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Posted to reviews@spark.apache.org by "LuciferYang (via GitHub)" <gi...@apache.org> on 2023/10/19 07:55:21 UTC
[PR] [SPARK-45605][CORE][SQL][SS][CONNECT][MLLIB][EXAMPLES] Replace `s.c.MapOps.mapValues` with `s.c.MapOps.view.mapValues` [spark]
LuciferYang opened a new pull request, #43448:
URL: https://github.com/apache/spark/pull/43448
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Re: [PR] [SPARK-45605][CORE][SQL][SS][CONNECT][MLLIB][GRAPHX][DSTREAM][PROTOBUF][EXAMPLES] Replace `s.c.MapOps.mapValues` with `s.c.MapOps.view.mapValues` [spark]
Posted by "LuciferYang (via GitHub)" <gi...@apache.org>.
LuciferYang commented on code in PR #43448:
URL: https://github.com/apache/spark/pull/43448#discussion_r1411850758
##########
common/sketch/src/test/scala/org/apache/spark/util/sketch/CountMinSketchSuite.scala:
##########
@@ -56,7 +56,7 @@ class CountMinSketchSuite extends AnyFunSuite { // scalastyle:ignore funsuite
val exactFreq = {
val sampledItems = sampledItemIndices.map(allItems)
- sampledItems.groupBy(identity).mapValues(_.length.toLong)
+ sampledItems.groupBy(identity).view.mapValues(_.length.toLong)
Review Comment:
Yes, Agree with your point of view, I will do this thing.
##########
common/sketch/src/test/scala/org/apache/spark/util/sketch/CountMinSketchSuite.scala:
##########
@@ -56,7 +56,7 @@ class CountMinSketchSuite extends AnyFunSuite { // scalastyle:ignore funsuite
val exactFreq = {
val sampledItems = sampledItemIndices.map(allItems)
- sampledItems.groupBy(identity).mapValues(_.length.toLong)
+ sampledItems.groupBy(identity).view.mapValues(_.length.toLong)
Review Comment:
Yes, Agree with your point, I will do this thing.
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Re: [PR] [SPARK-45605][CORE][SQL][SS][CONNECT][MLLIB][GRAPHX][DSTREAM][PROTOBUF][EXAMPLES] Replace `s.c.MapOps.mapValues` with `s.c.MapOps.view.mapValues` [spark]
Posted by "LuciferYang (via GitHub)" <gi...@apache.org>.
LuciferYang commented on code in PR #43448:
URL: https://github.com/apache/spark/pull/43448#discussion_r1411568249
##########
common/sketch/src/test/scala/org/apache/spark/util/sketch/CountMinSketchSuite.scala:
##########
@@ -56,7 +56,7 @@ class CountMinSketchSuite extends AnyFunSuite { // scalastyle:ignore funsuite
val exactFreq = {
val sampledItems = sampledItemIndices.map(allItems)
- sampledItems.groupBy(identity).mapValues(_.length.toLong)
+ sampledItems.groupBy(identity).view.mapValues(_.length.toLong)
Review Comment:
@cloud-fan
Thank you very much for pointing this out, it's a great observation.
Let me explain first, in Scala 2.13, changing to use `.transform` would change the semantics,
```
sampledItems.groupBy(identity).mapValues(_.length.toLong)
```
and
```
sampledItems.groupBy(identity).view.mapValues(_.length.toLong)
```
both return a `MapView`.
While
```
sampledItems.groupBy(identity).transform((_, v) => v.length.toLong)
```
returns a `Map`.
The main difference between `MapView` and `Map` lies in their computation methods and memory usage:
- `MapView` is a kind of lazy computation collection view, it does not immediately calculate the result, but calculates when needed. This means that if you create a `MapView` but don't actually use it, the related calculations will not occur. This can improve performance when dealing with large data sets, as it can avoid unnecessary calculations. However, each time `MapView` is accessed, the calculation will be performed again, which may lead to performance degradation, especially in cases where multiple accesses are required.
- On the other hand, `Map` is an immediate computation collection, it calculates all the results at creation and stores the results in memory. This means that whether or not you actually use this `Map`, the related calculations will occur. This may lead to higher memory usage, but in cases where the same `Map` needs to be accessed multiple times, it can provide better performance because the results have been calculated and stored in memory, no need to recalculate each time it is accessed.
I will keep an eye on this case and adjust the cases where `Map` is suitable for use.
