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• Polling a web URL until event

  - by Jaxo

  I'm really sorry about the crappy title - if anybody has a better way of wording it, please edit it! I basically need to have a C# application run a function if the output of a URL is a certain value. For example, if the website says blue the background colour will be blue, red to make it red, etc. The problem is I don't want to spam my webserver with checks. The 4 bytes it downloads each time is negligible, but if I were to deploy this type of system on multiple computers, it would get slower and slower and the bandwidth would add up quickly. So my question is: How can my desktop application run a piece of code only when a web URL has a different output without checking each time? I can't use sockets, and any sort of LAN protocol won't end up working. My reasoning behind this potentially nefarious code is to be able to mute computers by updating a file on the website (as you may have seen in my previous question today, sorry!). I'd like it to be rather quick, and not have the refresh time minutes apart, a few seconds at the most would be ideal. How can I accomplish this? The website's code is easy, but getting the C# application to check when it changes is the part I'm stuck on. Nothing shows up on the website other than the command. Thanks!

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• LINQ to SQL Queries odd Materialization

  - by ptoinson

  I ran across an interesting Linq to SQL, uh, feature, the other day. Perhaps someone can give me a logical explanation for the reasoning behind the results. Take the code below as my example which utilizes the AdventureWorks database setup in a Linq to SQL DataContext. This is a clip from my unit test. The resulting customer returned from a call to both CustomerQuery_Test_01() and CustomerQuery_Test_02() is the same. However, the query executed on the SQLServer are different is a major way. The method CustomerQuery_Test_01 us causing the entire Customer table to be materialized, which the call to CustomerQuery_Test_02 is only causing the single customer to be materialized. The resulting SQL Queries are at the bottom of this post. Anyone have a good reason for this? To me, it was highly non-intuitive. protected virtual Customer GetByPrimaryKey(Func<Customer, bool> keySelection) { AdventureWorksDataContext context = new AdventureWorksDataContext(); return (from r in context.Customers select r).SingleOrDefault(keySelection); } [TestMethod] public void CustomerQuery_Test_01() { Customer customer = GetByPrimaryKey(c => c.CustomerID == 2); } [TestMethod] public void CustomerQuery_Test_02() { AdventureWorksDataContext context = new AdventureWorksDataContext(); Customer customer = (from r in context.Customers select r).SingleOrDefault(c => c.CustomerID == 2); } Query for CustomerQuery_Test_01 (notice the lack of a where clause) SELECT [t0].[CustomerID], [t0].[NameStyle], [t0].[Title], [t0].[FirstName], [t0].[MiddleName], [t0].[LastName], [t0].[Suffix], [t0].[CompanyName], [t0].[SalesPerson], [t0].[EmailAddress], [t0].[Phone], [t0].[PasswordHash], [t0].[PasswordSalt], [t0].[rowguid], [t0].[ModifiedDate] FROM [SalesLT].[Customer] AS [t0] Query for CustomerQuery_Test_02 (notice the where clause) SELECT [t0].[CustomerID], [t0].[NameStyle], [t0].[Title], [t0].[FirstName], [t0].[MiddleName], [t0].[LastName], [t0].[Suffix], [t0].[CompanyName], [t0].[SalesPerson], [t0].[EmailAddress], [t0].[Phone], [t0].[PasswordHash], [t0].[PasswordSalt], [t0].[rowguid], [t0].[ModifiedDate] FROM [SalesLT].[Customer] AS [t0] WHERE [t0].[CustomerID] = @p0

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• hash fragments and collisions cont.

  - by Mark

  For this application I've mine I feel like I can get away with a 40 bit hash key, which seems awfully low, but see if you can confirm my reasoning (I want a small key because I want a small filename and the key will be converted to a filename): (Note: only accidental collisions a concern - no security issues.) A key point here is that the population in question is divided into groups, and a collision is only relevant if it occurs within the same group. A "group" is a directory on a user's system (the contents of files are hashed and a collision is only relevant if it occurs for files within the same directory). So with speculating roughly 100,000 potential users, say 2^17, that corresponds to 2^18 "groups" assuming 2 directories per user on average. So with a 40 bit key I can expect 2^(20+9) files created (among all users) before a collision occurs for some user somewhere. (Or IOW 2^((40+18)/2), due to the "birthday effect".) That's an average 4096 unique files created per user, for 2^17 users, before a single collision occurs for some user somewhere. And then that long again before another collision occurs somewhere (right?)

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• Guidance on E-commerce in a Python Framework

  - by Ant

  I am looking for guidance in making decisions on using Python for E-commerce. My reasoning to use Python in the first place is i do a lot of 3D so it's a real help to use Python for web server side as well as 3D so I do not need to learn a new language. When I say E-commerce i mean the logic behind displaying products and a check out system that is Robust....and yes I really want to build this myself so I can change it. I do not want to use an out the box solution that costs a lot of money every month. I want control of server side, data bases, e-commerce etc. My questions are: What Frameworks are out there? I looked at previous questions on stackoverflow but only found old posts about Sachmo and Get paid. What is the learning path, I do not want to make a mistake that costs six months of studying? Python then Django? How long if I spent 10 hours a day studying this would it take to get up and running? I write javaScript badly, so I am not a complete noob, I understand the basics of programming languages. many thanks in advance

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• Heapsort not working in Python for list of strings using heapq module

  - by VSN

  I was reading the python 2.7 documentation when I came across the heapq module. I was interested in the heapify() and the heappop() methods. So, I decided to write a simple heapsort program for integers: from heapq import heapify, heappop user_input = raw_input("Enter numbers to be sorted: ") data = map (int, user_input.split(",")) new_data = [] for i in range(len(data)): heapify(data) new_data.append(heappop(data)) print new_data This worked like a charm. To make it more interesting, I thought I would take away the integer conversion and leave it as a string. Logically, it should make no difference and the code should work as it did for integers: from heapq import heapify, heappop user_input = raw_input("Enter numbers to be sorted: ") data = user_input.split(",") new_data = [] for i in range(len(data)): heapify(data) print data new_data.append(heappop(data)) print new_data Note: I added a print statement in the for loop to see the heapified list. Here's the output when I ran the script: `$ python heapsort.py Enter numbers to be sorted: 4, 3, 1, 9, 6, 2 [' 1', ' 3', ' 2', ' 9', ' 6', '4'] [' 2', ' 3', '4', ' 9', ' 6'] [' 3', ' 6', '4', ' 9'] [' 6', ' 9', '4'] [' 9', '4'] ['4'] [' 1', ' 2', ' 3', ' 6', ' 9', '4']` The reasoning I applied was that since the strings are being compared, the tree should be the same if they were numbers. As is evident, the heapify didn't work correctly after the third iteration. Could someone help me figure out if I am missing something here? I'm running Python 2.4.5 on RedHat 3.4.6-9. Thanks, VSN

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• Having trouble deleting a node from a linked list

  - by Requiem

  I've been working on this code for my shell that I'm creating and for some reason it isn't working. I'm implementing a watchuser function that watch's a user when an argument is given (args[1]). However, when a second argument (args[2]) of "off" is given, the user should be deleted from the linked list and should no longer be watched. struct userList * goList; goList = userInventory; do{ if (strcmp(userInventory->username, args[1]) == 0){ printf("%s\n", args[1]); printf("%s\n",userInventory->username); struct userList * temp2; temp2 = userInventory->next; if (userInventory->next != NULL){ userInventory->next = temp2->next; userInventory->next->prev = userInventory; } free(temp2); } goList = goList->next; }while (goList != userInventory); My global struct is also as follows: struct userList{ char * username; struct userList * prev; struct userList * next; } For reason, this code won't delete the user node from my linked list. The adding works, but this remove function won't and I'm not sure why. The print statements are there just to make sure it's executing the condition, which it is. If anyone could help me find the reasoning behind my error, I'd greatly appreciate it. Till then, I'll be trying to debug this. Thanks.

