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_r305608655
########## File path: docs/content/configuration/index.md ########## @@ -1319,6 +1321,8 @@ You can optionally only configure caching to be enabled on the Historical by set |`druid.historical.cache.useCache`|true, false|Enable the cache on the Historical.|false| |`druid.historical.cache.populateCache`|true, false|Populate the cache on the Historical.|false| |`druid.historical.cache.unCacheable`|All druid query types|All query types to not cache.|["groupBy", "select"]| +|`druid.historical.cache.numBackgroundThreads`|If greater than 0, cache will be populated in the background thread pool of the configured size|0| Review comment: I did a bit of searching and came across some stuff, but nothing conclusive. [This comment](https://github.com/apache/incubator-druid/issues/3313#issuecomment-236914678), in an issue about missing documentation, indicates what you are suggesting. But there also exists #3943 which purports to fix thread safety issues with the background cache and is more recent than the discussion in that issue. Issue #4199, which I found linked to #3943 and indicates that the problem wasn't visible with cache disabled, but ultimately seemed related to aggregator thread safety since it was marked resolved by #4304, so whether or not this is broken might tie into that? (So #3956, #4304, https://github.com/apache/incubator-druid/pull/5148#discussion_r170906998, proposal #8031, and many other related discussions.) Maybe if we document the setting as experimental and mention the potential for oom it would be ok to document? That would be my preference over leaving it undocumented unless it is truly broken always, but I haven't been able to fully determine that yet. ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: [email protected] With regards, Apache Git Services --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
