@Dan: Upon restart of the broker, if a segment already has data, the broker resets the firstAppendTime of the segment to the time when that segment's file handles are being loaded into memory. Thus as you correctly explained, every time you shut down a broker, the broker essentially forgets the firstAppendTime. This behavior is present in both 0.7.2 and 0.8.
As Jun said, ideally we should set firstAppendTime to the file creation time. Unfortunately Java nio can provide you provide you that information only if the underlying filesystem implementation supports the notion of file creation time. Thanks for filing the JIRA, these are good suggestions. @Jason: Thanks for pointing out that log.roll.hours is not documented on the website. This config was added late in 0.7 and we probably forgot to update the website. We have filed KAFKA-834/KAFKA-835 to update the configs and other documentation on the website in general. Please let us know if you see any other missing piece. Thanks, Swapnil On 4/27/13 2:36 PM, "Dan Frankowski" <dfran...@gmail.com> wrote: >I believe there is a separate watcher thread. The only issue is upon >restart the broker forgets when the file was created. The behavior I >described (files can be appended to infinitely) is awkward for us. We have >tried to work around it. > > >On Fri, Apr 26, 2013 at 10:32 AM, Adam Talaat <atal...@extole.com> wrote: > >> I don't know how Kafka's rollover algorithm is implemented, but this is >> common behavior for other logging frameworks. You would need a separate >> watcher/scheduled thread to rollover a log file, even if no events were >> coming in. Logback (and probably log4j, by the same author) dispenses >>with >> the watcher thread. Instead, it checks each message as it comes in and >> decides whether the message should belong in a new file. If it should, a >> rollover of the old file is triggered and the message is deposited in >>the >> new file. But no rollover will occur until a message that belongs in a >>new >> file arrives. >> >> Cheers, >> Adam >> >> >> >> On Fri, Apr 26, 2013 at 9:52 AM, Jason Rosenberg <j...@squareup.com> >>wrote: >> >> > By the way, is there a reason why 'log.roll.hours' is not documented >>on >> the >> > apache configuration page: >>http://kafka.apache.org/configuration.html ? >> > >> > It's possible to find this setting (and several other undocumented >> > settings) by looking at the source code. I'm just not sure why the >> > complete set of options is not documented on the site (is it meant to >>be >> > experimental?). >> > >> > Jason >> > >> > >> > On Fri, Apr 26, 2013 at 8:19 AM, Dan Frankowski <dfran...@gmail.com> >> > wrote: >> > >> > > https://issues.apache.org/jira/browse/KAFKA-881 >> > > >> > > Thanks. >> > > >> > > >> > > On Fri, Apr 26, 2013 at 7:40 AM, Jun Rao <jun...@gmail.com> wrote: >> > > >> > > > Yes, for low volume topic, the time-based rolling can be >>imprecise. >> > Could >> > > > you file a jira and describe your suggestions there? Ideally, we >> should >> > > set >> > > > firstAppendTime to the file creation time. However, it doesn't >>seem >> you >> > > can >> > > > get the creation time in java. >> > > > >> > > > Thanks, >> > > > >> > > > Jun >> > > > >> > > > >> > > > On Thu, Apr 25, 2013 at 11:12 PM, Dan Frankowski >><dfran...