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  • JVM memory management & garbage collection book?

    - by Max
    Hi. Could anyone advice a book (or any other source) that would thoroughly reveal internals of JVM memory management & garbage collection (optimization, work, circular references, pecularities, discussions for various JVM impls...)? [What I've found so far are separate articles devoted to various aspects but no weighty tome :). Some good materials for Hotspot implementation are here. ] Thanks a lot for any advice you give.

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  • Perl graph garbage collection usage

    - by Kevin
    Hi, I have built a tiny application in Perl that displays a graph over time. It graphs garbage collection usage over time. I use gnuplot to display the actual graph. This works fine if the time period is short, like a few hours. However, as the time increases (say a few days), the graph becomes difficult to read as the information gets crammed. Note that there is a tool called gcviewer which performs a similar function, it works by allowing you to choose the percentage of the graph. http://www.tagtraum.com/gcviewer.html Ideally I would like to take this further by adding the ability to "move" within the graph. I am not a developer but am good at scripting, so if there is some module in Perl which would provide this functionality it would be excellent! However, if it cannot be done in Perl, I am not averse to learning a new technology. Inputs are highly appreciated. Thanks!

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  • QPainter paints garbage

    - by DSblizzard
    Fragment of program code: def add_link(Item0Num, Item1Num): global Mw, View # Mw - MainWindow if Item0Num != Item1Num and not link_exists(Item0Num, Item1Num): append( links_to(Item1Num), Item0Num ) append( links_from(Item0Num), Item1Num ) LinkGi = TLinkGi() Mw.Scene.addItem(LinkGi) LinkGi.setZValue(200) LinkGi.scale(1 / View.Scale, 1 / View.Scale) LinkGi.Item0Num = Item0Num LinkGi.Item1Num = Item1Num class TLinkGi(QGraphicsItem): def paint(self, Painter, StyleOptionGraphicsItem, Widget): global Mw, View Pen = QPen(Qt.black, 1) Painter.setPen(Pen) X0, Y0 = task_center(self.Item0Num) self.setPos(X0, Y0) X1, Y1 = task_center(self.Item1Num) X, Y = int( (X1 - X0) * View.Scale ), int( (Y1 - Y0) * View.Scale ) Painter.drawLine(0, 0, X, Y) #Mw.Scene.update(0, 0, Plan.Size, Plan.Size) # (1) #Mw.gvMain.repaint() # (2) def boundingRect(self): global View Rect = QRectF(0, 0, Plan.Size, Plan.Size) return Rect This paints such garbage: http://img697.imageshack.us/content_round.php?page=done&l=img697/5395/qpaintergarbage1.jpg When lines (1) and (2) are uncommented things doesn't become much better: http://img63.imageshack.us/content_round.php?page=done&l=img63/9693/qpaintergarbage0.jpg Please help me to solve this problem.

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  • .NET Windows Service, threads and garbage collection (possible memory leaks)

    - by Evgeny
    I am developing a .NET Windows service that is creating a couple of threads and then uses these threads to send print jobs to printers (there is a thread for each printer). I have some issues which sometimes can be fixed by restarting the service. Some issues also arise when the service has been running for a while. This makes me suspect a possible memory leak. So, a couple of questions: Would a garbage collector collect an object if it was created inside a thread, or will the object exist until the thread is stopped/terminated? What tools can I use to monitor the amount of memory used by a Windows service and by a thread that I am starting programmatically?