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• Windows: Impact of clean install Service Pack 2 to applications & data?

  - by Thomas Matthews

  My Windows Vista Home Premium system is corrupt and won't install Service Pack 2. I have followed all the advice from Microsoft and still no luck. I would like to perform a clean install of Vista, then SP1, and then SP2. My concern is the effect of the clean install on the registry, my apps and all my data. My plan: 1. Download Vista Service Pack 1 (SP1) ISO and write to DVD. 2. Download Vista Service Pack 2 (SP2) ISO and write to DVD. 3. Backup all data, applications and registry to external hard drive (file copy not disk image) 4. ?? Format hard drive?? (is this necessary?) 5. Install Vista from DVDs / CDs. 6. Install SP1 from DVD 7. Install SP2 from DVD 8. Restore registry, applications and data from external hard drive. My questions: 1. Is formatting the hard drive a necessary step? 2. Will restoring the registry from the backup corrupt the system? 3. Should I use Windows Backup or ZIP/RAR? 4. Any gotcha's that I should look out for? Background: I am using Windows Vista Home Premium with SP1. The sfc program does not finish due to a resources problem (even when run as administrator). I have 5 users on it. After a while, the screen goes black and shows an error message window about an error with login.scr. Standard accounts display a black screen and can't run any applications. Administrative accounts have no problems (even standard accounts when converted to Administrative have no problem). The CBS log contains a lot of 0x8000ffff and E_UNEXPECTED errors (which Microsoft defines as catastrophic failure). This is the reasoning behind performing a clean install up to service pack 2.

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• Converting an EC2 AMI to vmdk image

  - by Reed G. Law

  I've come quite close to getting Amazon Linux to boot inside VirtualBox, thanks to this answer and these websites. A quick overview of the steps I've taken: Launch EC2 instance with Amazon Linux 2011.09 64-bit AMI dd the contents of the EBS volume over ssh to a local image file. Mount the image file as a loopback device and then to a local mount point. Create a new empty disk image file, partition with an offset for a bootloader, and create an ext4 filesystem. Mount the new image's partition and copy everything from the EC2 image. Install grub (using Ubuntu's grub-legacy-ec2 package, not grub2). Convert the image file to vmdk using qemu-img. Create a new VirtualBox VM with the vmdk. Now the VM boots, grub loads, and the kernel is found. But it fails when it tries to mount the root device: dracut Warning: No root device "block:/dev/xvda1" found dracut Warning: Boot has failed. To debug this issue add "rdshell" to the kernel command line. dracut Warning: Signal caught! dracut Warning: Boot has failed. To debug this issue add "rdshell" to the kernel command line. Kernel panic - not syncing: Attempted to kill init! Pid: 1, comm: init Not tainted 2.6.35.14-107.1.39.amzn1.x86_64 #1 I have tried changing /boot/grub/menu.lst to find the root device by label and UUID, but nothing works. I'm guessing the xen kernel is not compatible with VirtualBox. The reasoning behind all this effort is to make a Vagrant box that is as close to possible as the production enviroment, so deploys can be tested locally. I know it's cheap to do test runs on EC2, but poor connectivity often ruins the experience. Plus it would be really nice to have a virtual machine with the production environment so that co-workers don't have to install everything under the sun just to get up and running with app development. If I were to try running a different kernel, what kernel could I get to be as close as possible to Amazon Linux 2011.09?

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• SQL SERVER – PAGEIOLATCH_DT, PAGEIOLATCH_EX, PAGEIOLATCH_KP, PAGEIOLATCH_SH, PAGEIOLATCH_UP – Wait Type – Day 9 of 28

  - by pinaldave

  It is very easy to say that you replace your hardware as that is not up to the mark. In reality, it is very difficult to implement. It is really hard to convince an infrastructure team to change any hardware because they are not performing at their best. I had a nightmare related to this issue in a deal with an infrastructure team as I suggested that they replace their faulty hardware. This is because they were initially not accepting the fact that it is the fault of their hardware. But it is really easy to say “Trust me, I am correct”, while it is equally important that you put some logical reasoning along with this statement. PAGEIOLATCH_XX is such a kind of those wait stats that we would directly like to blame on the underlying subsystem. Of course, most of the time, it is correct – the underlying subsystem is usually the problem. From Book On-Line: PAGEIOLATCH_DT Occurs when a task is waiting on a latch for a buffer that is in an I/O request. The latch request is in Destroy mode. Long waits may indicate problems with the disk subsystem. PAGEIOLATCH_EX Occurs when a task is waiting on a latch for a buffer that is in an I/O request. The latch request is in Exclusive mode. Long waits may indicate problems with the disk subsystem. PAGEIOLATCH_KP Occurs when a task is waiting on a latch for a buffer that is in an I/O request. The latch request is in Keep mode. Long waits may indicate problems with the disk subsystem. PAGEIOLATCH_SH Occurs when a task is waiting on a latch for a buffer that is in an I/O request. The latch request is in Shared mode. Long waits may indicate problems with the disk subsystem. PAGEIOLATCH_UP Occurs when a task is waiting on a latch for a buffer that is in an I/O request. The latch request is in Update mode. Long waits may indicate problems with the disk subsystem. PAGEIOLATCH_XX Explanation: Simply put, this particular wait type occurs when any of the tasks is waiting for data from the disk to move to the buffer cache. ReducingPAGEIOLATCH_XX wait: Just like any other wait type, this is again a very challenging and interesting subject to resolve. Here are a few things you can experiment on: Improve your IO subsystem speed (read the first paragraph of this article, if you have not read it, I repeat that it is easy to say a step like this than to actually implement or do it). This type of wait stats can also happen due to memory pressure or any other memory issues. Putting aside the issue of a faulty IO subsystem, this wait type warrants proper analysis of the memory counters. If due to any reasons, the memory is not optimal and unable to receive the IO data. This situation can create this kind of wait type. Proper placing of files is very important. We should check file system for the proper placement of files – LDF and MDF on separate drive, TempDB on separate drive, hot spot tables on separate filegroup (and on separate disk), etc. Check the File Statistics and see if there is higher IO Read and IO Write Stall SQL SERVER – Get File Statistics Using fn_virtualfilestats. It is very possible that there are no proper indexes on the system and there are lots of table scans and heap scans. Creating proper index can reduce the IO bandwidth considerably. If SQL Server can use appropriate cover index instead of clustered index, it can significantly reduce lots of CPU, Memory and IO (considering cover index has much lesser columns than cluster table and all other it depends conditions). You can refer to the two articles’ links below previously written by me that talk about how to optimize indexes. Create Missing Indexes Drop Unused Indexes Updating statistics can help the Query Optimizer to render optimal plan, which can only be either directly or indirectly. I have seen that updating statistics with full scan (again, if your database is huge and you cannot do this – never mind!) can provide optimal information to SQL Server optimizer leading to efficient plan. Checking Memory Related Perfmon Counters SQLServer: Memory Manager\Memory Grants Pending (Consistent higher value than 0-2) SQLServer: Memory Manager\Memory Grants Outstanding (Consistent higher value, Benchmark) SQLServer: Buffer Manager\Buffer Hit Cache Ratio (Higher is better, greater than 90% for usually smooth running system) SQLServer: Buffer Manager\Page Life Expectancy (Consistent lower value than 300 seconds) Memory: Available Mbytes (Information only) Memory: Page Faults/sec (Benchmark only) Memory: Pages/sec (Benchmark only) Checking Disk Related Perfmon Counters Average Disk sec/Read (Consistent higher value than 4-8 millisecond is not good) Average Disk sec/Write (Consistent higher value than 4-8 millisecond is not good) Average Disk Read/Write Queue Length (Consistent higher value than benchmark is not good) Note: The information presented here is from my experience and there is no way that I claim it to be accurate. I suggest reading Book OnLine for further clarification. All of the discussions of Wait Stats in this blog is generic and varies from system to system. It is recommended that you test this on a development server before implementing it to a production server. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, SQL Wait Stats, SQL Wait Types, T SQL, Technology

