samarthjain commented on a change in pull request #7088: Improve parallelism of
zookeeper based segment change processing
URL: https://github.com/apache/incubator-druid/pull/7088#discussion_r275021326
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File path: docs/content/configuration/index.md
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@@ -1251,7 +1251,11 @@ These Historical configurations can be defined in the
`historical/runtime.proper
|`druid.segmentCache.infoDir`|Historical nodes keep track of the segments they
are serving so that when the process is restarted they can reload the same
segments without waiting for the Coordinator to reassign. This path defines
where this metadata is kept. Directory will be created if
needed.|${first_location}/info_dir|
|`druid.segmentCache.announceIntervalMillis`|How frequently to announce
segments while segments are loading from cache. Set this value to zero to wait
for all segments to be loaded before announcing.|5000 (5 seconds)|
|`druid.segmentCache.numLoadingThreads`|How many segments to drop or load
concurrently from from deep storage.|10|
-|`druid.segmentCache.numBootstrapThreads`|How many segments to load
concurrently from local storage at startup.|Same as numLoadingThreads|
+|`druid.coordinator.loadqueuepeon.curator.numCreateThreads`|Number of threads
creating zk nodes corresponding to segments that need to be loaded or
dropped.|10|
+|`druid.coordinator.loadqueuepeon.curator.numCallbackThreads`|Number of
threads for executing callback actions associated with loading or dropping of
segments.|2|
+|`druid.coordinator.loadqueuepeon.curator.numMonitorThreads`|Number of threads
to use for monitoring deletion of zk nodes|1|
+|`druid.coordinator.curator.create.zknode.batchSize`|Number of zk nodes to
create in one iteration.|5000|
+|`druid.coordinator.curator.create.zknode.repeatDelay`|Delay before creating
next batch of zk nodes|PT1M|
Review comment:
Looks like there already is a config ```maxSegmentsInNodeLoadingQueue```
which controls how many segments queued up for a historical node to load.
http://druid.io/docs/latest/configuration/index.html#dynamic-configuration
The default value of this dynamic config is 0 meaning there is no queue and
the coordinator is going to assign segments for historicals. In practice
though, I have found that this default value ends up causing clusters to be a
bit unbalanced. In our production clusters, where we have this pull request, we
have set this value to 1000 (which is what the config documentation also
recommends).
What this means is that, we don't need to worry about batching or control
the rate at which historicals are going to download segments. The above config
is already providing that behavior. I am going to get rid off them.
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