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• Confused about std::runtime_error vs. std::logic_error

  - by David Gladfelter

  I recently saw that the boost program_options library throws a logic_error if the command-line input was un-parsable. That challenged my assumptions about logic_error vs. runtime_error. I assumed that logic errors (logic_error and its derived classes) were problems that resulted from internal failures to adhere to program invariants, often in the form of illegal arguments to internal API's. In that sense they are largely equivalent to ASSERT's, but meant to be used in released code (unlike ASSERT's which are not usually compiled into released code.) They are useful in situations where it is infeasible to integrate separate software components in debug/test builds or the consequences of a failure are such that it is important to give runtime feedback about the invalid invariant condition to the user. Similarly, I thought that runtime_errors resulted exclusively from runtime conditions outside of the control of the programmer: I/O errors, invalid user input, etc. However, program_options is obviously heavily (primarily?) used as a means of parsing end-user input, so under my mental model it certainly should throw a runtime_error in the case of bad input. Where am I going wrong? Do you agree with the boost model of exception typing?

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• How do you protect yourself from runaway memory consumption bringing down the PC?

  - by romkyns

  Every now and again I find myself doing something moderately dumb that results in my program allocating all the memory it can get and then some. This kind of thing used to cause the program to die fairly quickly with an "out of memory" error, but these days Windows will go out of its way to give this non-existent memory to the application, and in fact is apparently prepared to commit suicide doing so. Not literally of course, but it will starve itself of usable physical RAM so badly that even running the task manager will require half an hour of swapping (after all the runaway application is still allocating more and more memory all the time). This doesn't happen too often, but when it does it's disastrous. I usually have to reset my machine, causing data loss from time to time and generally a lot of inconvenience. Do you have any practical advice on making the consequences of such a mistake less dire? Perhaps some registry tweak to limit the max amount of virtual memory an app is allowed to allocate? Or some CLR flag that will limit this only for the current application? (It's usually in .NET that I do this to myself.) ("Don't run out of RAM" and "Buy more RAM" are no use - the former I have no control over, and the latter I've already done.)

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• Disaster Recovery Discovery

  - by Rodney Landrum

  Last weekend I joined several of my IT staff on a mission to perform a DR test in our remote CoLo center in a large South East city of the US. Can I be more obtuse? The goal was simple for me as the sole DBA in a throng of Windows, Storage, Network and SAN admins – restore the databases and make them work. There were 4 applications that back ended to 7 SQL Server databases on 4 different SQL Server instances. We would maintain the original server names, but beyond that it was fair game. We had time to prepare so I was able to script out or otherwise automate the recovery process. I used sp_help_revlogin for three of the servers, a bit of a cheat actually because restoring the Master database on the target DR servers was the specified course of action according to the DR procedures ( the caveat “IF REQUIRED” left it open to interpretation. I really wanted to avoid the step of restoring Master for a number of reasons but mainly because I did not want to deal with issues starting SQL Services afterward. Having to account for the location of TempDB and the version conflicts of the resource DBs were just two of the battles I chose not to fight. Not to mention other system database location problems that might arise and prevent SQL from starting.  I was going to have to restore all of the user databases anyway, so I would not really gain any benefit, outside of logins, for taking the time to restore the source Master database over the newly installed one on the fresh server. What I wanted was the ability to restore the Master database as a user database, call it Master_Mine, from a backup on the source system and then use that restored database to script the SQL Logins and passwords on the DR systems. While I did not attempt this on the trip, the thought stuck in my mind and this past week I succeeded at scripting user accounts and passwords using only a restored copy of the Master database. Granted there were several challenges to overcome.  Also, as is usual for any work like this the usual disclaimers apply:  This is not something that I would imagine Microsoft would condone or support and this was really only an experiment for me to learn if it was even possible. While I have tested the process with success, I do not know that I would use this technique in a documented procedure because future updates for SQL Server will render this technique non-functional. I thought at first, incorrectly of course, that I could use sp_help_revlogin on a restored copy of the master database I named Master_Mine.   Since sp_help_revlogin uses system schema objects, sys.syslogins and sys.server_principals, this was not going to work because all results would come from the main Master database. To test this I added a SQL login via SSMS, backed up Master, restored  it as Master_Mine, and then deleted the login.  Even though the test account I created should presumably still be in the Master_Mine database, I should be able to get to it and script out its creation with its password hash so that I would not need to know the password, but any applications that stored that password would not have to be altered in the DR scenario. They would just work as expected. Once I realized that would not work I began looking deeper.  Knowing that sys.syslogins and sys.server_principals are system views, their underlying code should be available with sp_helptext, right? They were. And this led me to discover the two tables sys.sysxlgns and sys.sysprivs, where the data I needed was stored. These tables existed in both the real Master and the restored copy, Master_Mine.  I used this information to tweak the sp_help_revlogin stored procedure to use these tables instead to create the logins cursor used in sp_help_revlogin. For the password hash,  sp_help_revlogin uses the function LoginProperty() which takes a user name and option ‘passwordhash’ to return the hash for the user. Unfortunately, it requires the login to exist in the Master database. This would not work. So another slight modification I had to make was to pull the password hash itself (pwdhash from sys.sysxlgns) into the logins cursor and comment out the section of sp_help_revlogin that uses LoginProperty. Instead, I pass the pwdhash value as the variable @PWD_varbinary to the sp_hexadecimal stored procedure which is also created by and used within the code provided by Microsoft in the link above for sp_help_revlogin. The final challenge: sys.sysxlgns and sys.server_principals are visible only within a Dedicated Administrator Connection (DAC) query window in SSMS or within SQLCDMD.  To open a DAC connection you have to be logged in on the SQL Server itself, via RDP in my case,  and you preface the server name in the query connection with ADMIN:, so that the server connection looks like ADMIN:ServerName. From there you can create the modified stored procedure in the restored copy of a Master database from a source system as whatever name you like, and then run the modified stored procedure. I named my new stored procedure usp_help_revlogin_MyMaster. Upon execution I was happy to see the logins and password hashes that I needed to apply from the source Master database without having to restore over the new Master system database and without the need to access the original server (assuming it was down due to whatever disaster put it in that state). You will note that I am not providing full code samples here of the modifications. I will say that it was a slight bit of work and anyone who needed to do this for whatever reason, could fairly easily roll their own solution with the information provided herein.  My goal, as I said was to prove that this could be done and provide another option if required to ease the burden of getting SQL Servers up and available in an emergency situation where alternatives may be more challenging or otherwise unavailable.  

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• Multi-Role Domain Controllers for Small Offices (< 50 clients)

  - by kce

  Warning: I'm a Linux/*NIX admin so this is all new to me. I understand that it's not considered a good idea to have only a single domain controller, and that it is also probably a good idea for a domain controller to only do AD/DHCP/DNS (Here). We have two offices, location A with 30 users and location B with 10 users. Our two offices are separated by a WAN that is not particularly robust so I have be instructed that we need to have standalone services in each office. This means that according to "best practices" we will need to build a domain controller and a separate file server in each office. Again, I am not knowledgeable in the ways of Windows but this seems a little unnecessary for an organization of 40 users. People have commented that I could "get away with" running file services on the domain controller as long as the "load is light". That just seems to generate more questions than it answers. What constitutes light load? What are the potential consequences of mixing these roles? Ideally I would prefer to only have one physical machine at each location. The one in location A (the location with IT staff) can act as the primary domain controller and the one in the smaller office can act as the backup domain controller. If either domain controller fails we can still use the other one for authentication (albeit with some latency) and if the WAN connection fails each office still has access to their respective "local" domain controller. If the file services are ALSO run on each server (and synchronized with something like DFS), a similar arrangement in terms of redundancy can be had without having to purchase, build and install two additional separate servers. It's not that I'm adverse to that (well, any more adverse than I am to whole thing to begin with) but to my simple mind it just seems, well a bit overkill. I can definitely see the benefits of functional separation when we're talking larger organizations, but I need to consider the additional overhead too. None of this excludes having a DRP setup for the domain controller/s. I assume you can lose two domain controllers just as easily as one.

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• How is incoming SMTP mail being delivered despite blocked port

  - by Josh

  I setup a MX mail server, everything works despite port 25 being blocked, I'm stumped as to why I am able to receive email with this setup, and what the consequences might be if I leave it this way. Here are the details: Connections to SMTP over port 25 and 587 both reliably connect over my local network. Connections to SMTP over port 25 are blocked from external IPs (the ISP is blocking the port). Connections to Submission SMTP over port 587 from external IPs are reliable. Emails sent from gmail, yahoo, and a few other addresses all are being delivered. I haven't found an email provider that fails to deliver mail to my MX. So, with port 25 blocked, I am assuming other MTA servers fallback to port 587, otherwise I can't imagine how the mail is received. I know port 25 shouldn't be blocked, but so far it works. Are there mail servers that this will not work with? Where can I find more about how this is working? -- edit More technical detail, to validate that I'm not missing something silly. Obviously in the transcript below I've replaced my actual domain with example.com. # DNS MX record points to the A record. $ dig example.com MX +short 1 example.com $ dig example.com A +short <Public IP address> # From a public server (not my ISP hosting the mail server) # We see port 25 is blocked, but port 587 is open $ telnet example.com 25 Trying <public ip>... telnet: Unable to connect to remote host: Connection refused # Let's try openssl $ openssl s_client -starttls smtp -crlf -connect example.com:25 connect: Connection refused connect:errno=111 # Again from a public server, we see port 587 is open $ telnet example.com 587 Trying <public ip>... Connected to example.com. Escape character is '^]'. 220 example.com ESMTP Postfix ehlo example.com 250-example.com 250-PIPELINING 250-SIZE 10485760 250-VRFY 250-ETRN 250-STARTTLS 250-ENHANCEDSTATUSCODES 250-8BITMIME 250-DSN 250-BINARYMIME 250 CHUNKING quit 221 2.0.0 Bye Connection closed by foreign host. Here is a portion from the mail log when receiving a message from gmail: postfix/postscreen[93152]: CONNECT from [209.85.128.49]:48953 to [192.168.0.10]:25 postfix/postscreen[93152]: PASS NEW [209.85.128.49]:48953 postfix/smtpd[93160]: connect from mail-qe0-f49.google.com[209.85.128.49] postfix/smtpd[93160]: 7A8C31C1AA99: client=mail-qe0-f49.google.com[209.85.128.49] The log shows that a connection was made to the local IP on port 25 (I'm not doing any port mapping, so it is port 25 on the public IP too). Seeing this leads me to hypothesize that the ISP block on port 25 only occurs when a connection is made from an IP address that is not known to be a mail server. Any other theories?