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• To ORM or Not to ORM. That is the question&hellip;

  - by Patrick Liekhus

  UPDATE:  Thanks for the feedback and comments.  I have adjusted my table below with your recommendations.  I had missed a point or two. I wanted to do a series on creating an entire project using the EDMX XAF code generation and the SpecFlow BDD Easy Test tools discussed in my earlier posts, but I thought it would be appropriate to start with a simple comparison and reasoning on why I choose to use these tools. Let’s start by defining the term ORM, or Object-Relational Mapping.  According to Wikipedia it is defined as the following: Object-relational mapping (ORM, O/RM, and O/R mapping) in computer software is a programming technique for converting data between incompatible type systems in object-oriented programming languages. This creates, in effect, a "virtual object database" that can be used from within the programming language. Why should you care?  Basically it allows you to map your business objects in code to their persistence layer behind them. And better yet, why would you want to do this?  Let me outline it in the following points: Development speed.  No more need to map repetitive tasks query results to object members.  Once the map is created the code is rendered for you. Persistence portability.  The ORM knows how to map SQL specific syntax for the persistence engine you choose.  It does not matter if it is SQL Server, Oracle and another database of your choosing. Standard/Boilerplate code is simplified.  The basic CRUD operations are consistent and case use database metadata for basic operations. So how does this help?  Well, let’s compare some of the ORM tools that I have used and/or researched.  I have been interested in ORM for some time now.  My ORM of choice for a long time was NHibernate and I still believe it has a strong case in some business situations.  However, you have to take business considerations into account and the law of diminishing returns.  Because of these two factors, my recent activity and experience has been around DevExpress eXpress Persistence Objects (XPO).  The primary reason for this is because they have the DevExpress eXpress Application Framework (XAF) that sits on top of XPO.  With this added value, the data model can be created (either database first of code first) and the Web and Windows client can be created from these maps.  While out of the box they provide some simple list and detail screens, you can verify easily extend and modify these to your liking.  DevExpress has done a tremendous job of providing enough framework while also staying out of the way when you need to extend it.  This sounds worse than it really is.  What I mean by this is that if you choose to follow DevExpress coding style and recommendations, the hooks and extension points provided allow you to do some pretty heavy lifting while also not worrying about the basics. I have put together a list of the top features that I have used to compare the limited list of ORM’s that I have exposure with.  Again, the biggest selling point in my opinion is that XPO is just a solid as any of the other ORM’s but with the added layer of XAF they become unstoppable.  And then couple that with the EDMX modeling tools and code generation, it becomes a no brainer. Designer Features Entity Framework NHibernate Fluent w/ Nhibernate Telerik OpenAccess DevExpress XPO DevExpress XPO/XAF plus Liekhus Tools Uses XML to map relationships - Yes - - -   Visual class designer interface Yes - - - - Yes Management integrated w/ Visual Studio Yes - - Yes - Yes Supports schema first approach Yes - - Yes - Yes Supports model first approach Yes - - Yes Yes Yes Supports code first approach Yes Yes Yes Yes Yes Yes Attribute driven coding style Yes - Yes - Yes Yes                 I have a very small team and limited resources with a lot of responsibilities.  In order to keep up with our customers, we must rely on tools like these.  We use the EDMX tool so that we can create a visual representation of the applications with our customers.  Second, we rely on the code generation so that we can focus on the business problems at hand and not whether a field is mapped correctly.  This keeps us from requiring as many junior level developers on our team.  I have also worked on multiple teams where they believed in writing their own “framework”.  In my experiences and opinion this is not the route to take unless you have a team dedicated to supporting just the framework.  Each time that I have worked on custom frameworks, the framework eventually becomes old, out dated and full of “performance” enhancements specific to one or two requirements.  With an ORM, there are a lot smarter people than me working on the bigger issue of persistence and performance.  Again, my recommendation would be to use an available framework and get to working on your business domain problems.  If your coding is not making money for you, why are you working on it?  Do you really need to be writing query to object member code again and again? Thanks

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• Partition Wise Joins

  - by jean-pierre.dijcks

  Some say they are the holy grail of parallel computing and PWJ is the basis for a shared nothing system and the only join method that is available on a shared nothing system (yes this is oversimplified!). The magic in Oracle is of course that is one of many ways to join data. And yes, this is the old flexibility vs. simplicity discussion all over, so I won't go there... the point is that what you must do in a shared nothing system, you can do in Oracle with the same speed and methods. The Theory A partition wise join is a join between (for simplicity) two tables that are partitioned on the same column with the same partitioning scheme. In shared nothing this is effectively hard partitioning locating data on a specific node / storage combo. In Oracle is is logical partitioning. If you now join the two tables on that partitioned column you can break up the join in smaller joins exactly along the partitions in the data. Since they are partitioned (grouped) into the same buckets, all values required to do the join live in the equivalent bucket on either sides. No need to talk to anyone else, no need to redistribute data to anyone else... in short, the optimal join method for parallel processing of two large data sets. PWJ's in Oracle Since we do not hard partition the data across nodes in Oracle we use the Partitioning option to the database to create the buckets, then set the Degree of Parallelism (or run Auto DOP - see here) and get our PWJs. The main questions always asked are: How many partitions should I create? What should my DOP be? In a shared nothing system the answer is of course, as many partitions as there are nodes which will be your DOP. In Oracle we do want you to look at the workload and concurrency, and once you know that to understand the following rules of thumb. Within Oracle we have more ways of joining of data, so it is important to understand some of the PWJ ideas and what it means if you have an uneven distribution across processes. Assume we have a simple scenario where we partition the data on a hash key resulting in 4 hash partitions (H1 -H4). We have 2 parallel processes that have been tasked with reading these partitions (P1 - P2). The work is evenly divided assuming the partitions are the same size and we can scan this in time t1 as shown below. Now assume that we have changed the system and have a 5th partition but still have our 2 workers P1 and P2. The time it takes is actually 50% more assuming the 5th partition has the same size as the original H1 - H4 partitions. In other words to scan these 5 partitions, the time t2 it takes is not 1/5th more expensive, it is a lot more expensive and some other join plans may now start to look exciting to the optimizer. Just to post the disclaimer, it is not as simple as I state it here, but you get the idea on how much more expensive this plan may now look... Based on this little example there are a few rules of thumb to follow to get the partition wise joins. First, choose a DOP that is a factor of two (2). So always choose something like 2, 4, 8, 16, 32 and so on... Second, choose a number of partitions that is larger or equal to 2* DOP. Third, make sure the number of partitions is divisible through 2 without orphans. This is also known as an even number... Fourth, choose a stable partition count strategy, which is typically hash, which can be a sub partitioning strategy rather than the main strategy (range - hash is a popular one). Fifth, make sure you do this on the join key between the two large tables you want to join (and this should be the obvious one...). Translating this into an example: DOP = 8 (determined based on concurrency or by using Auto DOP with a cap due to concurrency) says that the number of partitions >= 16. Number of hash (sub) partitions = 32, which gives each process four partitions to work on. This number is somewhat arbitrary and depends on your data and system. In this case my main reasoning is that if you get more room on the box you can easily move the DOP for the query to 16 without repartitioning... and of course it makes for no leftovers on the table... And yes, we recommend up-to-date statistics. And before you start complaining, do read this post on a cool way to do stats in 11.