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  • .NET Garbage Collection behavior (with DataTable)

    - by gmac
    I am wonder why after creating a very simple DataTable and then setting it to null why Garbage Collection does not clear out all the memory used by that DataTable. Here is an example. The variable Before should be equal to Removed but it is not. { long Before = 0, After = 0, Removed = 0, Collected = 0; Before = GC.GetTotalMemory(true); DataTable dt = GetSomeDataTableFromSql(); After = GC.GetTotalMemory(true); dt = null; Removed = GC.GetTotalMemory(true); GC.Collect(); Collected = GC.GetTotalMemory(true); } Gives the following results. Before = 388116 After = 731248 Removed = 530176 Collected = 530176

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  • Java Collections and Garbage Collector

    - by Anth0
    A little question regarding performance in a Java web app. Let's assume I have a List<Rubrique> listRubriques with ten Rubrique objects. A Rubrique contains one list of products (List<product> listProducts) and one list of clients (List<Client> listClients). What exactly happens in memory if I do this: listRubriques.clear(); listRubriques = null; My point of view would be that, since listRubriques is empty, all my objects previously referenced by this list (including listProducts and listClients) will be garbage collected pretty soon. But since Collection in Java are a little bit tricky and since I have quite performance issues with my app i'm asking the question :) edit : let's assume now that my Client object contains a List<Client>. Therefore, I have kind of a circular reference between my objects. What would happen then if my listRubrique is set to null? This time, my point of view would be that my Client objects will become "unreachable" and might create a memory leak?

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  • FLV performance and garbage collection

    - by justinbach
    I'm building a large flash site (AS3) that uses huge FLVs as transition videos from section to section. The FLVs are 1280x800 and are being scaled to 1680x1050 (much of which is not displayed to users with smaller screens), and are around 5-8 seconds apiece. I'm encoding the videos using On2's hi-def codec, VP6-S, and playback is pretty good with native FLV players, Perian-equipped Quicktime, and simple proof-of-concept FLV playback apps built in AS3. The problem I'm having is that in the context of the actual site, playback isn't as smooth; the framerate isn't quite as good as it should be, and more problematically, there's occasional jerkiness and dropped frames (sometimes pausing the video for as long as a quarter of a second or so). My guess is that this is being caused by garbage collection in the Flash player, which happens nondeterministically and is therefore hard to test and control for. I'm using a single instance of FLVPlayback to play the videos; I originally was using NetStream objects and so forth directly but switched to FLVPlayback for this reason. Has anyone experienced this sort of jerkiness with FLVPlayback (or more generally, with hi-def Flash video)? Am I right about GC being the culprit here, and if so, is there any way to prevent it during playback of these system-intensive transitions?

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  • garbage collector Issue

    - by Eslam
    this question is like my previous one Given: 3. interface Animal { void makeNoise(); } 4. class Horse implements Animal { 5. Long weight = 1200L; 6. public void makeNoise() { System.out.println("whinny"); } 7. } 8. public class Icelandic extends Horse { 9. public void makeNoise() { System.out.println("vinny"); } 10. public static void main(String[] args) { 11. Icelandic i1 = new Icelandic(); 12. Icelandic i2 = new Icelandic(); 13. Icelandic i3 = new Icelandic(); 14. i3 = i1; i1 = i2; i2 = null; i3 = i1; 15. } 16. } When line 14 is reached, how many objects are eligible for the garbage collector? A. 0 B. 1 C. 2 D. 3 E. 4 F. 6 i choosed A but the right answer is E, but i don't know Why?

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  • Android ListActivity with Bitmaps and Garbage Collection issue

