clintropolis commented on a change in pull request #8116: remove unnecessary 
lock in ForegroundCachePopulator leading to a lot of contention
URL: https://github.com/apache/incubator-druid/pull/8116#discussion_r306461099
 
 

 ##########
 File path: docs/content/configuration/index.md
 ##########
 @@ -1176,6 +1176,8 @@ You can optionally configure caching to be enabled on 
the peons by setting cachi
 |`druid.realtime.cache.useCache`|true, false|Enable the cache on the 
realtime.|false|
 |`druid.realtime.cache.populateCache`|true, false|Populate the cache on the 
realtime.|false|
 |`druid.realtime.cache.unCacheable`|All druid query types|All query types to 
not cache.|`["groupBy", "select"]`|
+|`druid.realtime.cache.numBackgroundThreads`|If greater than 0, cache will be 
populated in the background thread pool of the configured size. By default 
cache is populated in the foreground, which can more efficiently handle 
reaching `maxEntrySize` than when done in the background. Note that there is no 
load shedding for background cache population, so it can also lead to out of 
memory scenarios depending on background threadpool utilization.|0|
 
 Review comment:
   There is also already [this caching doc 
page](https://github.com/apache/incubator-druid/blob/master/docs/content/querying/caching.md)
 which might be appropriate for such future docs?

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