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• The clock hands of the buffer cache

  - by Tony Davis

  Over a leisurely beer at our local pub, the Waggon and Horses, Phil Factor was holding forth on the esoteric, but strangely poetic, language of SQL Server internals, riddled as it is with 'sleeping threads', 'stolen pages', and 'memory sweeps'. Generally, I remain immune to any twinge of interest in the bowels of SQL Server, reasoning that there are certain things that I don't and shouldn't need to know about SQL Server in order to use it successfully. Suddenly, however, my attention was grabbed by his mention of the 'clock hands of the buffer cache'. Back at the office, I succumbed to a moment of weakness and opened up Google. He wasn't lying. SQL Server maintains various memory buffers, or caches. For example, the plan cache stores recently-used execution plans. The data cache in the buffer pool stores frequently-used pages, ensuring that they may be read from memory rather than via expensive physical disk reads. These memory stores are classic LRU (Least Recently Updated) buffers, meaning that, for example, the least frequently used pages in the data cache become candidates for eviction (after first writing the page to disk if it has changed since being read into the cache). SQL Server clearly needs some mechanism to track which pages are candidates for being cleared out of a given cache, when it is getting too large, and it is this mechanism that is somewhat more labyrinthine than I previously imagined. Each page that is loaded into the cache has a counter, a miniature "wristwatch", which records how recently it was last used. This wristwatch gets reset to "present time", each time a page gets updated and then as the page 'ages' it clicks down towards zero, at which point the page can be removed from the cache. But what is SQL Server is suffering memory pressure and urgently needs to free up more space than is represented by zero-counter pages (or plans etc.)? This is where our 'clock hands' come in. Each cache has associated with it a "memory clock". Like most conventional clocks, it has two hands; one "external" clock hand, and one "internal". Slava Oks is very particular in stressing that these names have "nothing to do with the equivalent types of memory pressure". He's right, but the names do, in that peculiar Microsoft tradition, seem designed to confuse. The hands do relate to memory pressure; the cache "eviction policy" is determined by both global and local memory pressures on SQL Server. The "external" clock hand responds to global memory pressure, in other words pressure on SQL Server to reduce the size of its memory caches as a whole. Global memory pressure – which just to confuse things further seems sometimes to be referred to as physical memory pressure – can be either external (from the OS) or internal (from the process itself, e.g. due to limited virtual address space). The internal clock hand responds to local memory pressure, in other words the need to reduce the size of a single, specific cache. So, for example, if a particular cache, such as the plan cache, reaches a defined "pressure limit" the internal clock hand will start to turn and a memory sweep will be performed on that cache in order to remove plans from the memory store. During each sweep of the hands, the usage counter on the cache entry is reduced in value, effectively moving its "last used" time to further in the past (in effect, setting back the wrist watch on the page a couple of hours) and increasing the likelihood that it can be aged out of the cache. There is even a special Dynamic Management View, sys.dm_os_memory_cache_clock_hands, which allows you to interrogate the passage of the clock hands. Frequently turning hands equates to excessive memory pressure, which will lead to performance problems. Two hours later, I emerged from this rather frightening journey into the heart of SQL Server memory management, fascinated but still unsure if I'd learned anything that I'd put to any practical use. However, I certainly began to agree that there is something almost Tolkeinian in the language of the deep recesses of SQL Server. Cheers, Tony.

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• Short Season, Long Models - Dealing with Seasonality

  - by Michel Adar

  Accounting for seasonality presents a challenge for the accurate prediction of events. Examples of seasonality include: ·         Boxed cosmetics sets are more popular during Christmas. They sell at other times of the year, but they rise higher than other products during the holiday season. ·         Interest in a promotion rises around the time advertising on TV airs ·         Interest in the Sports section of a newspaper rises when there is a big football match There are several ways of dealing with seasonality in predictions. Time Windows If the length of the model time windows is short enough relative to the seasonality effect, then the models will see only seasonal data, and therefore will be accurate in their predictions. For example, a model with a weekly time window may be quick enough to adapt during the holiday season. In order for time windows to be useful in dealing with seasonality it is necessary that: The time window is significantly shorter than the season changes There is enough volume of data in the short time windows to produce an accurate model An additional issue to consider is that sometimes the season may have an abrupt end, for example the day after Christmas. Input Data If available, it is possible to include the seasonality effect in the input data for the model. For example the customer record may include a list of all the promotions advertised in the area of residence. A model with these inputs will have to learn the effect of the input. It is possible to learn it specific to the promotion – and by the way learn about inter-promotion cross feeding – by leaving the list of ads as it is; or it is possible to learn the general effect by having a flag that indicates if the promotion is being advertised. For inputs to properly represent the effect in the model it is necessary that: The model sees enough events with the input present. For example, by virtue of the model lifetime (or time window) being long enough to see several “seasons” or by having enough volume for the model to learn seasonality quickly. Proportional Frequency If we create a model that ignores seasonality it is possible to use that model to predict how the specific person likelihood differs from average. If we have a divergence from average then we can transfer that divergence proportionally to the observed frequency at the time of the prediction. Definitions: Ft = trailing average frequency of the event at time “t”. The average is done over a suitable period of to achieve a statistical significant estimate. F = average frequency as seen by the model. L = likelihood predicted by the model for a specific person Lt = predicted likelihood proportionally scaled for time “t”. If the model is good at predicting deviation from average, and this holds over the interesting range of seasons, then we can estimate Lt as: Lt = L * (Ft / F) Considering that: L = (L – F) + F Substituting we get: Lt = [(L – F) + F] * (Ft / F) Which simplifies to: (i)                  Lt = (L – F) * (Ft / F)  +  Ft This latest expression can be understood as “The adjusted likelihood at time t is the average likelihood at time t plus the effect from the model, which is calculated as the difference from average time the proportion of frequencies”. The formula above assumes a linear translation of the proportion. It is possible to generalize the formula using a factor which we will call “a” as follows: (ii)                Lt = (L – F) * (Ft / F) * a  +  Ft It is also possible to use a formula that does not scale the difference, like: (iii)               Lt = (L – F) * a  +  Ft While these formulas seem reasonable, they should be taken as hypothesis to be proven with empirical data. A theoretical analysis provides the following insights: The Cumulative Gains Chart (lift) should stay the same, as at any given time the order of the likelihood for different customers is preserved If F is equal to Ft then the formula reverts to “L” If (Ft = 0) then Lt in (i) and (ii) is 0 It is possible for Lt to be above 1. If it is desired to avoid going over 1, for relatively high base frequencies it is possible to use a relative interpretation of the multiplicative factor. For example, if we say that Y is twice as likely as X, then we can interpret this sentence as: If X is 3%, then Y is 6% If X is 11%, then Y is 22% If X is 70%, then Y is 85% - in this case we interpret “twice as likely” as “half as likely to not happen” Applying this reasoning to (i) for example we would get: If (L < F) or (Ft < (1 / ((L/F) + 1)) Then  Lt = L * (Ft / F) Else Lt = 1 – (F / L) + (Ft * F / L)  

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• About Solaris 11 and UltraSPARC II/III/IV/IV+

  - by nospam(at)example.com (Joerg Moellenkamp)

