网络故障原因，超乎想象-凯发app官方网站

dba对网络知识一般比较薄弱，但影响巨大，如何诊断网络故障呢？

诊断方向：
配置了防火墙
1.网线/网卡/交换机问题
2.udp receive(rx) buffer sizes设置过小/udp buffer socket溢出
3.私网性能差并且cpu使用率高，`netstat -s` 出现packet reassembly failures。
4.网络传输坏块（corruption）导致的udp checksum errors 和/或 send (tx) / receive (rx) transmission errors
5.在通信通道中设置了不匹配的mtu的值

共有26个

select sysdate snap_time,a.inst_id "instance", a.value "gc blocks lost",
b.value "gc cur blocks served",
c.value "gc cr blocks served",
round(a.value/(b.valuec.value0.01),2) ratio
from gv$sysstat a, gv$sysstat b, gv$sysstat c
where a.name='gc blocks lost' and
b.name='gc current blocks served' and
c.name='gc cr blocks served' and
b.inst_id=a.inst_id and
c.inst_id = a.inst_id
order by 2;
select a.inst_id "instance", a.value "gc blocks lost",
b.value "gc cur blocks served",
c.value "gc cr blocks served",
a.value/(b.valuec.value0.01) ratio
from gv$sysstat a, gv$sysstat b, gv$sysstat c
where a.name='gc blocks lost' and
b.name='gc current blocks served' and
c.name='gc cr blocks served' and
b.inst_id=a.inst_id and
c.inst_id = a.inst_id ;
select inst_id, event, total_waits,time_waited
from gv$system_event
where event in ('gc current block lost','gc cr block lost')
order by inst_id, total_waits desc;

参考：
rac 环境中 gc block lost 和私网通信性能问题的诊断 (doc id 1674865.1)

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