What is difference between sort and orderBy in Spark?
sort() is more efficient compared to orderBy() because the data is sorted on each partition individually and this is why the order in the output data is not guaranteed. On the other hand, orderBy() collects all the data into a single executor and then sorts them.
What is sorting in Spark?
Sorting in Spark is a multiphase process which requires shuffling: input RDD is sampled and this sample is used to compute boundaries for each output partition ( sample followed by collect ) input RDD is partitioned using rangePartitioner with boundaries computed in the first step ( partitionBy )
Does Spark support indexing?
The reason why indexing over external data sources is not supported by Spark is that Spark is not a data management system but a batch data processing engine. And as a consequence it cannot maintain indices.
What is a DataFrame in Spark and how is it different from a SQL table?
In Spark, a DataFrame is a distributed collection of data organized into named columns. It is conceptually equivalent to a table in a relational database or a data frame in R/Python, but with richer optimizations under the hood.
What is the difference between sort and ORDER BY?
The difference between “order by” and “sort by” is that the former guarantees total order in the output while the latter only guarantees ordering of the rows within a reducer. If there are more than one reducer, “sort by” may give partially ordered final results.
Is ORDER BY and sort by same?
3 Answers. OrderBy is just an alias for the sort function. From spark documentation, it seems that SORT BY and ORDER BY are not the same.
What is the difference between order by and sort by in hive?
Hive supports SORT BY which sorts the data per reducer. The difference between “order by” and “sort by” is that the former guarantees total order in the output while the latter only guarantees ordering of the rows within a reducer. If there are more than one reducer, “sort by” may give partially ordered final results.
How do I order DESC in spark?
In order to sort by descending order in Spark DataFrame, we can use desc property of the Column class or desc() sql function.
What is SQL indexing?
A SQL index is used to retrieve data from a database very fast. Indexing a table or view is, without a doubt, one of the best ways to improve the performance of queries and applications. A SQL index is a quick lookup table for finding records users need to search frequently.
What is hyperspace index?
Hyperspace is an early-phase indexing subsystem for Apache Spark™ that introduces the ability for users to build indexes on their data, maintain them through a multi-user concurrency mode, and leverage them automatically – without any change to their application code – for query/workload acceleration.
What is difference between DataFrame and Dataset in spark?
Conceptually, consider DataFrame as an alias for a collection of generic objects Dataset[Row], where a Row is a generic untyped JVM object. Dataset, by contrast, is a collection of strongly-typed JVM objects, dictated by a case class you define in Scala or a class in Java.
Is spark SQL different from SQL?
Spark SQL is a Spark module for structured data processing. It provides a programming abstraction called DataFrames and can also act as a distributed SQL query engine. It enables unmodified Hadoop Hive queries to run up to 100x faster on existing deployments and data.