  I know that I will get the usual amount of comments like "Oh, Jörg ? you can't be negative about Oracle" for this article. However as usual I want to explain the logic behind my reasoning. Yes ? I know that there is a lot of UltraSPARC III, IV and IV+ gear out there. But there are some very basic questions: Does your application you are currently running on this gear stops running just because you can't run Solaris 11 on it? What is the need to upgrade a system already in production to Solaris 11? I have the impression, that some people think that the systems get useless in the moment Oracle releases Solaris 11. I know that Sun sold UltraSPARC IV+ systems until 2009. The Sun SF490 introduced 2004 for example, that was a Sun SF480 with UltraSPARC IV and later with UltraSPARC IV+. And yes, Sun made some speedbumps. At that time the systems of the UltraSPARC III to IV+ generations were supported on Solaris 8, on Solaris 9 and on Solaris 10. However from my perspective we sold them to customers, which weren't able to migrate to Solaris 10 because they used applications not supported on Solaris 9 or who just didn't wanted to migrate to Solaris 10. Believe it or not ? I personally know two customers that migrated core systems to Solaris 10 in ? well 2008/9. This was especially true when the M3000 was announced in 2008 when it closed the darned single socket gap. It may be different at you site, however that's what I remember about that time when talking with customers. At first: Just because there is no Solaris 11 for UltraSPARC III, IV and IV+, it doesn't mean that Solaris 10 will go away anytime soon. I just want to point you to "Expect Lifetime Support - Hardware and Operating Systems". It states about Premier Support:Maintenance and software upgrades are included for Oracle operating systems and Oracle VM for a minimum of eight years from the general availability date.GA for Solaris 10 was in 2005. Plus 8 years ? 2013 ? at minimum. Then you can still opt for 3 years of "Extended Support" ? 2016 ? at minimum. 2016 your systems purchased in 2009 are 7 years old. Even on systems purchased at the very end of the lifetime of that system generation. That are the rules as written in the linked document. I said minimum The actual dates are even further in the future: Premier Support for Solaris 10 ends in 2015, Extended support ends 2018. Sustaining support ? indefinite. You will find this in the document "Oracle Lifetime Support Policy: Oracle Hardware and Operating Systems".So I don't understand when some people write, that Oracle is less protective about hardware investments than Sun. And for hardware it's the same as with Sun: Service 5 years after EOL as part of Premier Support. I would like to write about a different perspective as well: I have to be a little cautious here, because this is going in the roadmap area, so I will mention the public sources here: John Fowler told last year that we have to expect at at least 3x the single thread performance of T3 for T4. We have 8 cores in T4, as stated by Rick Hetherington. Let's assume for a moment that a T4 core will have the performance of a UltraSPARC core (just to simplify math and not to disclosing anything about the performance, all existing SPARC cores are considered equal). So given this pieces of information, you could consolidate 8 V215, 4 or 8 V245, 2 full blown V445,2 full blown 490, 2 full blown M3000 on a single T4 SPARC processor. The Fowler roadmap prezo talked about 4-socket systems with T4. So 32 V215, 16 to 8 V245, 8 fullblown V445, 8 full blown V490, 8 full blown M3000 in a system image. I think you get the idea. That said, most of the systems we are talking about have already amortized and perhaps it's just time to invest in new systems to yield other advantages like reduced space consumptions, like reduced power consumption, like some of the neat features sun4v gives you, and yes ? reduced number of processor licenses for Oracle and less money for Oracle HW/SW support. As much as I dislike it myself that my own UltraSPARC III and UltraSPARC II based systems won't run on Solaris 11 (and I have quite a few of them in my personal lab), I really think that the impact on production environments will be much less than most people think now. By the way: The reason for this move is a quite significant new feature. I will tell you that it was this feature, when it's out. I assume, telling just a word more could lead to much more time to blog.

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• Is Data Science “Science”?

  - by BuckWoody

  I hold the term “science” in very high esteem. I grew up on the Space Coast in Florida, and eventually worked at the Kennedy Space Center, surrounded by very intelligent people who worked in various scientific fields. Recently a new term has entered the computing dialog – “Data Scientist”. Since it’s not a standard term, it has a lot of definitions, and in fact has been disputed as a correct term. After all, the reasoning goes, if there’s no such thing as “Data Science” then how can there be a Data Scientist? This argument has been made before, albeit with a different term – “Computer Science”. In Peter Denning’s excellent article “Is Computer Science Science” (April  2005/Vol. 48, No. 4 COMMUNICATIONS OF THE ACM) there are many points that separate “science” from “engineering” and even “art”.  I won’t repeat the content of that article here (I recommend you read it on your own) but will leverage the points he makes there. Definition of Science To ask the question “is data science ‘science’” then we need to start with a definition of terms. Various references put the definition into the same basic areas: Study of the physical world Systematic and/or disciplined study of a subject area ...and then they include the things studied, the bodies of knowledge and so on. The word itself comes from Latin, and means merely “to know” or “to study to know”. Greek divides knowledge further into “truth” (episteme), and practical use or effects (tekhne). Normally computing falls into the second realm. Definition of Data Science And now a more controversial definition: Data Science. This term is so new and perhaps so niche that the major dictionaries haven’t yet picked it up (my OED reference is older – can’t afford to pop for the online registration at present). Researching the term's general use I created an amalgam of the definitions this way: “Studying and applying mathematical and other techniques to derive information from complex data sets.” Using this definition, data science certainly seems to be science - it's learning about and studying some object or area using systematic methods. But implicit within the definition is the word “application”, which makes the process more akin to engineering or even technology than science. In fact, I find that using these techniques – and data itself – part of science, not science itself. I leave out the concept of studying data patterns or algorithms as part of this discipline. That is actually a domain I see within research, mathematics or computer science. That of course is a type of science, but does not seek for practical applications. As part of the argument against calling it “Data Science”, some point to the scientific method of creating a hypothesis, testing with controls, testing results against the hypothesis, and documenting for repeatability.  These are not steps that we often take in working with data. We normally start with a question, and fit patterns and algorithms to predict outcomes and find correlations. In this way Data Science is more akin to statistics (and in fact makes heavy use of them) in the process rather than starting with an assumption and following on with it. So, is Data Science “Science”? I’m uncertain – and I’m uncertain it matters. Even if we are facing rampant “title inflation” these days (does anyone introduce themselves as a secretary or supervisor anymore?) I can tolerate the term at least from the intent that we use data to study problems across a wide spectrum, rather than restricting it to a single domain. And I also understand those who have worked hard to achieve the very honorable title of “scientist” who have issues with those who borrow the term without asking. What do you think? Science, or not? Does it matter?

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• Pirates, Treasure Chests and Architectural Mapping