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• Can someone explain RAID-0 in plain English?

  - by Edward Tanguay

  I've heard about and read about RAID throughout the years and understand it theoretically as a way to help e.g. server PCs reduce the chance of data loss, but now I am buying a new PC which I want to be as fast as possible and have learned that having two drives can considerably increase the perceived performance of your machine. In the question Recommendations for hard drive performance boost, the author says he is going to RAID-0 two 7200 RPM drives together. What does this mean in practical terms for me with Windows 7 installed, e.g. can I buy two drives, go into the device manager and "raid-0 them together"? I am not a network administrator or a hardware guy, I'm just a developer who is going to have a computer store build me a super fast machine next week. I can read the wikipedia page on RAID but it is just way too many trees and not enough forest to help me build a faster PC: RAID-0: "Striped set without parity" or "Striping". Provides improved performance and additional storage but no redundancy or fault tolerance. Because there is no redundancy, this level is not actually a Redundant Array of Inexpensive Disks, i.e. not true RAID. However, because of the similarities to RAID (especially the need for a controller to distribute data across multiple disks), simple strip sets are normally referred to as RAID 0. Any disk failure destroys the array, which has greater consequences with more disks in the array (at a minimum, catastrophic data loss is twice as severe compared to single drives without RAID). A single disk failure destroys the entire array because when data is written to a RAID 0 drive, the data is broken into fragments. The number of fragments is dictated by the number of disks in the array. The fragments are written to their respective disks simultaneously on the same sector. This allows smaller sections of the entire chunk of data to be read off the drive in parallel, increasing bandwidth. RAID 0 does not implement error checking so any error is unrecoverable. More disks in the array means higher bandwidth, but greater risk of data loss. So in plain English, how can "RAID-0" help me build a faster Windows-7 PC that I am going to order next week?

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• Sending large serialized objects over sockets is failing only when trying to grow the byte Array, bu

  - by FinancialRadDeveloper

  I have code where I am trying to grow the byte array while receiving the data over my socket. This is erroring out. public bool ReceiveObject2(ref Object objRec, ref string sErrMsg) { try { byte[] buffer = new byte[1024]; byte[] byArrAll = new byte[0]; bool bAllBytesRead = false; int iRecLoop = 0; // grow the byte array to match the size of the object, so we can put whatever we // like through the socket as long as the object serialises and is binary formatted while (!bAllBytesRead) { if (m_socClient.Receive(buffer) > 0) { byArrAll = Combine(byArrAll, buffer); iRecLoop++; } else { m_socClient.Close(); bAllBytesRead = true; } } MemoryStream ms = new MemoryStream(buffer); BinaryFormatter bf1 = new BinaryFormatter(); ms.Position = 0; Object obj = bf1.Deserialize(ms); objRec = obj; return true; } catch (System.Runtime.Serialization.SerializationException se) { objRec = null; sErrMsg += "SocketClient.ReceiveObject " + "Source " + se.Source + "Error : " + se.Message; return false; } catch (Exception e) { objRec = null; sErrMsg += "SocketClient.ReceiveObject " + "Source " + e.Source + "Error : " + e.Message; return false; } } private byte[] Combine(byte[] first, byte[] second) { byte[] ret = new byte[first.Length + second.Length]; Buffer.BlockCopy(first, 0, ret, 0, first.Length); Buffer.BlockCopy(second, 0, ret, first.Length, second.Length); return ret; } Error: mscorlibError : The input stream is not a valid binary format. The starting contents (in bytes) are: 68-61-73-43-68-61-6E-67-65-73-3D-22-69-6E-73-65-72 ... Yet when I just cheat and use a MASSIVE buffer size its fine. public bool ReceiveObject(ref Object objRec, ref string sErrMsg) { try { byte[] buffer = new byte[5000000]; m_socClient.Receive(buffer); MemoryStream ms = new MemoryStream(buffer); BinaryFormatter bf1 = new BinaryFormatter(); ms.Position = 0; Object obj = bf1.Deserialize(ms); objRec = obj; return true; } catch (Exception e) { objRec = null; sErrMsg += "SocketClient.ReceiveObject " + "Source " + e.Source + "Error : " + e.Message; return false; } } This is really killing me. I don't know why its not working. I have lifted the Combine from a suggestion on here too, so I am pretty sure this is not doing the wrong thing? I hope someone can point out where I am going wrong

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• Single console in eclipse for both Server and Client

  - by rits

  I am building a client server application using Java Sockets (in Windows XP). For that I need different consoles for both Client and Server(for Input and Output operations). But in eclipse both share a single console. Is there any plugin or some sort of cheat through which I can do this. After googling I got this, http://dev.eclipse.org/newslists/news.eclipse.newcomer/msg17138.html But, this seems to be only for write operations, not read operations. Also, I tried the following to launch application manually, but even this is not working........ package mypack; import java.io.BufferedOutputStream; import java.io.File; import java.io.FileOutputStream; import java.io.IOException; import java.io.OutputStream; import java.io.PrintStream; public class MySystem { public static void changeStream(String mainFile) throws IOException{ File temp = new File(".") ; String parentPath = temp.getCanonicalPath() ; System.out.println(parentPath); //creation of batch file starts here try{ File f = new File(parentPath + "\\a.bat") ; System.out.println("Created : " + f.createNewFile()); //f.deleteOnExit() ; FileOutputStream fos = new FileOutputStream(f) ; String str = "java " + mainFile ; String batchCommand="@echo off\n"+str+"\npause\nexit"; char arr[] = batchCommand.toCharArray() ; System.out.println(str) ; for(int i = 0 ; i < arr.length ; i++){ fos.write(arr[i]) ; } fos.close() ; } catch(Exception e){ } //creation of batch file ends here //execution of batch file starts here try{ Runtime r = Runtime.getRuntime() ; System.out.println(parentPath + "\\a.bat") ; Process p = r.exec(new String[]{"cmd","/k","start a.bat"},null,new File(parentPath)) ; OutputStream os = (OutputStream)p.getOutputStream() ; System.setOut( new PrintStream(os) ) ; System.out.println("Hello"); } catch(Exception e){ e.printStackTrace(); } //execution of batch file ends here } public static void main(String[] args) throws IOException { MySystem.changeStream("MySystem") ; } }

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• What is your most productive shortcut with Vim?

  - by Olivier Pons

  I've heard a lot about Vim, both pros and cons. It really seems you should be (as a developer) faster with Vim than with any other editor. I'm using Vim to do some basic stuff and I'm at best 10 times less productive with Vim. The only two things you should care about when you talk about speed (you may not care enough about them, but you should) are: Using alternatively left and right hands is the fastest way to use the keyboard. Never touching the mouse is the second way to be as fast as possible. It takes ages for you to move your hand, grab the mouse, move it, and bring it back to the keyboard (and you often have to look at the keyboard to be sure you returned your hand properly to the right place) Here are two examples demonstrating why I'm far less productive with Vim. Copy/Cut & paste. I do it all the time. With all the classical editors you press Shift with the left hand, and you move the cursor with your right hand to select text. Then Ctrl+C copies, you move the cursor and Ctrl+V pastes. With Vim it's horrible: yy to copy one line (you almost never want the whole line!) [number xx]yy to copy xx lines into the buffer. But you never know exactly if you've selected what you wanted. I often have to do [number xx]dd then u to undo! Another example? Search & replace. In PSPad: Ctrl+f then type what you want you search for, then press Enter. In Vim: /, then type what you want to search for, then if there are some special characters put \ before each special character, then press Enter. And everything with Vim is like that: it seems I don't know how to handle it the right way. NB : I've already read the Vim cheat sheet :) My question is: What is the way you use Vim that makes you more productive than with a classical editor?

