In addition to filtering
log events by thresholds, using logger and appender configurations,
the logging facility has filter classes to filter log events, based
on character strings and thresholds:
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filters repeated log
messages.
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filters log messages
based on a character string in the log message.
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filters log messages
based on a range of message thresholds.
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filters log messages
based on a single message threshold.
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filters log messages
based on the results of a list of other filters.
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denies log events that
did not meet the criteria of previous filters in a filter policy.
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By using filter classes
to filter messages, you can choose whether to accept or deny a log
event if a match occurs between a filter parameter and the string
or threshold in the log event.
You configure filter
classes by using the <filter> subelements within an appender
configuration.
Filters
are processed in the order in which they appear in the appender definition,
creating a filtering policy for the appender.
The results of filtering
depend on filter arguments. The AcceptOnMatch argument in the RepeatMatchFilter,
StringMatchFilter, LevelMatchFilter, and LevelRangeFilter filters
indicate whether to accept the log event if there is a match. The
following lists describe the process of deciding whether a log event
is accepted or denied:
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If the immediate previous message
(%m) is the same as the message (%m) specified in the log event and
if AcceptOnMatch is TRUE, then the appender processes the log event.
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If the previous message (%m) is
the same as the message (%m) specified in the log event and if AcceptOnMatch
is FALSE, then the appender denies the log event.
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StringMatchFilter and LevelMatchFilter
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If there is a match between the
filter string or the filter threshold (level) and the log event, and
if AcceptOnMatch is TRUE, then the appender processes the log event.
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If there is a match between the
filter string or the filter threshold (level) and the log event, and
if AcceptOnMatch is FALSE, then the appender denies the log event.
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If there is no match between the
filter and the log event, then the appender processes the next filter
in the filtering policy. If the log event has not been denied and
if there are no other filters in the filtering policy, then the appender
processes the log event.
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If there is a match between the
minimum and maximum thresholds (inclusive) in the filter and the log
event, and if AcceptOnMatch is TRUE, the appender processes the log
event.
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If there is no match, the appender
denies the log event.
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If there is a match between the
minimum and maximum thresholds (inclusive) in the filter and the log
event, and if AcceptOnMatch is FALSE, then the appender processes
the next filter in the filtering policy. If the log event has not
been denied and if there are no other filters in the filtering policy,
the appender accepts and processes the log event.
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AndFilter uses StringMatchFilter,
LevelMatchFilter, and LevelRangeFilter as arguments. The results of
these filters as arguments to the AndFilter class is the same as it
is in the individual filters.
You can include DenyAllFilter
as the last filter in the filtering policy to deny any log events
that do not meet the filtering policy for the appender.
The following example
is a simple filtering policy to log only performance messages for
the ARM subsystem:
<filter class="StringMatchFilter">
<param name="StringToMatch" value="Perf.ARM"/>
<param name="AcceptOnMatch" value="true"/>
</filter>
<filter class="DenyAllFilter">
</filter>
Note: Filter definitions are not
available in the logging facility language elements for SAS programs.