Spark: rdd.countApprox() vs rdd.count()

spark countapprox
spark dataframe countapprox
spark countbyvalue
javadoc spark rdd
spark dataframe count rows
rdd subtract
rdd id
pyspark map

Could someone please explain the difference between RDD countApprox() vs count() and also if possible can answer which is the fastest ? it would be of great help we have a requirement where count() is very slow takes about 30 min's ** ...tried countApprox() it was **fast for the first run (**About 1.2 min) and then slowed to 30 min's .....

this is how we used it not sure if it's the best way to use

rdd.countApprox(timeout=800, confidence=0.5)

Spark: rdd.countApprox() vs rdd.count() - apache-spark - html, Could someone please explain the difference between RDD countApprox() vs count() and also if possible can answer which is the fastest ? it would be of great​  A Resilient Distributed Dataset (RDD), the basic abstraction in Spark. Represents an immutable, partitioned collection of elements that can be operated on in parallel.

Not my answer, but there is a very useful and important answer here.

In very short, countApprax.getFinalValue blocks even if this is longer than the timeout.

getInitialValue does not block and so you will get a response within the timeout.

BUT, as I learned from painful experience, even if you use getInitalValue the process will continue to final value.

If you are repeating this in a loop, the getFinalValue will be running for multiple RDDs long after you have retrieved the result from getInitialValue. This can then lead to OOM conditions and broadcast errors that are difficult to diagnose

Spark: rdd.countApprox() vs rdd.count() - apache-spark, Could someone please explain the difference between RDD countApprox() vs count() and also if possible can answer which is the fastest ? it would be of great​  Zips this RDD with another one, returning key-value pairs with the first element in each RDD, second element in each RDD, etc. Assumes that the two RDDs have the *same number of partitions* and the *same number of elements in each partition* (e.g. one was made through a map on the other).

rdd.count() is an action, which is an eager operation.

This means that all the other transformations that you had written before that will start executing now because of Spark's lazy evaluation. So, essentially its not only Count() operation that's taking all the time but, all the other operations which were waiting to get executed.

Now coming back to the question of count() vs countApprox(). Count is just like doing a select count(*) from Table. countApprox can have a timeout and confidence level which returns back a result which is approximately correct and a number you can live with.

We should use countApprox when we are more interested in knowing an approximate number and save time for example in a streaming application. Count() should be used when you need the exact count for example to log something or for auditing.

RDD (Spark 2.0.1 JavaDoc), Approximate version of count() that returns a potentially incomplete result Internal method to this RDD; will read from cache if applicable, or otherwise compute it. That is, if countApprox were called repeatedly with confidence 0.9, we would  SparkByExamples.com is a BigData and Spark examples community page, all examples are simple and easy to understand and well tested in our development environment using Scala and Maven.

Re: how to use rdd.countApprox, sparkContext.setJobGroup(jobGroupId)val approxCount = rdd. initialValue()" to get the approximate count at that point of time (that is after timeout). Or do I need to define onComplete/onFail handlers to extract count value  The following are code examples for showing how to use pyspark.sql.functions.count () . They are from open source Python projects. You can vote up the examples you like or vote down the ones you don't like. Project: datafaucet Author: natbusa File: dataframe.py MIT License. #N#def diff(df_a, df_b, exclude_cols= []): """ Returns all rows of a

Count number of rows in an RDD, As far as my experience rdd.count() is the best way to count the number of rows or to count no. of elements in an RDD. There is no faster way. Compute the size of dataset, rdd.count(), skip it maybe you know it already and take as argument. Rather then sorting the whole dataset, I will find out top(N) from each partition. For that I would have to find out N = what is N% of rdd.count, then sort the partitions and take top(N) from each partition. Now you have a much smaller dataset to sort.

Spark RDD Actions with examples, In this tutorial, we will learn RDD actions with Scala examples. //aggregate def param0= (accu:Int, v:Int) => accu + v def param1= (accu1:Int countApprox() – Return approximate count of elements in the dataset, this  Express. Match. Date. Spark is the authentic dating app powered by self expression. Available on iOS now.

Comments
  • FYI: The timeout is in milliseconds
  • How are the timeout and confidence applied? Obviously, 1ms and 1.0 (100%) confidence is something it cannot guarantee. Does one parameter take precedence? Does it wait until the confidence is met, or the timeout is reached?