性能问题解决案例01sybase数据库内存问题
最近现场反馈问题,所有电子签章页面打不开文书(pdf式),后台日志没报任何错误,效果就是空白: 1、首先想到是签章的ocx控件问题,检查ocx控件安装,发现其他电脑也打不开文书,测试页面可以直接打开pdf文档,排除控件的问题。 vcD4KPHA+CiAgICAyoaK7s9LJy
最近现场反馈问题,所有电子签章页面打不开文书(pdf格式),后台日志没报任何错误,效果就是空白:
1、首先想到是签章的ocx控件问题,检查ocx控件安装,发现其他电脑也打不开文书,测试页面可以直接打开pdf文档,排除控件的问题。喎?http://www.2cto.com/kf/ware/vc/" target="_blank" class="keylink">vcD4KPHA+CiAgICAyoaK7s9LJysfOxMrpz8LU2LP2zsrM4sHLo6y87LLpzsTK6c/C1Ni5psTco6zO0sPHysew0XBkZs7EyunPwtTYtb2xvrXYobDO0rXEzsS1taGxxL/CvNbQo6zIu7rzyrnTw29jeL/YvP608r+qzsTK6aOsvOyy6beiz9bT0LXEzsTK6cTc1f2zo8/C1Ni1vbG+tdijrNPQtcS4ybTgsrvPwtTYo6zE3M/C1Ni1vbG+tdi1xM7Eyum/ydLU1f2zo7Tyv6qho7zssulmdHC3os/WzsTK6ba8w7vOyszio6y2qM67zsrM4r7Ns/bU2rTTZnRwz8LU2NXiv+mhozwvcD4KPHA+CiAgICAzoaJmdHDPwtTY09Aysr2jrM/IyKXK/b7dv+LW0LLp0a+1vWNjYmijrNTZuPm+3WNjYmi002Z0cM/C1NijrLzssum3os/Wz8LU2MO7zsrM4qOssunRr2NjYmi3x7Ojwv2jrNfuv+zSstKqNTBzssXE3LLp0a+z9sC0o6zC/bXE0qo0oaI1t9bW06Os09DEzdDEtcS7sKOstci0/by4t9bW06OszsTK6crHv8nS1NW5yr6jrNLRvq22qM67tb3Oyszi1K3S8sHLo6yy6dGvY2NiaLXEc3Fs1rTQ0LfHs6PC/aGjPC9wPgo8cD4KICAgIDShorfWzvZzcWyjrLzyu6+683NxbM6qo7o8L3A+CjxwPgo8L3A+CjxwcmUgY2xhc3M9"brush:sql;">SELECT * FROM T_ZXLD_SYYH_FJ WHERE C_BH_SQ='76A1737D773BE344B7154AA479634FED' AND C_FJLX='syyhcx.zz.cxs.gy'
查询条件中C_BH_SQ是有索引的,理论上不应该这么慢呀,查看执行计划发现:
竟然没有用到索引,执行时间是274s。有索引却没用到,而且C_BH_SQ这个字段是主表主键,被选中概率应该非常高,怀疑是统计信息出问题了,使用
UPDATE all STATISTICS T_ZXLD_SYYH_FJ
更新统计信息,更新后执行原始sql,用了0.12s,执行计划也显示出使用了索引
问题看似解决了,但是偶尔还会出现打开非常慢(快的10s左右,慢的几分钟)的情况,怎么回事呢?检查过程中发现不仅仅这个页面偶尔慢,很多页面都偶尔非常慢,第一次打开慢,后续就很快了,等一会再打开又慢了。
查看p6spy日志发现(深颜色列是sql执行时间,只记录了执行2s以上的sql),把执行时间长的sql拿出来单独执行,很多第一次执行几十秒,第二次执行不到1s,可以确定问题原因了,系统内存较小。
sybase数据可以使用下面命令查看io情况:SET STATISTICS io ON"OFF
第一次执行结果:
第二次执行结果:
可以看到第一次从磁盘和内存都读取了内容,第二次physical reads是0,完全从内存读取当然查询快了,内存较小的话,其他查询数据读进内存后,把旧的数据从内存中清除,再查询旧数据还需要从磁盘读取到内存,所以经常出现第一次较慢,后续较快情况。最好办法就是加大内存,把常用的数据都读取到内存中缓存起来。
解决办法建议现场升级sybase到15.7,因为sybase12.5.3没有64位版本,32位最多使用内存2G,好多表都是上百万的数据,确实查询较慢。

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