    - by chis54
    I have a ListActivity and in it I set my list items with a class that extends SimpleCursorAdapter. I'm overriding bindView to set my Views. I have some TextViews and ImageViews. This is how I set my list items in my cursor adapter: String variableName = "drawable/q" + num + "_200px"; int imageResource = context.getResources().getIdentifier(variableName, "drawable", context.getPackageName()); if (imageResource != 0 ) { // The drawable exists Bitmap b = BitmapFactory.decodeResource(context.getResources(), imageResource); width = b.getWidth(); height = b.getHeight(); imageView.getLayoutParams().width = (int) (width); imageView.getLayoutParams().height = (int) (height); imageView.setImageResource(imageResource); } else { imageView.setImageResource(R.drawable.25trans_200px); } The problem I'm having is whenever I update my list with setListAdapter I get a large amount of garbage collection: D/dalvikvm(18637): GC_EXTERNAL_ALLOC freed 125K, 51% free 2710K/5447K, external 2022K/2137K, paused 75ms D/dalvikvm(18637): GC_EXTERNAL_ALLOC freed 30K, 51% free 2701K/5447K, external 2669K/2972K, paused 64ms D/dalvikvm(18637): GC_EXTERNAL_ALLOC freed 23K, 51% free 2713K/5447K, external 3479K/3579K, paused 53ms D/dalvikvm(18637): GC_EXTERNAL_ALLOC freed 22K, 51% free 2706K/5447K, external 3303K/3352K, paused 64ms D/dalvikvm(18637): GC_EXTERNAL_ALLOC freed 21K, 51% free 2722K/5447K, external 3569K/3685K, paused 102ms D/dalvikvm(18637): GC_EXTERNAL_ALLOC freed 23K, 50% free 2755K/5447K, external 3499K/3605K, paused 65ms D/dalvikvm(18637): GC_EXTERNAL_ALLOC freed 23K, 50% free 2771K/5447K, external 4213K/4488K, paused 53ms D/dalvikvm(18637): GC_EXTERNAL_ALLOC freed 18K, 49% free 2796K/5447K, external 5057K/5343K, paused 75ms D/dalvikvm(18637): GC_EXTERNAL_ALLOC freed 28K, 49% free 2803K/5447K, external 5944K/5976K, paused 53ms D/dalvikvm( 435): GC_EXPLICIT freed 6K, 54% free 2544K/5511K, external 1625K/2137K, paused 50ms D/dalvikvm( 165): GC_EXPLICIT freed 85K, 52% free 2946K/6087K, external 4838K/5980K, paused 111ms D/dalvikvm( 448): GC_EXPLICIT freed 1K, 54% free 2540K/5511K, external 1625K/2137K, paused 50ms D/dalvikvm( 294): GC_EXPLICIT freed 8K, 55% free 2598K/5703K, external 1625K/2137K, paused 64ms What can I do to avoid this? It's causing my UI to be sluggish and when I scroll, too.

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  • Criteria for triggering garbage collection in .Net

    - by Kennet Belenky
    I've come across some curious behavior with regard to garbage collection in .Net. The following program will throw an OutOfMemoryException very quickly (after less than a second on a 32-bit, 2GB machine). The Foo finalizer is never called. class Foo { static Dictionary<Guid, WeakReference> allFoos = new Dictionary<Guid, WeakReference>(); Guid guid = Guid.NewGuid(); byte[] buffer = new byte[1000000]; static Random rand = new Random(); public Foo() { // Uncomment the following line and the program will run forever. // rand.NextBytes(buffer); allFoos[guid] = new WeakReference(this); } ~Foo() { allFoos.Remove(guid); } static public void Main(string args[]) { for (; ; ) { new Foo(); } } } If the rand.nextBytes line is uncommented, it will run ad infinitum, and the Foo finalizer is regularly invoked. Why is that? My best guess is that in the former case, either the CLR or the Windows VMM is lazy about allocating physical memory. The buffer never gets written to, so the physical memory is never used. When the address space runs out, the system crashes. In the latter case, the system runs out of physical memory before it runs out of address space, the GC is triggered and the objects are collected. However, here's the part I don't get. Assuming my theory is correct, why doesn't the GC trigger when the address space runs low? If my theory is incorrect, then what's the real explanation?

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  • Second user-defined function returns garbage value?

