[IMPALA-9473] Add counts of the number of hits, misses, and cache entries

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: Impala 3.4.0
• Fix Version/s: Impala 4.0.0
• Component/s: Backend
• Epic Link: Improve data cache metrics
• Epic Color: ghx-label-13
• Assignee: Joe McDonnell
• Reporter: Joe McDonnell
• Created: 06/Mar/20 19:12
• Updated: 04/Apr/20 00:10
• Resolved: 04/Apr/20 00:10

Description

The data cache currently reports metrics about hit bytes, miss bytes, and total bytes in the cache. Since there are entries of a variety of sizes in the cache, it is useful to have the actual counts for hits, misses, and total number of entries in the cache.

The cache improves performance more by reducing the latency of requests (proportional to # of hits) than by increasing the bandwidth of transfers (proportional to # of bytes). Cache performance may improve by preferring smaller entries and thus hit bytes. It is useful to track both types of metrics.