I was never sure what resources in JDBC must be explicitely closed and wasn’t able to find it anywhere explained. Finally my good colleague, Magne Mære, has explained it to me: In JDBC there are several kinds of resources that ideally should be closed after use. Even though every Statement and PreparedStatement is specified to be implicitly closed when the Connection object is closed, you can’t be guaranteed when (or if) this happens, especially if it’s used with connection pooling. You should explicitly close your Statement and PreparedStatement objects to be sure. ResultSet objects might also be an issue, but as they are guaranteed to be closed when the corresponding Statement/PreparedStatement object is closed, you can usually disregard it. Summary: Always close PreparedStatement/Statement and Connection. (Of course, with Java 7+ you’d use the try-with-resources idiom to make it happen automatically.) PS: I believe that the close() method on pooled connections doesn’t actually close them but just returns them to the pool. A request to my dear users: References to any good resources would be appreciate.

This post comes from Ignacio Nin at the MySQL Performance Blog. Lately we’ve had many reports of the RPM packages for CentOS 5 (mostly) and CentOS 6 having issues when installing different combinations of our products, particularly with Percona Toolkit. Examples of bugs related to these issues are lp:1031427 and lp:1051874. These problems arise when trying to install a package from the distribution that is linked against the version of libmysqlclient.so shipped by the distribution (libmysqlclient.so.15 for CentOS 5/libmysqlclient.so.16 for CentOS 6) and a version of Percona Server that depends on another version of libmysqlclient.so, usually more recent. Bug lp:1031427 is an example of this, and shows how the packages would conflict when trying to install libmysqlclient.so. For example, when installing php-mysql alongside PS 5.5 in CentOS 6: # yum -q install Percona-Server-server-55 php-mysql Installing: Percona-Server-server-55 x86_64 5.5.29-rel29.4.401.rhel6 percona 15 M php-mysql x86_64 5.3.3-14.el6_3 updates 79 k Installing for dependencies: Percona-Server-client-55 x86_64 5.5.29-rel29.4.401.rhel6 percona 7.0 M Percona-Server-shared-51 x86_64 5.1.67-rel14.3.506.rhel6 percona 2.8 M Percona-Server-shared-55 x86_64 5.5.29-rel29.4.401.rhel6 percona 787 k Transaction Summary ===================================================================================================================================================== Install 5 Package(s) Is this ok [y/N]: y Transaction Check Error: file /usr/lib64/libmysqlclient.so conflicts between attempted installs of Percona-Server-shared-51-5.1.67-rel14.3.506.rhel6.x86_64 and Percona-Server-shared-55-5.5.29-rel29.4.401.rhel6.x86_64 file /usr/lib64/libmysqlclient_r.so conflicts between attempted installs of Percona-Server-shared-51-5.1.67-rel14.3.506.rhel6.x86_64 and Percona-Server-shared-55-5.5.29-rel29.4.401.rhel6.x86_64 The traditional solution for this situation was to provide a special package, Percona-Server-shared-compat (modeled after upstream’s MySQL-shared-compat) which would contain ALL versions of libmysqlclient.so.* together and wouldn’t conflict. Probably some of you are familiar with this approach. # yum -q install Percona-Server-server-55 Percona-Server-shared-compat php-mysql Installing: Percona-Server-server-55 x86_64 5.5.29-rel29.4.401.rhel6 percona 15 M Percona-Server-shared-compat x86_64 5.5.29-rel29.4.401.rhel6 percona 3.4 M php-mysql x86_64 5.3.3-14.el6_3 updates 79 k Installing for dependencies: Percona-Server-client-55 x86_64 5.5.29-rel29.4.401.rhel6 percona 7.0 M Percona-Server-shared-55 x86_64 5.5.29-rel29.4.401.rhel6 percona 787 k Transaction Summary ===================================================================================================================================================== Install 5 Package(s) Notice how PS-shared-compat installs along the -shared package, providing the older libmysqlclient.so.16 required by php-mysql. However, this has proved non-intuitive and problematic, since the shared-compat package wouldn’t get selected unless explicitely installed — and many of our users would rather have it “just work” without requiring additional knowledge of what the particular workaround was, etc.. We’re now trying a solution in which our -shared packages won’t conflict anymore at libmysqlclient.so, so we are able to install them side-by-side, modelled after the mysql-libs packages provided by CentOS/Redhat. So even if the user wants to install PS 5.5 alongside packages that depend on 5.1/5.0, the -shared packages will work together. For example installing 5.5 and postfix in CentOS: # yum -q install Percona-Server-server-55 postfix Installing: Percona-Server-server-55 x86_64 5.5.29-rel29.4.402.rhel5 percona-testing 19 M postfix x86_64 2:2.3.3-6.el5 base 3.8 M Installing for dependencies: Percona-SQL-shared-50 x86_64 5.0.92-b23.89.rhel5 percona-testing 1.8 M Percona-Server-client-55 x86_64 5.5.29-rel29.4.402.rhel5 percona-testing 9.1 M Percona-Server-shared-55 x86_64 5.5.29-rel29.4.402.rhel5 percona-testing 993 k … and this will install without problems. Additionally, this has the advantage of allowing an upgrade from 5.1 to 5.5 without uninstalling any software that depended on the old version. # rpm -qa | grep ^Percona Percona-Server-client-51-5.1.67-rel14.3.507.rhel6.x86_64 Percona-Server-shared-51-5.1.67-rel14.3.507.rhel6.x86_64 Percona-Server-server-51-5.1.67-rel14.3.507.rhel6.x86_64 In this case only Percona-Server-client-51 and Percona-Server-server-51 need be removed, allowing any package that depends on Percona-Server-shared-51 (providing libmysqlclient.so.16) to remain installed. After the server and client packages are uninstalled, you can install PS 5.5 without conflict. The current package candidates for versions 5.0.92 (which required an update), 5.1.67-14.3 and 5.5.29-29.4 can be tested from the percona-testing repository. We encourage you to try these out and send us your feedback and/or file any bugs you find. Installation instructions for Percona Testing repositories. We’re aiming to include these fixes in our next releases of 5.1 and 5.5. Percona Toolkit users in particular will enjoy this update since it’ll mean no more trouble when installing it from repository!

The post titled Installing Packages described the basics of package installation with R. The process is wonderfully simple when everything goes well. But it can be maddening when it does not. Error messages give a hint as to what went wrong but do not necessarily tell you how to resolve the problem. This post will collect some of the error messages we’ve encountered while installing R packages and describe the reasons for the error and the workarounds we’ve found. 1) Older version of R Warning message: In install.packages(c("sp")) : package ‘sp’ is not available This is the message that you get when the CRAN package you’re interested in requires a more recent version of R than you have. Remember, the default behavior ofinstall.packages() is to grab the latest version of a package. In this case you have to poke around in the “Old sources” link on the CRAN page for that package and use trial-and-error to find an older version of the package that will work with your version of R. You should start by determining what version of R you have: 1 2 $R--version Rversion2.8.1(2008-12-22) This version of R was released at the end of 2008 and any version of the “sp” package released in 2008 should work. At least some of the 2009 releases should also work. Perusing the sp archive, we might try installing version 0.9-37, the last of the 0.9-3x series which was released in May of 2009: 1 2 3 4 $wget http://cran.r-project.org/src/contrib/Archive/sp/sp_0.9-37.tar.gz $sudo CMD INSTALL sp_0.9-37.tar.gz ... $# Success! 2) Unable to execute files in /tmp directory ERROR: 'configure' exists but is not executable -- see the 'R Installation and Administration Manual' By default, R uses the /tmp directory to install packages. On security conscious machines, the /tmp directory is often marked as “noexec” in the /etc/fstab file. This means that no file under /tmp can ever be executed. Packages that require compilation or that have self-inflating data will fail with the error above. One such package isRJSONIO. The solution is to set the TMPDIR environment variable which R will use as the compilation directory. For csh shell: 1 2 $mkdir~/tmp $setenv TMPDIR~/tmp And for bash: 1 2 $mkdir~/tmp $export TMPDIR=~/tmp Other problems Please leave comments describing other package installation problems and solutions you’ve encountered to help us build a more complete listing.

When I want to insert figures generated in R into a LaTeX document, it looks better if I first remove the white space around the figure. Unfortunately, R does not make this easy as the graphs are generated to look good on a screen, not in a document. There are two things that can be done to fix this problem. First, you can reduce the white space generated by R. I use the following function when saving figures in R. savepdf <- function(file, width=16, height=10) { fname <- paste("figures/",file,".pdf",sep="") pdf(fname, width=width/2.54, height=height/2.54, pointsize=10) par(mgp=c(2.2,0.45,0), tcl=-0.4, mar=c(3.3,3.6,1.1,1.1)) } The width and height are in centimetres. The ratio is about right for a beamer presentation, and also to fit two figures on an A4 page. Then I use the commands savepdf("filename") # Plotting commands here dev.off() That will generate a pdf figure of about the right size and shape for a document, and with narrow margins of white space, and save it in my figures sub-directory. The second trick is to trim the pdf files so there is no white space left. On a unix system, this is easily achieved as follows. pdfcrop filename.pdf filename.pdf There are probably windows and mac versions of the same, but I haven’t used them. Adobe Acrobat will also crop pdfs, but not from the command line as far as I know. To apply pdfcrop to every file in a directory (using unix), save the following to a file called cropall.sh: #!/bin/bash for FILE in ./*.pdf; do pdfcrop "${FILE}" "${FILE}" done Make the file executable and run it. In my post on Makefiles, I explain how to include pdfcrop within a Makefile. If you just use pdfcrop without first reducing the white space in R, the proportions come out a little odd. So I tend to use both approaches together.