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• Testing for existence using SELECT WHERE HAVING and NOT HAVING in a grouped subset

  - by IanC

  I have data on which I need to count +1 if a particular condition exists or another condition doesn't exist. I'm using SQL Server 2008. I shred the following simplified sample XML into a temp table and validate it: <product type="1"> <param type="1"> <item mode="0" weight="1" /> </param> <param type="2"> <item mode="1" weight="1" /> <item mode="0" weight="0.1" /> </param> <param type="3"> <item mode="1" weight="0.75" /> <item mode="1" weight="0.25" /> </param> </product> The validation in concern is the following rule: For each product type, for each param type, mode may be 0 & (1 || 2). In other words, there may be a 0(s), but then 1s or 2s are required, or there may be only 1(s) or 2(s). There cannot be only 0s, and there cannot be 1s and 2s. The only part I haven't figured out is how to detect if there are only 0s. This seems like a "not having" problem. The validation code (for this part): WITH t1 AS ( SELECT SUM(t.ParamWeight) AS S, COUNT(1) AS C, t.ProductTypeID, t.ParamTypeID, t.Mode FROM @t AS t GROUP BY t.ProductTypeID, t.ParamTypeID, t.Mode ), ... UNION ALL SELECT TOP (1) 1 -- only mode 0 & (1 || 2) is allowed FROM t1 WHERE t1.Mode IN (1, 2) GROUP BY t1.ProductTypeID, t1.ParamTypeID HAVING COUNT(1) > 1 UNION ALL ... ) SELECT @C = COUNT(1) FROM t2 This will show if any mode 1s & 2s are mixed, but not if the group contains only a 0. I'm sure there is a simple solution, but it's evading me right now. EDIT: I thought of a "cheat" that works perfectly. I added the following to the above: SELECT TOP (1) 1 -- only mode 0 & (null || 1 || 2) is allowed FROM t1 GROUP BY t1.ProductTypeID, t1.ParamTypeID HAVING SUM(t1.Mode) = 0 However, I'd still like to know how to do this without cheating.

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• Where can I find "canonical" sample programs that give quick refreshers for any given language? [on hold]

  - by acheong87

  Note to those close-voting this question: I understand this isn't a conventional programming question and I can agree with the reasoning that it's in the subjective domain (like best-of lists). In other ways though I think it's appropriate because, though it's not a "a specific programming problem," nor concerning "a software algorithm", nor (strictly) concerning "software tools commonly used by programmers", I think it is a "practical, answerable [problem that is] unique to the programming profession," and I think it is "based on an actual [problem I] face." I've been wanting this for some time now, because both approaches of (a) Googling for samples as I write every other line of code and (b) just winging it and seeing what errors crop up, distract me from coding efficiently. This note will be removed if the question gains popularity; this question will be deleted otherwise. I spend most of my time developing in C++, PHP, or Javascript, and every once in a while I have to do something in, say, VBA. In those times, it'd be convenient if I could just put up some sample code on a second monitor, something in between a cheat sheet (often too compact; and doesn't resemble anything that could actually compile/run), and a language reference (often too verbose, or segmented; requires extra steps to search or click through an index), so I can just glance at it and recall things, like how to loop through non-empty cells in a column. I think there's a hidden benefit to seeing formed code, that triggers the right spots in our brains to get back into a language we only need to brush up on. Similar in spirit is how http://ideone.com lets you click "Template" in any given language so you can get started without even doing a search. That template alone tells a lot, sometimes! Case-sensitivity, whitespace conventions, identifier conventions, the spelling of certain types, etc. I couldn't find a resource that pulled together such samples, so if there indeed doesn't exist such a repository, I was hoping this question would inspire professionals and experts to contribute links to the most useful sample code they've used for just this purpose: a keep-on-the-side, form-as-well-as-content, compilable/executable, reminder of a language's basic and oft-used features. Personally I am interested in seeing "samplers" for: VBA, Perl, Python, Java, C# (though for some of these autocompleters in Eclipse, Visual Studio, etc. help enough), awk, and sed. I'm tagging c++, php, and javascript because these are languages for which I'd best be able to evaluate whether proffered sample code matches what I had in mind.

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• Form, function and complexity in rule processing

  - by Charles Young

  Tim Bass posted on ‘Orwellian Event Processing’. I was involved in a heated exchange in the comments, and he has more recently published a post entitled ‘Disadvantages of Rule-Based Systems (Part 1)’. Whatever the rights and wrongs of our exchange, it clearly failed to generate any agreement or understanding of our different positions. I don't particularly want to promote further argument of that kind, but I do want to take the opportunity of offering a different perspective on rule-processing and an explanation of my comments. For me, the ‘red rag’ lay in Tim’s claim that “...rules alone are highly inefficient for most classes of (not simple) problems” and a later paragraph that appears to equate the simplicity of form (‘IF-THEN-ELSE’) with simplicity of function.   It is not the first time Tim has expressed these views and not the first time I have responded to his assertions.   Indeed, Tim has a long history of commenting on the subject of complex event processing (CEP) and, less often, rule processing in ‘robust’ terms, often asserting that very many other people’s opinions on this subject are mistaken.   In turn, I am of the opinion that, certainly in terms of rule processing, which is an area in which I have a specific interest and knowledge, he is often mistaken. There is no simple answer to the fundamental question ‘what is a rule?’ We use the word in a very fluid fashion in English. Likewise, the term ‘rule processing’, as used widely in IT, is equally difficult to define simplistically. The best way to envisage the term is as a ‘centre of gravity’ within a wider domain. That domain contains many other ‘centres of gravity’, including CEP, statistical analytics, neural networks, natural language processing and so much more. Whole communities tend to gravitate towards and build themselves around some of these centres. The term 'rule processing' is associated with many different technology types, various software products, different architectural patterns, the functional capability of many applications and services, etc. There is considerable variation amongst these different technologies, techniques and products. Very broadly, a common theme is their ability to manage certain types of processing and problem solving through declarative, or semi-declarative, statements of propositional logic bound to action-based consequences. It is generally important to be able to decouple these statements from other parts of an overall system or architecture so that they can be managed and deployed independently.  As a centre of gravity, ‘rule processing’ is no island. It exists in the context of a domain of discourse that is, itself, highly interconnected and continuous.   Rule processing does not, for example, exist in splendid isolation to natural language processing.   On the contrary, an on-going theme of rule processing is to find better ways to express rules in natural language and map these to executable forms.   Rule processing does not exist in splendid isolation to CEP.   On the contrary, an event processing agent can reasonably be considered as a rule engine (a theme in ‘Power of Events’ by David Luckham).   Rule processing does not live in splendid isolation to statistical approaches such as Bayesian analytics. On the contrary, rule processing and statistical analytics are highly synergistic.   Rule processing does not even live in splendid isolation to neural networks. For example, significant research has centred on finding ways to translate trained nets into explicit rule sets in order to support forms of validation and facilitate insight into the knowledge stored in those nets. What about simplicity of form?   Many rule processing technologies do indeed use a very simple form (‘If...Then’, ‘When...Do’, etc.)   However, it is a fundamental mistake to equate simplicity of form with simplicity of function.   It is absolutely mistaken to suggest that simplicity of form is a barrier to the efficient handling of complexity.   There are countless real-world examples which serve to disprove that notion.   Indeed, simplicity of form is often the key to handling complexity. Does rule processing offer a ‘one size fits all’. No, of course not.   No serious commentator suggests it does.   Does the design and management of large knowledge bases, expressed as rules, become difficult?   Yes, it can do, but that is true of any large knowledge base, regardless of the form in which knowledge is expressed.   The measure of complexity is not a function of rule set size or rule form.  It tends to be correlated more strongly with the size of the ‘problem space’ (‘search space’) which is something quite different.   Analysis of the problem space and the algorithms we use to search through that space are, of course, the very things we use to derive objective measures of the complexity of a given problem. This is basic computer science and common practice. Sailing a Dreadnaught through the sea of information technology and lobbing shells at some of the islands we encounter along the way does no one any good.   Building bridges and causeways between islands so that the inhabitants can collaborate in open discourse offers hope of real progress.

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• How to Troubleshoot TFS Build Server Failure?

