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Kafka, mail # user - race condition with log flush interval settings...


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Re: race condition with log flush interval settings...
Jun Rao 2013-03-28, 15:11
Jason,

Could you file a jira so that we can track it?

Thanks,

Jun

On Thu, Mar 28, 2013 at 12:43 AM, Jason Rosenberg <[EMAIL PROTECTED]> wrote:

> It looks like there is a race condition between the settings for the 2
> properties:  log.default.flush.scheduler.interval.ms &
> log.default.flush.interval.ms.  I'm using 0.7.2.
>
> By default, both of these get set to 3000ms (and in the docs, it
> recommends setting flushInterval to be a multiple of the
> flushSchedulerInterval).
>
> However, the code in LogManager.flushAllLogs (which is scheduled to
> run at a fixed rate using the flushSchedulerInterval property) looks
> like this:
>
>         val timeSinceLastFlush = System.currentTimeMillis -
> log.getLastFlushedTime
>         var logFlushInterval = config.defaultFlushIntervalMs
>         ....
>         ....
>         if(timeSinceLastFlush >= logFlushInterval)
>           log.flush
>
> So, it will only flush logs if the the time since the last flush is
> longer than the flush interval.   But, the log.lastFlushedTime is not
> set until after flushing is completed (which can incur some io time).
> Thus, by enabling TRACE logging for this method, I was able to see
> that with the defaults, timeSinceLastFlush was usually about 2998
> (which is less than the logFlushInterval of 3000).  Thus, setting a
> flushInterval the same as the scheduler.flushInterval essentially
> devolves to an effective flushInterval = 2X the
> schedulerFlushInterval.
>
> So, setting a flushIinterval slightly less than the
> flushSchedulerInterval (e.g. 2500) will guarantee that the flush will
> happen on each scheduler invocation.
>
> I'm guessing that it might make sense to change the logic gating the
> flush to something like:
>
>       if(timeSinceLastFlush >= 0.90 * logFlushInterval)
>
> might be reasonable.  Also, the scheduler probably ought to use a
> 'fixedDelay' rather than a 'fixedRate' schedule.....
>
> Jason
>