数据.
解决办法：
show_compatibility_56=1
4. 问题4：表空间分析没有数据。
5. 问题5:慢查询没有数据。
前提：
MySQL的my.cnf配置文件中已经配置了慢查询日志。
slow_query_log=1
long_query_time=10
log_slow_admin_statements=1
log_slow_slave_statements=1
原因：
1.lepus慢查询分析基于pecona-toolkit工具包中的pt-query-digest程序。需要先安装这个工具包。
2. pt-query-digest程序与lepus3.7建的表有点冲突。