http://docs.splunk.com/Documentation/DBX/3.1.3/DeployDBX/Createandmanagedatabaseinputs#Choose_input_type
Note that timestamps are not ideal for rising columns, though they often are the best available choice. Using a timestamp for rising column can produce the following problem conditions:
A high rate of event generation can cause data duplication or loss, because checkpointing in a stream of timestamp-distinguished records assumes there is never more than one row created in a given time. If you set the time to a one second level of resolution and get five records per second, you lose or duplicate four records from every run.
Clock skew, NTP skew corrections, physical moves between timezones, and daylight savings events can cause data mis-ordering, duplication, or loss. If the skew is towards the future, then the resulting checkpoint value may temporarily or permanently stop data collection.
Non-numeric datetime values cannot be evaluated numerically, and lexical sorting can produce unpredictable results. If time series data is ordered lexically, then the resulting checkpoint value may temporarily or permanently stop data collection.
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