How Does CreateOrReplaceTempView Work In Spark?

412 Asked by AnishaDalal in Spark , Asked on Nov 17, 2022

I am new to Spark and Spark SQL.

How does createOrReplaceTempView work in Spark? If we register an RDD of objects as a table will spark keep all the data in memory?

Answered by ananya Pawar

createOrReplaceTempView creates (or replaces if that view name already exists) a lazily evaluated "view" that you can then use like a hive table in Spark SQL. It does not persist to memory unless you cache the dataset that underpins the view.

scala> val s = Seq(1,2,3).toDF("num")

s: org.apache.spark.sql.DataFrame = [num: int]

scala> s.createOrReplaceTempView("nums")

scala> spark.table("nums")

res22: org.apache.spark.sql.DataFrame = [num: int]

scala> spark.table("nums").cache

res23: org.apache.spark.sql.Dataset[org.apache.spark.sql.Row] = [num: int]

scala> spark.table("nums").count

res24: Long = 3

The data is cached fully only after the .count call. 

Related SO: spark createOrReplaceTempView vs createGlobalTempView

Relevant quote (comparing to persistent table): "Unlike the createOrReplaceTempView command, saveAsTable will materialise the contents of the DataFrame and create a pointer to the data in the Hive metastore." from https://spark.apache.org/docs/latest/sql-programming-guide.html#saving-to-persistent-tables

Note : createOrReplaceTempView was formerly registerTempTable

How Does CreateOrReplaceTempView Work In Spark?

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