JDK6 update 7 and onward include a tool called VisualVM. VisualVM is a visual tool with monitoring and profiling capabilities for the JVM. With VisualVM you can: Monitor heap usage Monitor CPU usage Monitor Threads Initiate garbage collections Profile CPU and memory And more… Although VisualVM is distributed with the Oracle JDK, it can also be used to monitor IBM JVM’s. VisualVM is not able to connect to the IBM JVM locally. JMX must be used instead. To enable JMX monitoring on the IBM JVM open the WebSphere administrative console and: navigate to: Server -> Server Types -> WebSphere application servers ->[SERVER_NAME] Expand Java and Process Management and click Process definition Click Java Virtual Machine In the Generic JVM arguments field append the following properties: -Djavax.management.builder.initial= -Dcom.sun.management.jmxremote -Dcom.sun.management.jmxremote.authenticate=false -Dcom.sun.management.jmxremote.ssl=false -Dcom.sun.management.jmxremote.port=1099 Restart the server To start monitoring the JVM with VisualVM start VisualVM by navigating to [JDK_HOME]\bin and start jvisualvm.exe (please note that when VisualVM is downloaded as a separate package the executable is called visualvm.exe instead). In VisualVM click File -> Add JMX Connection. Specify localhost:1099 in the connection field and click OK. If everything went OK, you should see the localhost:1099 connection under the Local node in the tree on the left. Double-click this node to start monitoring. See the following screenshot for an example: When using a JMX connection to monitor the JVM please be aware that not all functionality can be used compared to monitoring a local JVM. Profiling memory is for example not possible. The above configuration was tested on: Windows 7 64-bit IBM JDK1.6 64 bit WebSphere Application Server version 7.0 Note: Before JDK6 update 7, VisualVM can also be downloaded separately from http://visualvm.java.net/download.html Note: To actually test if port 1099 is listening for connections use (on Windows) the netstat –a command and check wether the port is present and listening.

Scala offers a functionality known as Structural Types which allows to set a behaviour very similar to what dynamic languages allow to do when they support Duck Typing (http://en.wikipedia.org/wiki/Duck_typing) The main difference is that it is a type safe, static typed implementation checked up at compile time. This means that you can create a function (or method) that receives an expected duck. But at compile time it would be checked that anything that is passed can actually quack like a Duck. Here is an example. Let’s say we want to create a function that expects anything that can quack like a duck. This is how we would do it in Scala with Structural Typing: def quacker(duck: {def quack(value: String): String}) { println (duck.quack("Quack")) } You can see that in the definition of the function we are not expecting a particular class or type. We are specifying an Structural Type which in this case means that we are expecting any type that has a method with the signature quack(string: String): String. So all the following examples will work with that function: object BigDuck { def quack(value: String) = { value.toUpperCase } } object SmallDuck { def quack(value: String) = { value.toLowerCase } } object IamNotReallyADuck { def quack(value: String) = { "prrrrrp" } } quacker(BigDuck) quacker(SmallDuck) quacker(IamNotReallyADuck) You can see that there is no interface or anything being implemented by any of the three objects we have defined. They simply have to define the method quack in order to work in our function. If you run the code above you get the output: QUACK quack prrrrrp If on the other hand you try to create an object without a quack method and try to call the function with that object you would get a compile error. For example trying to do this: object NoQuaker { } quacker(NoQuaker) You would get the error: error: type mismatch; found : this.NoQuaker.type required: AnyRef{def quack(value: String): String} quacker(NoQuaker) Also, you don’t even need to create a new type or class. You could use AnyRef to create an object with the quack method. Like this: val x = new AnyRef { def quack(value: String) = { "No type needed "+ value } } and you can use that object to call the function: quacker(x) You can also specify in the function that expects the structural type, the the parameter object must respond to more than one method. Like this: def quacker(duck: {def quack(value: String): String; def walk(): String}) { println (duck.quack("Quack")) } There you are saying that any object you pass to the function needs to respond to both methods quack and walk. This is also checked at compile time. Under the covers the use of Structural Types in this way will be handled by reflection. This means that it is a more expensive operation than the standard method call. So use only when it actually makes sense to use it.

Dependency inversion is the idea that interfaces should depend on abstractions not on specifics. According to Wikipedia, the principle states: A. High-level modules should not depend on low-level modules. Both should depend on abstractions. B. Abstractions should not depend upon details. Details should depend upon abstractions. Of course the second part of this principle is impossible if read literally. You can't have an abstraction until you know what details are to be covered, and so the abstraction and details are both co-dependent. If the covered details change sufficiently the abstraction will become either leaky or inadequate and so it is worth seeing these as intertwined to some extent. The focus on abstraction is helpful because it suggests that the interface contract should be designed in such a way that neither side really has to understand any internal details of the other in order to make things work. Both sides depend on well-encapsulated API's and neither side has to worry about what the other side is really doing. This is what is meant by details depending on abstractions rather than the other way around. This concept is quite applicable beyond object oriented programming because it covers a very basic aspect of API contract design, namely how well an API should encapsulate behavior. This principle is first formulated in its current form in the object oriented programming paradigm but is generally applicable elsewhere. SQL as an Abstraction Layer, or Why RDBMS are Still King There are plenty of reasons to dislike SQL, such as the fact that nulls are semantically ambiguous. As a basic disclaimer I am not holding SQL up to be a paragon of programming languages or even db interfaces, but I think it is important to discuss what SQL does right in this regard. SQL is generally understood to be a declarative language which approximates relational mathematics for database access purposes. With SQL, you specify what you want returned, not how to get it, and the planner determines the best way to get it. SQL is thus an interface language rather than a programming language per se. With SQL, you can worry about the logical structure, leaving the implementation details to the db engine. SQL queries are basically very high level specifications of operations, not detailed descriptions of how to do something efficiently. Even update and insert statements (which are by nature more imperative than select statements) leave the underlying implementation entirely to the database management system. I think that this, along with many concessions the language has made to real-world requirements (such as bags instead of sets and the addition of ordering to bags) largely account for the success of this language. SQL, in essence, encapsulates a database behind a mature mathematical, declarative model in the same way that JSON and REST do (in a much less comprehensive way) in many NoSQL db's. In essence SQL provides encapsulation, interface, and abstraction in a very full-featured way and this is why it has been so successful. SQL Abstraction as Imperfect One obvious problem with treating SQL as an abstraction layer in its own right is that one is frequently unable to write details in a way that is clearly separate from the interface. Often storage tables are hit directly, and therefore there is little separation between logical detail and logical interface, and so this can break down when database complexity reaches a certain size. Approaches to managing this problem include using stored procedures or user defined functions, and using views to encapsulate storage tables. Stored Procedures and User Defined Functions Done Wrong Of the above methods, stored procedures and functional interfaces have bad reputations frequently because of bad experiences that many people have with them. These include developers pushing too much logic into stored procedures, and the fact that defining functional interfaces in this way usually produces a very tight binding between database code and application code, often leading to maintainability problems. The first case is quite obvious, and includes the all-too-frequent case of trying to send emails directly from stored procedures (always a bad idea). This mistake leads to certain types of problems, including the fact that ACID-compliant operations may be mixed with non-ACID-compliant ones, leading to cases where a transaction can only be partially rolled back. Oops, we didn't actually record the order as shipped, but we told the customer it was..... MySQL users will also note this is an argument against mixing transactional and nontransactional backend table types in the same db..... However that problem is outside the scope of this post. Additionally, MySQL is not well suited for many applications against a single set of db relations. The second problem, though, is more insidious. The traditional way stored procedures and user defined functions are typically used, the application has to be deeply aware of the interface to the database, but the rollout for these aspects is different leading to the possibility or service interruptions, and a need to very carefully and closely time rollout of db changes with application changes. As more applications use the database, this becomes harder and the chance of something being overlooked becomes greater. For this reason the idea that all operations must go through a set of stored procedures is a decision fraught with hazard as the database and application environment evolves. Typically it is easier to manage backwards-compatibility in schemas than it is in functions and so a key question is how many opportunities you have to create new bugs when a new column is added. There are, of course, more hazards which I have dealt with before, but the point is that stored procedures are potentially harmful and a major part of the reason is that they usually form a fairly brittle contract with the application layer. In a traditional stored procedure, adding a column to be stored will require changing the number of variables in the stored procedure's argument list, the queries to access it, and each application's call to that stored procedure. In this way, they provide (in the absence of other help) at best a leaky abstraction layer around the database details. This is the sort of problem that dependency inversion helps to avoid. Stored Procedures and User Defined Functions Done Right Not all stored procedures are done wrong. In the LedgerSMB project we have at least partially solved the abstraction/brittleness issue by looking to web services for inspiration. Our approach provides an additional mapping layer and dynamic query generation around a stored procedure interface. By using a service locator pattern, and overloading the system tables in PostgreSQL as the service registry, we solve the problem of brittleness. Our approach of course is not perfect and it is not the only possibility. One shortcoming is that our approach is that the invocation of the service locator is relatively spartan. We intend to allow more options there in the future. However one thing I have noticed is the fact that there are far fewer places where bugs can hide and therefore faster and more robust development takes place. Additionally a focus on clarity of code in stored procedures has eliminated a number of important performance bottlenecks, and it limits the number of places where a given change propagates to. Other Important Options in PostgreSQL Stored procedures are not the only abstraction mechanisms available from PostgreSQL. In addition to views, there are also other interesting ways of using functions to accomplish this without insisting that all access goes through stored procedures. In addition these methods can be freely mixed to produce very powerful, intelligent database systems. Such options include custom types, written in C, along with custom operators, functions and the like. These would then be stored in columns and SQL can be used to provide an abstraction layer around the types. In this way SQL becomes the abstraction and the C programs become the details. A future post will cover the use of ip4r in network management with PostgreSQL db's as an example of what can be done here. Additionally, things like triggers and notifications can be used to ensure that appropriate changes trigger other changes in the same transaction or, upon transaction commit, hand off control to other programs in subsequent transactions (allowing for independent processing and error control for things like sending emails). Recommendations Rather than specific recommendations, the overall point here is to look at the database itself as a an application running in an application server (the RDBMS) and design it as an application with an appropriate API. There are many ways to do this, from writing components in C and using SQL as an abstraction mechanism to writing things in SQL and using stored procedures as a mechanism. One could even write code in SQL and still use SQL as an abstraction mechanism. The key point however is to be aware of the need for discoverable abstraction, a need which to date things like ORMs and stored procedures often fill very imperfectly. A well designed db with appropriate abstraction in interfaces, should be able to be seen as an application in its own right, engineered as such, and capable of serving multiple client apps through a robust and discoverable API. As with all things, it starts by recognizing the problems and putting solutions as priorities from the design stage onward.

