Any query to a partition column should access the metastore and not the data
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Key: HIVE-2232
URL: https://issues.apache.org/jira/browse/HIVE-2232
Project: Hive
Issue Type: Improvement
Components: Metastore, Query Processor, Server Infrastructure
Reporter: Adam Kramer
Priority: Minor
The metastore contains all of the data on the possible values, etc., for all
partition columns (including subpartitions). So, any query that actually reads
or uses data from partition columns should avoid table scans.
For example:
CREATE TABLE t1 (value1 STRING) PARTITIONED ON (ds STRING, key STRING);
CREATE TABLE t2 (key STRING, value2 STRING) PARTITIONED ON (ds STRING);
...
SELECT t2.key, t1.value1, t2.value2 FROM t1 JOIN t2 ON t1.key=t2.key AND
t1.ds='2010-01-01' AND t2.ds='2010-01-01';
...ideally, the JOIN in this case would operate very very quickly without
scanning every row of t1--because every value of t1.key is in the metastore
because it is a partition column. This is just one example. Partition pruning
is another example that currently works well.
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