[jira] [Created] (KUDU-3193) Per-tablet histogram for scan predicate efficiency

["Andrew Wong (Jira)" <ji...@apache.org>]

Andrew Wong created KUDU-3193:
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             Summary: Per-tablet histogram for scan predicate efficiency
                 Key: KUDU-3193
                 URL: https://issues.apache.org/jira/browse/KUDU-3193
             Project: Kudu
          Issue Type: Task
          Components: metrics, ops-tooling, perf, tablet
            Reporter: Andrew Wong


Often times slow queries can be the result of a sub-optimal schema for a given workload, e.g. if a scan's predicate is not on a prefix of the primary key. Diagnosing such issues typically takes some understanding of the workloads that are being run against a given table. It'd be nice if there were something more quantitative to understand whether a table(t)'s schema is to blame for a slow scan.

One thought that comes to mind is maintaining a histogram metric per-tablet of the ratio between the number of rows returned during a given and the number of rows iterated through during that scan. A consistently low value of this metric would indicate that predicates applied to the given tablet are not very effective.



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