Has the block sampling feature been added to one of the latest (Hive 0.8 or
Hive 0.9) releases. The wiki has the blurb below on block sampling
Block Sampling
It is a feature that is still on trunk and is not yet in any release version.
block_sample: TABLESAMPLE (n PERCENT)
This will allow Hive to pick up at least n% data size (notice it doesn't
necessarily mean number of rows) as inputs. Only CombineHiveInputFormat is
supported and some special compression formats are not handled. If we fail to
sample it, the input of MapReduce job will be the whole table/partition. We do
it in HDFS block level so that the sampling granularity is block size. For
example, if block size is 256MB, even if n% of input size is only 100MB, you
get 256MB of data.
In the following example the input size 0.1% or more will be used for the query.
SELECT *
FROM source TABLESAMPLE(0.1 PERCENT) s;
Sometimes you want to sample the same data with different blocks, you can
change this seed number:
set hive.sample.seednumber=<INTEGER>;
