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• Configuring MySQL Cluster Data Nodes

  - by Mat Keep

  0 0 1 692 3948 Homework 32 9 4631 14.0 Normal 0 false false false EN-US JA X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:Cambria; mso-ascii-font-family:Cambria; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Cambria; mso-hansi-theme-font:minor-latin; mso-ansi-language:EN-US;} In my previous blog post, I discussed the enhanced performance and scalability delivered by extensions to the multi-threaded data nodes in MySQL Cluster 7.2. In this post, I’ll share best practices on the configuration of data nodes to achieve optimum performance on the latest generations of multi-core, multi-thread CPU designs. Configuring the Data Nodes The configuration of data node threads can be managed in two ways via the config.ini file: - Simply set MaxNoOfExecutionThreads to the appropriate number of threads to be run in the data node, based on the number of threads presented by the processors used in the host or VM. - Use the new ThreadConfig variable that enables users to configure both the number of each thread type to use and also which CPUs to bind them too. The flexible configuration afforded by the multi-threaded data node enhancements means that it is possible to optimise data nodes to use anything from a single CPU/thread up to a 48 CPU/thread server. Co-locating the MySQL Server with a single data node can fully utilize servers with 64 – 80 CPU/threads. It is also possible to co-locate multiple data nodes per server, but this is now only required for very large servers with 4+ CPU sockets dense multi-core processors. 24 Threads and Beyond! An example of how to make best use of a 24 CPU/thread server box is to configure the following: - 8 ldm threads - 4 tc threads - 3 recv threads - 3 send threads - 1 rep thread for asynchronous replication. Each of those threads should be bound to a CPU. It is possible to bind the main thread (schema management domain) and the IO threads to the same CPU in most installations. In the configuration above, we have bound threads to 20 different CPUs. We should also protect these 20 CPUs from interrupts by using the IRQBALANCE_BANNED_CPUS configuration variable in /etc/sysconfig/irqbalance and setting it to 0x0FFFFF. The reason for doing this is that MySQL Cluster generates a lot of interrupt and OS kernel processing, and so it is recommended to separate activity across CPUs to ensure conflicts with the MySQL Cluster threads are eliminated. When booting a Linux kernel it is also possible to provide an option isolcpus=0-19 in grub.conf. The result is that the Linux scheduler won't use these CPUs for any task. Only by using CPU affinity syscalls can a process be made to run on those CPUs. By using this approach, together with binding MySQL Cluster threads to specific CPUs and banning CPUs IRQ processing on these tasks, a very stable performance environment is created for a MySQL Cluster data node. On a 32 CPU/Thread server: - Increase the number of ldm threads to 12 - Increase tc threads to 6 - Provide 2 more CPUs for the OS and interrupts. - The number of send and receive threads should, in most cases, still be sufficient. On a 40 CPU/Thread server, increase ldm threads to 16, tc threads to 8 and increment send and receive threads to 4. On a 48 CPU/Thread server it is possible to optimize further by using: - 12 tc threads - 2 more CPUs for the OS and interrupts - Avoid using IO threads and main thread on same CPU - Add 1 more receive thread. Summary As both this and the previous post seek to demonstrate, the multi-threaded data node extensions not only serve to increase performance of MySQL Cluster, they also enable users to achieve significantly improved levels of utilization from current and future generations of massively multi-core, multi-thread processor designs. A big thanks to Mikael Ronstrom, Senior MySQL Architect at Oracle, for his work in developing these enhancements and best practices. You can download MySQL Cluster 7.2 today and try out all of these enhancements. The Getting Started guides are an invaluable aid to quickly building a Proof of Concept Don’t forget to check out the MySQL Cluster 7.2 New Features whitepaper to discover everything that is new in the latest GA release

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• How do I update blackberry UI items from a thread?