    - by mintyfresh
    I have been teaching myself C programming, and I've come to a difficult point with using variables across functions. When, I compile this program and run it, the function askBirthYear returns the correct value, but sayAgeInYears returns either 0 or a garbage value. I believe it has something to do with how I used the variable birthYear, but I'm stumped on how to fix the issue. Here is the code: #include <stdio.h> #include <stdlib.h> int askBirthYear(int); void sayAgeInYears(int); int birthYear; int main(void) { askBirthYear(birthYear); sayAgeInYears(birthYear); return EXIT_SUCCESS; } void askBirthYear(int birthYear) { printf("Hello! In what year were you born?\n"); scanf("%d", &birthYear); printf("Your birth year is %d.\n", birthYear); return birthYear; } void sayAgeInYears(int birthYear) { int age; age = 2012 - birthYear; printf("You are %d years old.\n", age); }

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  • Large memory chunk not garbage collected

    - by Niels
    In a hunt for a memory-leak in my app I chased down a behaviour I can't understand. I allocate a large memory block, but it doesn't get garbage-collected resulting in a OOM, unless I explicit null the reference in onDestroy. In this example I have two almost identical activities that switch between each others. Both have a single button. On pressing the button MainActivity starts OOMActivity and OOMActivity returns by calling finish(). After pressing the buttons a few times, Android throws a OOMException. If i add the the onDestroy to OOMActivity and explicit null the reference to the memory chunk, I can see in the log that the memory is correctly freed. Why doesn't the memory get freed automatically without the nulling? MainActivity: package com.example.oom; import android.app.Activity; import android.content.Intent; import android.os.Bundle; import android.view.View; import android.view.View.OnClickListener; import android.widget.Button; public class MainActivity extends Activity implements OnClickListener { private int buttonId; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); System.gc(); Button OOMButton = new Button(this); OOMButton.setText("OOM"); buttonId = OOMButton.getId(); setContentView(OOMButton); OOMButton.setOnClickListener(this); } @Override public void onClick(View v) { if (v.getId() == buttonId) { Intent leakIntent = new Intent(this, OOMActivity.class); startActivity(leakIntent); } } } OOMActivity: public class OOMActivity extends Activity implements OnClickListener { private static final int WASTE_SIZE = 20000000; private byte[] waste; private int buttonId; protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); Button BackButton = new Button(this); BackButton.setText("Back"); buttonId = BackButton.getId(); setContentView(BackButton); BackButton.setOnClickListener(this); waste = new byte[WASTE_SIZE]; } public void onClick(View view) { if (view.getId() == buttonId) { finish(); } } }

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  • Java HotSpot 1.6 VM, Garbage Collection - Scary PermGen

    - by Gala101
    Hi, My app shows rising 'Old Generation'/'Tenured Generation' size, and when this reaches the max limit for 'Old Gen', then suddenly PermGen size increases. Here are my generation sizings: -Xmx1200m -Xms1200m -Xmn450m -XX:MaxPermSize=600m -XX:+UseParallelGC This is on 32 bit Fedora so can't have a bigger heap than this. The app is not doing any fancy classloading, though it is using Spring IOC and Hibernate, the Spring App-context.xml defines some 1000 Beans. This app starts with 175MB PermGen, which steadily increases to ~250MB in few hrs, stays that way till Tenured Generation reached ~780 MB, then permgen jumps to ~500MB while Old Gen drops to ~500MB. This forces me to restart the App on daily basis, and gives me real scare of looming OutOfMemory Error.. Any insights would be very helpful. Thanks Gala101

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  • String Constant Pool memory sector and garbage collection

    - by WickeD
    I read this question on the site How is the java memory pool divided? and i was wondering to which of these sectors does the "String Constant Pool" belongs? And also does the String literals in the pool ever get GCed? The intern() method returns the base link of the String literal from the pool. If the pool does gets GCed then wouldn't it be counter-productive to the idea of the string pool? New String literals would again be created nullifying the GC. (It is assuming that only a specific set of literals exist in the pool, they never go obsolete and sooner or later they will be needed again)

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  • Garbage collection - manually wiping EVERYTHING!