  - by Tarun Arora

  Ever found your self in this helpless situation where you think you have tried every possible suggestion on the internet to bring the build server back but it just won’t work. Well some times before hunting around for a solution it is important to understand what the problem is, if the error messages in the build logs don’t seem to help you can always enable tracing on the build server to get more information on what could possibly be the root cause of failure. In this blog post today I’ll be showing you how to enable tracing on, - TFS 2010/11 Server - Build Server - Client Enable Tracing on Team Foundation Server 2010/2011 On the Team Foundation Server navigate to C:\Program Files\Microsoft Team Foundation Server 2010\Application Tier\Web Services, right click web.config and from the context menu select edit.          Search for the <appSettings> node in the config file and set the value of the key ‘traceWriter’ to true.          In the <System.diagnostics> tag set the value of switches from 0 to 4 to set the trace level to maximum to write diagnostics level trace information.          Restart the TFS Application pool to force this change to take effect. The application pool restart will impact any one using the TFS server at present. Note - It is recommended that you do not make any changes to the TFS production application server, this can have serious consequences and can even jeopardize the installation of your server.          Download the Debug view tool from http://technet.microsoft.com/en-us/sysinternals/bb896647.aspx and set it to capture “Global Events”. Perform any actions in the Team Explorer on the client machine, you should be able to see a series of trace data in the debug view tool now.         Enable Tracing on Build Controller/Agents Log on to the Build Controller/Agent and Navigate to the directory C:\Program Files\Microsoft Team Foundation Server 2010\Tools         Look for the configuration file ‘TFSBuildServiceHost.exe.config’ if it is not already there create a new text file and rename it to ‘TFSBuildServiceHost.exe.config’         To Enable tracing uncomment the <system.diagnostics> and paste the snippet below if it is not already there. <configuration> <system.diagnostics> <switches> <add name="BuildServiceTraceLevel" value="4"/> </switches> <trace autoflush="true" indentsize="4"> <listeners> <add name="myListener" type="Microsoft.TeamFoundation.TeamFoundationTextWriterTraceListener, Microsoft.TeamFoundation.Common, Version=10.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" initializeData="c:\logs\TFSBuildServiceHost.exe.log" /> <remove name="Default" /> </listeners> </trace> </system.diagnostics> </configuration> The highlighted path above is where the Log file will be created. If the folder is not already there then create the folder, also, make sure that the account running the build service has access to write to this folder.         Restart the build Controller/Agent service from the administration console (or net stop tfsbuildservicehost & net start tfsbuildservicehost) in order for the new setting to be picked up.         Enable TFS Tracing on the Client Machine On the client machine, shut down Visual Studio, navigate to C:\Program Files\Microsoft Visual Studio 10.0\Common 7\IDE          Search for devenv.exe.config, make a backup copy of the config file and right click the file and from the context menu select edit. If its not already there create this file.          Edit devenv.exe.config by adding the below code snippet before the last </configuration> tag <system.diagnostics> <switches> <add name="TeamFoundationSoapProxy" value="4" /> <add name="VersionControl" value="4" /> </switches> <trace autoflush="true" indentsize="3"> <listeners> <add name="myListener" type="Microsoft.TeamFoundation.TeamFoundationTextWriterTraceListener,Microsoft.TeamFoundation.Common, Version=10.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" initializeData="c:\tf.log" /> <add name="perfListener" type="Microsoft.TeamFoundation.Client.PerfTraceListener, Microsoft.TeamFoundation.Client, Version=10.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a"/> </listeners> </trace> </system.diagnostics> The highlighted path above is where the Log file will be created. If the folder is not already there then create the folder. Start Visual Studio and after a bit of activity you should be able to see the new log file being created on the folder specified in the config file. Other Resources Below are some Key resource you might like to review. I would highly recommend the documentation, walkthroughs and videos available on MSDN.   Thank you for taking the time out and reading this blog post. If you enjoyed the post, remember to subscribe to http://feeds.feedburner.com/TarunArora. Have you come across an interesting one to one with the build server, please share your experience here. Questions/Feedback/Suggestions, etc please leave a comment. Thank You! Share this post : CodeProject

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• A Quick Primer on SharePoint Customization

  - by PeterBrunone

  Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman","serif";} This one goes out to all the people who have been asked to change the way a SharePoint site looks.  Management wants to know how long it will take, and you can whip that out by tomorrow, right?  If you don't have time to prepare a treatise on what's involved, or if you just want to lend some extra weight to your case by quoting a blogger who was an MVP for seven years, then dive right in; this post is for you. There are three main components of SharePoint visual customization:   1)       Theme – A theme encompasses all the standardized text formatting and coloring (borders, fonts, etc), including the background images of various sections. All told, there could be around 50 images involved, and a few hundred CSS (style) classes.  Installing a theme once it’s been created is no great feat.  Given the number of pieces, of course, creating a new theme could take anywhere from a day to a week… once decisions have been made about the desired appearance. 2)      Master Page – A master page provides the framework for page layout.  This includes all the top and side menus, where content shows up, et cetera.  Master pages have been around for a long time in ASP.NET (Microsoft’s web development platform), and they do require some .NET programming knowledge.  Beyond that, in SharePoint, there are a few dozen controls which the system expects find on a given page.  They’re not all used at once, but if they’re not there when they’re needed, chaos ensues.  Estimating a custom master page is difficult, as it depends on the level of customization.  I’ve been on projects where I was brought in simply to fix some problems and add a few finishing touches, and it took 2-3 weeks.  Master page customization requires a large amount of testing time to make sure that the HTML, JavaScript, CSS, and control placement all work well together. 3)      Individual page layout – Each page (ideally) uses a master page for its template, but within the content areas defined by the master page, web parts can be added, removed, and configured from within the browser.  The wireframe that Brent provided could most likely be completed simply by manipulating the content on the home page in this fashion, and we had allowed about a day of effort for the task.  If needed, further functionality can be provided by an experienced ASP.NET developer; custom forms are a common example.  This of course is a bit more in-depth than simple content manipulation and could take several days per page (or more; there’s really no way to quantify this without a set of requirements).   That’s basically it.  To recap:  Fonts and coloring are done with themes, and can take anywhere from a day to a week to create (not counting creative time); required technical skills include HTML, CSS, and image manipulation.  Templated layout is done with master pages, and generally requires a developer familiar with both ASP.NET and SharePoint in particular; it can have far-reaching consequences depending on the complexity of the changes, and could add weeks or months to a project.  Page layout can be as simple as content manipulation in the web browser, taking a few hours per page, or it can involve more detail, like custom forms, and can require programming expertise and significantly more development time.

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• Red Gate does Byte Night 2012

  - by red(at)work

  On the 5th of October 2012, a team of nine plucky Red Gaters braved the howling wind and the driving rain to sleep outside. No tents or mattresses were allowed – all we took for protection were sleeping bags, groundsheets, plastic sacks and Colin’s enormous fishing umbrella (a godsend in umbrella-y disguise). Why would we do such a thing? For Byte Night, an annual tech sector sleepout in support of Action for Children, who tackle the causes as well as the consequences of youth homelessness. Byte Night encourages technology professionals to do for one night a year what thousands of young people have to do every night – sleep rough.  We signed up for Byte Night in the warm, heady midst of the British summer, thinking it couldn’t possibly be all that bad. Even on the night itself – before the rain began to fall, sat in the comfort and warmth of a company canteen, drinking wine and eating chill and preparing to win the pub quiz – we were excited and optimistic about the night that lay ahead of us. All of that changed as soon as we stepped out into one of the worst rainstorms of the year. Brian, the team’s birthday boy, describes it best: Picture the scene: it’s 3 am on a Friday. I’m lying outside, fully clothed in a sleeping bag, wearing a raincoat, trussed up inside a large plastic pocket, on a ground sheet beneath a giant umbrella, wedged so tightly between two of my colleagues that I can’t move my arms. I’m wide awake, staring up at the grey sky beyond the edge of the umbrella; a limp, flickering white glow hints at a moon somewhere behind the drifting clouds. I haven’t slept since we first moved outside at 11 pm. Outside. Did I mention we were outside? I’m hung over. I need the loo. But there is no way on earth that I’m getting out of this sleeping bag. It’s cold. It’s raining. Not just raining, but chucking it down. It’s been doing this non-stop since 10pm. The rain sounds like a hyperactive drummer on the fishing umbrella, and the noise is loud and relentless. Puddles of water are forming all over the groundsheet, and, despite being ensconced inside the plastic pouch, I am wet. The fishing umbrella is protecting me from the worst of the driving rain, but not all of me is under it, and five hours of rain is no match for it. Everything is wet. My left side has become horribly damp. My trainers, which I placed next to my sleeping bag, are now completely soaked through. Mmm. That’ll be fun in the morning. My head is next to Colin’s head on one side, and a multi-pack of McCoy’s cheddar and onion crisps on the other. Don’t ask about the tub of hummus. That’s somewhere down by my ankles, abandoned to the night. Jess, who is lying next to me, rolls over onto her side. A mini waterfall cascades from her rain-pouch onto my face. Bah. I continue to stare into the heavens, willing the dawn to hurry up. Something lands on my face. It’s a mosquito. Great. Midnight, when this still seemed like fun – when we opened some champagne and my colleagues presented me with a caterpillar birthday cake, when everyone was drunk and jolly and full of stoic resolve – feels like a long time ago. Did I mention that today is my birthday? The remains of the caterpillar cake endure the same fate as the hummus, left out in the rain like a metaphor for sadness. It’s getting colder. I can see my breath. Silence has descended on the group, apart from the rustle of plastic. And the rain, obviously. Someone snores, and I envy whoever it is the sweet escape of sleep. I try to wriggle a bit further down inside my sleeping bag, but it doesn’t want to be wriggled into. Only 3 hours till dawn. 180 minutes. I begin to count them off, one at a time.  All nine of us got to go home in the morning, but thousands of children across the UK don’t have that luxury. If you’d like to sponsor the Red Gate Byte Night team, our JustGiving page can be found here.   Chris, before the outside bit actually happened. More photos from Byte Night Cambridge 2012 can be found here.

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• How does one find out which application is associated with an indicator icon?

