What is a sequence file in Hadoop?
A SequenceFile is a flat, binary file type that serves as a container for data to be used in Apache Hadoop distributed computing projects. SequenceFiles are used extensively with MapReduce.
What are the sequence files and why are they important?
Sequence files are binary files containing serialized key/value pairs. You can compress a sequence file at the record (key-value pair) or block levels. This is one of the advantage of using sequence file. Also, sequebce files are binary files, they provide faster read/write than that of text file format.
What is sequence file in Spark?
Sequence File format have become popular with HDFS. As Spark uses HDFS APIs to interact with files we can save data in Sequence file format as well as read it as long as we have some information about metadata. Here are few things that need to keep in mind while dealing with Sequence Files. Define key and value.
What is sequence file format in hive?
SequenceFiles are flat files consisting of binary key/value pairs. SequenceFile is basic file format which provided by Hadoop, and Hive also provides it to create a table. The USING sequencefile keywords let you create a SequecneFile.
How do I read a sequence file?
To read a SequenceFile using Java API in Hadoop create an instance of SequenceFile. Reader. Using that reader instance you can iterate the (key, value) pairs in the SequenceFile using the next() method. Then you can read the previously written SequenceFile using the following command.
What is ORC format?
The Optimized Row Columnar (ORC) file format provides a highly efficient way to store Hive data. It was designed to overcome limitations of the other Hive file formats. Using ORC files improves performance when Hive is reading, writing, and processing data.
What are the different sequence file formats?
DNA Sequence formats
- Plain sequence format. A sequence in plain format may contain only IUPAC characters and spaces (no numbers!).
- FASTQ format. A sequence file in FASTQ format can contain several sequences.
- EMBL format.
- FASTA format.
- GCG format.
- GenBank format.
- IG format.
- Genomatix annotation syntax.
How do you write a sequence file?
Using the createWriter() method of the SeqeunceFile you can get a writer that can then be used to write a SequenceFile. In this Java program a file from local file system is written as a SequenceFile into HDFS. To run this Java program in Hadoop environment export the class path where your .
How do you convert RDD to DF?
Converting Spark RDD to DataFrame can be done using toDF(), createDataFrame() and transforming rdd[Row] to the data frame.
What is ORC and Parquet file?
ORC files are made of stripes of data where each stripe contains index, row data, and footer (where key statistics such as count, max, min, and sum of each column are conveniently cached). Parquet is a row columnar data format created by Cloudera and Twitter in 2013.
What is RC and ORC file format?
ORC File Format Full Form is Optimized Row Columnar File Format.ORC File format provides very efficient way to store relational data then RC file,By using ORC File format we can reduce the size of original data up to 75%.Comparing to Text,Sequence,Rc file formats ORC is better. Column stored separately.
What is ORC and parquet file?
Why ORC is faster than Parquet?
ORC vs. PARQUET is more capable of storing nested data. ORC is more capable of Predicate Pushdown. ORC supports ACID properties. ORC is more compression efficient.
What is sequence format?
A sequence format defines the permitted layout and content of text in a file. This includes text tokens that define fields used in a databank. These fields include the sequence itself, the sequence identifier name and accession number, amongst others.
What is the difference between RDD and DataFrame in Spark?
3.2. RDD – RDD is a distributed collection of data elements spread across many machines in the cluster. RDDs are a set of Java or Scala objects representing data. DataFrame – A DataFrame is a distributed collection of data organized into named columns. It is conceptually equal to a table in a relational database.
Can we create RDD from DataFrame?
rdd is used to convert PySpark DataFrame to RDD; there are several transformations that are not available in DataFrame but present in RDD hence you often required to convert PySpark DataFrame to RDD. Since PySpark 1.3, it provides a property .
What is ORC file in Hadoop?
Apache ORC (Optimized Row Columnar) is a free and open-source column-oriented data storage format. It is similar to the other columnar-storage file formats available in the Hadoop ecosystem such as RCFile and Parquet.
Why ORC file format is faster?
ORC stands for Optimized Row Columnar which means it can store data in an optimized way than the other file formats. ORC reduces the size of the original data up to 75%. As a result the speed of data processing also increases and shows better performance than Text, Sequence and RC file formats.
What is sequence file in Hadoop?
Sequence file is the native binary file format supported by Hadoop so extensively used in MapReduce as input/output formats. In fact with in the Hadoop framework internally, the temporary outputs of maps are stored using SequenceFile.
What are binary files in Hadoop?
Apart from text files Hadoop framework also supports binary files. One of the binary file format in Hadoop is Sequence file which is a flat file consisting of binary key/value pairs. Since sequence file stores data in the form of serialized key/value pair so it is good for storing images, binary data.
Does Hadoop support input and output file formats?
Yes. Hadoop supports various input and output File formats, such as: TextOutputFormat – This is the default output format and it writes records as lines of text. SequenceFileOutputFormat – This is used to write sequence files when the output files need to be fed into another MapReduce job as input files.
How many Hadoop interview questions are there?
If you’re interviewing for a role within data management and analytics, you may be expected to answer questions about Hadoop, a framework that stores data. In this article, we review 16 common Hadoop interview questions and provide sample answers to help you can prepare for your next interview.