As I mentioned in a previous post I’ve been playing around with some football related data over the last few days and one query I ran (using cypher) was to find all the players who’ve been sent off this season in the Premiership. The model in the graph around sending offs looks like this: My initial query looked like this: START player = node:players('name:*') MATCH player-[:sent_off_in]-game-[:in_month]-month RETURN player.name, month.name First we get the names of all the players which are stored in an index and then we follow relationships to the games they were sent off in and then find which months those games were played in. That query returns: +----------------------------+ | player.name | month.name | +----------------------------+ | "Jenkinson" | "February" | | "Chico" | "September" | | "Odemwingie" | "September" | | "Agger" | "August" | | "Cole" | "December" | | "Whitehead" | "August" | ... +----------------------------+ I thought it’d be interesting to see how many sending offs there were in each month which we’d achieve in SQL by making use of a GROUP BY. cypher has a bunch of aggregation functions which allow us to achieve the same outcome. In our case we want to use the COUNT function and we want our grouping key to be the month of the year so we need to include that as part of our RETURN statement as well: START player = node:players('name:*') MATCH player-[:sent_off_in]-game-[:in_month]-month RETURN COUNT(player.name) AS numberOfReds, month.name ORDER BY numberOfReds DESC which returns: +----------------------------+ | numberOfReds | month.name | +----------------------------+ | 7 | "October" | | 6 | "December" | | 4 | "September" | | 4 | "November" | | 3 | "August" | | 2 | "January" | | 2 | "February" | +----------------------------+ As far as I can tell anything which isn’t an aggregate function is used as part of the grouping key which means we could include more than one field in our grouping key. This isn’t particularly relevant for us for this particular query but would become useful if we add the teams that the players play for. I extended the graph to included a player’s statistics for each game which also includes a relationship indicating which team they played for in a specific game. The model now looks like this: It does now look quite a bit more complicated but this was the best way I could think of modelling player specific details for a match. I couldn’t see another way of modelling the fact that a player played for a certain team in a match which I want to use for some other queries but if you can see a simpler way please let me know. To get a list of the red cards and the name of the team the offender played for we can write the following query: START player = node:players('name:*') MATCH player-[:sent_off_in]-game-[:in_month]-month, game-[:in_match]-stats-[:stats]-player, stats-[:played_for]-team RETURN player.name, month.name, team.name ORDER BY month.name The original query traversed a path from a player to games they were sent off in and then from the games to the month the game was played in. We’ve now added a traversal from the game to the game stats for that player and we also traverse from the game stats to the team node that the player played for in that game. When we run this we get the following results: +--------------------------------------------+ | player.name | month.name | team.name | +--------------------------------------------+ | "Agger" | "August" | "Liverpool" | | "Whitehead" | "August" | "Stoke" | ... | "Shotton" | "December" | "Stoke" | | "Nzonzi" | "December" | "Stoke" | | "Jenkinson" | "February" | "Arsenal" | ... | "Ivanovic" | "October" | "Chelsea" | | "Torres" | "October" | "Chelsea" | +--------------------------------------------+ So we can see that Stoke got 2 players sent off in December and Chelsea got 2 sent off in October. We can write the following query to return a result set which uses team and month as the grouping key i.e. we count how many paths there are which have the same team and month: START player = node:players('name:*') MATCH player-[:sent_off_in]-game-[:in_month]-month, game-[:in_match]-stats-[:stats]-player, stats-[:played_for]-team RETURN month.name, team.name, COUNT(player.name) AS numberOfReds ORDER BY numberOfReds DESC When we run that query we see the following results: +--------------------------------------------+ | month.name | team.name | numberOfReds | +--------------------------------------------+ | "December" | "Stoke" | 2 | | "October" | "Chelsea" | 2 | ... | "August" | "Stoke" | 1 | | "November" | "Tottenham" | 1 | | "December" | "Everton" | 1 | +--------------------------------------------+ This is all explained in more detail in the documentation but I thought it’d be interesting to write about it from the perspective of someone more used to writing SQL and trying to work out how to achieve the same thing in cypher.

