Please see http://answers.splunk.com/answers/188784/after-update-to-splunk-enterprise-62-why-does-the.html for the answer.
To Summarize: It is a product defect, I believe for the deployment monitor. Cause: In Splunk Enterprise 6.2, indexers are logging new events to metrics.log/group=tcpin_connections to record forwarder connection events, such as a connection closing.
Fix is to change macros.conf in deployment monitor. Details are here
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