  Pirate 1: Why do pirates create treasure maps? Pirate 2: I do not know.Pirate 1: So they can find their gold. Yes, that was a bad joke, but it does illustrate a point. Pirates are known for drawing treasure maps to their most prized possession. These documents detail the decisions pirates made in order to hide and find their chests of gold. The map allows them to trace the steps they took originally to hide their treasure so that they may return. As software engineers, programmers, and architects we need to treat software implementations much like our treasure chest. Why is software like a treasure chest? It cost money, time,  and resources to develop (Usually) It can make or save money, time, and resources (Hopefully) If we operate under the assumption that software is like a treasure chest then wouldn’t make sense to document the steps, rationale, concerns, and decisions about how it was designed? Pirates are notorious for documenting where they hide their treasure.  Shouldn’t we as creators of software do the same? By documenting our design decisions and rationale behind them will help others be able to understand and maintain implemented systems. This can only be done if the design decisions are correctly mapped to its corresponding implementation. This allows for architectural decisions to be traced from the conceptual model, architectural design and finally to the implementation. Mapping gives software professional a method to trace the reason why specific areas of code were developed verses other options. Just like the pirates we need to able to trace our steps from the start of a project to its implementation,  so that we will understand why specific choices were chosen. The traceability of a software implementation that actually maps back to its originating design decisions is invaluable for ensuring that architectural drifting and erosion does not take place. The drifting and erosion is prevented by allowing others to understand the rational of why an implementation was created in a specific manor or methodology The process of mapping distinct design concerns/decisions to the location of its implemented is called traceability. In this context traceability is defined as method for connecting distinctive software artifacts. This process allows architectural design models and decisions to be directly connected with its physical implementation. The process of mapping architectural design concerns to a software implementation can be very complex. However, most design decision can be placed in  a few generalized categories. Commonly Mapped Design Decisions Design Rationale Components and Connectors Interfaces Behaviors/Properties Design rational is one of the hardest categories to map directly to an implementation. Typically this rational is mapped or document in code via comments. These comments consist of general design decisions and reasoning because they do not directly refer to a specific part of an application. They typically focus more on the higher level concerns. Components and connectors can directly be mapped to architectural concerns. Typically concerns subdivide an application in to distinct functional areas. These functional areas then can map directly back to their originating concerns.Interfaces can be mapped back to design concerns in one of two ways. Interfaces that pertain to specific function definitions can be directly mapped back to its originating concern(s). However, more complicated interfaces require additional analysis to ensure that the proper mappings are created. Depending on the complexity some Behaviors\Properties can be translated directly into a generic implementation structure that is ready for business logic. In addition, some behaviors can be translated directly in to an actual implementation depending on the complexity and architectural tools used. Mapping design concerns to an implementation is a lot of work to maintain, but is doable. In order to ensure that concerns are mapped correctly and that an implementation correctly reflects its design concerns then one of two standard approaches are usually used. All Changes Come From ArchitectureBy forcing all application changes to come through the architectural model prior to implementation then the existing mappings will be used to locate where in the implementation changes need to occur. Allow Changes From Implementation Or Architecture By allowing changes to come from the implementation and/or the architecture then the other area must be kept in sync. This methodology is more complex compared to the previous approach.  One reason to justify the added complexity for an application is due to the fact that this approach tends to detect and prevent architectural drift and erosion. Additionally, this approach is usually maintained via software because of the complexity. Reference:Taylor, R. N., Medvidovic, N., & Dashofy, E. M. (2009). Software architecture: Foundations, theory, and practice Hoboken, NJ: John Wiley & Sons  

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• Data Source Security Part 2

  - by Steve Felts

  In Part 1, I introduced the default security behavior and listed the various options available to change that behavior.  One of the key topics to understand is the difference between directly using database user and password values versus mapping from WLS user and password to the associated database values.   The direct use of database credentials is relatively new to WLS, based on customer feedback.  Some of the trade-offs are covered in this article. Credential Mapping vs. Database Credentials Each WLS data source has a credential map that is a mechanism used to map a key, in this case a WLS user, to security credentials (user and password).  By default, when a user and password are specified when getting a connection, they are treated as credentials for a WLS user, validated, and are converted to a database user and password using a credential map associated with the data source.  If a matching entry is not found in the credential map for the data source, then the user and password associated with the data source definition are used.  Because of this defaulting mechanism, you should be careful what permissions are granted to the default user.  Alternatively, you can define an invalid default user to ensure that no one can accidentally get through (in this case, you would need to set the initial capacity for the pool to zero so that the pool is populated only by valid users). To create an entry in the credential map: 1) First create a WLS user.  In the administration console, go to Security realms, select your realm (e.g., myrealm), select Users, and select New.  2) Second, create the mapping.  In the administration console, go to Services, select Data sources, select your data source name, select Security, select Credentials, and select New.  See http://docs.oracle.com/cd/E24329_01/apirefs.1211/e24401/taskhelp/jdbc/jdbc_datasources/ConfigureCredentialMappingForADataSource.html for more information. The advantages of using the credential mapping are that: 1) You don’t hard-code the database user/password into a program or need to prompt for it in addition to the WLS user/password and 2) It provides a layer of abstraction between WLS security and database settings such that many WLS identities can be mapped to a smaller set of DB identities, thereby only requiring middle-tier configuration updates when WLS users are added/removed. You can cut down the number of users that have access to a data source to reduce the user maintenance overhead.  For example, suppose that a servlet has the one pre-defined, special WLS user/password for data source access, hard-wired in its code in a getConnection(user, password) call.  Every WebLogic user can reap the specific DBMS access coded into the servlet, but none has to have general access to the data source.  For instance, there may be a ‘Sales’ DBMS which needs to be protected from unauthorized eyes, but it contains some day-to-day data that everyone needs. The Sales data source is configured with restricted access and a servlet is built that hard-wires the specific data source access credentials in its connection request.  It uses that connection to deliver only the generally needed day-to-day information to any caller. The servlet cannot reveal any other data, and no WebLogic user can get any other access to the data source.  This is the approach that many large applications take and is the reasoning behind the default mapping behavior in WLS. The disadvantages of using the credential map are that: 1) It is difficult to manage (create, update, delete) with a large number of users; it is possible to use WLST scripts or a custom JMX client utility to manage credential map entries. 2) You can’t share a credential map between data sources so they must be duplicated. Some applications prefer not to use the credential map.  Instead, the credentials passed to getConnection(user, password) should be treated as database credentials and used to authenticate with the database for the connection, avoiding going through the credential map.  This is enabled by setting the “use-database-credentials” to true.  See http://docs.oracle.com/cd/E24329_01/apirefs.1211/e24401/taskhelp/jdbc/jdbc_datasources/ConfigureOracleParameters.html "Configure Oracle parameters" in Oracle WebLogic Server Administration Console Help. Use Database Credentials is not currently supported for Multi Data Source configurations.  When enabled, it turns off credential mapping on Generic and Active GridLink data sources for the following attributes: 1. identity-based-connection-pooling-enabled (this interaction is available by patch in 10.3.6.0). 2. oracle-proxy-session (this interaction is first available in 10.3.6.0). 3. set client identifier (this interaction is available by patch in 10.3.6.0).  Note that in the data source schema, the set client identifier feature is poorly named “credential-mapping-enabled”.  The documentation and the console refer to it as Set Client Identifier. To review the behavior of credential mapping and using database credentials: - If using the credential map, there needs to be a mapping for each WLS user to database user for those users that will have access to the database; otherwise the default user for the data source will be used.  If you always specify a user/password when getting a connection, you only need credential map entries for those specific users. - If using database credentials without specifying a user/password, the default user and password in the data source descriptor are always used.  If you specify a user/password when getting a connection, that user will be used for the credentials.  WLS users are not involved at all in the data source connection process.

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• "Mega Menus" for SEO [duplicate]

  - by Thought Space Designs

  This question already has an answer here: How do I handle having to many links on a webpage because of my menu 4 answers I'm using the term "Mega Menus" loosely here. I'm redesigning my WordPress site (it's going to be responsive), and as part of the redesign, I was debating incorporating some sort of descriptive menu setup. For example, normal navigation drop down menus come in the form of unordered lists of links like so: <nav> <ul> <li> <a href="#">Link1</a> </li> <li> <a href="#">Link2</a> </li> <li> <a href="#">Link3</a> <ul> <li> <a href="#">Sub Link1</a> </li> <li> <a href="#">Sub Link2</a> </li> <li> <a href="#">Sub Link3</a> </li> </ul> </li> <li> <a href="#">Link4</a> </li> </ul> </nav> What I'm looking to do is build my drop down menus with more information than your standard menu. For example, I have a top level link named "Team", and under that link, I want to make a large drop down that contains head shots, headers (in the form of styled p tags) and brief (<100 words) descriptions of each team member (only 2 currently). I want to accompany this with a "Read More" link that takes you to their actual team page. This is just one example, of course, and the other top level links would also have descriptive drop downs in the same fashion. On mobile, I was planning on hiding the "mega menu", and delivering a standard unordered list of links. Here's what I was thinking for overall structure and syntax: <nav> <ul> <li> <a href="#">Home</a> </li> <li> <a href="#">About</a> </li> <li> <a href="#">Team</a> <ul> <!-- DESKTOP --> <li class="mega-menu row"> <a class="col-sm-6" href="#"> <div class="row"> <div class="col-sm-4"> <img src="#" alt="Team Member 1" /> </div> <div class="col-sm-8"> <p class="header">Team Member 1</p> <p>Short description goes here.</p> </div> </div> </a> <a class="col-sm-6" href="#"> <!-- OTHER TEAM MEMBER INFO --> </a> </li> <!-- END DESKTOP --> <!-- MOBILE --> <li> <a href="#">Team Member 1</a> </li> <li> <a href="#">Team Member 2</a> </li> <!-- END MOBILE --> </ul> </li> <li> <a href="#">Contact</a> </li> </ul> </nav> Can anybody think of any potential SEO ramifications of doing this? I'm not going to be loading these menus full of links, so it shouldn't hurt page rank, but what are the effects of having a good bit of text and maybe even forms within nav elements? Is there such a thing as overloading nav with HTML? EDIT: Here's an example of what the menu would look like rendered on desktop. I'm currently hovering the "Team" menu, but you can't see because my mouse went away when I took the screenshot. EDIT 2: This question is not a duplicate. I'm not going to have "too many" links in my menus. I'm wondering how having images and text inside of header navigation will affect my menus. Also, I don't just want "yes, this is bad" answers. Please cite your sources and be specific with reasoning.