This article wants to bring some hints about how to use HTML5 canvas with Apache Wicket web framework. Inside a Wicket application we want to have a panel with something drawn inside a HTML5 canvas. To make this happen we have to think about following: Do we really need HTML5? If we need HTML5, how to do it? What to do if browser version is an issue and it does not support HTML5? 1. First we should ask if we really need HTML5 If we need just an image then we should consider to draw inside a Java2D Graphics object. If we need some animation we should consider to draw inside a HTML5 canvas, but even in this case we need a simple Java2D image implementation if browser version is a concern and canvas is not supported. Wicket has a RenderedDynamicImageResource class which is very handy for this because we can do Java2D stuff inside render(Graphics2D g2) method. A simple example may look like the following: public class MyDynamicImageResource extends RenderedDynamicImageResource { private int width; private int height; private MyData data; public MyDynamicImageResource (int width, int height, MYData data) { super(width, height); this.width = width; this.height = height; this.data = data; } protected boolean render(Graphics2D g2) { g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON); g2.setRenderingHint(RenderingHints.KEY_RENDERING, RenderingHints.VALUE_RENDER_QUALITY); // your code } } Because Java2d is used, we can set anti-aliasing to make the image look good. Then we can use this dynamic resource to create our panel. We will use Wicket's NonCachingImage class, a subclass of Image that adds random noise to the url at every request to prevent the browser from caching the image. If you do not care that browser caches your image then you should use a simple Image instead. public class MyJava2DImagePanel extends Panel { private MyDynamicImageResource imageResource; public MyJava2DImagePanel(String id, final int width, final int height, final IModel model) { super(id, model); NonCachingImage image = new NonCachingImage("myImage", new PropertyModel(this, "imageResource")) { private static final long serialVersionUID = 1L; @Override protected void onBeforeRender() { imageResource = new MyDynamicImageResource(width, height, model.getObject()); super.onBeforeRender(); } }; add(image); } } Markup html file for MyJava2DImagePanel will contain the image: 2. If we need some animation for our image, then we should think to draw it on a HTML5 canvas. We should pay attention to draw things just once, meaning for example if we draw a text twice in same position , then our result will look ugly (pix-elated) because an anti-aliasing for canvas cannot be set as for Java2D Graphics object. First we need to create our java script code. We can obtain a Java 2d context and use it to draw our image. I won't talk about canvas context and its methods here. For animation we use jquery in following snippet, but you can use anything you like. Knowing two values (from, to) we can have for example a drawColor method which can paint different segments, creating this way a filling effect which takes in this example 1000ms : var myWidget = function(id, color) { var can = document.getElementById(id); var ctx = can.getContext('2d'); // clear canvas ctx.clearRect(0, 0, can.width, can.height); // draw your image on ctx ..... // animate color fill $({ n: from }).animate({ n: to}, { duration: 1000, step: function(now, fx) { drawColor(id, now); } }); } } Second we have to create our Wicket panel. Canvas is just a WebMarkupContainer and we set width and height through some AttributeAppenders: public class MyHTML5Panel extends Panel { private final ResourceReference MY_JS = new JavaScriptResourceReference(MyHTML5Panel.class, "my.js"); public MyHTML5Panel(String id, String width, String height, IModel model) { super(id, model); WebMarkupContainer container = new WebMarkupContainer("canvas"); container.setOutputMarkupId(true); container.add(new AttributeAppender("width", width)); container.add(new AttributeAppender("height", height)); add(container); } @Override public void renderHead(IHeaderResponse response) { response.renderOnLoadJavaScript(getJavascriptCall()); //include js file response.renderJavaScriptReference(MY_JS); } private String getJavascriptCall() { MyData data = getModel().getObject(); StringBuilder sb = new StringBuilder(); sb.append("myWidget(\""). append(get("canvas").getMarkupId()). append("\",\"").append(data.getColor()). append("\");"); return sb.toString(); } } renderHead(IHeaderResponse response) method from Panel can use the IHeaderResponse object to render our java script call. Also, on the response object we should render our java script reference file. We can use one of the following methods: /** * Renders javascript that is executed right after the DOM is built, before external resources * (e.g. images) are loaded. * * @param javascript */ public void renderOnDomReadyJavaScript(String javascript); /** * Renders javascript that is executed after the entire page is loaded. * * @param javascript */ public void renderOnLoadJavaScript(String javascript); There are situations when we should call one or another depending on our business. As an example, if we need to expose our wicket component to an external iframe, we must call onLoad instead of onDomReady to make it appear inside iframe because $(document).ready in the iframe seems to be fired too soon and the iframe content isn't even loaded yet. HTML markup file MyHTML5Panel.html will contain the canvas tag: 3. If we choose to use HTML5 panel but we also have to think about older browser that cannot support canvas tag, we will have to create both a Java2D and a HTML5 panel and see what to render by ourselves. A solution is to have a wrapper panel with a container which initially contains an EmptyPanel and we add a Wicket Behavior to the container. That behavior will choose what to render (html5 or simple image): ..... container = new WebMarkupContainer("container"); container.setOutputMarkupId(true); container.add(new EmptyPanel("image")); add(container); add(new MyHTML5Behavior()); ....... The following java-script code is a way to test if canvas tag is supported by browser: function isCanvasEnabled() { return !!document.createElement('canvas').getContext; } This function starts by creating a dummy element which is never attached to the page, so no one will ever see it. As soon as we create the dummy element, we test for the presence of a getContext() method. This method will only exist if browser supports the canvas API. Finally, we use the double-negative trick to force the result to a Boolean value (true or false). To call this java script and make the result available to Wicket we use wicketAjaxGet javascript method as seen in following code. We append a result parameter to callback url and inside respond method we can read the value of this parameter. class MyHTML5Behavior extends AbstractDefaultAjaxBehavior { private String width; private String height; private String PARAM = "Param"; public MyHTML5Behavior() { super(); } @Override public void renderHead(Component component, IHeaderResponse response) { super.renderHead(component, response); //include js file response.renderJavaScriptReference(MY_UTIL_JS); response.renderOnLoadJavaScript(getJavascript()); } @Override protected void respond(AjaxRequestTarget target) { String param = this.getComponent().getRequest().getRequestParameters().getParameterValue(PARAM).toString(); // test if html5 canvas tag is supported if (Boolean.parseBoolean(param)) { container.replace(new MyHTML5Panel("image", width, height, model).setOutputMarkupId(true)); } else { container.replace(new MyImagePanel("image", width, height, model).setOutputMarkupId(true)); } target.add(container); } // this javascript call will make the PARAM available to wicket and can be read in respond method private String getJavascript() { StringBuilder sb = new StringBuilder(); sb.append("var data = isCanvasEnabled();"); sb.append("wicketAjaxGet('" + getCallbackUrl() + "&" + PARAM + "='+ data" + ", null, null, function() { return true; })"); return sb.toString(); } } These are just some hints on how to use HTML5 canvas inside Apache Wicket framework. I hope it will help others.

JavaFX provides certain colors by default when rendering charts. There are situations, however, when one wants to customize these colors. In this blog post I look at changing the colors of a JavaFX pie chart using an example I intend to include in my presentation this afternoon at RMOUG Training Days 2013. Some Java-based charting APIs provided Java methods to set colors. JavaFX, born in the days of HTML5 prevalence, instead uses Cascading Style Sheets (CSS) to allow developers to adjust colors, symbols, placement, alignment and other stylistic issues used in their charts. I demonstrate using CSS to change colors here. In this post, I will look at two code samples demonstrating simple JavaFX applications that render pie charts based on data from Oracle's sample 'hr' schema. The first example does not specify colors and so uses JavaFX's default colors for pie slices and for the legend background. That example is shown next. EmployeesPerDepartmentPieChart (Default JavaFX Styling) package rmoug.td2013.dustin.examples; import javafx.application.Application; import javafx.scene.Scene; import javafx.scene.chart.PieChart; import javafx.scene.layout.StackPane; import javafx.stage.Stage; /** * Simple JavaFX application that generates a JavaFX-based Pie Chart representing * the number of employees per department. * * @author Dustin */ public class EmployeesPerDepartmentPieChart extends Application { final DbAccess databaseAccess = DbAccess.newInstance(); @Override public void start(final Stage stage) throws Exception { final PieChart pieChart = new PieChart( ChartMaker.createPieChartDataForNumberEmployeesPerDepartment( this.databaseAccess.getNumberOfEmployeesPerDepartmentName())); pieChart.setTitle("Number of Employees per Department"); stage.setTitle("Employees Per Department"); final StackPane root = new StackPane(); root.getChildren().add(pieChart); final Scene scene = new Scene(root, 800 ,500); stage.setScene(scene); stage.show(); } public static void main(final String[] arguments) { launch(arguments); } } When the above simple application is executed, the output shown in the next screen snapshot appears. I am now going to adapt the above example to use a custom "theme" of blue-inspired pie slices with a brown background on the legend. Only one line is needed in the Java code to include the CSS file that has the stylistic specifics for the chart. In this case, I added several more lines to catch and print out any exception that might occur while trying to load the CSS file. With this approach, any problems loading the CSS file will lead simply to output to standard error stating the problem and the application will run with its normal default colors. EmployeesPerDepartmentPieChartWithCssStyling (Customized CSS Styling) package rmoug.td2013.dustin.examples; import javafx.application.Application; import javafx.scene.Scene; import javafx.scene.chart.PieChart; import javafx.scene.layout.StackPane; import javafx.stage.Stage; /** * Simple JavaFX application that generates a JavaFX-based Pie Chart representing * the number of employees per department and using style based on that provided * in CSS stylesheet chart.css. * * @author Dustin */ public class EmployeesPerDepartmentPieChartWithCssStyling extends Application { final DbAccess databaseAccess = DbAccess.newInstance(); @Override public void start(final Stage stage) throws Exception { final PieChart pieChart = new PieChart( ChartMaker.createPieChartDataForNumberEmployeesPerDepartment( this.databaseAccess.getNumberOfEmployeesPerDepartmentName())); pieChart.setTitle("Number of Employees per Department"); stage.setTitle("Employees Per Department"); final StackPane root = new StackPane(); root.getChildren().add(pieChart); final Scene scene = new Scene(root, 800 ,500); try { scene.getStylesheets().add("chart.css"); } catch (Exception ex) { System.err.println("Cannot acquire stylesheet: " + ex.toString()); } stage.setScene(scene); stage.show(); } public static void main(final String[] arguments) { launch(arguments); } } The chart.css file is shown next: chart.css /* Find more details on JavaFX supported named colors at http://docs.oracle.com/javafx/2/api/javafx/scene/doc-files/cssref.html#typecolor */ /* Colors of JavaFX pie chart slices. */ .data0.chart-pie { -fx-pie-color: turquoise; } .data1.chart-pie { -fx-pie-color: aquamarine; } .data2.chart-pie { -fx-pie-color: cornflowerblue; } .data3.chart-pie { -fx-pie-color: blue; } .data4.chart-pie { -fx-pie-color: cadetblue; } .data5.chart-pie { -fx-pie-color: navy; } .data6.chart-pie { -fx-pie-color: deepskyblue; } .data7.chart-pie { -fx-pie-color: cyan; } .data8.chart-pie { -fx-pie-color: steelblue; } .data9.chart-pie { -fx-pie-color: teal; } .data10.chart-pie { -fx-pie-color: royalblue; } .data11.chart-pie { -fx-pie-color: dodgerblue; } /* Pie Chart legend background color and stroke. */ .chart-legend { -fx-background-color: sienna; } Running this CSS-styled example leads to output as shown in the next screen snapshot. The slices are different shades of blue and the legend's background is "sienna." Note that while I used JavaFX "named colors," I could have also used "#0000ff" for blue, for example. I did not show the code here for my convenience classes ChartMaker and DbAccess. The latter simply retrieves the data for the charts from the Oracle database schema via JDBC and the former converts that data into the Observable collections appropriate for the PieChart(ObservableList) constructor. It is important to note here that, as Andres Almiray has pointed out, it is not normally appropriate to execute long-running processes from the main JavaFX UI thread (AKA JavaFX Application Thread) as I've done in this and other other blog post examples. I can get away with it in these posts because the examples are simple, the database retrieval is quick, and there is not much more to the chart rendering application than that rendering so it is difficult to observe any "hanging." In a future blog post, I intend to look at the better way of handling the database access (or any long-running action) using the JavaFX javafx.concurrent package (which is well already well described in Concurrency in JavaFX). JavaFX allows developers to control much more than simply chart colors with CSS. Two very useful resources detailing what can be done to style JavaFX charts with CSS are the Using JavaFX Charts section Styling Charts with CSS and the JavaFX CSS Reference Guide. CSS is becoming increasingly popular as an approach to styling web and mobile applications. By supporting CSS styling in JavaFX, the same styles can easily be applied to JavaFX apps as the HTML-based applications they might coexist with.

