[jira] [Commented] (LOG4J2-1441) Asynchronous logging + immediateFlush=false appenders : potential data retention on end of batch event

["Remko Popma (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/LOG4J2-1441?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15339593#comment-15339593 ] 

Remko Popma commented on LOG4J2-1441:
-------------------------------------

Anthony, would you be willing to provide a patch?

> Asynchronous logging + immediateFlush=false appenders : potential data retention on end of batch event
> ------------------------------------------------------------------------------------------------------
>
>                 Key: LOG4J2-1441
>                 URL: https://issues.apache.org/jira/browse/LOG4J2-1441
>             Project: Log4j 2
>          Issue Type: Bug
>    Affects Versions: 2.6
>            Reporter: Anthony Maire
>         Attachments: example_LOG4J2-1441.zip, flush_fail_1441.zip
>
>
> When using asynchronous logging, suggestion is made to use immediateFlush=false for file-based appenders and rely on the end of batch detection to perform the flush, which is supposed to happen in a timely manner
> As per AsyncLogger JavaDoc
> {quote}
> For best performance, use AsyncLogger with the RandomAccessFileAppender or RollingRandomAccessFileAppender, with immediateFlush=false
> {quote}
> As per File/RandomAccessFile appenders doc on the site
> {quote}
> Flushing after every write is only useful when using this appender with synchronous loggers. Asynchronous loggers and appenders will automatically flush at the end of a batch of events, even if immediateFlush is set to false. This also guarantees the data is written to disk but is more efficient.
> {quote}
> However if there are multiple appenders for the same asynchronous mechanism (either multiple appenderRef for an AsyncAppender or multiple AsyncLoggers since they share the same disruptor instance), the last event of the batch will only flush the appenders that are actually logging it, and data on other appenders won't be flushed.
> I made a small example using 2 asynchronous loggers, same kind of issue should occur with several appenders linked to the same AsyncAppender when the last event is filtered out because of it's level or a custom filter.
> - 10 second after the start, all events are processed but the main thread will not exit because of an infinite loop
> - 2 events where processed by root logger and correctly logged in the console appender
> - only one event has been flushed to the file (the file appender is attached to root logger too)
> - I made a heap dump on the JVM, it shows that the RandomAccessFileManager internal byte buffer has pending data ( byteBuffer.position=61)



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