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• Blocking access to websites with objective-C / root privileges in objective-C

  - by kvaruni

  I am writing a program in Objective-C (XCode 3.2, on Snow Leopard) that is capable of either selectively blocking certain sites for a duration or only allow certain sites (and thus block all others) for a duration. The reasoning behind this program is rather simple. I tend to get distracted when I have full internet access, but I do need internet access during my working hours to get to a number of work-related websites. Clearly, this is not a permanent block, but only helps me to focus whenever I find myself wandering a bit too much. At the moment, I am using a Unix script that is called via AppleScript to obtain Administrator permissions. It then activates a number of ipfw rules and clears those after a specific duration to restore full internet access. Simple and effective, but since I am running as a standard user, it gets cumbersome to enter my administrator password each and every time I want to go "offline". Furthermore, this is a great opportunity to learn to work with XCode and Objective-C. At the moment, everything works as expected, minus the actual blocking. I can add a number of sites in a list, specify whether or not I want to block or allow these websites and I can "start" the blocking by specifying a time until which I want to stay "offline". However, I find it hard to obtain clear information on how I can run a privileged Unix command from Objective-C. Ideally, I would like to be able to store information with respect to the Administrator account into the Keychain to use these later on, so that I can simply move into "offline" mode with the convenience of clicking a button. Even more ideally, there might be some class in Objective-C with which I can block access to some/all websites for this particular user without needing to rely on privileged Unix commands. A third possibility is in starting this program with root permissions and the reducing the permissions until I need them, but since this is a GUI application that is nested in the menu bar of OS X, the results are rather awkward and getting it to run each and every time with root permission is no easy task. Anyone who can offer me some pointers or advice? Please, no security-warnings, I am fully aware that what I want to do is a potential security threat.

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• WPF ListBox not binding to INotifyCollectionChanged or INotifyPropertyChanged Events

  - by Gabe Anzelini

  I have the following test code: private class SomeItem{ public string Title{ get{ return "something"; } } public bool Completed { get { return false; } set { } } } private class SomeCollection : IEnumerable<SomeItem>, INotifyCollectionChanged { private IList<SomeItem> _items = new List<SomeItem>(); public void Add(SomeItem item) { _items.Add(item); CollectionChanged(this, new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset)); } #region IEnumerable<SomeItem> Members public IEnumerator<SomeItem> GetEnumerator() { return _items.GetEnumerator(); } #endregion #region IEnumerable Members System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() { return _items.GetEnumerator(); } #endregion #region INotifyCollectionChanged Members public event NotifyCollectionChangedEventHandler CollectionChanged; #endregion } private SomeCollection collection = new SomeCollection(); private void Expander_Expanded(object sender, RoutedEventArgs e) { var expander = (Expander) sender; var list = expander.DataContext as ITaskList; var listBox = (ListBox)expander.Content; //list.Tasks.CollectionChanged += CollectionChanged; collection.Add(new SomeItem()); collection.Add(new SomeItem()); listBox.ItemsSource = collection; } and the XAML the outer listbox gets populated on load. when the expander gets expanded i then set the itemssource property of the inner listbox (the reason i do this hear instead of using binding is this operation is quite slow and i only want it to take place if the use chooses to view the items). The inner listbox renders fine, but it doesn't actually subscribe to the CollectionChanged event on the collection. I have tried this with ICollection instead of IEnumerable and adding INotifyPropertyChanged as well as replacing INotifyCollectionChanged with INotifyPropertyChanged. The only way I can actually get this to work is to gut my SomeCollection class and inherit from ObservableCollection. My reasoning for trying to role my own INotifyCollectionChanged instead of using ObservableCollection is because I am wrapping a COM collection in the real code. That collection will notify on add/change/remove and I am trying to convert these to INotify events for WPF. Hope this is clear enough (its late).

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• Lambda Expression to be used in Select() query

  - by jameschinnock

  Hi, I am trying to build a lambda expression, containing two assignments (as shown further down), that I can then pass to a Queryable.Select() method. I am trying to pass a string variable into a method and then use that variable to build up the lambda expression so that I can use it in a LINQ Select query. My reasoning behind it is that I have a SQL Server datasource with many column names, I am creating a charting application that will allow the user to select, say by typing in the column name, the actual column of data they want to view in the y-axis of my chart, with the x-axis always being the DateTime. Therefore, they can essentially choose what data they chart against the DateTime value (it’s a data warehouse type app). I have, for example, a class to store the retrieved data in, and hence use as the chart source of: public class AnalysisChartSource { public DateTime Invoicedate { get; set; } public Decimal yValue { get; set; } } I have (purely experimentaly) built an expression tree for the Where clause using the String value and that works fine: public void GetData(String yAxis) { using (DataClasses1DataContext db = new DataClasses1DataContext()) { var data = this.FunctionOne().AsQueryable<AnalysisChartSource>(); //just to get some temp data in.... ParameterExpression pe = Expression.Parameter(typeof(AnalysisChartSource), "p"); Expression left = Expression.MakeMemberAccess(pe, typeof(AnalysisChartSource).GetProperty(yAxis)); Expression right = Expression.Constant((Decimal)16); Expression e2 = Expression.LessThan(left, right); Expression expNew = Expression.New(typeof(AnalysisChartSource)); LambdaExpression le = Expression.Lambda(left, pe); MethodCallExpression whereCall = Expression.Call( typeof(Queryable), "Where", new Type[] { data.ElementType }, data.Expression, Expression.Lambda<Func<AnalysisChartSource, bool>>(e2, new ParameterExpression[] { pe })); } } However……I have tried a similar approach for the Select statement, but just can’t get it to work as I need the Select() to populate both X and Y values of the AnalysisChartSource class, like this: .Select(c => new AnalysisChartSource { Invoicedate = c.Invoicedate, yValue = c.yValue}).AsEnumerable(); How on earth can I build such an expression tree….or….possibly more to the point…..is there an easier way that I have missed entirely?