  - by Amos Annoy

  It is trivial to do this in Ubuntu 10.04. The question is specific to Ubuntu 12.04. some pertinent references (src: answer to What is the difference between indicators and a system tray?: Here is the documentation for indicators: Application indicators | Ubuntu App Developer libindicate Reference Manual libappindicator Reference Manual also DesktopExperienceTeam/ApplicationIndicators - Ubuntu Wiki ref: How can the application that makes an indicator icon be identified? bookmark: How does one find out which application is associated with an indicator icon in Ubuntu 12.04? is a serious question for reasons & problems outlined below and for which a significant investment has been made and is necessary for remedial purposes. reviewing refs. to find an orchestrated resolution ... (an indicator ap. indicator maybe needed) This has nothing to do (does it?) with right click. How can an indicator's icon in Ubuntu 12.04 be matched with the program responsible for it's manifestation on the top panel? A list of running applications can include all processes using System Monitor. How is the correct matching process found for an indicator? How are the sub-indicator applications identified? These are the aps associated with the components of an indicators drop-down menu. (This was to be a separate question and quite naturally follows up the progression. It is included here as it is obvious there is no provisioning to track down offending either sub or indicator aps. easily.) (The examination of SM points out a rather poignant factor in the faster battery depletion and shortened run time - the ambient quiescent CPU rate in 12.04 is now well over 20% when previously, in 10.04, it was well under 10%, between 5% and 7%! - the huge inordinate cpu overhead originates from Xorg and compiz - after booting the system, only SM is run and All Processes are selected, sorting on %CPU - switching between Resources and Processes profiles the execution overhead problem - running another ap like gedit "Text Editor" briefly gives it CPU priority - going back to S&M several aps. are at the top of the list in order: gnome-system-monitor as expected, then: Xorg, compiz, unity-panel-service, hud-service, with dbus-daemon and kworker/x:y's mixed in with some expected daemons and background tasks like nm-applet - not only do Xorg and compiz require excessive CPU time but their entourage has to come along too! further exacerbating the problem - our compute bound tasks no longer work effectively in the field - reduced battery life, reduced CPU time for custom ap.s etc. - and all this precipitated from an examination of what is going on with the battery ap. indicator - this was and is not a flippant, rhetorical or idle musing but has consequences for the credible deployment of 12.04 to reduce the negative impact of its overhead in a production environment) (I have a problem with the battery indicator - it sometimes has % and other times hh:mm - it is necessary to know the ap. & v. to get more info on controlling same. ditto: There are issues with other indicator aps.: NM vs. iwlist/iwconfig conflict, BT ap. vs RF switch, Battery ap. w/ no suspend/sleep for poor battery runtime, ... the list goes on) Details from: How can I find Application Indicator ID's? suggests looking at: file:///usr/share/indicator-application/ordering-override.keyfile [Ordering Index Overrides] nm-applet=1 gnome-power-manager=2 ibus=3 gst-keyboard-xkb=4 gsd-keyboard-xkb=5 which solves the battery ap. identification, and presumably nm is NetworkManager for the rf icon, but the envelope, blue tooth and speaker indicator aps. are still a mystery. (Also, the ordering is not correlated.) Mind you, it was simple in the past to simply right click to get the About option to find the ap. & v. info. browsing around and about: file:///usr/share/indicator-application/ordering-override.keyfile examined: file:///usr/share/indicators file:///usr/share/indicators/messages/applications/ ... perhaps?/presumably? the information sought may be buried in file:///usr/share/indicators A reference in the comments was given to: What is the difference between indicators and a system tray? quoting from that source ... Unfortunately desktop indicators are not well documented yet: I couldn't find any specification doc ... Well ... the actual document https://wiki.ubuntu.com/DesktopExperienceTeam/ApplicationIndicators#Summary does not help much but it's existential information provides considerable insight ...

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• What should you bring to the table as a Software Architect?

  - by Ahmad Mageed

  There have been many questions with good answers about the role of a Software Architect (SA) on StackOverflow and Programmers SE. I am trying to ask a slightly more focused question than those. The very definition of a SA is broad so for the sake of this question let's define a SA as follows: A Software Architect guides the overall design of a project, gets involved with coding efforts, conducts code reviews, and selects the technologies to be used. In other words, I am not talking about managerial rest and vest at the crest (further rhyming words elided) types of SAs. If I were to pursue any type of SA position I don't want to be away from coding. I might sacrifice some time to interface with clients and Business Analysts etc., but I am still technically involved and I'm not just aware of what's going on through meetings. With these points in mind, what should a SA bring to the table? Should they come in with a mentality of "laying down the law" (so to speak) and enforcing the usage of certain tools to fit "their way," i.e., coding guidelines, source control, patterns, UML documentation, etc.? Or should they specify initial direction and strategy then be laid back and jump in as needed to correct the ship's direction? Depending on the organization this might not work. An SA who relies on TFS to enforce everything may struggle to implement their plan at an employer that only uses StarTeam. Similarly, an SA needs to be flexible depending on the stage of the project. If it's a fresh project they have more choices, whereas they might have less for existing projects. Here are some SA stories I have experienced as a way of sharing some background in hopes that answers to my questions might also shed some light on these issues: I've worked with an SA who code reviewed literally every single line of code of the team. The SA would do this for not just our project but other projects in the organization (imagine the time spent on this). At first it was useful to enforce certain standards, but later it became crippling. FxCop was how the SA would find issues. Don't get me wrong, it was a good way to teach junior developers and force them to think of the consequences of their chosen approach, but for senior developers it was seen as somewhat draconian. One particular SA was against the use of a certain library, claiming it was slow. This forced us to write tons of code to achieve things differently while the other library would've saved us a lot of time. Fast forward to the last month of the project and the clients were complaining about performance. The only solution was to change certain functionality to use the originally ignored approach despite early warnings from the devs. By that point a lot of code was thrown out and not reusable, leading to overtime and stress. Sadly the estimates used for the project were based on the old approach which my project was forbidden from using so it wasn't an appropriate indicator for estimation. I would hear the PM say "we've done this before," when in reality they had not since we were using a new library and the devs working on it were not the same devs used on the old project. The SA who would enforce the usage of DTOs, DOs, BOs, Service layers and so on for all projects. New devs had to learn this architecture and the SA adamantly enforced usage guidelines. Exceptions to usage guidelines were made when it was absolutely difficult to follow the guidelines. The SA was grounded in their approach. Classes for DTOs and all CRUD operations were generated via CodeSmith and database schemas were another similar ball of wax. However, having used this setup everywhere, the SA was not open to new technologies such as LINQ to SQL or Entity Framework. I am not using this post as a platform for venting. There were positive and negative aspects to my experiences with the SA stories mentioned above. My questions boil down to: What should an SA bring to the table? How can they strike a balance in their decision making? Should one approach an SA job (as defined earlier) with the mentality that they must enforce certain ground rules? Anything else to consider? Thanks! I'm sure these job tasks are easily extended to people who are senior devs or technical leads, so feel free to answer at that capacity as well.

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• MDM for Tax Authorities

  - by david.butler(at)oracle.com

  In last week’s MDM blog, we discussed MDM in the Public Sector. I want to continue that thread. After all, no industry faces tougher data quality problems than governmental organizations, and few industries suffer more significant down side consequences to poor operations than local, state and federal governments. One key challenge area is taxation. Tax Authorities face a multitude of IT challenges. Firstly, the data used in tax calculations is increasing in volume and complexity. They must improve service by introducing multi-channel contact centers and self-service capabilities. Security concerns necessitate increasingly sophisticated data protection procedures. And cost constraints are driving Tax Authorities to rely on off-the-shelf software for many of their functional areas. Compounding these issues is the fact that the IT architectures in operation at most revenue and collections agencies are very complex. They typically include multiple, disparate operational and analytical systems across which the sum total of data about individual constituents is fragmented. To make matters more complicated, taxation is not carried out by a single jurisdiction, and often sources of income including employers, investments and other sources of taxable income and deductions must also be tracked and shared among tax authorities. Collectively, these systems are involved in tax assessment and collections, risk analysis, scoring, tracking, auditing and investigation case management. The Problem of Constituent Data Management The infrastructure described above makes it very difficult to create a consolidated representation of a given party. Differing formats and data models mean that a constituent may be represented in one way in one system and in a different way in another. Individual records are frequently inaccurate, incomplete, out of date and/or inconsistent with other records relating to the same constituent. When constituent data must be aggregated and scored, information within each system must be rationalized and normalized so the agency can produce a constituent information file (CIF) that provides a single source of truth about that party. If information about that constituent changes, each system in turn must be updated. There have been many attempts to solve this problem with technology: from consolidating transactional systems to conducting manual systems integration projects and superimposing layers of business intelligence and analytics. All these approaches can be successful in solving a portion of the problem at a specific point in time, but without an enterprise perspective, anything gained is quickly lost again. Oracle Constituent Data Mastering for Tax Authorities: A Single View of the Constituent Oracle has a flexible and long-term solution to the problem of securely integrating and managing constituent data. The Oracle Solution for mastering Constituent Data for Tax Authorities is based on two core product offerings: Oracle Customer Hub and – optionally – Oracle Application Integration Architecture (AIA). Customer Hub is a master data management (MDM) product that centralizes, de-duplicates, and enriches constituent data. It unifies fragmented information without disrupting existing business processes or IT investments. Role based data access and privacy rules guarantee maximum security and privacy. Data is continuously and automatically synchronized with all source systems. With the Oracle Customer Hub managing the master constituent identity, every department can capture transaction activity against the same record, improving reporting accuracy, employee productivity, reliability of constituent analytics, and day-to-day constituent relationships. Oracle Application Integration Architecture provides a collection of core pre-built processes to support out of the box Master Data Governance across Oracle Customer Hub, Siebel CRM, and Oracle E-Business Suite. It also provides a framework to enable MDM integrations with other Oracle and non-Oracle applications. Oracle AIA removes some of the key inhibitors to implementing a service-oriented architecture (SOA) by providing a pre-built SOA-based middleware foundation as well as industry-optimized service oriented applications, all built around a SOA governance model that encourages effective design and reuse. I encourage you to read Oracle Solution for Mastering Constituents Data for Public Sector – Tax Authorities by Roberto Negro. It is an outstanding whitepaper that describes how the Oracle MDM solution allows you to create a unified, reconciled source of high-quality constituent data and gain an accurate single view of each constituent. This foundation enables you to lower the costs associated with data quality and integration and create a tax organization that is efficient, secure and constituent-centric. Also, don’t forget the upcoming webcast on Thursday, February 10th: Deliver Improved Services to Citizens at Lower Cost to your Organization Our Guest Speaker is Ruben Spekle, from Capgemini. He will also provide insight into Public Sector Master Data Management and Case Management implementations including one that was executed for a Dutch Government Agency. If you are interested in how governmental organizations from around the world are using MDM to advance their cause, click here to register for the webcast.