Yes, it is long time since i posted… Was just trying to see how a XML can be converted to JSON and to HashMap. The situation is very imaginary. import java.io.File; import java.io.FileInputStream; import java.io.IOException; import java.io.InputStream; import java.util.ArrayList; import java.util.List; import java.util.Map; import net.sf.json.JSON; import net.sf.json.xml.XMLSerializer; import org.apache.commons.io.IOUtils; import org.codehaus.jackson.JsonGenerationException; import org.codehaus.jackson.map.JsonMappingException; import org.codehaus.jackson.map.ObjectMapper; import org.codehaus.jackson.type.TypeReference; public class XML2JSONConvertor { public static void main(String[] args) throws Exception { InputStream is = new FileInputStream(new File( “e:\\jagannathan\\personal\\java-projects\\secondtest.xml”)); String xml = IOUtils.toString(is); XMLSerializer xmlSerializer = new XMLSerializer(); JSON json = xmlSerializer.read(xml); System.out.println(json.toString(2)); printJSON(json.toString(2)); } public static void printJSON(String jsonString) { ObjectMapper mapper = new ObjectMapper(); try { Map jsonInMap = mapper.readValue(jsonString, new TypeReference>() { }); List keys = new ArrayList(jsonInMap.keySet()); for (String key : keys) { System.out.println(key + “: ” + jsonInMap.get(key)); } } catch (JsonGenerationException e) { e.printStackTrace(); } catch (JsonMappingException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } } } Dependencies net.sf.json-lib json-lib 2.4 jdk15 commons-io commons-io 2.3 compile xom xom 1.2.5 org.codehaus.jackson jackson-mapper-asl 1.9.0 The Input XML Jags Inc Jagan Male 24-jul Satya Male 24-apr The output 7 Feb, 2013 7:20:50 PM net.sf.json.xml.XMLSerializer getType INFO: Using default type string { “name”: “Jags Inc”, “employees”: [ { "name": "Jagan", "sex": "Male", "dob": "24-jul" }, { "name": "Satya", "sex": "Male", "dob": "24-apr" } ] } name: Jags Inc employees: [{name=Jagan, sex=Male, dob=24-jul}, {name=Satya, sex=Male, dob=24-apr}]

today, i thought a lot about how to examine different databases. choosing a database is often a daunting task. there's a lot of confusion, a 'theorem', and more than all, the immortal proverb 'not one size fits all'. as if it helps. one of the first things that you realize, when examining nosql distributed databases (and how could you not)is that these days databases are like cars: they're all good. old fashioned sql databases can scale in and out, horizontally sharded over several machines to achieve high availability. nosql systems claim to be consistent. what difference then does it make what database would you choose? the availability and consistency that i mentioned comes, of course, from the misunderstood cap theorem , that - so people say - states that you can only choose 2 out of the 3 consistency: every read would get you the most recent write availability: every node (if not failed) always executes queries partition-tolerance: even if the connections between nodes are down, the other two (a & c) promises, are kept. usually its depicted in a nicely equilaterl triangle, as this one from ofirm : there's a nice proof and explanation of it in this 4 minute video here . but if we think about it, and also see some of brewer's (the theorem author) later remarks , we'll see that the 2 out of 3 is really 1 out of 2: it's really just a vs c! and this is simply because: availability is achieved by replicating the data across different machines consistency is achieved by updating several nodes before allowing further reads total partitioning, meaning failure of part of the system is rare. however, we could look at a delay, a latency, of the update between nodes, as a temporary partitioning . it will then cause a temporary decision between a and c: on systems that allow reads before updating all the nodes, we will get high availability on systems that lock all the nodes before allowing reads, we will get consistency that's it! and since this decision is temporary, it exists only for the duration of the delay, some may say that we are really contrasting latency (another word for availability) against consistency. by the way, there's no distributed system that wants to live with "paritioning" - if it does, it's not distributed. that is why putting sql in this triangle may lead to confusion.

Hi, I have recently created www.php.is-best.net out of an actual business necessity: The need to quickly group lines of code into php functions. What www.php.is-best.net allows you to do is to quickly extract methods out of your code. Just Grab and paste any php script inside the designated area and WHALLA! you're done. A new method will be generated out of your code.

Lets continue the "Heroes of Java" series. Today's interview has been planned nearly since the launch of the series and I knew that it would be a tough one to get. I know Marcus since a few years now and he is always busy providing the best diagnostic tools to Java developers. Thanks for finally joining, Marcus! It is a pleasure to have you here! Marcus Hirt is one of the founders of Appeal Virtual Machines, the company that created the JRockit JVM. He is currently working as Team Lead for the Java Mission Control team. In his spare time he enjoys coding on his many pet projects, composing music, and scuba diving. Marcus has contributed JRockit related articles, whitepapers, tutorials, and webinars to the JRockit community, and has been an appreciated speaker at various conferences, such as Oracle Open World and Java One. He is also one of the two authors behind a popular book about JVM technology (link to my review). General Part Who are you? I am a computer aficionado with a strikingly unmodern and lengthy romance with typed languages, profiling and diagnostics. I have three kids and a lovely wife, so right now there isn't much spare time to go around. When there was, I used to compose music, play the piano, scuba dive and do martial arts. Your official job title at your company? Consulting Member of Technical Staff Do you care about it? I care about being appreciated for my work. The title itself means nothing. Do you speak foreign languages? Which ones? Swedish is my native tongue and my preferred language for anything that is not computer related. That said, since most of the terminology in our business is in English, I actually prefer English when talking shop. I am half Swiss, and I did spend some time at Real Gymnasium Kirchenfeld in Bern. I haven't used my German since then though, so it is beyond rusty. How long is your daily "bootstrap" process? (Coffee, news, email) If you don't count email, it is almost non-existent. However, in my role as a team leader, email is chewing up a good portion of the morning these days. Thanks to the excellent mass transit system in Stockholm, that is usually taken care of before I arrive at the office. At least during the winters. During the summers I usually drive my motorcycle to work. Twitter You have a twitter handle? Why? I indiscriminately sign up for all social services. Then I find that I don't use most of them. Twitter is a bit of a exception, since I do tend to read what others write. When I do tweet it is mostly about new obscure and/or unsupported features in the Hotspot JDK. My twitter handle is @hirt. Whom are you following in general? I mostly follow people that I know and respect in the Java community. Do you have a personal "policy" for twitter? I try to avoid it at work. Does your company restrict or encourage you with your twitter usage? Oracle has neither actively encouraged nor restricted my twitter usage. The only time I can recall a company actively encouraging me to engage in some official social capacity was some years ago, when BEA tried to encourage people to blog. I’ve since moved away from the official company blog, because of a tooling issue. Work What's your daily development setup? (OS/IDE/VC/other Tools) Since the first target platform for JRockit was Windows, I've stuck with Windows at work. I am using Windows 7/Eclipse/Perforce and Visual Studio. At home I am using Mac OS X/Eclipse/Git&Perforce and XCode. Which is the tool providing most productivity to your work? These days: Eclipse. No doubt. Your preferred way of interacting with co-workers? Face to face for longer discussions. IM is good for smaller things, since you can choose when to handle the interrupt, whilst still being fairly interactive. What's your favorite way of managing your todo's? Pen and paper. Stone age, right? If you could make a wish for a job at your favorite company: What would that be? Whichever would give me the resources to attack some of the high impact development projects on my "want to do" list. Oracle is currently quite a good place to be. Java You're programming in Java. Why? To be honest, I am not exclusively programming in Java. When I do, it is because it is one of the programming environments in which I find myself to be the most productive. It may not be the least verbose or most elegant of languages, but the tooling and debugging capabilities are top notch. Not to mention that some intrinsic features of the language itself, such as the memory management, makes it easier to write error free code. Also, since there has been competition around the JVM for more than a decade, the JVMs for Java are really quite sophisticated. Not to mention fast. What's least fun with Java? It is unnecessarily verbose (more type inference please), type erasure (ever sent in a class to your generic type to have a chance of knowing what runtime type it is?), and any and all things that makes the illusion of an all powerful runtime break down. In a perfect world, a Java programmer should not have to worry about the details of the JVM configuration. For instance, why should I need to estimate how much space I will need for constants and class metadata (perm gen)? Thankfully there is work being done on this as we speak; the perm gen is scheduled for removal in JDK 8. I think there is a lot to be said for improving the usability of the JVM. If you could change one thing with Java, what would that be? There are many who want Java to be everything to everyone. I don't subscribe to that view. Instead, let's make it easy to run whatever language you want on the JVM. That said, if I could change something about the implementation, I would probably want a thread local garbage collector. One with insanely good heuristics as to when to back off and stop handling an object thread locally. Then there are some other things, but since I may start working on them soon, I would rather keep them to myself for now. :) What's your personal favorite in dynamic languages? Ruby is cute. I especially like the implementation on the JVM (JRuby). Which programming technique has moved you forwards most and why? When I first started my education at the Royal Institute of Technology, I had already programmed in various languages, such as Pascal, C and assembly. I really thought I had things figured out, until I came to the first computer science course. There I got confronted with SICP and Scheme. That was IMHO a genius move by the computer science department. All the cocky kids with prior experience, such as myself, got a rich serving of humble-pie. Functional programming taught me very elegant ways of expressing myself. Kudos to MIT and Sussman et al. What was the biggest project you've ever worked on? JRockit and JRockit Mission Control. I was one of the founders of Appeal (Appeal Virtual Machines & Appeal Software Solutions), a big project in itself. Which was the worst programming mistake you did? Well, maybe not strictly a programming mistake, but one of the worst red-face issues I've done is when a JRockit performance counter was slightly misspelled - the 'o' was accidentally dropped from *count. The bug report stated that "the customer was not amused". I must admit I was though. Another fun, deliberate, "mistake" was when I added the following three lines to one of the Mission Control property files: ------ # :) We just felt that we needed this one translated... # /The MC team Template_DEFAULT_TEMPLATE_NAME=All your base are belong to us! ------ I was hoping to get a cynical remark back from the translation team, but they just translated it the best they could. Heh. Finally, one of the worst programming mistakes in recent history was in a small start-up project. A hash code calculation error caused some subtle errors to one of many data points in a running production system. I finally solved the problem when I got fiber installed at home and got bold. In desperation I started a node with jdwp turned on, and I then proceeded to set break points and evaluate code remotely over an ssh tunnel. The latency was so low that it almost felt like a local debugging session. Crazy, but you gotta love Java for providing you with options. ;)

