What is COGROUP?

Spark cogroup Function In Spark, the cogroup function performs on different datasets, let’s say, (K, V) and (K, W) and returns a dataset of (K, (Iterable , Iterable )) tuples. This operation is also known as groupWith.

What is the difference between group and co Group?

The only difference between the two operators is that the group operator is normally used with one relation, while the cogroup operator is used in statements involving two or more relations.

When to use COGROUP in spark?

The GROUP and COGROUP operators are identical but GROUP is used in statements involving one relation and COGROUP is used in statements involving two or more relations. In the above example, the first bag is the tuples from the first relation with the matching key field.

What is Cogroup in Pyspark?

cogroup (other, numPartitions=None)[source] For each key k in self or other , return a resulting RDD that contains a tuple with the list of values for that key in self as well as other .

How can I join spark?

Spark DataFrame supports all basic SQL Join Types like INNER , LEFT OUTER , RIGHT OUTER , LEFT ANTI , LEFT SEMI , CROSS , SELF JOIN. Spark SQL Joins are wider transformations that result in data shuffling over the network hence they have huge performance issues when not designed with care.

How do I join RDD in spark?

RDD join can only be done in the form of key value pair. Once it is joined, the value of both RDD are nested. Becasue we need courseID to further join with course RDD, we need name for final result. We need to remap the postion of join result.

What is parameter substitution in pig?

param. Similar to regular Pig parameter substitution, you can define parameters using -param/–param_file on Pig’s command line. This variable will be treated as one of the binding variables when binding the Pig Latin script. For example, you can invoke the below Python script using: pig –param loadfile=student.

What is flatten in pig?

The FLATTEN operator which is an arithmetic operator looks like a UDF syntactically, but it is actually an operator that changes the structure of tuples and bags in a way that a UDF cannot. For tuples, flatten substitutes the fields of a tuple in place of the tuple.

Which join is faster in spark?

Sort Merge join and Shuffle Hash join are the two major power horses which drive the Spark SQL joins. Despite the fact that Broadcast joins are the most preferable and efficient one because it is based on per-node communication strategy which avoids shuffles but it’s applicable only for a smaller set of data.

What does RDD join do?

join. Return an RDD containing all pairs of elements with matching keys in self and other . Each pair of elements will be returned as a (k, (v1, v2)) tuple, where (k, v1) is in self and (k, v2) is in other .

What will happen internally during joining the two tables in spark?

Sticking to use cases mentioned above, Spark will perform (or be forced by us to perform) joins in two different ways: either using Sort Merge Joins if we are joining two big tables, or Broadcast Joins if at least one of the datasets involved is small enough to be stored in the memory of the single all executors.

What’s the difference between CoGroup and join in pig?

PIg: group vs cogroup vs join. The basic difference between JOIN and COGROUP is that with COGROUP the tuples of one data set will actually be mapped to a set/bag of tuples from the second data set whereas the join result would contain pairs of tuples from both the data sets that match on the join attribute.

What’s the difference between CoGroup and FULL OUTER JOIN?

FULL JOIN and FULL OUTER JOIN are the same. Also Please go through the below link it had detailed explanation for the full joins. The GROUP and COGROUP operators are identical but GROUP is used in statements involving one relation and COGROUP is used in statements involving two or more relations.

When to use a group or a CoGroup?

The GROUP and COGROUP operators are identical. Both operators work with one or more relations. For readability GROUP is used in statements involving one relation and COGROUP is used in statements involving two or more relations. You can COGROUP up to but no more than 127 relations at a time.

How does a co group join a data set?

Co-group joins the data set by grouping one particular data set only. It groups the elements by their common field and then returns a set of records containing two separate bags.