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From Robert Rodgers <rsrodg...@gmail.com>
Subject Re: Broker rejoin with big replica lag
Date Wed, 05 Feb 2014 22:22:13 GMT
this would be great to add to the operational section of the Kafka documentation.

On Feb 5, 2014, at 2:18 PM, Andrew Otto <otto@wikimedia.org> wrote:

>> - Increasing num.replica.fetchers (defaults is one)
> Awesome!  I just tried this one, bumped it up to 8 (12 cores on this broker box).  It
is now catching up at around 17K msgs/sec, which will mean it will finish in about 4 or 5
hours.  I’ll check up on it again tomorrow.
> That should do it,  Thanks!
> On Feb 5, 2014, at 5:04 PM, Joel Koshy <jjkoshy.w@gmail.com> wrote:
>>> topics are all caught up, but I have one high volume topic (around
>>> 40K msgs/sec) that is taking much longer.  I just took a few samples
>>> of Replica-MaxLag to see how long it would take to catch up.
>>> Currently, it is behind about 12.5 million messages and is catching
>>> up at a rate of about 1600 msgs/sec.  At that rate, it’ll take
>>> around 9 days before the replica is caught up to the leader.
>>> Is there any way to speed this up?
>> During the period your high-volume topic is under-replicated you can
>> temporarily try one or both of the following:
>> - Increasing num.replica.fetchers (defaults is one)
>> - If you don't have too many topic-partitions you can also increase
>> replica.fetch.max.bytes.
>>> Or, alternatively, I don’t actually care about this topic’s
>>> history.  It is a new topic, and I know that it doesn't yet have any
>>> consumers.  I’d be fine with instructing both brokers to drop
>>> old logs and just start from the top of the log.  I could do this by
>>> manually deleting the topic (kafka data files and in zookeeper), but
>>> to do so properly with 0.8.0 I think I’d have to shut down the
>>> whole cluster, correct?  I’d rather not do this, as another
>>> topic does have a consumer and I don’t want to lose messages for
>>> it.
>> Right - or you could do a rolling bounce and change the retention
>> settings (http://kafka.apache.org/documentation.html#brokerconfigs) of
>> that topic to something low so it gets expired and then do another
>> rolling bounce to remove the override.
>> -- 
>> Joel

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