[GitHub] [hbase] ramkrish86 commented on issue #1187: HBASE-23631 : Allow cache on write during compactions when prefetchin…

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ramkrish86 commented on issue #1187: HBASE-23631 : Allow cache on write during compactions when prefetchin…
URL: https://github.com/apache/hbase/pull/1187#issuecomment-590990341
 
 
   @Reidddddd  - I  think what you mean is that if blocks are cached on compaction is there any impact the cache usage ? Ya it is. Since this is aggressive caching probably we need bigger caches avialable for this feature to work. Say for eg if cacheOnWrite is also enabled then blocks are cached during flushes and also during compactions. So at any point of time there could be duplicate blocks in the cache thus bloating the cache. LRU will remove the old blocks anyway but still the usage is going to be more. but in clould usages (as you can see in parent JIRa) a compaction will clear all the blocks from the cache. So any scans that happens after a compaction will have high latencies. So in such cases with bigger caches this new config will help to have the blocks in cache and thus having more predictable scan latencies. Hence it was later decided (if you see the subjiras in the parent JIRA) that lets cache the index blocks also if this property and cacheOnWrite is set to true. 

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