  - by Andrei T. Ursan

  public class PlayText extends Thread { private int duration; private String text; private PlayerScreen playerscrn; public PlayText(String text, int duration) { this.duration = duration; this.text = text; this.playerscrn = (PlayerScreen)UiApplication.getUiApplication().getActiveScreen(); } public void run() { synchronized(UiApplication.getEventLock()) { try{ RichTextField text1player = new RichTextField(this.text, Field.NON_FOCUSABLE); playerscrn.add(text1player); playerscrn.invalidate(); Thread.sleep(this.duration); RichTextField text2player = new RichTextField("hahhaha", Field.NON_FOCUSABLE); playerscrn.add(text2player); playerscrn.invalidate(); Thread.sleep(1000); RichTextField text3player = new RichTextField("Done", Field.NON_FOCUSABLE); playerscrn.add(text3player); playerscrn.invalidate(); }catch(Exception e){ System.out.println("I HAVE AN ERROR"); } } } } With the above code I'm trying to create a small text player. Instead to get all the text labels one by one, something like display text1player wait this.duration milliseconds display text2player wait 1000 milliseconds display text3player thread done. The screens waits this.duration + 1000 milliseconds and displays all the labels at once. I tried with a runnable and calling .invokeLater or .invokeAndWait but I still get the same behavior, and even if I get dirty like above using synchronized it still doesn't work. Does anyone know how I can display each label at a time? Thank you!

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• C# - How to change window state of Form, on a different thread?

  - by Dodi300

  Hello. Does anyone know how I can chage the window state of a form, from another thread? This is the code I'm using: private void button4_Click(object sender, EventArgs e) { string pathe = label1.Text; string name = Path.GetFileName(pathe); pathe = pathe.Replace(name, ""); string runpath = label2.Text; Process process; process = new Process(); process.EnableRaisingEvents = true; process.Exited += new System.EventHandler(process_Exited); process.StartInfo.FileName = @runpath; process.StartInfo.WorkingDirectory = @pathe; process.Start(); WindowState = FormWindowState.Minimized; } private void process_Exited(object sender, EventArgs e) { this.WindowState = FormWindowState.Normal; } It's meant to run a program and minimize, then return to the normal state once the program has closed. Although I get this error "Cross-thread operation not valid: Control 'Form1' accessed from a thread other than the thread it was created on." Any idea how to get this to work? Thanks.

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• How do I make my ArrayList Thread-Safe? Another approach to problem in Java?

  - by thechiman

  I have an ArrayList that I want to use to hold RaceCar objects that extend the Thread class as soon as they are finished executing. A class, called Race, handles this ArrayList using a callback method that the RaceCar object calls when it is finished executing. The callback method, addFinisher(RaceCar finisher), adds the RaceCar object to the ArrayList. This is supposed to give the order in which the Threads finish executing. I know that ArrayList isn't synchronized and thus isn't thread-safe. I tried using the Collections.synchronizedCollection(c Collection) method by passing in a new ArrayList and assigning the returned Collection to an ArrayList. However, this gives me a compiler error: Race.java:41: incompatible types found : java.util.Collection required: java.util.ArrayList finishingOrder = Collections.synchronizedCollection(new ArrayList(numberOfRaceCars)); Here is the relevant code: public class Race implements RaceListener { private Thread[] racers; private ArrayList finishingOrder; //Make an ArrayList to hold RaceCar objects to determine winners finishingOrder = Collections.synchronizedCollection(new ArrayList(numberOfRaceCars)); //Fill array with RaceCar objects for(int i=0; i<numberOfRaceCars; i++) { racers[i] = new RaceCar(laps, inputs[i]); //Add this as a RaceListener to each RaceCar ((RaceCar) racers[i]).addRaceListener(this); } //Implement the one method in the RaceListener interface public void addFinisher(RaceCar finisher) { finishingOrder.add(finisher); } What I need to know is, am I using a correct approach and if not, what should I use to make my code thread-safe? Thanks for the help!

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• Are Thread.stop and friends ever safe in Java?

  - by Stephen C

  The stop(), suspend(), and resume() in java.lang.Thread are deprecated because they are unsafe. The Sun recommended work around is to use Thread.interrupt(), but that approach doesn't work in all cases. For example, if you are call a library method that doesn't explicitly or implicitly check the interrupted flag, you have no choice but to wait for the call to finish. So, I'm wondering if it is possible to characterize situations where it is (provably) safe to call stop() on a Thread. For example, would it be safe to stop() a thread that did nothing but call find(...) or match(...) on a java.util.regex.Matcher? (If there are any Sun engineers reading this ... a definitive answer would be really appreciated.) EDIT: Answers that simply restate the mantra that you should not call stop() because it is deprecated, unsafe, whatever are missing the point of this question. I know that that it is genuinely unsafe in the majority of cases, and that if there is a viable alternative you should always use that instead. This question is about the subset cases where it is safe. Specifically, what is that subset?

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• How to make Exchange 2010 use In-Reply-To and References headers as well as Thread-Index?

