Jason Dere created HIVE-18430:
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Summary: Add new determinism category for runtime constants
(current_date, current_timestamp)
Key: HIVE-18430
URL: https://issues.apache.org/jira/browse/HIVE-18430
Project: Hive
Issue Type: Bug
Components: UDF
Reporter: Jason Dere
Assignee: Jason Dere
Add a new piece of metadata to the UDFs to specify if whether a UDF is a
runtime constant. Runtime constants also exist in SQL Server, and this is
similar to Postgres' concept of STABLE functions. This metadata may be useful
for materialized views and query caching.
Some Hive functions such as the ones listed below are currently labelled as
deterministic, but really are runtime constants:
current_timestamp
current_date
current_user
current_database
The values for these functions are not deterministic between different queries
- for example current_timestamp will most likely be different every query
executed. This makes these functions ineligible for things like materialized
views or cached query results.
However the value for the current_timestamp should not change during the life
of a single query, which allows these values to be used in optimizations such
as constant folding.
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