@gmail.com >> > >> > > > wrote: >> > > > >> > > > > We have high-volume topics and low-volume topics. The problem >> occurs >> > > more >> > > > > often for low-volume topics to be sure. >> > > > > >> > > > > But if my hypothesis is correct about why it is happening, here >>is >> a >> > > case >> > > > > where rolling is longer than an hour, even on a high volume >>topic: >> > > > > >> > > > > - write to a topic for 20 minutes >> > > > > - restart the broker >> > > > > - wait for 5 days >> > > > > - write to a topic for 20 minutes >> > > > > - restart the broker >> > > > > - write to a topic for an hour >> > > > > >> > > > > The rollover time was now 5 days, 1 hour, 40 minutes. You can >>make >> it >> > > as >> > > > > long as you want. Does this make sense? >> > > > > >> > > > > We would like the rollover time to be no more than an hour, >>even if >> > the >> > > > > broker is restarted, or the topic is low-volume. >> > > > > >> > > > > The cleanest way to do that might be to roll over on the hour no >> > matter >> > > > > when the file was started. That would be too fast sometimes, but >> > that's >> > > > > fine. A second way would be to embed the first append time in >>the >> > file >> > > > > name. A third way (not perfect, but an approximation at least) >> would >> > be >> > > > to >> > > > > not to write to a segment if firstAppendTime is not defined and >>the >> > > > > timestamp on the file is more than an hour old. There are >>probably >> > > other >> > > > > ways. >> > > > > >> > > > > What say you? >> > > > > >> > > > > >> > > > > On Thu, Apr 25, 2013 at 9:49 PM, Jun Rao <jun...@gmail.com> >>wrote: >> > > > > >> > > > > > That logic in 0.7.2 seems correct. Basically, firstAppendTime >>is >> > set >> > > on >> > > > > > first append to a log segment. Then, later on, when a new >>message >> > is >> > > > > > appended and the elapsed time since firstAppendTime is larger >> than >> > > the >> > > > > roll >> > > > > > time, a new segment is rolled. Is your data constantly being >> > > produced? >> > > > > > >> > > > > > Thanks, >> > > > > > >> > > > > > Jun >> > > > > > >> > > > > > >> > > > > > On Thu, Apr 25, 2013 at 12:44 PM, Dan Frankowski < >> > dfran...@gmail.com >> > > > >> > > > > > wrote: >> > > > > > >> > > > > > > We are running Kafka 0.7.2. We set log.roll.hours=1. I hoped >> that >> > > > meant >> > > > > > > logs would be rolled every hour, or more. Only, sometimes >>logs >> > that >> > > > are >> > > > > > > many hours (sometimes days) old have more data added to >>them. >> > This >> > > > > > perturbs >> > > > > > > our systems for reasons I won't get in to. >> > > > > > > >> > > > > > > Have others observed this? Is it a bug? Is there a planned >>fix? >> > > > > > > >> > > > > > > I don't know Scala or Kafka well, but I have proposal for >>why >> > this >> > > > > might >> > > > > > > happen: upon restart, a broker forgets when its log files >>have >> > been >> > > > > > > appended to ("firstAppendTime"). Then a potentially infinite >> > amount >> > > > of >> > > > > > time >> > > > > > > later, the restarted broker receives another message for the >> > > > particular >> > > > > > > (topic, partition), and starts the clock again. It will then >> roll >> > > > over >> > > > > > that >> > > > > > > log after an hour. >> > > > > > > >> > > > > > > >> > > > > > > >> > > > > > >> > > > > >> > > > >> > > >> > >> >>https://svn.apache.org/repos/asf/kafka/branches/0.7/core/src/main/scala/k >>afka/server/KafkaConfig.scalasays >> > > > > > > : >> > > > > > > >> > > > > > > /* the maximum time before a new log segment is rolled >>out */ >> > > > > > > val logRollHours = Utils.getIntInRange(props, >> "log.roll.hours", >> > > > 24*7, >> > > > > > (1, >> > > > > > > Int.MaxValue)) >> > > > > > > >> > > > > > > >> > > > > > > >> > > > > > >> > > > > >> > > > >> > > >> > >> >>https://svn.apache.org/repos/asf/kafka/branches/0.7/core/src/main/scala/k >>afka/log/Log.scalahas >> > > > > > > maybeRoll, which needs segment.firstAppendTime defined. It >>also >> > has >> > > > > > > updateFirstAppendTime() which says if it's empty, then set >>it. >> > > > > > > >> > > > > > >> > > > > >> > > > >> > > >> > >>
