问题
I have a few tables on Hive and my query is trying to retrieve the data for the past x days. Hive is pruning the partitions when I use a direct date, but is doing a full table scan when using a formula instead.
select *
from f_event
where date_key > 20160101;
scanned partitions..
s3://...key=20160102 [f]
s3://...key=20160103 [f]
s3://...key=20160104 [f]
If I use a formula, say, to get the past 4 weeks of data
Select count(*)
From f_event f
Where date_key > from_unixtime(unix_timestamp()-2*7*60*60*24, 'yyyyMMdd')
This is scanning all partitions in the table.
environment : Hadoop 2.6.0, EMR, Hive on S3, Hive 1.0.0
回答1:
Hive doesn't trigger partition pruning when the filtering expression contains non-deterministic functions such as unix_timestamp().
A good reason for this was mentioned in the discussion:
Imagine a situation where you had:
WHERE partition_column = f(unix_timestamp()) AND ordinary_column = f(unix_timestamp).The right hand side of the predicate has to be evaluated at map-time, whereas you're assuming that left hand side should be evaluated at compile time, which means you have two different values of unix_timestamp() floating around, which can only end badly.
来源：https://stackoverflow.com/questions/35782664/hive-partition-pruning-on-computed-column