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• BPM 11g - Dynamic Task Assignment with Multi-level Organization Units

  - by Mark Foster

  I've seen several requirements to have a more granular level of task assignment in BPM 11g based on some value in the data passed to the process. Parametric Roles is normally the first port of call to try to satisfy this requirement, but in this blog we will show how a lot of use-cases can be satisfied by the easier to implement and flexible Organization Unit. The Use-Case Task assignment is to an approval group containing several users. At runtime, a location value in the input data determines which of the particular users the task is ultimately assigned to. In this case we use the Demo Community referenced in the SOA Admin Guide, and specifically the "LoanAnalyticGroup" which contains three users; "szweig", "mmitch" & "fkafka". In our scenario we would like to assign a task to "szweig" if the input data specifies that the location is "JapanCentral", to "fkafka" if the location is "JapanNorth" and to "mmitch" if "JapanSouth", and to all of them if the location is "Japan" i.e....   The Process Simple one human task process.... In the output data association of the "Start" activity we need to set the value of the "Organization Unit" predefined variable based on the input data (note that the  predefined variables can only be set on output data associations)....  ...and in the output data association of the human activity we will reset the "Organization Unit" to empty, always good practice to ensure that the Organization Unit will not be used for any subsequent human activities for which we do not require it.... Set Up the Organization Unit  Log in to the BPM Workspace with an administrator user (weblogic/welcome1 in our case) and choose the "Administration" option. Within "Roles" assign the "ProcessOwner" swim-lane for our process to "LoanAnalyticGroup".... Within "Organization Units" we can model our organization.... "Root Organization Unit" as "Japan" and "Child Organization Unit" as "Central", "South" & "North" as shown. As described previously, add user "szweig" to "Central", "mmitch" to "South" and "fkafka" to "North"....   Test the Process Invalid Data  First let us test with invalid data in the input to see what the consequences are, here we use "X" as input.... ...and looking at the instance we can see it has errored.... Organization Unit Root Level Assignment  Now let us see what happens if we have "Japan" in the input data.... ...looking in the "flow trace" we can see that the task has been assigned....  ... but who has the task been assigned to ? Let us look in the BPM Workspace for user "szweig"....  ...and for "mmitch"....  ... and for "fkafka"....  ...so we can see that with an Organization Unit at "Root" level we have successfully assigned the task to all users. Organization Unit Child Level Assignment  Now let us test with "Japan/North" in the input data.... ...and looking in "fkafka" workspace we see the task has been assigned, remember, he was associated with "JapanNorth"....   ... but what about the workspace of "szweig"....  ...no tasks assigned, neither has "mmitch", just as we expected. Summary  We have seen in this blog how to easily implement multi-level dynamic task routing using Organization Units, a common use-case and a simpler solution than Parametric Roles. 

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• A Knights Tale

  - by Phil Factor

  There are so many lessons to be learned from the story of Knight Capital losing nearly half a billion dollars as a result of a deployment gone wrong. The Knight Capital Group (KCG N) was an American global financial services firm engaging in market making, electronic execution, and institutional sales and trading. According to the recent order (File No.3.15570) against Knight Capital by U.S. Securities and Exchange Commission?, Knight had, for many years used some software which broke up incoming “parent” orders into smaller “child” orders that were then transmitted to various exchanges or trading venues for execution. A tracking ‘cumulative quantity’ function counted the number of ‘child’ orders and stopped the process once the total of child orders matched the ‘parent’ and so the parent order had been completed. Back in the mists of time, some code had been added to it  which was excuted if a particular flag was set. It was called ‘power peg’ and seems to have had a similar design and purpose, but, one guesses, would have shared the same tracking function. This code had been abandoned in 2003, but never deleted. In 2005, The tracking function was moved to an earlier point in the main process. It would seem from the account that, from that point, had that flag ever been set, the old ‘Power Peg’ would have been executed like Godzilla bursting from the ice, making child orders without limit without any tracking function. It wasn’t, presumably because the software that set the flag was removed. In 2012, nearly a decade after ‘Power Peg’ was abandoned, Knight prepared a new module to their software to cope with the imminent Retail Liquidity Program (RLP) for the New York Stock Exchange. By this time, the flag had remained unused and someone made the fateful decision to reuse it, and replace the old ‘power peg’ code with this new RLP code. Had the two actions been done together in a single automated deployment, and the new deployment tested, all would have been well. It wasn’t. To quote… “Beginning on July 27, 2012, Knight deployed the new RLP code in SMARS in stages by placing it on a limited number of servers in SMARS on successive days. During the deployment of the new code, however, one of Knight’s technicians did not copy the new code to one of the eight SMARS computer servers. Knight did not have a second technician review this deployment and no one at Knight realized that the Power Peg code had not been removed from the eighth server, nor the new RLP code added. Knight had no written procedures that required such a review.” (para 15) “On August 1, Knight received orders from broker-dealers whose customers were eligible to participate in the RLP. The seven servers that received the new code processed these orders correctly. However, orders sent with the repurposed flag to the eighth server triggered the defective Power Peg code still present on that server. As a result, this server began sending child orders to certain trading centers for execution. Because the cumulative quantity function had been moved, this server continuously sent child orders, in rapid sequence, for each incoming parent order without regard to the number of share executions Knight had already received from trading centers. Although one part of Knight’s order handling system recognized that the parent orders had been filled, this information was not communicated to SMARS.” (para 16) SMARS routed millions of orders into the market over a 45-minute period, and obtained over 4 million executions in 154 stocks for more than 397 million shares. By the time that Knight stopped sending the orders, Knight had assumed a net long position in 80 stocks of approximately $3.5 billion and a net short position in 74 stocks of approximately $3.15 billion. Knight’s shares dropped more than 20% after traders saw extreme volume spikes in a number of stocks, including preferred shares of Wells Fargo (JWF) and semiconductor company Spansion (CODE). Both stocks, which see roughly 100,000 trade per day, had changed hands more than 4 million times by late morning. Ultimately, Knight lost over $460 million from this wild 45 minutes of trading. Obviously, I’m interested in all this because, at one time, I used to write trading systems for the City of London. Obviously, the US SEC is in a far better position than any of us to work out the failings of Knight’s IT department, and the report makes for painful reading. I can’t help observing, though, that even with the breathtaking mistakes all along the way, that a robust automated deployment process that was ‘all-or-nothing’, and tested from soup to nuts would have prevented the disaster. The report reads like a Greek Tragedy. All the way along one wants to shout ‘No! not that way!’ and ‘Aargh! Don’t do it!’. As the tragedy unfolds, the audience weeps for the players, trapped by a cruel fate. All application development and deployment requires defense in depth. All IT goes wrong occasionally, but if there is a culture of defensive programming throughout, the consequences are usually containable. For financial systems, these defenses are required by statute, and ignored only by the foolish. Knight’s mistakes weren’t made by just one hapless sysadmin, but were progressive errors by an  IT culture spanning at least ten years.  One can spell these out, but I think they’re obvious. One can only hope that the industry studies what happened in detail, learns from the mistakes, and draws the right conclusions.

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• Context is Everything

  - by Angus Graham

  Normal 0 false false false EN-CA X-NONE X-NONE MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin-top:0cm; mso-para-margin-right:0cm; mso-para-margin-bottom:10.0pt; mso-para-margin-left:0cm; line-height:115%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin;} Context is Everything How many times have you have you asked a question only to hear an answer like “Well, it depends. What exactly are you trying to do?”.  There are times that raw information can’t tell us what we need to know without putting it in a larger context. Let's take a real world example.  If I'm a maintenance planner trying to figure out which assets should be replaced during my next maintenance window, I'm going to go to my Asset Management System.  I can get it to spit out a list of assets that have failed several times over the last year.  But what are these assets connected to?  Is there any safety consequences to shutting off this pipeline to do the work?  Is some other work that's planned going to conflict with replacing this asset?  Several of these questions can't be answered by simply spitting out a list of asset IDs.  The maintenance planner will have to reference a diagram of the plant to answer several of these questions. This is precisely the idea behind Augmented Business Visualization. An Augmented Business Visualization (ABV) solution is one where your structured data (enterprise application data) and your unstructured data (documents, contracts, floor plans, designs, etc.) come together to allow you to make better decisions.  Essentially we're showing your business data into its context. AutoVue allows you to create ABV solutions by integrating your enterprise application with AutoVue’s hotspot framework. Hotspots can be defined for your document. Users can click these hotspots to trigger actions in your enterprise app. Similarly, the enterprise app can highlight the hotspots in your document based on its business data, creating a visual dashboard of your business data in the context of your document. ABV is not new. We introduced the hotspot framework in AutoVue 20.1 with text hotspots. Any text in a PDF or 2D CAD drawing could be turned into a hotspot. In 20.2 we have enhanced this to include 2 new types of hotspots: 3D and regional hotspots. 3D hotspots allow you to turn 3D parts into hotspots. Hotspots can be defined based on the attributes of the part, so you can create hotspots based on part numbers, material, date of delivery, etc.  Regional hotspots allow an administrator to define rectangular regions on any PDF, image, or 2D CAD drawing. This is perfect for cases where the document you’re using either doesn’t have text in it (a JPG or TIFF for example) or if you want to define hotspots that don’t correspond to the text in the document. There are lots of possible uses for AutoVue hotspots.  A great demonstration of how our hotspot capabilities can help add context to enterprise data in the Energy sector can be found in the following AutoVue movies: Maintenance Planning in the Energy Sector - Watch it Now Capital Construction Project Management in the Energy Sector  -  Watch it Now Commissioning and Handover Process for the Energy Sector  -  Watch it Now

