Informix DNS Warning
Celso Freitas de Andrade saw 'Detected slow or failing DNS service response' in the online.log of Informix 12.10.FC13. Hal Maner and SangGyu Jeong said it points to slow DNS resolution and the network administrator should check it. Andreas Legner suggested raising the NS_CACHE onconfig value (default 900 seconds), adjustable dynamically with onmode -wm/-wf.
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Hello everybody, I have an Informix 12.10.FC13 server running and lately I have been seeing the following message on my online.log: "02/24/20 13:31:02 WARNING: Detected slow or failing DNS service response 1 time(s)." Does anyone know what is this message about? Thanks, Regards ------------------------------ Celso Freitas de Andrade ------------------------------ #Informix
It is exactly what it says. Slow DNS name resolution is a huge performance problem on database connections. Have your network administrator check your DNS name resolution for your database server host and your network. This is a relatively recent (in the past couple of years to my knowledge) log message addition. We always had to check several other items to figure out the cause of slow connections. In my experience, this message in the log is accurate, so, involve your network administrator for DNS name resolution. Hal Maner M Systems International, Inc. ------Original Message------ Hello everybody, I have an Informix 12.10.FC13 server running and lately I have been seeing the following message on my online.log: "02/24/20 13:31:02 WARNING: Detected slow or failing DNS service response 1 time(s)." Does anyone know what is this message about? Thanks, Regards ------------------------------ Celso Freitas de Andrade ------------------------------ #Informix
Hello Celso, I have seen the same message from a customer using version 12.10.FC12. If you get rare warning messages, it's likely a network problem. If this happens frequently, you may want to review your DNS settings. https://www.ibm.com/support/pages/slow-connections-informix-dynamic-server-caused-dns-issues https://www.ibm.com/support/pages/possible-cause-slow-connection-database-server And I recommend reading Fernando's post when you have time. http://informix-technology.blogspot.com/2012/01/dns-impact-on-informix-impacto-do-dns.html ------------------------------ SangGyu Jeong Software Engineer Infrasoft Seoul Korea, Republic of ------------------------------
In case of network not changing frequently and only a known set of applications, from known set of hosts, connecting to Informix, you might want to be more independent from DNS (and maybe temporary glitches) by taking advantage of DNS caching which can be done on OS as well as on Informix level.
On Informix level you're configuring the Name Service Cache through NS_CACHE onconfig parameter, defaulting to 900 seconds (15 minutes) cache entry expiration time for each type of cache, i.e. a new DNS call would be required (and could slow you down), for a given host, every 15 minutes.
Nothing should keep you from increasing the cache duration to a much higher value, and should you eventually have a need to expire and re-load some outdated cached information, you can temporarily lower this dynmaically, even to zero seconds (disabling a cache), at any time (onmode -w{m|f}).
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Andreas Legner
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