Wellington Chevreuil created HBASE-28217:
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             Summary: PrefetchExecutor should not run for files from CFs that 
have disabled BLOCKCACHE
                 Key: HBASE-28217
                 URL: https://issues.apache.org/jira/browse/HBASE-28217
             Project: HBase
          Issue Type: Bug
            Reporter: Wellington Chevreuil
            Assignee: Wellington Chevreuil


HFilePReadReader relies on the return of CacheConfig.shouldPrefetchOnOpen 
return to decide if it should run the PrefetchExecutor for the files. 

Currently, CacheConfig.shouldPrefetchOnOpen returns true if 
"hbase.rs.prefetchblocksonopen" is set to true at the config, OR 
PREFETCH_BLOCKS_ON_OPEN is set to true at CF level.

There's also the CacheConfig.shouldCacheDataOnRead, which returns true if both 
hbase.block.data.cacheonread is set to true at the config AND BLOCKCACHE is set 
to true at CF level.

If BLOCKCACHE is set to false at CF level, HFilePReadReader will still run the 
PrefetchExecutor to read all the file's blocks from the FileSystem, but then 
would find out the given block shouldn't be cached. 

I believe we should change CacheConfig.shouldPrefetchOnOpen to return true only 
if CacheConfig.shouldCacheDataOnRead is also true.



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