What is replicated join?

In a replicated join, one of the inputs is distributed to all of the nodes on the cluster that have data from the other input. Repartitioned joins are good for larger inputs, as they need less memory on each node and allow Presto to handle larger joins overall.

What are different types of joins in hive?

Type of Joins in Hive

• Inner join in Hive.
• Left Outer Join in Hive.
• Right Outer Join in Hive.
• Full Outer Join in Hive.

How do I join two big tables in hive?

If the tables don’t meet the conditions, Hive will simply perform the normal Inner Join. If both tables have the same amount of buckets and the data is sorted by the bucket keys, Hive can perform the faster Sort-Merge Join. To activate it, you have to execute the following commands: set hive.

How does Hive join work?

Hive joins are executed by MapReduce jobs through different execution engines like for example Tez, Spark or MapReduce. Joins even of multiple tables can be achieved by one job only. Since it’s first release many optimizations have been added to Hive giving users various options for query improvements of joins.

Which Hadoop component should be used if a join of dataset is required?

Apache Pig is a high-level language platform for analyzing and querying huge dataset that are stored in HDFS. Pig as a component of Hadoop Ecosystem uses PigLatin language. It is very similar to SQL. It loads the data, applies the required filters and dumps the data in the required format.

What does commodity hardware in Hadoop world mean?

The Hadoop Distributed File System (HDFS) is a distributed file system designed to run on hardware based on open standards or what is called commodity hardware. This means the system is capable of running different operating systems (OSes) such as Windows or Linux without requiring special drivers.

What is Hive semi join?

The left semi join is used in place of the IN / EXISTS sub-query in Hive. In a traditional RDBMS, the IN and EXISTS clauses are widely used whereas in Hive, the left semi join is used as a replacement of the same.

Which is the default join in Hive?

Hive supports equi joins by default. You can optimize your join by using Map-side Join or a Merge Join depending upon the size and sort order of your tables.

What is self join in Hive?

By definition, self join is a join in which a table is joined itself. Self joins are usually used only when there is a parent child relationship in the given data.

What is under replication and over replication?

Normally, over-replication is not a problem, and HDFS will automatically delete excess replicas. Thats how its balanced in this case. Under-replicated blocks are blocks that do not meet their target replication for the file they belong to.

Why pig is faster than Hive?

Especially, for all the data load related work While you don’t want to create the schema. Since it has many SQL-related functions and additionally you have cogroup function as well. It does support Avro Hadoop file format. Pig is faster than Hive.

What is replication factor in Hadoop?

Replication Factor: It is basically the number of times Hadoop framework replicate each and every Data Block. Block is replicated to provide Fault Tolerance. The default replication factor is 3 which can be configured as per the requirement; it can be changed to 2 (less than 3) or can be increased (more than 3.).

What is replication factor?

The Replication Factor (RF) is equivalent to the number of nodes where data (rows and partitions) are replicated. Data is replicated to multiple (RF=N) nodes. An RF of one means there is only one copy of a row in a cluster, and there is no way to recover the data if the node is compromised or goes down.

Is Semi join same as inner join?

A semi join differs from an inner join because an inner join will return one row of x for each matching row of y, where a semi join will never duplicate rows of x. This is a filtering join. We get a similar result as with inner_join() but the join result contains only the variables originally found in x = superheroes .

Is Semi join faster than inner join?

LEFT SEMI JOIN is better performant when compared to the INNER JOIN.

What is difference between inner join and self join?

An inner join (sometimes called a simple join) is a join of two or more tables that returns only those rows that satisfy the join condition. A self join is a join of a table to itself. This table appears twice in the FROM clause and is followed by table aliases that qualify column names in the join condition.

What is cross join and self join?

Inner join or Left join is used for self join to avoid errors. 2. Cross Join : Cross join allows us to join each and every row of both the tables. It is similar to the cartesian product that joins all the rows.

What is replica in Hadoop?

How does replication work in HDFS?

Data Replication. HDFS is designed to reliably store very large files across machines in a large cluster. It stores each file as a sequence of blocks; all blocks in a file except the last block are the same size. The blocks of a file are replicated for fault tolerance.

What are the disadvantages of Hive?

Hive does not support update and delete operation on tables. Subqueries are not supported. The latency in the apache hive query is very high. Hive is not used for real-time data querying since it takes a while to produce a result.