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
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SELECT sysdate snap_time,a.inst_ID "INSTANCE", A.VALUE "GC BLOCKS LOST",
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B.VALUE "GC CUR BLOCKS SERVED",
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C.VALUE "GC CR BLOCKS SERVED",
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round(A.VALUE/(B.VALUE+C.VALUE+0.01),2) RATIO
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FROM GV$SYSSTAT A, GV$SYSSTAT B, GV$SYSSTAT C
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WHERE A.NAME='gc blocks lost' AND
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B.NAME='gc current blocks served' AND
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C.NAME='gc cr blocks served' and
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B.INST_ID=a.inst_id AND
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C.INST_ID = a.inst_id
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order by 2;
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select a.inst_id "instance", a.value "gc blocks lost",
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b.value "gc cur blocks served",
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c.value "gc cr blocks served",
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a.value/(b.value+c.value+0.01) ratio
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from gv$sysstat a, gv$sysstat b, gv$sysstat c
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where a.name='gc blocks lost' and
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b.name='gc current blocks served' and
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c.name='gc cr blocks served' and
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b.inst_id=a.inst_id and
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c.inst_id = a.inst_id ;
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select inst_id, event, total_waits,time_waited
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from gv$system_event
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where event in ('gc current block lost','gc cr block lost')
- order by inst_id, total_waits desc;
RAC 环境中 gc block lost 和私网通信性能问题的诊断 (Doc ID 1674865.1)