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https://issues.apache.org/jira/browse/LOG4J2-153?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13609079#comment-13609079
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Remko Popma commented on LOG4J2-153:
------------------------------------
It won't be a pain, I think.
1. includeLocation not specified:
a) sync: default = true, meaning lazy initialization, like current trunk
b) async: default = false, emphasize performance like log4j-1.x and logback
2. includeLocation="false"
a) sync: still lazy initialization, take stack trace snapshot if layout
requires it
b) async: don't take stack trace snapshot
3. includeLocation="true"
a) sync: still lazy initialization
b) async: take stacktrace snapshot before passing event to I/O thread
The logger knows if it is sync or async so it can just Do The Right Thing.
> Async Logger/Appender performance improvement: provide mechanism to discover
> if location StackTraceElement is actually required downstream.
> -------------------------------------------------------------------------------------------------------------------------------------------
>
> Key: LOG4J2-153
> URL: https://issues.apache.org/jira/browse/LOG4J2-153
> Project: Log4j 2
> Issue Type: Improvement
> Reporter: Remko Popma
>
> (update 2013 Feb 4: changed summary.
> Previous title: Add a method to the Layout interface to allow Loggers to
> discover if any of their Appenders need the location StackTraceElement.)
> ----
> Use Case: any asynchronous Logger or Appender has this problem:
> should it take a snapshot of the call stack (as implemented in
> Log4jLogEvent.getSource) or not?
> This is an expensive method (1600+ nanoseconds on a machine with 2.9GHz
> cores) so you only want to call it if you need it. Currently there is no way
> to discover if the location information is used by any of the configured
> layouts.
> If the Layout interface has a method that indicates whether the layout calls
> the LogEvent.getSource method, then the Logger can query its LoggerConfig if
> any of the configured Appenders has a Layout which needs location info.
> (Maybe boolean needsLocationInfo() would be a good name?)
> With this information, a Logger can construct Log4jLogEvents with a non-null
> dummy StackTraceElement location if none of the layouts downstream need
> location info. The non-null dummy location would prevent LogEvent.getSource
> from taking a call stack snapshot.
> The current AsynchAppender class would get an immediate performance boost
> from this, and custom asynchronous Loggers or Appenders would reap the same
> benefits.
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