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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