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• How does the Cloud compare to Colocation? And development too

  - by David

  Currently I/we run a SaaS web application where each subscriber has their own physical instance of the application in addition to their own database. The setup has each web application instance deployed on two different IIS boxes both for load-balancing and redundancy (the machines have their Windows Update install times 12 hours apart, for example). Databases are mirrored on two different SQL Server 2012 machines with AlwaysOn for uptime. I don't make use of SQL Server clustering (as it doesn't provide storage-level failover: we don't have a shared storage box). Because it's a Windows setup it means there are two Domain Controllers (we cheat: they're both Mac Minis, 17W each, which keeps our colo power costs low). Finally there's also an Exchange server (Mailbox, Hub Transport and Client Access). One of the SQL Servers also doubles-up as an Exchange Hub Transport. Running costs are about $700 a month for our quarter-rack colocation (which includes power and peering/transfer), then there's about $150 a month for SPLA licensing, so $850 a month in total. Then there's the hard-to-quantify cost of administration, but I reckon I spend a couple of hours a week checking-in on the servers: reviewing event logs, etc. I keep getting bombarded by ads and manufactured news stories about how great "the cloud" is. Back in 2008 when the cloud was taking off I was reading up about the proper "cloud" services like Google AppEngine, where you write in Python against Google's API and that's how they scale your application across servers and also use their database provider for scaling storage. Simple enough to understand. Then came along Amazon, and I understand how Amazon Storage works, but I'm not sure how Amazon Compute works: web application pages don't take much CPU time to compute, how do you even quantify usage anyway? Finally, RackSpace gets in the act and now I'm really confused. RackSpace advertise "Cloud" SQL Server 2012 available for about "$0.70 per hour", going by how they advertise it I thought the "hour" meant the sum of CPU time, IO blocking time, maybe time spent transferring data, so for a low-intensity application that works out pretty cheap then? Nope. I went on to a Sales Chat window and spoke to one of their advisors. They told me the $0.70/hour was actually for every hour the SQL Server is running... but who wants a SQL Server for only a few hours? You're going to need it available 24 hours a day for months on end. $0.70 * 24 * 31 works out at $520 a month, which is rediculously expensive for SQL Server. An SPLA license for SQL Server is only $50 a month or so. That $520 a month does not include "fanatical support", and you also need to stack on top the costs of the host Windows server instance too. From what I can tell, Rackspace's "Cloud" products seem like like an cynical rebranding of an overpriced VPS service, but priced by the hour. I have the same confusion about Windows Azure which uses similar terms to describe the products available, but I think that's because Azure offers both traditional shared webhosting in addition to their own APIs you can target for scalable applications.

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• SQL SERVER – Interview Questions and Answers – Frequently Asked Questions – Introduction – Day 1 of 31

  - by pinaldave

  List of all the Interview Questions and Answers Series blogs Posts covering interview questions and answers always make for interesting reading.  Some people like the subject for their helpful hints and thought provoking subject, and others dislike these posts because they feel it is nothing more than cheating.  I’d like to discuss the pros and cons of a Question and Answer format here. Interview Questions and Answers are Helpful Just like blog posts, books, and articles, interview Question and Answer discussions are learning material.  The popular Dummy’s books or Idiots Guides are not only for “dummies,” but can help everyone relearn the fundamentals.  Question and Answer discussions can serve the same purpose.  You could call this SQL Server Fundamentals or SQL Server 101. I have administrated hundreds of interviews during my career and I have noticed that sometimes an interviewee with several years of experience lacks an understanding of the fundamentals.  These individuals have been in the industry for so long, usually working on a very specific project, that the ABCs of the business have slipped their mind. Or, when a college graduate is looking to get into the industry, he is not expected to have experience since he is just graduated. However, the new grad is expected to have an understanding of fundamentals and theory.  Sometimes after the stress of final exams and graduation, it can be difficult to remember the correct answers to interview questions, though. An interview Question and Answer discussion can be very helpful to both these individuals.  It is simply a way to go back over the building blocks of a topic.  Many times a simple review like this will help “jog” your memory, and all those previously-memorized facts will come flooding back to you.  It is not a way to re-learn a topic, but a way to remind yourself of what you already know. A Question and Answer discussion can also be a way to go over old topics in a more interesting manner.  Especially if you have been working in the industry, or taking lots of classes on the topic, everything you read can sound like a repeat of what you already know.  Going over a topic in a new format can make the material seem fresh and interesting.  And an interested mind will be more engaged and remember more in the end. Interview Questions and Answers are Harmful A common argument against a Question and Answer discussion is that it will give someone a “cheat sheet.” A new guy with relatively little experience can read the interview questions and answers, and then memorize them. When an interviewer asks him the same questions, he will repeat the answers and get the job. Honestly, is he good hire because he memorized the interview questions? Wouldn’t it be better for the interviewer to hire someone with actual experience?  The answer is not as easy as it seems – there are many different factors to be considered. If the interviewer is asking fundamentals-related questions only, he gets the answers he wants to hear, and then hires this first candidate – there is a good chance that he is hiring based on personality rather than experience.  If the interviewer is smart he will ask deeper questions, have more than one person on the interview team, and interview a variety of candidates.  If one interviewee happens to memorize some answers, it usually doesn’t mean he will automatically get the job at the expense of more qualified candidates. Another argument against interview Question and Answers is that it will give candidates a false sense of confidence, and that they will appear more qualified than they are. Well, if that is true, it will not last after the first interview when the candidate is asked difficult questions and he cannot find the answers in the list of interview Questions and Answers.  Besides, confidence is one of the best things to walk into an interview with! In today’s competitive job market, there are often hundreds of candidates applying for the same position.  With so many applicants to choose from, interviewers must make decisions about who to call back and who to hire based on their gut feeling.  One drawback to reading an interview Question and Answer article is that you might sound very boring in your interview – saying the same thing as every single candidate, and parroting answers that sound like someone else wrote them for you – because they did.  However, it is definitely better to go to an interview prepared, just make sure that you give a lot of thought to your answers to make them sound like your own voice.  Remember that you will be hired based on your skills as well as your personality, so don’t think that having all the right answers will make get you hired.  A good interviewee will be prepared, confident, and know how to stand out. My Opinion A list of interview Questions and Answers is really helpful as a refresher or for beginners. To really ace an interview, one needs to have real-world, hands-on experience with SQL Server as well. Interview questions just serve as a starter or easy read for experienced professionals. When I have to learn new technology, I often search online for interview questions and get an idea about the breadth and depth of the technology. Next Action I am going to write about interview Questions and Answers for next 30 days. I have previously written a series of interview questions and answers; now I have re-written them keeping the latest version of SQL Server and current industry progress in mind. If you have faced interesting interview questions or situations, please write to me and I will publish them as a guest post. If you want me to add few more details, leave a comment and I will make sure that I do my best to accommodate. Tomorrow we will start the interview Questions and Answers series, with a few interesting stories, best practices and guest posts. We will have a prize give-away and other awards when the series ends. List of all the Interview Questions and Answers Series blogs Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL Interview Questions and Answers, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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• Using SQL Execution Plans to discover the Swedish alphabet

