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Kafka >> mail # user >> large amount of disk space freed on restart


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Re: large amount of disk space freed on restart
It looks like xfs will reclaim the preallocated space for a file, after it
is closed.

Does kafka close a file after it has reached it's max size and started
writing to the next log file in sequence?  Or does it keep all open until
they are deleted, or the server quits (that's what it seems like).

I could imagine that it might need to keep log files open, in order to
allow consumers access to them.  But does it keep them open indefinitely,
after there is no longer any data to be written to them, and no consumers
are currently attempting to read from them?

Jason
On Tue, Jul 16, 2013 at 4:32 PM, Jay Kreps <[EMAIL PROTECTED]> wrote:

> Interesting. Yes it will respect whatever setting it is given for new
> segments created from that point on.
>
> -Jay
>
>
> On Tue, Jul 16, 2013 at 11:23 AM, Jason Rosenberg <[EMAIL PROTECTED]>
> wrote:
>
> > Ok,
> >
> > An update on this.  It seems we are using XFS, which is available in
> newer
> > versions of Centos.  It definitely does pre-allocate space as a file
> grows,
> > see:
> >
> >
> http://serverfault.com/questions/406069/why-are-my-xfs-filesystems-suddenly-consuming-more-space-and-full-of-sparse-file
> >
> > Apparently it's not hard-allocated space, and would be released under
> > resource pressure....seems we may need to update how we monitor disk
> space
> > usage, etc....
> >
> > But, it seems that the default log file size of 1.1Gb, causes it to jump
> to
> > preallocate an extra Gb.  So, in theory, if  I set a strategic log file
> > size to be just under the threshold that forces it to exponentially
> double
> > the size from 1Gb to 2Gb, I should be able to mostly solve this issue.
> >  E.g. use 950Mb instead of 1.1Gb max log file size.
> >
> > If I change the max log file size for a broker, and restart it, will it
> > respect the new size going forward?
> >
> > Jason
> >
> >
> > On Sun, Jul 14, 2013 at 9:44 AM, Jay Kreps <[EMAIL PROTECTED]> wrote:
> >
> > > Hey Jason,
> > >
> > > As Jun says, we haven't seen that issue and no one else has reported
> that
> > > but it sounds like a bug of some kind.
> > >
> > > In 0.7 we don't do any preallocation of anything. The only time files
> > > shrink is during recovery--we re-checksum all messages that may not
> have
> > > been flushed and if any invalid messages are found we truncate them
> off.
> > > This would only occur after an unclean shutdown (kill -9) and you would
> > get
> > > a bunch of errors in log warning you this was happening.
> > >
> > > -Jay
> > >
> > >
> > >
> > > On Sun, Jul 14, 2013 at 1:36 AM, Jason Rosenberg <[EMAIL PROTECTED]>
> > wrote:
> > >
> > > > An update on this.  It appears that the phenomenon I'm seeing is that
> > > disk
> > > > space is freed on restart, but it's not due files getting deleted on
> > > > restart, but instead files are getting truncated on restart.  It
> > appears
> > > > that log files get pre-allocated to a larger size than is used right
> > > away.
> > > >  Upon restart, they get truncated to the size of the file that
> actually
> > > > contains data.  Does this make sense?
> > > >
> > > > Before restart, I see a large number of log files size 2.1Gb.  Upon
> > > > restart, the disk space reclaimed drops to almost half that, on
> > average.
> > > >
> > > > Thoughts?
> > > >
> > > > Jason
> > > >
> > > >
> > > > On Thu, May 23, 2013 at 8:55 PM, Jun Rao <[EMAIL PROTECTED]> wrote:
> > > >
> > > > > I haven't seen this issue before. We do have ~1K topics in one of
> the
> > > > Kafka
> > > > > clusters at LinkedIn.
> > > > >
> > > > > Thanks,
> > > > >
> > > > > Jun
> > > > >
> > > > >
> > > > > On Thu, May 23, 2013 at 11:05 AM, Jason Rosenberg <
> [EMAIL PROTECTED]>
> > > > > wrote:
> > > > >
> > > > > > Yeah, that's what it looks like to me (looking at the code).  So,
> > I'm
> > > > > > guessing it's some os level caching, resource recycling.  Have
> you
> > > ever
> > > > > > heard of this happening?  One thing that might be different in my
> > > usage
> > > > > > from the norm is a relatively large number of topics (e.g. ~2K

 
NEW: Monitor These Apps!
elasticsearch, apache solr, apache hbase, hadoop, redis, casssandra, amazon cloudwatch, mysql, memcached, apache kafka, apache zookeeper, apache storm, ubuntu, centOS, red hat, debian, puppet labs, java, senseiDB