This post comes from Miguel Angel Nieto at the MySQL Performance Blog. MySQL 5.6 is GA! Now we have new things to play with and in my personal opinion the most interesting one is the new Global Transaction ID (GTID) support in replication. This post is not an explanation of what is GTID and how it works internally because there are many documents about that: http://dev.mysql.com/doc/refman/5.6/en/replication-gtids-concepts.html One thing that worths to mention is that if you want GTID support log_slave_updates will need to be enabled in slave server and the performance impact should be taken in account. Anyway, this post tends to be more practical, we will see how to create/restore new slaves from a master using GTID. How to set up a new slave The first thing that we need to know is that now Binary Logs and Position are not needed anymore with GTID enabled. Instead we need to know in which GTID is the master and set it on the slave. MySQL keeps two global variables with GTID numbers on it: gtid_executed: it contains a representation of the set of all transaction logged in the binary log gtid_purged: it contains a representation of the set of all transactions deleted from the binary log So now, the process is the following: take a backup from the master and store the value of gtid_executed restore the backup on the slave and set gtid_purged with the value of gtid_executed from the master The new mysqldump can do those tasks for us. Let’s see an example of how to take a backup from the master and restore it on the slave to set up a new replication server. master > show global variables like 'gtid_executed'; +---------------+-------------------------------------------+ | Variable_name | Value | +---------------+-------------------------------------------+ | gtid_executed | 9a511b7b-7059-11e2-9a24-08002762b8af:1-13 | +---------------+-------------------------------------------+ master > show global variables like 'gtid_purged'; +---------------+------------------------------------------+ | Variable_name | Value | +---------------+------------------------------------------+ | gtid_purged | 9a511b7b-7059-11e2-9a24-08002762b8af:1-2 | +---------------+------------------------------------------+ Now we take a backup with mysqldump from the master: # mysqldump --all-databases --single-transaction --triggers --routines --host=127.0.0.1 --port=18675 --user=msandbox --password=msandbox > dump.sql It will contain the following line: # grep PURGED dump.sql SET @@GLOBAL.GTID_PURGED='9a511b7b-7059-11e2-9a24-08002762b8af:1-13'; Therefore during the dump recover process on the slave it will set GTID_PURGED to the GTID_EXECUTED value from the master. So now, we just need to recover the dump and start the replication: slave1 > show global variables like 'gtid_executed'; +---------------+-------+ | Variable_name | Value | +---------------+-------+ | gtid_executed | | +---------------+-------+ slave1 > show global variables like 'gtid_purged'; +---------------+-------+ | Variable_name | Value | +---------------+-------+ | gtid_purged | | +---------------+-------+ slave1 > slave1> source test.sql; [...] slave1 > show global variables like 'gtid_executed'; +---------------+-------------------------------------------+ | Variable_name | Value | +---------------+-------------------------------------------+ | gtid_executed | 9a511b7b-7059-11e2-9a24-08002762b8af:1-13 | +---------------+-------------------------------------------+ slave1 > show global variables like 'gtid_purged'; +---------------+-------------------------------------------+ | Variable_name | Value | +---------------+-------------------------------------------+ | gtid_purged | 9a511b7b-7059-11e2-9a24-08002762b8af:1-13 | +---------------+-------------------------------------------+ The last step is to configure the slave using the auto-configuration method of GTID: slave1 > CHANGE MASTER TO MASTER_HOST="127.0.0.1", MASTER_USER="msandbox", MASTER_PASSWORD="msandbox", MASTER_PORT=18675, MASTER_AUTO_POSITION = 1; How to restore a slave in a bad and fast way Let’s imagine that our slave has been down for several days and the binary logs from the master have been purged. This is the error we are going to get: Slave_IO_Running: No Slave_SQL_Running: Yes Last_IO_Error: Got fatal error 1236 from master when reading data from binary log: 'The slave is connecting using CHANGE MASTER TO MASTER_AUTO_POSITION = 1, but the master has purged binary logs containing GTIDs that the slave requires.' So, let’s try to solve it. First we have the bad and fast way, that is, point to another GTID that the master has in the binary logs. First, we get the GTID_EXECUTED from the master: master > show global variables like 'GTID_EXECUTED'; +---------------+-------------------------------------------+ | Variable_name | Value | +---------------+-------------------------------------------+ | gtid_executed | 9a511b7b-7059-11e2-9a24-08002762b8af:1-14 | +---------------+-------------------------------------------+ And we set it on the slave: slave> set global GTID_EXECUTED="9a511b7b-7059-11e2-9a24-08002762b8af:1-14" ERROR 1238 (HY000): Variable 'gtid_executed' is a read only variable Error! Remember, we get the GTID_EXECUTED from the master and set is as GTID_PURGED on the slave. slave1 > set global GTID_PURGED="9a511b7b-7059-11e2-9a24-08002762b8af:1-14"; ERROR 1840 (HY000): GTID_PURGED can only be set when GTID_EXECUTED is empty. Error again, GTID_EXECUTED should be empty before changing GTID_PURGED manually but we can’t change it with SET because is a read only variable. The only way to change it is with reset master (yes, on a slave server): slave1> reset master; slave1 > show global variables like 'GTID_EXECUTED'; +---------------+-------+ | Variable_name | Value | +---------------+-------+ | gtid_executed | | +---------------+-------+ slave1 > set global GTID_PURGED="9a511b7b-7059-11e2-9a24-08002762b8af:1-14"; slave1> start slave io_thread; slave1> show slave status\G [...] Slave_IO_Running: Yes Slave_SQL_Running: Yes [...] Now, if you don’t get any error like primary/unique key duplication then you can run the pt-table-checksum and pt-table-sync. How to restore a slave in a good and slow way The good way is mysqldump again. We take a dump from the master like we saw before and try to restore it on the slave: slave1 [localhost] {msandbox} ((none)) > source test.sql; [...] ERROR 1840 (HY000): GTID_PURGED can only be set when GTID_EXECUTED is empty. [...] Wop! It is important to mention that these kind of error messages can dissapear on the shell buffer because the restore of the dump will continue. Be cautious. Same problem again so same solution too: slave1> reset master; slave1> source test.sql; slave1> start slave; slave1> show slave status\G [...] Slave_IO_Running: Yes Slave_SQL_Running: Yes [...] Conclusion With the new GTID we need to change our minds. Now binary log and position is not something we need to take in account, gtid_executed and gtid_purged are our new friends. Xtrabackup still doesn’t support it but we are working on it. I will update this post and create a one when we publish a xtrabackup version with full support of GTID.