  - by Paul Wagland

  The problem that I have is simple. We have recently upgraded from Exchange 2003 to Exchange 2010. Everything went fine, and there are very few complaints. In Exchange 2003, some of our OWA users liked the Threading view, these users love the conversations view, especially with the cross-mailbox threading. The problem is that some of these users are now complaining that old e-mails that they got from systems like bugzilla were migrated across correctly threaded, but the new e-mails are not being correctly threaded. If I look at the mail source using an IMAP client then I can see that all of the mails that are turning up as being threaded have the (Microsoft specific) Thread-Index header, and the mails that are not getting grouped do not have this header. The question is, how can I make the webmail client respect the normal threading? That is, is there a way to Make the OWA client use the standard In-Reply-To and References headers, or Make Exchange generate the Thread-Index headers for Outlook and OWA to use?

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• What are "Missing thread recordng" erros when running fsck -fy?

  - by ohho

  There is some error reported when I run Disk Utility and verify the root volume on my OS X MacBook. So I boot and CMD-S into the shell mode and run /sbin/fsck -fy. Errors are like: ** Checking catalog file. Missing thread record (id = ...) In correct number of thread records ** Checking catalog hierarchy. Invalid volume file count (It should be ... instead of ...) ** Repairing Volume Missing directory record (id = ...) I'd like to know what is the cause of the above errors? Hopefully I will be more careful in the future to prevent them from happening again. p.s. I am using a SSD and so I assume mechanical hard disk error is less likely. Thanks!

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• What are "Missing thread recordng" erros when running fsck -fy ?

  - by Horace Ho

  There is some error reported when I run Disk Utility and verify the root volume on my OS X MacBook. So I boot and CMD-S into the shell mode and run /sbin/fsck -fy. Errors are like: ** Checking catalog file. Missing thread record (id = ...) In correct number of thread records ** Checking catalog hierarchy. Invalid volume file count (It should be ... instead of ...) ** Repairing Volume Missing directory record (id = ...) I'd like to know what is the cause of the above errors? Hopefully I will be more careful in the future to prevent them from happening again. p.s. I am using a SSD and so I assume mechanical hard disk error is less likely. Thanks!

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• What are "Missing thread recordng" erros when running fsck -fy ?

  - by user32616

  There is some error reported when I run Disk Utility and verify the root volume on my OS X MacBook. So I boot and CMD-S into the shell mode and run /sbin/fsck -fy. Errors are like: ** Checking catalog file. Missing thread record (id = ...) In correct number of thread records ** Checking catalog hierarchy. Invalid volume file count (It should be ... instead of ...) ** Repairing Volume Missing directory record (id = ...) I'd like to know what is the cause of the above errors? Hopefully I will be more careful in the future to prevent them from happening again. p.s. I am using a SSD and so I assume mechanical hard disk error is less likely. Thanks!

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• UML Diagrams of Multi-Threaded Applications

  - by PersonalNexus

  For single-threaded applications I like to use class diagrams to get an overview of the architecture of that application. This type of diagram, however, hasn’t been very helpful when trying to understand heavily multi-threaded/concurrent applications, for instance because different instances of a class "live" on different threads (meaning accessing an instance is save only from the one thread it lives on). Consequently, associations between classes don’t necessarily mean that I can call methods on those objects, but instead I have to make that call on the target object's thread. Most literature I have dug up on the topic such as Designing Concurrent, Distributed, and Real-Time Applications with UML by Hassan Gomaa had some nice ideas, such as drawing thread boundaries into object diagrams, but overall seemed a bit too academic and wordy to be really useful. I don’t want to use these diagrams as a high-level view of the problem domain, but rather as a detailed description of my classes/objects, their interactions and the limitations due to thread-boundaries I mentioned above. I would therefore like to know: What types of diagrams have you found to be most helpful in understanding multi-threaded applications? Are there any extensions to classic UML that take into account the peculiarities of multi-threaded applications, e.g. through annotations illustrating that some objects might live in a certain thread while others have no thread-affinity; some fields of an object may be read from any thread, but written to only from one; some methods are synchronous and return a result while others are asynchronous that get requests queued up and return results for instance via a callback on a different thread.

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• How is thread synchronization implemented, at the assembly language level?

