How Does CreateOrReplaceTempView Work In Spark?

408    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
Note : createOrReplaceTempView was formerly registerTempTable

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