    - by Glycerine
    I have been building a game for a while (nearly done) - But the game needs a replay button and its a big task. I know the GC is dreadful in flash, but I wanted to know if there is a way to wipe EVERYTHING as if the flash app has just begun. Clearing memory, game data - I haven't to worry about game loading as its not really heavy on data. Everything pretty much lives in a DataModel - but I fear if I just clear the all variables, I'll have pockets of orphaned memory. Any forwarding idea would be great. cheers guys.

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  • Garbage Collection Java

    - by simion
    On the slides i am revising from it says the following; Live objects can be identified either by maintaining a count of the number of references to each object, or by tracing chains of references from the roots. Reference counting is expensive – it needs action every time a reference changes and it doesn’t spot cyclical structures, but it can reclaim space incrementally. Tracing involves identifying live objects only when you need to reclaim space – moving the cost from general access to the time at which the GC runs, typically only when you are out of memory. I understand the principles of why reference counting is expensive but do not understand what "doesn’t spot cyclical structures, but it can reclaim space incrementally." means. Could anyone help me out a little bit please? Thanks

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  • Garbage Collection in Java

    - by simion
    On the slides I am revising from it says the following: Live objects can be identified either by maintaining a count of the number of references to each object, or by tracing chains of references from the roots. Reference counting is expensive – it needs action every time a reference changes and it doesn’t spot cyclical structures, but it can reclaim space incrementally. Tracing involves identifying live objects only when you need to reclaim space – moving the cost from general access to the time at which the GC runs, typically only when you are out of memory. I understand the principles of why reference counting is expensive but do not understand what "doesn’t spot cyclical structures, but it can reclaim space incrementally." means. Could anyone help me out a little bit please? Thanks

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  • How can I disable Java garbage collector ?

    - by Nelson
    Hi, we have a PHP webapp that calls a java binary to produce a pdf report (with jasperreport), the java binary outpus pdf to standart output and exits, the php then send the pdf to browser. This java command lasts about 3 to 6 seconds, I think when it lasts 6 second it's because the GC kicks in, so I would like to disable it because anyway when the command exits all memory is returned.. I would like to know how to disable it for Java 1.4.2 and for Java 1.6.0 because we are currently testing both JVM to see which performs faster.. Thanks

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  • Between-request Garbage Collection using Passenger

