Jesus Camacho Rodriguez created HIVE-23530:
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Summary: Use SQL functions instead of compute_stats UDAF to
compute column statistics
Key: HIVE-23530
URL: https://issues.apache.org/jira/browse/HIVE-23530
Project: Hive
Issue Type: Improvement
Components: Statistics
Reporter: Jesus Camacho Rodriguez
Assignee: Jesus Camacho Rodriguez
Currently we compute column statistics by relying on the {{compute_stats}}
UDAF. For instance, for a given table {{tbl}}, the query to compute statistics
for columns is translated internally into:
{code}
SELECT compute_stats(c1),
compute_stats(c2),
...
FROM tbl;
{code}
{{compute_stats}} produces data for the stats available for each column type,
e.g., struct<"max":long,"min":long,"countnulls":long,...>.
This issue is to produce a query that relies purely on SQL functions instead:
{code}
SELECT max(c1), min(c1), count(case when c1 is null then 1 else null end),
...
FROM tbl;
{code}
This will allow us to deprecate the {{compute_stats}} UDAF since it mostly
duplicates functionality found in those other functions. Additionally, many of
those functions already provide a vectorized implementation so the approach
could potentially improve the performance of column stats collection.
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