An example Analysis of predicate push-down in Hive

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Predicate pushdown

The default generated execution plan executes the filter in a visible location, but in some cases, some filter expressions can be pushed closer to the operator that first saw this particular data.

For example, the following query:

Select

A. *

B. *

From

A join b on (a.col1 = b.col1)

Where a.col1 > 15 and b.col2 > 16

If there is no predicate push-down, the filter condition * * (a.col1 > 15 and b.col2 > 16) * * will be executed after the JOIN processing is completed. Therefore, in this case, JOIN will occur first, and more rows may be generated, and then the filtering operation will be performed.

Using predicate pushdown, these two predicates * * (a.col1 > 15 and b.col2 > 16) * * will be processed before JOIN, so it may filter out most of the data rows processed earlier in the connection from an and b, so it is recommended that you enable predicate pushdown.

You can enable predicate push-down by setting hive.optimize.ppd to true.

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