[GitHub] spark pull request #22995: [SPARK-25998] [CORE] Change TorrentBroadcast to h...
Github user asfgit closed the pull request at: https://github.com/apache/spark/pull/22995 --- - To unsubscribe, e-mail: reviews-unsubscr...@spark.apache.org For additional commands, e-mail: reviews-h...@spark.apache.org
[GitHub] spark pull request #22995: [SPARK-25998] [CORE] Change TorrentBroadcast to h...
Github user bkrieger commented on a diff in the pull request:
https://github.com/apache/spark/pull/22995#discussion_r236775302
--- Diff:
core/src/main/scala/org/apache/spark/broadcast/TorrentBroadcast.scala ---
@@ -92,8 +95,15 @@ private[spark] class TorrentBroadcast[T: ClassTag](obj:
T, id: Long)
/** The checksum for all the blocks. */
private var checksums: Array[Int] = _
- override protected def getValue() = {
-_value
+ override protected def getValue() = synchronized {
--- End diff --
done
---
-
To unsubscribe, e-mail: reviews-unsubscr...@spark.apache.org
For additional commands, e-mail: reviews-h...@spark.apache.org
[GitHub] spark pull request #22995: [SPARK-25998] [CORE] Change TorrentBroadcast to h...
Github user srowen commented on a diff in the pull request:
https://github.com/apache/spark/pull/22995#discussion_r236726776
--- Diff:
core/src/main/scala/org/apache/spark/broadcast/TorrentBroadcast.scala ---
@@ -92,8 +95,15 @@ private[spark] class TorrentBroadcast[T: ClassTag](obj:
T, id: Long)
/** The checksum for all the blocks. */
private var checksums: Array[Int] = _
- override protected def getValue() = {
-_value
+ override protected def getValue() = synchronized {
--- End diff --
We need two locks, one to protect the local reference to the block, and one
to protect the shared cache object. I was thinking of the former.
---
-
To unsubscribe, e-mail: reviews-unsubscr...@spark.apache.org
For additional commands, e-mail: reviews-h...@spark.apache.org
[GitHub] spark pull request #22995: [SPARK-25998] [CORE] Change TorrentBroadcast to h...
Github user bkrieger commented on a diff in the pull request:
https://github.com/apache/spark/pull/22995#discussion_r236724749
--- Diff:
core/src/main/scala/org/apache/spark/broadcast/TorrentBroadcast.scala ---
@@ -92,8 +95,15 @@ private[spark] class TorrentBroadcast[T: ClassTag](obj:
T, id: Long)
/** The checksum for all the blocks. */
private var checksums: Array[Int] = _
- override protected def getValue() = {
-_value
+ override protected def getValue() = synchronized {
--- End diff --
Do you mean switching `TorrentBroadcast.synchronized` to
`broadcastCache.synchronized` inside `readBroadcastBlock`, or changing
`this.synchronized` to `broadcastCache.synchronized` inside `getValue()` (and
getting rid of the lock in `readBroadcastBlock`?
---
-
To unsubscribe, e-mail: reviews-unsubscr...@spark.apache.org
For additional commands, e-mail: reviews-h...@spark.apache.org
[GitHub] spark pull request #22995: [SPARK-25998] [CORE] Change TorrentBroadcast to h...
Github user srowen commented on a diff in the pull request:
https://github.com/apache/spark/pull/22995#discussion_r236721318
--- Diff:
core/src/main/scala/org/apache/spark/broadcast/TorrentBroadcast.scala ---
@@ -92,8 +95,15 @@ private[spark] class TorrentBroadcast[T: ClassTag](obj:
T, id: Long)
/** The checksum for all the blocks. */
private var checksums: Array[Int] = _
- override protected def getValue() = {
-_value
+ override protected def getValue() = synchronized {
--- End diff --
Hm, that `TorrentBroadcast.synchronized` is from a very old version of the
code in 2013, when more things used that lock. I'm pretty certain it's
obsolete. However this code accesses broadcastCache and that needs
synchronization. (It's kind of unfortunate where this object is). I think we
could actually improve this by locking on broadcastCache for basically the
whole block. I think that's a safe improvement as nothing else uses
broadcastCache, nothing else is synchronized here, and should behave just the
same.