  - by Rob Farley

  SQL Server is quite remarkable in a bunch of ways. In this post, I’m using the way that the Query Optimizer handles LIKE to keep it SARGable, the Execution Plans that result, Collations, and PowerShell to come up with the Swedish alphabet. SARGability is the ability to seek for items in an index according to a particular set of criteria. If you don’t have SARGability in play, you need to scan the whole index (or table if you don’t have an index). For example, I can find myself in the phonebook easily, because it’s sorted by LastName and I can find Farley in there by moving to the Fs, and so on. I can’t find everyone in my suburb easily, because the phonebook isn’t sorted that way. I can’t even find people who have six letters in their last name, because also the book is sorted by LastName, it’s not sorted by LEN(LastName). This is all stuff I’ve looked at before, including in the talk I gave at SQLBits in October 2010. If I try to find everyone who’s names start with F, I can do that using a query a bit like: SELECT LastName FROM dbo.PhoneBook WHERE LEFT(LastName,1) = 'F'; Unfortunately, the Query Optimizer doesn’t realise that all the entries that satisfy LEFT(LastName,1) = 'F' will be together, and it has to scan the whole table to find them. But if I write: SELECT LastName FROM dbo.PhoneBook WHERE LastName LIKE 'F%'; then SQL is smart enough to understand this, and performs an Index Seek instead. To see why, I look further into the plan, in particular, the properties of the Index Seek operator. The ToolTip shows me what I’m after: You’ll see that it does a Seek to find any entries that are at least F, but not yet G. There’s an extra Predicate in there (a Residual Predicate if you like), which checks that each LastName is really LIKE F% – I suppose it doesn’t consider that the Seek Predicate is quite enough – but most of the benefit is seen by its working out the Seek Predicate, filtering to just the “at least F but not yet G” section of the data. This got me curious though, particularly about where the G comes from, and whether I could leverage it to create the Swedish alphabet. I know that in the Swedish language, there are three extra letters that appear at the end of the alphabet. One of them is ä that appears in the word Västerås. It turns out that Västerås is quite hard to find in an index when you’re looking it up in a Swedish map. I talked about this briefly in my five-minute talk on Collation from SQLPASS (the one which was slightly less than serious). So by looking at the plan, I can work out what the next letter is in the alphabet of the collation used by the column. In other words, if my alphabet were Swedish, I’d be able to tell what the next letter after F is – just in case it’s not G. It turns out it is… Yes, the Swedish letter after F is G. But I worked this out by using a copy of my PhoneBook table that used the Finnish_Swedish_CI_AI collation. I couldn’t find how the Query Optimizer calculates the G, and my friend Paul White (@SQL_Kiwi) tells me that it’s frustratingly internal to the QO. He’s particularly smart, even if he is from New Zealand. To investigate further, I decided to do some PowerShell, leveraging the Get-SqlPlan function that I blogged about recently (make sure you also have the SqlServerCmdletSnapin100 snap-in added). I started by indicating that I was going to use Finnish_Swedish_CI_AI as my collation of choice, and that I’d start whichever letter cam straight after the number 9. I figure that this is a cheat’s way of guessing the first letter of the alphabet (but it doesn’t actually work in Unicode – luckily I’m using varchar not nvarchar. Actually, there are a few aspects of this code that only work using ASCII, so apologies if you were wanting to apply it to Greek, Japanese, etc). I also initialised my $alphabet variable. $collation = 'Finnish_Swedish_CI_AI'; $firstletter = '9'; $alphabet = ''; Now I created the table for my test. A single field would do, and putting a Clustered Index on it would suffice for the Seeks. Invoke-Sqlcmd -server . -data tempdb -query "create table dbo.collation_test (col varchar(10) collate $collation primary key);" Now I get into the looping. $c = $firstletter; $stillgoing = $true; while ($stillgoing) { I construct the query I want, seeking for entries which start with whatever $c has reached, and get the plan for it: $query = "select col from dbo.collation_test where col like '$($c)%';"; [xml] $pl = get-sqlplan $query "." "tempdb"; At this point, my $pl variable is a scary piece of XML, representing the execution plan. A bit of hunting through it showed me that the EndRange element contained what I was after, and that if it contained NULL, then I was done. $stillgoing = ($pl.ShowPlanXML.BatchSequence.Batch.Statements.StmtSimple.QueryPlan.RelOp.IndexScan.SeekPredicates.SeekPredicateNew.SeekKeys.EndRange -ne $null); Now I could grab the value out of it (which came with apostrophes that needed stripping), and append that to my $alphabet variable.   if ($stillgoing)   {  $c=$pl.ShowPlanXML.BatchSequence.Batch.Statements.StmtSimple.QueryPlan.RelOp.IndexScan.SeekPredicates.SeekPredicateNew.SeekKeys.EndRange.RangeExpressions.ScalarOperator.ScalarString.Replace("'","");     $alphabet += $c;   } Finally, finishing the loop, dropping the table, and showing my alphabet! } Invoke-Sqlcmd -server . -data tempdb -query "drop table dbo.collation_test;"; $alphabet; When I run all this, I see that the Swedish alphabet is ABCDEFGHIJKLMNOPQRSTUVXYZÅÄÖ, which matches what I see at Wikipedia. Interesting to see that the letters on the end are still there, even with Case Insensitivity. Turns out they’re not just “letters with accents”, they’re letters in their own right. I’m sure you gave up reading long ago, and really aren’t that fazed about the idea of doing this using PowerShell. I chose PowerShell because I’d already come up with an easy way of grabbing the estimated plan for a query, and PowerShell does allow for easy navigation of XML. I find the most interesting aspect of this as the fact that the Query Optimizer uses the next letter of the alphabet to maintain the SARGability of LIKE. I’m hoping they do something similar for a whole bunch of operations. Oh, and the fact that you know how to find stuff in the IKEA catalogue. Footnote: If you are interested in whether this works in other languages, you might want to consider the following screenshot, which shows that in principle, it should work with Japanese. It might be a bit harder to run this in PowerShell though, as I’m not sure how it translates. In Hiragana, the Japanese alphabet starts ?, ?, ?, ?, ?, ...

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• Movement prediction for non-shooters

  - by ShadowChaser

  I'm working on an isometric 2D game with moderate-scale multiplayer, approximately 20-30 players connected at once to a persistent server. I've had some difficulty getting a good movement prediction implementation in place. Physics/Movement The game doesn't have a true physics implementation, but uses the basic principles to implement movement. Rather than continually polling input, state changes (ie/ mouse down/up/move events) are used to change the state of the character entity the player is controlling. The player's direction (ie/ north-east) is combined with a constant speed and turned into a true 3D vector - the entity's velocity. In the main game loop, "Update" is called before "Draw". The update logic triggers a "physics update task" that tracks all entities with a non-zero velocity uses very basic integration to change the entities position. For example: entity.Position += entity.Velocity.Scale(ElapsedTime.Seconds) (where "Seconds" is a floating point value, but the same approach would work for millisecond integer values). The key point is that no interpolation is used for movement - the rudimentary physics engine has no concept of a "previous state" or "current state", only a position and velocity. State Change and Update Packets When the velocity of the character entity the player is controlling changes, a "move avatar" packet is sent to the server containing the entity's action type (stand, walk, run), direction (north-east), and current position. This is different from how 3D first person games work. In a 3D game the velocity (direction) can change frame to frame as the player moves around. Sending every state change would effectively transmit a packet per frame, which would be too expensive. Instead, 3D games seem to ignore state changes and send "state update" packets on a fixed interval - say, every 80-150ms. Since speed and direction updates occur much less frequently in my game, I can get away with sending every state change. Although all of the physics simulations occur at the same speed and are deterministic, latency is still an issue. For that reason, I send out routine position update packets (similar to a 3D game) but much less frequently - right now every 250ms, but I suspect with good prediction I can easily boost it towards 500ms. The biggest problem is that I've now deviated from the norm - all other documentation, guides, and samples online send routine updates and interpolate between the two states. It seems incompatible with my architecture, and I need to come up with a better movement prediction algorithm that is closer to a (very basic) "networked physics" architecture. The server then receives the packet and determines the players speed from it's movement type based on a script (Is the player able to run? Get the player's running speed). Once it has the speed, it combines it with the direction to get a vector - the entity's velocity. Some cheat detection and basic validation occurs, and the entity on the server side is updated with the current velocity, direction, and position. Basic throttling is also performed to prevent players from flooding the server with movement requests. After updating its own entity, the server broadcasts an "avatar position update" packet to all other players within range. The position update packet is used to update the client side physics simulations (world state) of the remote clients and perform prediction and lag compensation. Prediction and Lag Compensation As mentioned above, clients are authoritative for their own position. Except in cases of cheating or anomalies, the client's avatar will never be repositioned by the server. No extrapolation ("move now and correct later") is required for the client's avatar - what the player sees is correct. However, some sort of extrapolation or interpolation is required for all remote entities that are moving. Some sort of prediction and/or lag-compensation is clearly required within the client's local simulation / physics engine. Problems I've been struggling with various algorithms, and have a number of questions and problems: Should I be extrapolating, interpolating, or both? My "gut feeling" is that I should be using pure extrapolation based on velocity. State change is received by the client, client computes a "predicted" velocity that compensates for lag, and the regular physics system does the rest. However, it feels at odds to all other sample code and articles - they all seem to store a number of states and perform interpolation without a physics engine. When a packet arrives, I've tried interpolating the packet's position with the packet's velocity over a fixed time period (say, 200ms). I then take the difference between the interpolated position and the current "error" position to compute a new vector and place that on the entity instead of the velocity that was sent. However, the assumption is that another packet will arrive in that time interval, and it's incredibly difficult to "guess" when the next packet will arrive - especially since they don't all arrive on fixed intervals (ie/ state changes as well). Is the concept fundamentally flawed, or is it correct but needs some fixes / adjustments? What happens when a remote player stops? I can immediately stop the entity, but it will be positioned in the "wrong" spot until it moves again. If I estimate a vector or try to interpolate, I have an issue because I don't store the previous state - the physics engine has no way to say "you need to stop after you reach position X". It simply understands a velocity, nothing more complex. I'm reluctant to add the "packet movement state" information to the entities or physics engine, since it violates basic design principles and bleeds network code across the rest of the game engine. What should happen when entities collide? There are three scenarios - the controlling player collides locally, two entities collide on the server during a position update, or a remote entity update collides on the local client. In all cases I'm uncertain how to handle the collision - aside from cheating, both states are "correct" but at different time periods. In the case of a remote entity it doesn't make sense to draw it walking through a wall, so I perform collision detection on the local client and cause it to "stop". Based on point #2 above, I might compute a "corrected vector" that continually tries to move the entity "through the wall" which will never succeed - the remote avatar is stuck there until the error gets too high and it "snaps" into position. How do games work around this?

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