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Re: [PR] [SPARK-45605][CORE][SQL][SS][CONNECT][MLLIB][GRAPHX][DSTREAM][PROTOBUF][EXAMPLES] Replace `s.c.MapOps.mapValues` with `s.c.MapOps.view.mapValues` [spark]
Posted by "srowen (via GitHub)" <gi...@apache.org>.
srowen closed pull request #43448: [SPARK-45605][CORE][SQL][SS][CONNECT][MLLIB][GRAPHX][DSTREAM][PROTOBUF][EXAMPLES] Replace `s.c.MapOps.mapValues` with `s.c.MapOps.view.mapValues`
URL: https://github.com/apache/spark/pull/43448
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Re: [PR] [SPARK-45605][CORE][SQL][SS][CONNECT][MLLIB][GRAPHX][DSTREAM][PROTOBUF][EXAMPLES] Replace `s.c.MapOps.mapValues` with `s.c.MapOps.view.mapValues` [spark]
Posted by "srowen (via GitHub)" <gi...@apache.org>.
srowen commented on PR #43448:
URL: https://github.com/apache/spark/pull/43448#issuecomment-1784127322
Merged to master
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Re: [PR] [SPARK-45605][CORE][SQL][SS][CONNECT][MLLIB][GRAPHX][DSTREAM][PROTOBUF][EXAMPLES] Replace `s.c.MapOps.mapValues` with `s.c.MapOps.view.mapValues` [spark]
Posted by "LuciferYang (via GitHub)" <gi...@apache.org>.
LuciferYang commented on PR #43448:
URL: https://github.com/apache/spark/pull/43448#issuecomment-1784067639
cc @HyukjinKwon @srowen FYI
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Re: [PR] [SPARK-45605][CORE][SQL][SS][CONNECT][MLLIB][EXAMPLES] Replace `s.c.MapOps.mapValues` with `s.c.MapOps.view.mapValues` [spark]
Posted by "LuciferYang (via GitHub)" <gi...@apache.org>.
LuciferYang commented on PR #43448:
URL: https://github.com/apache/spark/pull/43448#issuecomment-1770267852
Please wait while I manually validate the modifications to the examples.
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Re: [PR] [SPARK-45605][CORE][SQL][SS][CONNECT][MLLIB][GRAPHX][DSTREAM][PROTOBUF][EXAMPLES] Replace `s.c.MapOps.mapValues` with `s.c.MapOps.view.mapValues` [spark]
Posted by "cloud-fan (via GitHub)" <gi...@apache.org>.
cloud-fan commented on code in PR #43448:
URL: https://github.com/apache/spark/pull/43448#discussion_r1410982798
##########
common/sketch/src/test/scala/org/apache/spark/util/sketch/CountMinSketchSuite.scala:
##########
@@ -56,7 +56,7 @@ class CountMinSketchSuite extends AnyFunSuite { // scalastyle:ignore funsuite
val exactFreq = {
val sampledItems = sampledItemIndices.map(allItems)
- sampledItems.groupBy(identity).mapValues(_.length.toLong)
+ sampledItems.groupBy(identity).view.mapValues(_.length.toLong)
Review Comment:
I'm not a Scala expert, but `.view.mapValues` looks verbose to me. I feel the deprecated method is actually better. It's annoying to see the compilation warnings about deprecated API, how about we use `.transform` for these cases?
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Re: [PR] [SPARK-45605][CORE][SQL][SS][CONNECT][MLLIB][GRAPHX][DSTREAM][PROTOBUF][EXAMPLES] Replace `s.c.MapOps.mapValues` with `s.c.MapOps.view.mapValues` [spark]
Posted by "cloud-fan (via GitHub)" <gi...@apache.org>.
cloud-fan commented on code in PR #43448:
URL: https://github.com/apache/spark/pull/43448#discussion_r1411844730
##########
common/sketch/src/test/scala/org/apache/spark/util/sketch/CountMinSketchSuite.scala:
##########
@@ -56,7 +56,7 @@ class CountMinSketchSuite extends AnyFunSuite { // scalastyle:ignore funsuite
val exactFreq = {
val sampledItems = sampledItemIndices.map(allItems)
- sampledItems.groupBy(identity).mapValues(_.length.toLong)
+ sampledItems.groupBy(identity).view.mapValues(_.length.toLong)
Review Comment:
As an early Spark contributor, I can bet that when most people write `.mapValue`, they never consider this lazy thing but just treat it the same as `Seq.map`.
For example, this is a test, who cares if the map is lazy or not?
@LuciferYang can you help to go through all the changes in this PR, and identify the places that do need a lazy map?
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