---
-
To unsubscribe, e-mail: reviews-unsubscr...@spark.apache.org
For additional commands, e-mail: reviews-h...@spark.apache.org
[GitHub] spark pull request #22995: [SPARK-25998] [CORE] Change TorrentBroadcast to h...
Github user bkrieger commented on a diff in the pull request:
https://github.com/apache/spark/pull/22995#discussion_r23671
--- Diff:
core/src/main/scala/org/apache/spark/broadcast/TorrentBroadcast.scala ---
@@ -92,8 +95,15 @@ private[spark] class TorrentBroadcast[T: ClassTag](obj:
T, id: Long)
/** The checksum for all the blocks. */
private var checksums: Array[Int] = _
- override protected def getValue() = {
-_value
+ override protected def getValue() = synchronized {
--- End diff --
I think we can remove the `TorrentBroadcast.synchronized` in
`readBroadcastBlock`, since we're already synchronizing in its only caller?
Though I'm not sure why it was necessary in the first place, as
`readBroadcastBlock` should only have been called once before this PR.
Regardless, I agree that the perf hit should be ok. Let me know if you want
any of this changed.
---
-
To unsubscribe, e-mail: reviews-unsubscr...@spark.apache.org
For additional commands, e-mail: reviews-h...@spark.apache.org
[GitHub] spark pull request #22995: [SPARK-25998] [CORE] Change TorrentBroadcast to h...
Github user srowen commented on a diff in the pull request:
https://github.com/apache/spark/pull/22995#discussion_r236471154
--- Diff:
core/src/main/scala/org/apache/spark/broadcast/TorrentBroadcast.scala ---
@@ -92,8 +95,15 @@ private[spark] class TorrentBroadcast[T: ClassTag](obj:
T, id: Long)
/** The checksum for all the blocks. */
private var checksums: Array[Int] = _
- override protected def getValue() = {
-_value
+ override protected def getValue() = synchronized {
--- End diff --
I noticed that below, the readBroadcastBlock() method is synchronized on
the companion object, which makes me nervous. However a lazy val is also
implemented with `this.synchronized`, so I suspect this is fine. We pay the
cost of synchronization on every call now, but I think that is OK here, as a
simple flag won't help us figure out whether the SoftReference has been cleared.
---
-
To unsubscribe, e-mail: reviews-unsubscr...@spark.apache.org
For additional commands, e-mail: reviews-h...@spark.apache.org
[GitHub] spark pull request #22995: [SPARK-25998] [CORE] Change TorrentBroadcast to h...
Github user srowen commented on a diff in the pull request:
https://github.com/apache/spark/pull/22995#discussion_r236394496
--- Diff:
core/src/main/scala/org/apache/spark/broadcast/TorrentBroadcast.scala ---
@@ -93,7 +96,14 @@ private[spark] class TorrentBroadcast[T: ClassTag](obj:
T, id: Long)
private var checksums: Array[Int] = _
override protected def getValue() = {
-_value
+val memoized: T = if (_value == null) null.asInstanceOf[T] else
_value.get
--- End diff --
Hm, weird, I thought it would work based on a little local example, but
yeah leave the cast in of course.
---
-
To unsubscribe, e-mail: reviews-unsubscr...@spark.apache.org
For additional commands, e-mail: reviews-h...@spark.apache.org
[GitHub] spark pull request #22995: [SPARK-25998] [CORE] Change TorrentBroadcast to h...
Github user bkrieger commented on a diff in the pull request:
https://github.com/apache/spark/pull/22995#discussion_r236391043
--- Diff:
core/src/main/scala/org/apache/spark/broadcast/TorrentBroadcast.scala ---
@@ -93,7 +96,14 @@ private[spark] class TorrentBroadcast[T: ClassTag](obj:
T, id: Long)
private var checksums: Array[Int] = _
override protected def getValue() = {
-_value
+val memoized: T = if (_value == null) null.asInstanceOf[T] else
_value.get
--- End diff --
Good catch. I'll make it synchronized, so it only loads one at a time.
Re: WeakReference, sure, I can change it to SoftReference. That'll be
closer to the original behavior, and should still give the improvement we want.