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• Tactics for using PHP in a high-load site

  - by Ross

  Before you answer this I have never developed anything popular enough to attain high server loads. Treat me as (sigh) an alien that has just landed on the planet, albeit one that knows PHP and a few optimisation techniques. I'm developing a tool in PHP that could attain quite a lot of users, if it works out right. However while I'm fully capable of developing the program I'm pretty much clueless when it comes to making something that can deal with huge traffic. So here's a few questions on it (feel free to turn this question into a resource thread as well). Databases At the moment I plan to use the MySQLi features in PHP5. However how should I setup the databases in relation to users and content? Do I actually need multiple databases? At the moment everything's jumbled into one database - although I've been considering spreading user data to one, actual content to another and finally core site content (template masters etc.) to another. My reasoning behind this is that sending queries to different databases will ease up the load on them as one database = 3 load sources. Also would this still be effective if they were all on the same server? Caching I have a template system that is used to build the pages and swap out variables. Master templates are stored in the database and each time a template is called it's cached copy (a html document) is called. At the moment I have two types of variable in these templates - a static var and a dynamic var. Static vars are usually things like page names, the name of the site - things that don't change often; dynamic vars are things that change on each page load. My question on this: Say I have comments on different articles. Which is a better solution: store the simple comment template and render comments (from a DB call) each time the page is loaded or store a cached copy of the comments page as a html page - each time a comment is added/edited/deleted the page is recached. Finally Does anyone have any tips/pointers for running a high load site on PHP. I'm pretty sure it's a workable language to use - Facebook and Yahoo! give it great precedence - but are there any experiences I should watch out for? Thanks, Ross

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• Is this a good way to do a game loop for an iPhone game?

  - by Danny Tuppeny

  Hi all, I'm new to iPhone dev, but trying to build a 2D game. I was following a book, but the game loop it created basically said: function gameLoop update() render() sleep(1/30th second) gameLoop The reasoning was that this would run at 30fps. However, this seemed a little mental, because if my frame took 1/30th second, then it would run at 15fps (since it'll spend as much time sleeping as updating). So, I did some digging and found the CADisplayLink class which would sync calls to my gameLoop function to the refresh rate (or a fraction of it). I can't find many samples of it, so I'm posting here for a code review :-) It seems to work as expected, and it includes passing the elapsed (frame) time into the Update method so my logic can be framerate-independant (however I can't actually find in the docs what CADisplayLink would do if my frame took more than its allowed time to run - I'm hoping it just does its best to catch up, and doesn't crash!). // // GameAppDelegate.m // // Created by Danny Tuppeny on 10/03/2010. // Copyright Danny Tuppeny 2010. All rights reserved. // #import "GameAppDelegate.h" #import "GameViewController.h" #import "GameStates/gsSplash.h" @implementation GameAppDelegate @synthesize window; @synthesize viewController; - (void) applicationDidFinishLaunching:(UIApplication *)application { // Create an instance of the first GameState (Splash Screen) [self doStateChange:[gsSplash class]]; // Set up the game loop displayLink = [CADisplayLink displayLinkWithTarget:self selector:@selector(gameLoop)]; [displayLink setFrameInterval:2]; [displayLink addToRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode]; } - (void) gameLoop { // Calculate how long has passed since the previous frame CFTimeInterval currentFrameTime = [displayLink timestamp]; CFTimeInterval elapsed = 0; // For the first frame, we want to pass 0 (since we haven't elapsed any time), so only // calculate this in the case where we're not the first frame if (lastFrameTime != 0) { elapsed = currentFrameTime - lastFrameTime; } // Keep track of this frames time (so we can calculate this next time) lastFrameTime = currentFrameTime; NSLog([NSString stringWithFormat:@"%f", elapsed]); // Call update, passing the elapsed time in [((GameState*)viewController.view) Update:elapsed]; } - (void) doStateChange:(Class)state { // Remove the previous GameState if (viewController.view != nil) { [viewController.view removeFromSuperview]; [viewController.view release]; } // Create the new GameState viewController.view = [[state alloc] initWithFrame:CGRectMake(0, 0, IPHONE_WIDTH, IPHONE_HEIGHT) andManager:self]; // Now set as visible [window addSubview:viewController.view]; [window makeKeyAndVisible]; } - (void) dealloc { [viewController release]; [window release]; [super dealloc]; } @end Any feedback would be appreciated :-) PS. Bonus points if you can tell me why all the books use "viewController.view" but for everything else seem to use "[object name]" format. Why not [viewController view]?

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• Strategy pattern and "action" classes explosion

  - by devoured elysium

  Is it bad policy to have lots of "work" classes(such as Strategy classes), that only do one thing? Let's assume I want to make a Monster class. Instead of just defining everything I want about the monster in one class, I will try to identify what are its main features, so I can define them in interfaces. That will allow to: Seal the class if I want. Later, other users can just create a new class and still have polymorphism by means of the interfaces I've defined. I don't have to worry how people (or myself) might want to change/add features to the base class in the future. All classes inherit from Object and they implement inheritance through interfaces, not from mother classes. Reuse the strategies I'm using with this monster for other members of my game world. Con: This model is rigid. Sometimes we would like to define something that is not easily achieved by just trying to put together this "building blocks". public class AlienMonster : IWalk, IRun, ISwim, IGrowl { IWalkStrategy _walkStrategy; IRunStrategy _runStrategy; ISwimStrategy _swimStrategy; IGrowlStrategy _growlStrategy; public Monster() { _walkStrategy = new FourFootWalkStrategy(); ...etc } public void Walk() { _walkStrategy.Walk(); } ...etc } My idea would be next to make a series of different Strategies that could be used by different monsters. On the other side, some of them could also be used for totally different purposes (i.e., I could have a tank that also "swims"). The only problem I see with this approach is that it could lead to a explosion of pure "method" classes, i.e., Strategy classes that have as only purpose make this or that other action. In the other hand, this kind of "modularity" would allow for high reuse of stratagies, sometimes even in totally different contexts. What is your opinion on this matter? Is this a valid reasoning? Is this over-engineering? Also, assuming we'd make the proper adjustments to the example I gave above, would it be better to define IWalk as: interface IWalk { void Walk(); } or interface IWalk { IWalkStrategy WalkStrategy { get; set; } //or something that ressembles this } being that doing this I wouldn't need to define the methods on Monster itself, I'd just have public getters for IWalkStrategy (this seems to go against the idea that you should encapsulate everything as much as you can!) Why? Thanks

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• Determine the 'Overtype' mode using Javascript

  - by Snorkpete

  We are creating a web app to replace an old-school green-screen application. In the green-screen app, as the user presses the Insert key to switch between overtype and insert modes, the cursor changes to indicate which input mode the user is currently in. In IE (which is the official browser of the company), overtype mode also works, but there's no visual indication as to whether overtype mode is on or not, until the user starts typing and possibly over-writes existing information unexpectedly. I'd like to put some sort of visual indicator on the screen if in overtype mode. How can you determine if the browser is in 'overtype mode' from Javascript? Is there some property or function i can query to determine if the browser is in overtype mode? Even an IE-specific solution would be helpful, since our corporate policy dictates the browser to use as IE7 (pure torture, btw). (I do know that one solution is to do check for key presses of the Insert key. However, it's a solution that I'd prefer to avoid since that method seems a bit flaky & error-prone because I can't guarantee what mode the user would be in BEFORE he/she hits my page. ) The reasoning behind this question: The functionality of this portion of the green-screen app is such that the user can select from a list of 'preformatted bodies of text'. crude eg. The excess for this policy is: $xxxxxx and max limit is:$xxxxxx Date of policy is: xx/xx/xxxx and expires : xx/xx/xxxx Some other irrelevant text After selecting this 'preformatted text', the user would then use overtype to replace the x's with actual values, without disturbing the alignment of the rest of the text. (To be clear, they can still edit any part of the 'preformatted text' if they so wished. It's just that usually, they just wish to replace specific portions of the text. Keeping the alignment is important since these sections of text can end up on printed documents.) Of course, the same effect can be achieved by just selecting the x's to replace first, but it would be helpful (with respect to easing the transition to the web app) to allow old methods of doing things to continue to work, while still allowing 'web methods' to be used by the more tech-savvy users. Essentially, we're trying to make the initial transition from the green-screen app to the web app be as seemless as possible to minimise the resistance from the long-time green-screeners.

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