Partitioned Hive recipes¶
This page deals with the specific case of partitioned datasets in Hive recipes. For general information about Hive recipes, see Hive recipes
If your Hive recipe is a “simple” one, ie if:
- You have only one output dataset
- Your query starts with SELECT
Then you don’t need to do anything special to deal with partitioning : your query will only run over the selected input partitions and will write directly in the requested output partition.
Even though Hive recipes look like SQL recipes, they act on HDFS datasets, which use files-based partitioning, while some SQL recipes use column-based partitioning.
What data is read at input ?¶
Each Hive recipe runs in a separate Hive environment (called a metastore). In this isolated environment, only the datasets that you declared as inputs exist as tables and only the partitions that are needed by the dependencies system are available. Therefore, you do not need to write any WHERE clause to restrict the selected partitions. Only the required partitions will be included in the query.
This is only true for Hive recipes. For traditional SQL recipes, you need to restrict what you read.
For the query
SELECT * FROM foo, Hive includes the partitioning column in the result,
even if it is not physically written on HDFS.
If you don’t want it, name all columns in the request:
SELECT a,b,c FROM foo (click the column names in the left side panel to do so quickly).
How to write data ?¶
If you have only one output dataset and your query starts with a SELECT, Data Science Studio automatically transforms it to a proper INSERT OVERWRITE statement in the proper partition.
If you want to take control over your insert (see Hive recipes) and the output datasets are partitioned, then you must explicitely write the proper INSERT OVERWRITE statement in the output partition.
The Hive syntax for writing in a partition is :
INSERT OVERWRITE TABLE output_dataset_name PARTITION (dimension='value', dimension2='value2') SELECT your_select_query
The values in the PARTITION clause must be static, i.e., they cannot be computed using the query itself. Each time the recipe is run, the values must be the ones of the partition being computed of this dataset. To automatically set the proper values depending on which partition is being built, you can use Partitioning variables substitutions
For example (supposing that the ‘customers’ dataset is partitioned by ‘date’ and ‘country’):
INSERT OVERWRITE TABLE customers PARTITION (date='$DKU_DST_date', country='$DKU_DST_country') SELECT your_select_query