  - by Martin

  While I'm familiar with concurrent programming concepts such as mutexes and semaphores, I have never understood how they are implemented at the assembly language level. I imagine there being a set of memory "flags" saying: lock A is held by thread 1 lock B is held by thread 3 lock C is not held by any thread etc But how is access to these flags synchronized between threads? Something like this naive example would only create a race condition: mov edx, [myThreadId] wait: cmp [lock], 0 jne wait mov [lock], edx ; I wanted an exclusive lock but the above ; three instructions are not an atomic operation :(

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• Is a signal sent with kill to a parent thread guaranteed to be processed before the next statement?

  - by Jonathan M Davis

  Okay, so if I'm running in a child thread on linux (using pthreads if that matters), and I run the following command kill(getpid(), someSignal); it will send the given signal to the parent of the current thread. My question: Is it guaranteed that the parent will then immediately get the CPU and process the signal (killing the app if it's a SIGKILL or doing whatever else if it's some other signal) before the statement following kill() is run? Or is it possible - even probable - that whatever command follows kill() will run before the signal is processed by the parent thread?

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• How do you call a generic method on a thread?

  - by cw

  How would I call a method with the below header on a thread? public void ReadObjectAsync<T>(string filename) { // Can't use T in a delegate, moved it to a parameter. ThreadStart ts = delegate() { ReadObjectAcync(filename, typeof(T)); }; Thread th = new Thread(ts); th.IsBackground = true; th.Start(); } private void ReadObjectAcync(string filename, Type t) { // HOW? } public T ReadObject<T>(string filename) { // Deserializes a file to a type. }

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• Is it possible to create thread-safe collections without locks?

  - by Andrey

  This is pure just for interest question, any sort of questions are welcome. So is it possible to create thread-safe collections without any locks? By locks I mean any thread synchronization mechanisms, including Mutex, Semaphore, and even Interlocked, all of them. Is it possible at user level, without calling system functions? Ok, may be implementation is not effective, i am interested in theoretical possibility. If not what is the minimum means to do it? EDIT: Why immutable collections don't work. This of class Stack with methods Add that returns another Stack. Now here is program: Stack stack = new ...; ThreadedMethod() { loop { //Do the loop stack = stack.Add(element); } } this expression stack = stack.Add(element) is not atomic, and you can overwrite new stack from other thread. Thanks, Andrey

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• Java: Stopping a thread that has run for too long?

  - by Thomas King

  Say I've got something like this public void run(){ Thread behaviourThread = new Thread(abstractBehaviours[i]); behaviourThread.start(); } And I want to wait until abstractBehaviours[i] run method has either finished or run for 5000 milliseconds. How do I do that? behaviourThread.join(5000) doesn't seem to do that afaik (something is wrong with my code and I've put it down to that). All the abstract abstractBehaviour class is of course Runnable. I don't want to implement it inside each run method as that seems ugly and there are many different behaviours, I'd much rather have it in the calling/executing thread and do it just once. Solutions? First time doing something as threaded as this. Thanks!

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• I/O Asynchronous Completion

  - by lockedscope

  In the following, it is said that an I/O handle must be associated with the thread pool but i could not find where in the given example an handle is associated with the thread. Which function or code helps to bind the file handle in that example? Using asynchronous I/O completion events, a thread from the thread pool processes data only when the data is received, and once the data has been processed, the thread returns to the thread pool. To make an asynchronous I/O call, an operating-system I/O handle must be associated with the thread pool and a callback method must be specified. When the I/O operation completes, a thread from the thread pool invokes the callback method. http://msdn.microsoft.com/en-us/library/aa720215(VS.71).aspx

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• Using the windows api and C++, how could I load an exe from the hard drive and run it in its own thread?

  - by returneax

  For the sake of learning I'm trying to do what the OS does when launching a program ie. parsing a PE file and giving it a thread of execution. If I have two exe's one called foo.exe and the other bar.exe, how could I have foo.exe load the contents of bar.exe into memory then have it execute from there in its own thread? I know how to get it into memory using MapViewOfFile or by simple loading the contents on the hard drive into a buffer. I'm assuming simply copying the contents of bar.exe on disk into its own suspended thread and running it wouldn't work. I am semi-familiar with PE file internals. All help is very much appreciated, of course :)

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• Should I Use GUID or IDENTITY as Thread Number?