    - by raphaelcm
    We're using Rails 3.0.7 and REE 1.8.7. Long-term, we will be upgrading, but at the moment it's not feasible. Following the advice of several blog posts, we've been tuning our GC, and have settings that work pretty well. But we would really like to run GC outside of the request-response cycle. I've tried patching Passenger per this post, and using the code supplied in this SO question. In both cases, GC does indeed happen between requests. However, every time the between-request GC happens, I see a bunch of this: MONGODB [INFO] Connecting... MONGODB admin['$cmd'].find({:ismaster=>1}).limit(-1) MONGODB admin['$cmd'].find({:ismaster=>1}).limit(-1) MONGODB admin['$cmd'].find({:ismaster=>1}).limit(-1) Starting the New Relic Agent. Installed New Relic Browser Monitoring middleware SQL (0.0ms) SHOW TABLES SQL (0.0ms) SHOW TABLES RefinerySetting Load (0.0ms) SELECT `refinery_settings`.* FROM `refinery_settings` WHERE `refinery_settings`.`scoping` = 'pages' AND `refinery_settings`.`name` = 'use_marketable_urls' LIMIT 1 SQL (0.0ms) BEGIN RefinerySetting Load (0.0ms) SELECT `refinery_settings`.* FROM `refinery_settings` WHERE `refinery_settings`.`id` = 1 LIMIT 1 AREL (0.0ms) UPDATE `refinery_settings` SET `value` = '--- \"false\"\n', `callback_proc_as_string` = NULL WHERE `refinery_settings`.`id` = 1 SQL (0.0ms) SHOW TABLES RefinerySetting Load (0.0ms) SELECT `refinery_settings`.* FROM `refinery_settings` SQL (0.0ms) COMMIT SQL (0.0ms) SHOW TABLES RefinerySetting Load (4.0ms) SELECT `refinery_settings`.* FROM `refinery_settings` WHERE `refinery_settings`.`scoping` IS NULL AND `refinery_settings`.`name` = 'user_image_sizes' LIMIT 1 SQL (0.0ms) BEGIN RefinerySetting Load (0.0ms) SELECT `refinery_settings`.* FROM `refinery_settings` WHERE `refinery_settings`.`id` = 17 LIMIT 1 AREL (0.0ms) UPDATE `refinery_settings` SET `value` = '--- \n:small: 120x120>\n:medium: 280x280>\n:large: 580x580>\n', `callback_proc_as_string` = NULL WHERE `refinery_settings`.`id` = 17 SQL (0.0ms) SHOW TABLES RefinerySetting Load (0.0ms) SELECT `refinery_settings`.* FROM `refinery_settings` SQL (0.0ms) COMMIT ******** Engine Extend: app/helpers/blog_posts_helper SQL (0.0ms) SHOW TABLES SQL (0.0ms) SHOW TABLES SQL (0.0ms) SHOW TABLES SQL (4.0ms) SHOW TABLES SQL (0.0ms) SHOW TABLES SQL (0.0ms) SHOW TABLES SQL (0.0ms) SHOW TABLES ******** Engine Extend: app/models/user SQL (0.0ms) describe `roles_users` SQL (0.0ms) SHOW TABLES SQL (0.0ms) SHOW TABLES SQL (4.0ms) describe `roles_users` SQL (0.0ms) SHOW TABLES SQL (4.0ms) SHOW TABLES SQL (0.0ms) SHOW TABLES SQL (0.0ms) SHOW TABLES (etc, etc, etc) Which is what happens when rails "loads the world" when the app starts up. Basically, GC.start is re-loading the app for some reason. Because of this, between-request GC is much slower than inline GC. Is there a way around this? I would love to have snappy, between-request GC if possible. Thanks.

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  • Garbage Collection Basics

    - by mikew_co
    Java Is an awesome programming language and platform. One of its better features is automatic garbage collection. Ever wondered how that works? I have written an online web course outlining the basics. Much of what is included has been published before in various white papers and such. However, this is updated for JDK 7 and includes some nice illustrations of the steps involved. Hope you like it. Garbage Collection Basics. A follow-on web course on the G1 garbage collector should follow in a week or so.

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  • C# : Forcing a clean run in a long running SQL reader loop?

    - by Wardy
    I have a SQL data reader that reads 2 columns from a sql db table. once it has done its bit it then starts again selecting another 2 columns. I would pull the whole lot in one go but that presents a whole other set of challenges. My problem is that the table contains a large amount of data (some 3 million rows or so) which makes working with the entire set a bit of a problem. I'm trying to validate the field values so i'm pulling the ID column then one of the other cols and running each value in the column through a validation pipeline where the results are stored in another database. My problem is that when the reader hits the end of handlin one column I need to force it to immediately clean up every little block of ram used as this process uses about 700MB and it has about 200 columns to go through. Without a full Garbage Collect I will definately run out of ram. Anyone got any ideas how I can do this? I'm using lots of small reusable objects, my thought was that I could just call GC.Collect() on the end of each read cycle and that would flush everything out, unfortunately that isn't happening for some reason.

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  • How to reduce java concurrent mode failure and excessive gc

    - by jimx
    In Java, the concurrent mode failure means that the concurrent collector failed to free up enough memory space form tenured and permanent gen and has to give up and let the full stop-the-world gc kicks in. The end result could be very expensive. I understand this concept but never had a good comprehensive understanding of A) what could cause a concurrent mode failure and B) what's the solution?. This sort of unclearness leads me to write/debug code without much of hints in mind and often has to shop around those performance flags from Foo to Bar without particular reasons, just have to try. I'd like to learn from developers here how your experience is. If you had previous encountered such performance issue, what was the cause and how you addressed it? If you have coding recommendations, please don't be too general. Thanks!

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