When I try with `.asInstanceOf[T]` it fails to compile with:
```
[error]
/Users/bkrieger/Documents/git/spark/core/src/main/scala/org/apache/spark/broadcast/TorrentBroadcast.scala:98:
type mismatch;
[error] found : Null(null)
[error] required: T
[error] val memoized: T = if (_value == null) null else _value.get
[error] ^
[info] Null(null) <: T?
[info] false
[error] one error found
```
---
-
To unsubscribe, e-mail: reviews-unsubscr...@spark.apache.org
For additional commands, e-mail: reviews-h...@spark.apache.org
[GitHub] spark pull request #22995: [SPARK-25998] [CORE] Change TorrentBroadcast to h...
Github user srowen commented on a diff in the pull request:
https://github.com/apache/spark/pull/22995#discussion_r234396107
--- Diff:
core/src/main/scala/org/apache/spark/broadcast/TorrentBroadcast.scala ---
@@ -93,7 +96,14 @@ private[spark] class TorrentBroadcast[T: ClassTag](obj:
T, id: Long)
private var checksums: Array[Int] = _
override protected def getValue() = {
-_value
+val memoized: T = if (_value == null) null.asInstanceOf[T] else
_value.get
--- End diff --
I suppose there is a race condition here, in that several threads could end
up simultaneously setting the reference. It won't be incorrect as the data
ought to be the same. I am not sure of the access pattern for this object;
maybe it's always single-threaded. But if lots are reading, you can imagine
them all causing a call to `readBroadcastBlock()` simultaneously.
Introducing another object to lock on is safe and not too much extra
legwork. Might be worth it.
Isn't WeakReference cleared on any GC? would SoftReference be better to
hold out until memory is exhausted? to avoid re-reading. There's a tradeoff
there.
Good idea, just surprisingly full of possible gotchas.
Nit: isn't `val memoized = if (_value == null) null else _value.get`
sufficient?
---
-
To unsubscribe, e-mail: reviews-unsubscr...@spark.apache.org
For additional commands, e-mail: reviews-h...@spark.apache.org
[GitHub] spark pull request #22995: [SPARK-25998] [CORE] Change TorrentBroadcast to h...
GitHub user bkrieger opened a pull request: https://github.com/apache/spark/pull/22995 [SPARK-25998] [CORE] Change TorrentBroadcast to hold weak reference of broadcast object ## What changes were proposed in this pull request? This PR changes the broadcast object in TorrentBroadcast from a strong reference to a weak reference. This allows it to be garbage collected even if the Dataset is held in memory. This is ok, because the broadcast object can always be re-read. ## How was this patch tested? Tested in Spark shell by taking a heap dump, full repro steps listed in https://issues.apache.org/jira/browse/SPARK-25998. You can merge this pull request into a Git repository by running: $ git pull https://github.com/bkrieger/spark bk/torrent-broadcast-weak Alternatively you can review and apply these changes as the patch at: https://github.com/apache/spark/pull/22995.patch To close this pull request, make a commit to your master/trunk branch with (at least) the following in the commit message: This closes #22995 commit a2683b62985fc9c7d15fb92f3bb170a4b5225058 Author: Brandon Krieger Date: 2018-11-08T23:04:06Z use weak reference for torrent broadcast commit 99fbeecf43a289648a56d178fa55e188ce75bdb7 Author: Brandon Krieger Date: 2018-11-09T21:04:51Z fix compile commit 5e0a179c168a70b0166abe4bb51a1d26a2f1d666 Author: Brandon Krieger Date: 2018-11-09T21:33:22Z fix commit 1908b5b8dfa6c0b55db3bd9a90e21ca713e5bf25 Author: Brandon Krieger Date: 2018-11-09T21:48:44Z no npe commit 24183e5b8b63e0b4e117856ab4de7eb1b0ea6c9a Author: Brandon Krieger Date: 2018-11-09T21:52:21Z no option commit f212da322242386ce3b71e9961a964e60b587287 Author: Brandon Krieger Date: 2018-11-09T22:08:23Z typo --- - To unsubscribe, e-mail: reviews-unsubscr...@spark.apache.org For additional commands, e-mail: reviews-h...@spark.apache.org