  - by user311509

  offerID is the thread # which represents the thread posted. I see in forums posts are represented by random numbers. Is this achieved by IDENTITY? If not, please advice. nvarchar(max) will carry all kind of texts along with HTML tags. CREATE TABLE Offer ( offerID int IDENTITY (4382,15) PRIMARY KEY, memberID int NOT NULL REFERENCES Member(memberID), title nvarchar(200) NOT NULL, thread nvarchar(max) NOT NULL, . . . );

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• How to debug lost events posted from non-GUI thread in Qt?

  - by gp

  As the subject says, I'm posting events from non-GUI thread (some GStreamer thread, to be precise). Code looks like this: GstBusSyncReply on_bus_message(GstBus* bus, GstMessage* message, gpointer data) { bool ret = QMetaObject::invokeMethod(static_cast<QObject*>(data), "stateChanged", Qt::QueuedConnection); Q_ASSERT(ret); return GST_BUS_PASS; } The problem is, stateChanged (doesn't matter whether it is a slot or signal) is not called. I've stepped into QMetaObject::invokeMethod with debugger, followed it till it called PostMessage (it is Qt 4.6.2 on Windows, by the way) – everything seemed to be OK. Object pointed to by data lives in GUI thread, I've double-checked this. How can I debug this problem? Or, better, maybe sidestep it altogether?

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• Mixing synchronized() with ReentrantLock.lock()

  - by yarvin

  In Java, do ReentrantLock.lock() and ReetrantLock.unlock() use the same locking mechanism as synchronized()? My guess is "No," but I'm hoping to be wrong. Example: Imagine that Thread 1 and Thread 2 both have access to: ReentrantLock lock = new ReentrantLock(); Thread 1 runs: synchronized (lock) { // blah } Thread 2 runs: lock.lock(); try { // blah } finally { lock.unlock(); } Assume Thread 1 reaches its part first, then Thread 2 before Thread 1 is finished: will Thread 2 wait for Thread 1 to leave the synchronized() block, or will it go ahead and run?

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• In C# or .NET, is there a way to prevent other threads from invoking methods on a particular thread?

  - by YWE

  I have a Windows Forms application with a BackgroundWorker. In a method on the main form, a MessageBox is shown and the user must click the OK button to continue. Meanwhile, while the messagebox is being displayed, the BackgroundWorker finishes executing and calls the RunWorkerCompleted event. In the method I have assigned to that event, which runs on the UI thread, the Close method is called on the form. Even though the method that shows the message box is still running, the UI thread is not blocking other threads from invoking methods on it. So the Close method gets called on the form. What I want is for the UI thread to block other threads' invokes until the method with the message box has finished. Is there an easy way to do that?

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• how to print correctly the handling thread on Windows?

  - by make

  Hi, Could someone please tell us on how to print correctly the handling thread in windows? Actually I tried several ways but it doesn't return the right number as in Unix-variant, as such e.g.: cout << " with thread " << pthread_self << endl; cout << " with thread " << pthread_self().p << endl; Thanks for your replies:

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• Is it possible to put a form control on its own thread?

  - by BVernon

  I'm using a DataGridView and some operations that I do cause it to become unresponsive for periods of time. Normally I would put data processing in its own thread to make the form more responsive, but in this case it's the DataGridView itself that's taking so long. This leads me to wonder whether it's possible to have the main form on one thread and the DataGridView on another thread so it doesn't prevent the main form from responding. I completely understand that doing so is probably not 'safe' and likely opens up a can of worms that makes it hardly worth trying and I fully expect this post will be getting down votes for merely suggesting such a ridiculous idea. Is this possible? And if so how would you go about it?

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• Benchmarking MySQL Replication with Multi-Threaded Slaves

