pzhdfy commented on a change in pull request #6988: [Improvement] historical 
fast restart by lazy load columns metadata(20X faster)
URL: https://github.com/apache/incubator-druid/pull/6988#discussion_r353211479
 
 

 ##########
 File path: docs/configuration/index.md
 ##########
 @@ -1359,6 +1359,7 @@ These Historical configurations can be defined in the 
`historical/runtime.proper
 |`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 deep storage. Note that the work of loading segments involves 
downloading segments from deep storage, decompressing them and loading them to 
a memory mapped location. So the work is not all I/O Bound. Depending on CPU 
and network load, one could possibly increase this config to a higher 
value.|Number of cores|
 |`druid.segmentCache.numBootstrapThreads`|How many segments to load 
concurrently during historical startup.|`druid.segmentCache.numLoadingThreads`|
+|`druid.segmentCache.lazyLoadOnStart`|Whether or not to load segment columns 
metadata lazily during historical startup. When set to true, Historical startup 
time will be dramatically improved by deferring segment loading until the first 
time that segment takes part in a query, which will incur this cost 
instead.|false|
 
 Review comment:
   thx for review. docs updated

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