littlehorse-eng commented on code in PR #13082:
URL: https://github.com/apache/kafka/pull/13082#discussion_r1101981008
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docs/streams/developer-guide/config-streams.html:
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@@ -778,10 +778,21 @@ <h4><a class="toc-backref"
href="#id34">rack.aware.assignment.tags</a><a class="
<span id="streams-developer-guide-max-warmup-replicas"></span><h4><a
class="toc-backref" href="#id29">max.warmup.replicas</a><a class="headerlink"
href="#max-warmup-replicas" title="Permalink to this headline"></a></h4>
<blockquote>
<div>
- The maximum number of warmup replicas (extra standbys beyond the
configured num.standbys) that can be assigned at once for the purpose of keeping
- the task available on one instance while it is warming up on
another instance it has been reassigned to. Used to throttle how much extra
broker
- traffic and cluster state can be used for high availability.
Increasing this will allow Streams to warm up more tasks at once, speeding up
the time
- for the reassigned warmups to restore sufficient state for them
to be transitioned to active tasks. Must be at least 1.
+ <p>
+ The maximum number of warmup replicas (extra standbys beyond
the configured num.standbys) that can be assigned at once for the purpose of
keeping
+ the task available on one instance while it is warming up on
another instance it has been reassigned to. Used to throttle how much extra
broker
+ traffic and cluster state can be used for high availability.
Increasing this will allow Streams to warm up more tasks at once, speeding up
the time
+ for the reassigned warmups to restore sufficient state for
them to be transitioned to active tasks. Must be at least 1.
+ </p>
+ <p>
+ Note that one warmup replica corresponds to one Stream Task.
Furthermore, note that each warmup replica can only be promoted to an active
Task during
+ a rebalance (normally a Probing Rebalance, which occur at a
frequency specified by the
+ <code class="docutils literal"><span
class="pre">probing.rebalance.interval.ms</span></code> config). This means
that the
+ maximum rate at which Stream Tasks can be migrated from
over-burdened Streams Instances to fresher Streams Instances can be determined
by
+ (<code class="docutils literal"><span
class="pre">max.warmup.replicas</span></code> /
+ <code class="docutils literal"><span
class="pre">probing.rebalance.interval.ms</span></code>). If it takes longer
than the probing rebalance interval
+ for the data for a Task to be migrated, then that rate will be
lower.
Review Comment:
Thanks for the review!
What I meant here is that, if it takes a long time (eg. 60 minutes) for a
Task to catch up, then decreasing the probing rebalance interval from, let's
say, 30 minutes to 10 minutes won't have any effect on the speed at which you
catch up.
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