Java慢查询排查与性能调优完整实战指南

timeline
    title 故障时间轴
    00:00 : 监控系统首次告警
    00:05 : 数据库连接池使用率突破90%
    00:08 : 网关开始出现503错误
    00:12 : 自动扩容触发
    00:15 : 人工介入排查

// 监控工具清单
public class TroubleshootingTools {
    String[] tools = {
        "SkyWalking 8.7.0", 
        "Arthas 3.6.7",
        "Prometheus + Grafana",
        "MySQL Slow Query Log"
    };
}

-- 问题SQL示例
EXPLAIN SELECT * FROM member_info 
WHERE status = 1 
ORDER BY create_time DESC 
LIMIT 10000, 20;

-- 优化后SQL（基于ID分页）
SELECT * FROM member_info 
WHERE status = 1 AND id > #{lastId}
ORDER BY id ASC 
LIMIT 20;

-- 新增复合索引
ALTER TABLE member_info 
ADD INDEX idx_status_createtime (status, create_time);

-- 改写SQL
SELECT * FROM member_info 
WHERE status = 1 
ORDER BY create_time DESC 
LIMIT 20;

public interface MemberMapper {
    // 旧方法（问题代码）
    @Select("SELECT * FROM member_info WHERE status = #{status} LIMIT #{offset}, #{limit}")
    List<Member> listByPage(@Param("status") int status, 
                          @Param("offset") int offset,
                          @Param("limit") int limit);

    // 新方法（优化后）
    @Select("SELECT * FROM member_info WHERE status = #{status} AND id > #{lastId} ORDER BY id ASC LIMIT #{limit}")
    List<Member> listByCursor(@Param("status") int status,
                            @Param("lastId") long lastId,
                            @Param("limit") int limit);
}

public PageResult<Member> getMemberList(int pageSize, Long lastId) {
    // 游标分页查询
    List<Member> members = memberMapper.listByCursor(1, lastId, pageSize);
    
    // 获取下一页的游标
    Long nextLastId = members.isEmpty() ? null : members.get(members.size()-1).getId();
    
    return new PageResult<>(members, nextLastId);
}

# my.cnf 慢查询配置
slow_query_log = 1
slow_query_log_file = /var/log/mysql/mysql-slow.log
long_query_time = 1
log_queries_not_using_indexes = 1