内核超时等待机制的原理:
应用程序通过操作系统提供的系统调用接口获取资源时，在系统调用的入口参数里可以指定超时等待的最大时间，通常以毫秒为单位，内核会将其转化为系统的时钟（tick）
-Timeout waiting for core principles of mechanism: the application through the operating system
SHOW FULL COLUMNS FROM `jrk_downrecords` [ RunTime:0.001345s ]
SELECT `a`.`aid`,`a`.`title`,`a`.`create_time`,`m`.`username` FROM `jrk_downrecords` `a` INNER JOIN `jrk_member` `m` ON `a`.`uid`=`m`.`id` WHERE `a`.`status` = 1 GROUP BY `a`.`aid` ORDER BY `a`.`create_time` DESC LIMIT 10 [ RunTime:0.090842s ]
SHOW FULL COLUMNS FROM `jrk_tagrecords` [ RunTime:0.001242s ]
SELECT * FROM `jrk_tagrecords` WHERE `status` = 1 ORDER BY `num` DESC LIMIT 20 [ RunTime:0.001904s ]
SHOW FULL COLUMNS FROM `jrk_member` [ RunTime:0.001250s ]
SELECT `id`,`username`,`userhead`,`usertime` FROM `jrk_member` WHERE `status` = 1 ORDER BY `usertime` DESC LIMIT 10 [ RunTime:0.003556s ]
SHOW FULL COLUMNS FROM `jrk_searchrecords` [ RunTime:0.001082s ]
SELECT * FROM `jrk_searchrecords` WHERE `status` = 1 ORDER BY `num` DESC LIMIT 5 [ RunTime:0.003315s ]
SELECT aid,title,count(aid) as c FROM `jrk_downrecords` GROUP BY `aid` ORDER BY `c` DESC LIMIT 10 [ RunTime:0.015083s ]
SHOW FULL COLUMNS FROM `jrk_articles` [ RunTime:0.001375s ]
UPDATE `jrk_articles` SET `hits` = 1 WHERE `id` = 315596 [ RunTime:0.001228s ]
