You generate a summary log file by creating a LogFormat object in the XML-based logging configuration file (logs_xml.config) using the following SQL-like aggregate operators:
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1.
Navigate to Configure > Subsystems > Logging > Custom to display the logs_xml.config file.
<Format = "%<operator(field)> : %<operator(field)>"/>
operator is one of the five aggregate operators (COUNT, SUM, AVERAGE, FIRST, LAST). You can specify more than one operator in the format line.
field is the logging field that you want to aggregate.
n is the interval in seconds between summary log entries.
Important 
3.
Define a LogObject that uses this format.
4.
Click Apply.