As you may be aware, the JDK 8 Early Access is now available for download. This allows Java developers to experiment with some of the new language and runtime features of Java 8. One of these features is the complete removal of the Permanent Generation (PermGen) space which has been announced by Oracle since the release of JDK 7. Interned strings, for example, have already been removed from the PermGen space since JDK 7. The JDK 8 release finalizes its decommissioning. This article will share the information that we found so far on the PermGen successor: Metaspace. We will also compare the runtime behavior of the HotSpot 1.7 vs. HotSpot 1.8 (b75) when executing a Java program “leaking” class metadata objects. The final specifications, tuning flags and documentation around Metaspace should be available once Java 8 is officially released. Metaspace: A new memory space is born The JDK 8 HotSpot JVM is now using native memory for the representation of class metadata and is called Metaspace; similar to the Oracle JRockit and IBM JVM's. The good news is that it means no more java.lang.OutOfMemoryError: PermGen space problems and no need for you to tune and monitor this memory space anymore…not so fast. While this change is invisible by default, we will show you next that you will still need to worry about the class metadata memory footprint. Please also keep in mind that this new feature does not magically eliminate class and classloader memory leaks. You will need to track down these problems using a different approach and by learning the new naming convention. I recommend that you read the PermGen removal summary and comments from Jon on this subject. In summary: PermGen space situation This memory space is completely removed. The PermSize and MaxPermSize JVM arguments are ignored and a warning is issued if present at start-up. Metaspace memory allocation model Most allocations for the class metadata are now allocated out of native memory. The klasses that were used to describe class metadata have been removed. Metaspace capacity By default class metadata allocation is limited by the amount of available native memory (capacity will of course depend if you use a 32-bit JVM vs. 64-bit along with OS virtual memory availability). A new flag is available (MaxMetaspaceSize), allowing you to limit the amount of native memory used for class metadata. If you don’t specify this flag, the Metaspace will dynamically re-size depending of the application demand at runtime. Metaspace garbage collection Garbage collection of the dead classes and classloaders is triggered once the class metadata usage reaches the “MaxMetaspaceSize”. Proper monitoring & tuning of the Metaspace will obviously be required in order to limit the frequency or delay of such garbage collections. Excessive Metaspace garbage collections may be a symptom of classes, classloaders memory leak or inadequate sizing for your application. Java heap space impact Some miscellaneous data has been moved to the Java heap space. This means you may observe an increase of the Java heap space following a future JDK 8 upgrade. Metaspace monitoring Metaspace usage is available from the HotSpot 1.8 verbose GC log output. Jstat & JVisualVM have not been updated at this point based on our testing with b75 and the old PermGen space references are still present. Enough theory now, let’s see this new memory space in action via our leaking Java program… PermGen vs. Metaspace runtime comparison In order to better understand the runtime behavior of the new Metaspace memory space, we created a class metadata leaking Java program. You can download the source here. The following scenarios will be tested: Run the Java program using JDK 1.7 in order to monitor & deplete the PermGen memory space set at 128 MB. Run the Java program using JDK 1.8 (b75) in order to monitor the dynamic increase and garbage collection of the new Metaspace memory space. Run the Java program using JDK 1.8 (b75) in order to simulate the depletion of the Metaspace by setting the MaxMetaspaceSize value at 128 MB. JDK 1.7 @64-bit – PermGen depletion Java program with 50K configured iterations Java heap space of 1024 MB Java PermGen space of 128 MB (-XX:MaxPermSize=128m) As you can see form JVisualVM, the PermGen depletion was reached after loading about 30K+ classes. We can also see this depletion from the program and GC output. Class metadata leak simulator Author: Pierre-Hugues Charbonneau http://javaeesupportpatterns.blogspot.com ERROR: java.lang.OutOfMemoryError: PermGen space Now let’s execute the program using the HotSpot JDK 1.8 JRE. JDK 1.8 @64-bit – Metaspace dynamic re-size Java program with 50K configured iterations Java heap space of 1024 MB Java Metaspace space: unbounded (default) As you can see from the verbose GC output, the JVM Metaspace did expand dynamically from 20 MB up to 328 MB of reserved native memory in order to honor the increased class metadata memory footprint from our Java program. We could also observe garbage collection events in the attempt by the JVM to destroy any dead class or classloader object. Since our Java program is leaking, the JVM had no choice but to dynamically expand the Metaspace memory space. The program was able to run its 50K of iterations with no OOM event and loaded 50K+ Classes. Let's move to our last testing scenario. JDK 1.8 @64-bit – Metaspace depletion Java program with 50K configured iterations Java heap space of 1024 MB Java Metaspace space: 128 MB (-XX:MaxMetaspaceSize=128m) As you can see form JVisualVM, the Metaspace depletion was reached after loading about 30K+ classes; very similar to the run with the JDK 1.7. We can also see this from the program and GC output. Another interesting observation is that the native memory footprint reserved was twice as much as the maximum size specified. This may indicate some opportunities to fine tune the Metaspace re-size policy, if possible, in order to avoid native memory waste. Now find below the Exception we got from the Java program output. Class metadata leak simulator Author: Pierre-Hugues Charbonneau http://javaeesupportpatterns.blogspot.com ERROR: java.lang.OutOfMemoryError: Metadata space Done! As expected, capping the Metaspace at 128 MB like we did for the baseline run with JDK 1.7 did not allow us to complete the 50K iterations of our program. A new OOM error was thrown by the JVM. The above OOM event was thrown by the JVM from the Metaspace following a memory allocation failure. #metaspace.cpp Final words I hope you appreciated this early analysis and experiment with the new Java 8 Metaspace. The current observations definitely indicate that proper monitoring & tuning will be required in order to stay away from problems such as excessive Metaspace GC or OOM conditions triggered from our last testing scenario. Future articles may include performance comparisons in order to identify potential performance improvements associated with this new feature. Please feel free to provide any comment.

I’ve been working in some Python Solr client code. One area where bugs have cropped up is in query terms that need to be escaped before passing to Solr. For example, how do you send Solr an argument term with a “:” in it? Or a “(“? It turns out that generally you just put a \ in front of the character you want to escape. So to search for “:” in the “funnychars” field, you would send q=funnychars:\:. Php programmer Mats Lindh has solved this pretty well, using str_replace. str_replace is a convenient, general-purpose string replacement function that lets you do batch string replacement. For example you can do: $matches = array("Mary","lamb","fleece"); $replacements = array("Harry","dog","fur"); str_replace($matches, $replacements,"Mary had a little lamb, its fleece was white as snow"); Python doesn’t quite have str_replace. There is translate which does single character to single character batch replacement. That can’t be used for escaping because the destination values are strings(ie “\:”), not single characters. There’s a general purpose “str_replace” drop-in replacement at this Stackoverflow question: edits =[("Mary","Harry"),("lamb","dog"),("fleece","fur")]# etc.for search, replace in edits: s = s.replace(search, replace) You’ll notice that this algorithm requires multiple passes through the string for search/replacement. This is because that earlier search/replaces may impact later search/replaces. For example, what if edits was this: edits =[("Mary","Harry"),("Harry","Larry"),("Larry","Barry")] First our str_replace will replace Mary with Harry in pass 1, then Harry with Larry in pass 2, etc. It turns out that escaping characters is a narrower string replacement case that can be done more efficiently without too much complication. The only character that one needs to worry about impacting other rules is escaping the \, as the other rules insert \ characters, we wouldn’t want them double escaped. Aside from this caveat, all the escaping rules can be processed from a single pass through the string which my solution below does, performing a heck of a lot faster: # These rules all independent, order of# escaping doesn't matter escapeRules ={'+':r'\+','-':r'\-','&':r'\&','|':r'\|','!':r'\!','(':r'\(',')':r'\)','{':r'\{','}':r'\}','[':r'\[',']':r'\]','^':r'\^','~':r'\~','*':r'\*','?':r'\?',':':r'\:','"':r'\"',';':r'\;',' ':r'\ '}defescapedSeq(term):""" Yield the next string based on the next character (either this char or escaped version """forcharin term:ifcharin escapeRules.keys():yield escapeRules[char]else:yieldchardefescapeSolrArg(term):""" Apply escaping to the passed in query terms escaping special characters like : , etc""" term = term.replace('\\',r'\\')# escape \ firstreturn"".join([nextStr for nextStr in escapedSeq(term)]) Aside from being a good general solution to this problem, in some basic benchmarks, this turns out to be about 5 orders of magnitude faster than doing it the naive way! Pretty cool, but you’ll probably rarely notice the difference. Nevertheless it could matter in specialized cases if you are automatically constructing and batching large/gnarly queries that require a lot of work to escape. Anyway, enjoy! I’d love to hear what you think!

Here is a small code snippet which shows an utility class that offers two methods to compress and extract a Java byte array.

