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From "Gary Gregory (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (LOG4J2-1630) Unit of Work Logging
Date Sat, 08 Oct 2016 17:41:20 GMT

    [ https://issues.apache.org/jira/browse/LOG4J2-1630?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15558395#comment-15558395

Gary Gregory commented on LOG4J2-1630:

The EventBuffer is starting to sound like a CollectionAppender or a data structure a CollectionAppender
would use...

> Unit of Work Logging
> --------------------
>                 Key: LOG4J2-1630
>                 URL: https://issues.apache.org/jira/browse/LOG4J2-1630
>             Project: Log4j 2
>          Issue Type: Story
>          Components: API, Core, Filters
>    Affects Versions: 2.7
>            Reporter: Remko Popma
>             Fix For: 2.8
> h3. Intent
> Provide a way to filter log events, where the decision on whether to discard the message
or actually log them cannot be made until after the application has already logged the message.
> h3. Motivation
> In many systems, particularly event processing applications, log files contain a lot
of repetitive log messages. Suppose an application needs to do some calculation to decide
whether or not to react to some event, and a lot of detail is logged during this calculation.
Imagine that 99% of the time, the application decides to take no action. Once the application
arrived at that conclusion it would be nice if we could go back and undo all the detailed
logging and print a summary instead. When the application _does_ decide to take some action,
however, we _do_ want the detailed log messages. 
> A Unit of Work for logging would allow us to group a set of log messages and either discard
them or log them together. (Inspired by Martin Fowler's [Unit of Work|http://martinfowler.com/eaaCatalog/unitOfWork.html]
> This should result in log files where a lot of the "uninteresting" logging is filtered
out, significantly reducing the amount of data logged.
> Some applications do this in an ad hoc manner, for example by passing a Collection to
its components, where these components can add log message strings to this Collection. When
the discard/retain decision is made, the application then either clears the Collection or
logs the contents of the Collection. This works, but having to pass the Collection down the
component tree is clunky and the result often omits details like logger name, timestamp and
other details that come for free with normal logging. Log4j can provide a reusable and less
intrusive way to accomplish this.
> h3. How it works
> There would need to be some API for the application to mark the _start_ of the unit of
work, and some API to signal whether the log messages that are part of that unit of work need
to be _discarded_ or _logged_ (retained).
> Not all logging that occurs after a unit of work was started is part of that unit of
work. The application may want some messages to be logged regardless of whether the unit of
work was discarded or not. There needs to be a flexible way (or multiple ways) to include
or exclude logging statements from the unit of work. 
> The application may also designate multiple units of work, which may be sequential, nested
or partially overlapping. Each unit of work may define its own rules for which log messages
are considered included in or excluded from the unit of work.

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