  - by Mat Keep

  0 0 1 1145 6530 Homework 54 15 7660 14.0 Normal 0 false false false EN-US JA X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:Cambria; mso-ascii-font-family:Cambria; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Cambria; mso-hansi-theme-font:minor-latin; mso-ansi-language:EN-US;} The objective of this benchmark is to measure the performance improvement achieved when enabling the Multi-Threaded Slave enhancement delivered as a part MySQL 5.6. As the results demonstrate, Multi-Threaded Slaves delivers 5x higher replication performance based on a configuration with 10 databases/schemas. For real-world deployments, higher replication performance directly translates to: · Improved consistency of reads from slaves (i.e. reduced risk of reading "stale" data) · Reduced risk of data loss should the master fail before replicating all events in its binary log (binlog) The multi-threaded slave splits processing between worker threads based on schema, allowing updates to be applied in parallel, rather than sequentially. This delivers benefits to those workloads that isolate application data using databases - e.g. multi-tenant systems deployed in cloud environments. Multi-Threaded Slaves are just one of many enhancements to replication previewed as part of the MySQL 5.6 Development Release, which include: · Global Transaction Identifiers coupled with MySQL utilities for automatic failover / switchover and slave promotion · Crash Safe Slaves and Binlog · Optimized Row Based Replication · Replication Event Checksums · Time Delayed Replication These and many more are discussed in the “MySQL 5.6 Replication: Enabling the Next Generation of Web & Cloud Services” Developer Zone article  Back to the benchmark - details are as follows. Environment The test environment consisted of two Linux servers: · one running the replication master · one running the replication slave. Only the slave was involved in the actual measurements, and was based on the following configuration: - Hardware: Oracle Sun Fire X4170 M2 Server - CPU: 2 sockets, 6 cores with hyper-threading, 2930 MHz. - OS: 64-bit Oracle Enterprise Linux 6.1 - Memory: 48 GB Test Procedure Initial Setup: Two MySQL servers were started on two different hosts, configured as replication master and slave. 10 sysbench schemas were created, each with a single table: CREATE TABLE `sbtest` (    `id` int(10) unsigned NOT NULL AUTO_INCREMENT,    `k` int(10) unsigned NOT NULL DEFAULT '0',    `c` char(120) NOT NULL DEFAULT '',    `pad` char(60) NOT NULL DEFAULT '',    PRIMARY KEY (`id`),    KEY `k` (`k`) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 10,000 rows were inserted in each of the 10 tables, for a total of 100,000 rows. When the inserts had replicated to the slave, the slave threads were stopped. The slave data directory was copied to a backup location and the slave threads position in the master binlog noted. 10 sysbench clients, each configured with 10 threads, were spawned at the same time to generate a random schema load against each of the 10 schemas on the master. Each sysbench client executed 10,000 "update key" statements: UPDATE sbtest set k=k+1 WHERE id = <random row> In total, this generated 100,000 update statements to later replicate during the test itself. Test Methodology: The number of slave workers to test with was configured using: SET GLOBAL slave_parallel_workers=<workers> Then the slave IO thread was started and the test waited for all the update queries to be copied over to the relay log on the slave. The benchmark clock was started and then the slave SQL thread was started. The test waited for the slave SQL thread to finish executing the 100k update queries, doing "select master_pos_wait()". When master_pos_wait() returned, the benchmark clock was stopped and the duration calculated. The calculated duration from the benchmark clock should be close to the time it took for the SQL thread to execute the 100,000 update queries. The 100k queries divided by this duration gave the benchmark metric, reported as Queries Per Second (QPS). Test Reset: The test-reset cycle was implemented as follows: · the slave was stopped · the slave data directory replaced with the previous backup · the slave restarted with the slave threads replication pointer repositioned to the point before the update queries in the binlog. The test could then be repeated with identical set of queries but a different number of slave worker threads, enabling a fair comparison. The Test-Reset cycle was repeated 3 times for 0-24 number of workers and the QPS metric calculated and averaged for each worker count. MySQL Configuration The relevant configuration settings used for MySQL are as follows: binlog-format=STATEMENT relay-log-info-repository=TABLE master-info-repository=TABLE As described in the test procedure, the slave_parallel_workers setting was modified as part of the test logic. The consequence of changing this setting is: 0 worker threads:    - current (i.e. single threaded) sequential mode    - 1 x IO thread and 1 x SQL thread    - SQL thread both reads and executes the events 1 worker thread:    - sequential mode    - 1 x IO thread, 1 x Coordinator SQL thread and 1 x Worker thread    - coordinator reads the event and hands it to the worker who executes 2+ worker threads:    - parallel execution    - 1 x IO thread, 1 x Coordinator SQL thread and 2+ Worker threads    - coordinator reads events and hands them to the workers who execute them Results Figure 1 below shows that Multi-Threaded Slaves deliver ~5x higher replication performance when configured with 10 worker threads, with the load evenly distributed across our 10 x schemas. This result is compared to the current replication implementation which is based on a single SQL thread only (i.e. zero worker threads). Figure 1: 5x Higher Performance with Multi-Threaded Slaves The following figure shows more detailed results, with QPS sampled and reported as the worker threads are incremented. The raw numbers behind this graph are reported in the Appendix section of this post. Figure 2: Detailed Results As the results above show, the configuration does not scale noticably from 5 to 9 worker threads. When configured with 10 worker threads however, scalability increases significantly. The conclusion therefore is that it is desirable to configure the same number of worker threads as schemas. Other conclusions from the results: · Running with 1 worker compared to zero workers just introduces overhead without the benefit of parallel execution. · As expected, having more workers than schemas adds no visible benefit. Aside from what is shown in the results above, testing also demonstrated that the following settings had a very positive effect on slave performance: relay-log-info-repository=TABLE master-info-repository=TABLE For 5+ workers, it was up to 2.3 times as fast to run with TABLE compared to FILE. Conclusion As the results demonstrate, Multi-Threaded Slaves deliver significant performance increases to MySQL replication when handling multiple schemas. This, and the other replication enhancements introduced in MySQL 5.6 are fully available for you to download and evaluate now from the MySQL Developer site (select Development Release tab). You can learn more about MySQL 5.6 from the documentation  Please don’t hesitate to comment on this or other replication blogs with feedback and questions. Appendix – Detailed Results

