Joe McDonnell created IMPALA-10147:
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Summary: Avoid getting a file handle for data cache hits
Key: IMPALA-10147
URL: https://issues.apache.org/jira/browse/IMPALA-10147
Project: IMPALA
Issue Type: Improvement
Components: Backend
Affects Versions: Impala 4.0
Reporter: Joe McDonnell
When reading from the data cache, the DiskIo thread first gets a file handle,
then it checks the data cache for a hit. If there is a cache hit, then the file
handle is not actually used. It is only used if there is a cache miss. There is
no real reason to have the file handle open for cache hits. It doesn't really
serve any additional purpose, and it adds overhead to cache hits.
For platforms that do not have the file handle cache, this can be a significant
overhead.
We should only open the file handle after we have checked the data cache and
know that we need to read from regular storage.
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