When using an external API for WebHooks or Callbacks as discussed in Chapters 3 and 5 of Getting Started with Mule Cloud Connect; The API provider running somewhere out there on the web needs to callback your application that is happily running in isolation on your local machine. For an API provider to callback your application, the application must be accessible over the web. Sure, you could upload and test your application on a public facing server, but you may find it quicker and easier to work on your local development machine and these are typically behind firewalls, NAT, or otherwise not able to provide a public URL. You need a way to make your local application available over the web. There are a few good services and tools out there to help with this. Examples include ProxyLocal, and Forward.io. Alternatively, you can set up your own reverse SSH Tunnel if you already have a remote system to forward your requests, but this is cumbersome to say the least. I find Localtunnel to be an excellent fit for this need and localtunnel have just recently released v2 of its service with a host of new features and enhancements. More information can be found here: http://progrium.com/blog/2012/12/25/localtunnel-v2-available-in-beta/ Installing Localtunnel Those familiar with version 1 of the service will know that the v1 Localtunnel client was written in Ruby and required Rubygems to install it. The v2 client is now written in Python and can instead be installed via easy_install or pip. If instead you're interested in using Localtunnel v1, then I have wrote a previous blog post on the subject here: http://blogs.mulesoft.org/connector-callback-testing-local/ To get started, you will first need to check that you have Python installed. Localtunnel requires Python 2.6 or later. Most systems come with Python installed as standard, but if not you can check via the following command: $ python -version More info on installing Python can be found here: http://wiki.python.org/moin/BeginnersGuide/Download Once complete, you will need easy_install to install the Localtunnel client.If you don't have easy_install after you install Python, you can install it with this bootstrap script: $ curl http://peak.telecommunity.com/dist/ez_setup.py | python Once complete, you can install the Localtunnel client using the following command: $ easy_install localtunnel First run with LocalTunnel Once installed, creating a tunnel is as simple as running the following command: $ localtunnel-beta 8082 The parameter after the command: "8000" is the local port we want Localtunnel to forward to. So whatever port your app is running on should replace this value. Each time you run the command you should get output similar to the following: Port 8082 is now accessible from http://fb0322605126.v2.localtunnel.com ... Note: As v2 is still in beta; the command local-tunnel-beta will eventually be installed as just localtunnel. This lets you keep the v1 just in case anything goes wrong with v2 during the beta. Configuring the Connector Now onto Mule! To demonstrate I will use the Twilio Cloud Connector example from Chapter 5. Twilio has an awesome WebHook implementation with great debugging tools. Twilio uses callbacks to tell you about the status of your requests; When you use Twilio to a place a phone call or send an SMS the Twilio API allows you to send a URL where you'll receive information about the phone call once it ends or the status of the outbound SMS message after it's processed. This example uses the Twilio Cloud Connector to send a simple SMS message. The most important thing to note is that the "status-callback-flow-ref" attribute. All connector operations that support callback's will have an optional attribute ending in "-flow-ref". In this case : "status-callback-flow-ref". As the name suggests, this attribute should reference a flow. This value must be a valid flow id from within your configuration. It is this flow that will be used to listen for the callback. Notice that the flow has no inbound endpoint? This is where the magic happens; when Twilio process the SMS message it will send a callback automatically to that flow without you having to define an inbound endpoint. The connector automatically generates an inbound endpoint and sends the auto generated URL to Twilio for you. Customizing the Callback The URL generated for the callback URL is built using 'localhost' as the host, the 'http.port' environment variable or 'localPort' value as the port and the path of the URL is typically just a random generated string or static value. So if I run this locally it would send Twilio my non public address, something like: http://localhost:80/...vv3v3er342fvvn. Each connector that accepts HTTP callbacks will provide you with an optional http-callback-config child element to override these settings. These settings can be set at the connector's config level as follows: Here we have amended the previous example to add the additonal http-callback-config configuration. The configuration takes three additional arguments: domain, localPort and remotePort. These settings will be used to constuct the URL that is passed to the external system. The URL will be the same as the default generated URL of the HTTP inbound-endpoint except that the host is replaced by the 'domain' setting (or its default value) and the port is replaced by the 'remotePort' setting (or its default value). In this case we have used the domain from the URL that Localtunnel generated for us earlier: fb0322605126.v2.localtunnel.com and set the localPort to 8082 as we run the Localtunnel command using port 8082 and the remotePort to 80 as the localtunnel server just runs on port 80. And that's it! If you run this configuration you should start seeing your callback being printed to the console. The same goes for any OAuth connectors too. If your using any OAuth connectors built using the DevKit OAuth modules, you can configure the OAuth callback in a similar fashion. A full Mule/Twilio WebHook project can be found here: https://github.com/ryandcarter/GettingStarted-MuleCloudConnect-OReilly/tree/master/chapter05/twilio-webhooks

Groovy 2.0 brought us extension modules. An extension module is a JAR file with classes that provide extra methods to existing other classes like in the JDK or third-party libraries. Groovy uses this mechanism to add for example extra methods to the File class. We can implement our own extension module to add new extension methods to existing classes. Once we have written the module we can add it to the classpath of our code or application and all the new methods are immediately available. We define the new extension methods in helper classes, which are part of the module. We can create instance and static extension methods, but we need a separate helper class for each type of extension method. We cannot mix static and instance extension methods in one helper class. First we create a very simple class with an extension method for the String class. The first argument of the extension method defines the type or class we want the method to be added to. The following code shows the method likeAPirate. The extension method needs to be public and static even though we are creating an instance extension method. // File: src/main/groovy/com/mrhaki/groovy/PirateExtension.groovy package com.mrhaki.groovy class PirateExtension { static String likeAPirate(final String self) { // List of pirate language translations. def translations = [ ["hello", "ahoy"], ["Hi", "Yo-ho-ho"], ['are', 'be'], ['am', 'be'], ['is', 'be'], ['the', "th'"], ['you', 'ye'], ['your', 'yer'], ['of', "o'"] ] // Translate the original String to a // pirate language String. String result = self translations.each { translate -> result = result.replaceAll(translate[0], translate[1]) } result } } Next we need to create an extension module descriptor file. In this file we define the name of the helper class, so Groovy will know how to use it. The descriptor file needs to be placed in the META-INF/services directory of our module archive or classpath. The name of the file is org.codehaus.groovy.runtime.ExtensionModule. In the file we define the name of our module, version and the name of the helper class. The name of the helper class is defined with the property extensionClasses: # File: src/main/resources/META-INF/services/org.codehaus.groovy.runtime.ExtensionModule moduleName = pirate-module moduleVersion = 1.0 extensionClasses = com.mrhaki.groovy.PirateExtension Now are extension module is ready. The easiest way to distribute the module is by packaging the code and descriptor file in a JAR file and put it in a artifact repository manager. Other developers can then use build tools like Gradle or Maven to include the extension module in their projects and applications. If we use Gradle to create a JAR file we only needs this small build script: / File: build.gradle apply plugin: 'groovy' repositories.mavenCentral() dependencies { // Since Gradle 1.4 we don't use the groovy configuration // to define dependencies. We can simply use the // compile and testCompile configurations. compile 'org.codehaus.groovy:groovy-all:2.0.6' } Now we can invoke $ gradle build and we got ourselves an extension module. Let's add a test for our new extension method. Because we use Gradle the test classpath already will contain our extension module helper class and descriptor file. In our test we can simply invoke the method and test the results. We are going to use Spock to write a simple specification: // File: src/test/groovy/com/mrhaki/groovy/PirateExtensionSpec.groovy package com.mrhaki.groovy import spock.lang.Specification class PirateExtensionSpec extends Specification { def "likeAPirate method should work as instance method on a String value"() { given: final String originalText = "Hi, Groovy is the greatest language of the JVM." expect: originalText.likeAPirate() == "Yo-ho-ho, Groovy be th' greatest language o' th' JVM." } } We add the dependency to Spock in our Gradle build file: / File: build.gradle apply plugin: 'groovy' repositories.mavenCentral() dependencies { // Since Gradle 1.4 we don't use the groovy configuration // to define dependencies. We can simply use the // compile and testCompile configurations. compile 'org.codehaus.groovy:groovy-all:2.0.6' testCompile 'org.spockframework:spock-core:0.7-groovy-2.0' } We can run $ gradle test to run the Spock specification and test our new extension method. To add a static method to an existing class we need to add an extra helper class to our extension module and an extra property to our descriptor file to register the helper class. The first argument of the extension method define the type we want to add a static method to. In the following helper class we add the extension method talkLikeAPirate() to the String class. / File: src/main/groovy/com/mrhaki/groovy/PirateStaticExtension.groovy package com.mrhaki.groovy class PirateStaticExtension { static String talkLikeAPirate(final String type) { "Arr, me hearty," } We change the descriptor file and add the staticExtensionClasses property: # File: src/main/resources/META-INF/services/org.codehaus.groovy.runtime.ExtensionModule moduleName = pirate-module moduleVersion = 1.0 extensionClasses = com.mrhaki.groovy.PirateExtension staticExtensionClasses = com.mrhaki.groovy.PirateStaticExtension In our Spock specification we add an extra test for our new static method talkLikeAPirate() on the String class: // File: src/test/groovy/com/mrhaki/groovy/PirateExtensionSpec.groovy package com.mrhaki.groovy import spock.lang.Specification class PirateExtensionSpec extends Specification { def "likeAPirate method should work as instance method on a String value"() { given: final String originalText = "Hi, Groovy is the greatest language of the JVM." expect: originalText.likeAPirate() == "Yo-ho-ho, Groovy be th' greatest language o' th' JVM." } def "talkLikeAPirate method should work as static method on String class"() { expect: "Arr, me hearty, Groovy rocks!" == String.talkLikeAPirate() + " Groovy rocks!" } } Written with Groovy 2.1