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• Safe, standard way to load images in ListView on a different thread?

  - by Po

  Before making this question, I have searched and read these ones: http://stackoverflow.com/questions/541966/android-how-do-i-do-a-lazy-load-of-images-in-listview http://stackoverflow.com/questions/1409623/android-issue-with-lazy-loading-images-into-a-listview My problem is I have a ListView, where: Each row contains an ImageView, whose content is to be loaded from the internet Each row's view is recycled as in ApiDemo's List14 What I want ultimately: Load images lazily, only when the user scrolls to them Load images on different thread(s) to maintain responsiveness My current approach: In the adapter's getView() method, apart from setting up other child views, I launch a new thread that loads the Bitmap from the internet. When that loading thread finishes, it returns the Bitmap to be set on the ImageView (I do this using AsyncTask or Handler). Because I recycle ImageViews, it may be the case that I first want to set a view with Bitmap#1, then later want to set it to Bitmap#2 when the user scrolls down. Bitmap#1 may happen to take longer than Bitmap#2 to load, so it may end up overwriting Bitmap#2 on the view. I solve this by maintaining a WeakHashMap that remembers the last Bitmap I want to set for that view. Below is somewhat a pseudocode for my current approach. I've ommitted other details like caching, just to keep the thing clear. public class ImageLoader { // keeps track of the last Bitmap we want to set for this ImageView private static final WeakHashMap<ImageView, AsyncTask> assignments = new WeakHashMap<ImageView, AsyncTask>(); /** Asynchronously sets an ImageView to some Bitmap loaded from the internet */ public static void setImageAsync(final ImageView imageView, final String imageUrl) { // cancel whatever previous task AsyncTask oldTask = assignments.get(imageView); if (oldTask != null) { oldTask.cancel(true); } // prepare to launch a new task to load this new image AsyncTask<String, Integer, Bitmap> newTask = new AsyncTask<String, Integer, Bitmap>() { protected void onPreExecute() { // set ImageView to some "loading..." image } protected Bitmap doInBackground(String... urls) { return loadFromInternet(imageUrl); } protected void onPostExecute(Bitmap bitmap) { // set Bitmap if successfully loaded, or an "error" image if (bitmap != null) { imageView.setImageBitmap(bitmap); } else { imageView.setImageResource(R.drawable.error); } } }; newTask.execute(); // mark this as the latest Bitmap we want to set for this ImageView assignments.put(imageView, newTask); } /** returns (Bitmap on success | null on error) */ private Bitmap loadFromInternet(String imageUrl) {} } Problem I still have: what if the Activity gets destroyed while some images are still loading? Is there any risk when the loading thread calls back to the ImageView later, when the Activity is already destroyed? Moreover, AsyncTask has some global thread-pool underneath, so if lengthy tasks are not canceled when they're not needed anymore, I may end up wasting time loading things users don't see. My current design of keeping this thing globally is too ugly, and may eventually cause some leaks that are beyond my understanding. Instead of making ImageLoader a singleton like this, I'm thinking of actually creating separate ImageLoader objects for different Activities, then when an Activity gets destroyed, all its AsyncTask will be canceled. Is this too awkward? Anyway, I wonder if there is a safe and standard way of doing this in Android. In addition, I don't know iPhone but is there a similar problem there and do they have a standard way to do this kind of task? Many thanks.

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