High Recv-Q Causing Slow Response

Jiann-Ming Su su_js1 at yahoo.com
Tue Feb 22 19:16:47 UTC 2011

Running 9.6.1-P1 on CentOS 5 with 8 CPU cores.  We're anycasting our DNS service 
address.  We observe the UDP Recv-Q get as high as 109540 and 2-4 second 
response times.  The simplest fix is to simply restart the bind process.  When 
the response time is slow on the DNS service address, I can do a query against 
another address on the server, and the response time is normal, so it's 
definitely correlated to DNS service address.  The number of queries during the 
restart didn't change, so obviously the way the bind process handles it is 
different.  Is there any way to further debug this behavior? Is this a bug, and 
has it been fixed in newer versions?  Thanks for any tips and insights.


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