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From "Gary Gregory (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (LOG4J2-1270) Garbage-free steady-state logging
Date Fri, 12 Feb 2016 09:30:18 GMT

    [ https://issues.apache.org/jira/browse/LOG4J2-1270?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15144309#comment-15144309

Gary Gregory commented on LOG4J2-1270:

We probably create too many temporary Strings out of convenience. Some judicious use of StringBuilders
would help.

> Garbage-free steady-state logging
> ---------------------------------
>                 Key: LOG4J2-1270
>                 URL: https://issues.apache.org/jira/browse/LOG4J2-1270
>             Project: Log4j 2
>          Issue Type: New Feature
>          Components: API, Appenders, Core, Layouts, Pattern Converters
>    Affects Versions: 2.5
>            Reporter: Remko Popma
> In certain fields like finance, predictable latency is very important, and applications
in this space tend to carefully manage their object allocation to avoid unpredictable GC pauses.
As of 2.5, Log4j is not suitable to be included in such applications since it allocates new
objects while running in its steady state.
> This ticket is to investigate the feasibility of modifying some key components in Log4j
to provide a configuration that does not allocate new objects in its steady state. (Initialization
or shutdown don't need to be allocation-free.)
> To clarify, I am not proposing to make all of Log4j allocation-free. My goal is to create
an allocation-free execution path in Log4j with some reasonable subset of the Log4j functionality.
For example, make logging garbage-free if all of these conditions are met: 
> * all loggers are AsyncLoggers
> * you only use the RandomAccessFileAppender
> * you only use a PatternLayout without any regular expression replacements, without lookups
and with one of the pre-defined date formats. 
> Further restrictions may be necessary.
> AsyncLogger already has a ring buffer of pre-allocated LogEvents, so some of the work
here is already done.
> Components that currently allocate objects in the critical path:
> # (API) Logger methods with vararg parameters
> # (API) All MessageFactory implementations
> # LoggerConfig.getProperties (if non-null) - wraps in Collections.unmodifiableMap
> # RingBufferLogEvent.mergePropertiesIntoContextMap (if LoggerConfig properties is non-null)
> # LoggerConfig.callAppenders (for-each loop over CopyOnWriteArraySet creates iterator)
> # Layout.toByteArray(LogEvent) - this API makes it difficult to avoid allocating a new
byte[] array for each log event
> # AbstractStringLayout.toByteArray() - turns each LogEvent into a new String before turning
the String into a byte[] array
> # DatePatternConverter - new CachedTime if event.millis differs from previous event
> # DatePatternConverter.CachedTime - new String caching the result
> # FixedDateFormat - new char[] array
> # (FastDateFormat - for each event: new GregorianCalendar, new StringBuilder, new char[],
new String)
> # String.getBytes - creates initial byte array, CharBuffer, ByteBuffer, trimmed resulting
byte array
> The Layout API and turning Strings into bytes are probably the most tricky areas. One
advantage of restricting ourselves to async logging is that there is only a single background
thread that does all the formatting and I/O, so we don't have to worry about concurrency issues
when re-using buffers etc.

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