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• What can be done to improve time synchronization on networks with sporadic internet access?

  - by anregen

  I'm looking for advice setting up time servers for a very non-typical network. I support many closed networks that have occasional access to the internet. A network would get access most days for a few hours, but would frequently go 1-3 weeks blacked-out. The computers/servers on this network are mostly *nix-based, but not all the same flavor. The entire network is mobile, so when it connects, it will have very different hops/latency to internet time servers. The servers on the closed network are powered-off frequently (at least daily). Right now, my gut tells me to use NTP (because I hate re-learning all the stuff that someone else already got working pretty well). But I have several issues, and am looking for someone with experience in this type of strange situation. I currently have no solution in place, I'm simply letting the internal clocks drift. This results in errors of ~600s in a majority of networks. I have seen mismatch worse than 10,000s. Is there something "better" than NTP in this situation? I know NTP likes to have very frequent, consistent access to servers that give nearly identical answers. I won't have that. How many internal NTP servers should I configure, so that during periods of internet blackout, I have internal time that is consistent within the closed network? There is no human access. No matter how large the mismatch, the server(s) must attempt to correct itself. Discrete steps are very bad. No matter how large the mismatch, the correction must be "slewed", not "stepped". I understand that this could take many hours to correct.

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• How to set a static system date for one user or application--"Groundhog Day"

  - by aixylinux

  I have a vendor application on AIX which requires the system date to be set to an arbitrary value for QA testing purposes. The application gets its date from the system, and there is no possibility of changing it to get the date from a parameter. The application runs under a specific userid. I'd like to find a way to set the date for this application or user to a private value without affecting all the other users and applications on the system. So far the only thing I have been able to do is dedicate an LPAR to this application. Every day at midnight a root crontab job resets the date to the static value. This works, but it is wasteful of resources; and now I am faced the requirement to do this for other applications, which, of course, require different dates. Is there any clever solution to this? I need a way to create a sandboxed environment where the date returned from the system can be set to a private value. As I said, the OS is AIX, and that can't be changed for this application either.

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• Dumping active directory

  - by Nop at NaDa

  I work in the IT support department of a branch of a huge company. I have to take care of a database with all the users, computers, etc. I'm trying to find a way to automatically update the database as much as possible, but the IT infrastructure guys doesn't give me enough privileges to use Active Directory in order to dump the users, nor they have the time to give me the information that I need. Some days ago I found Active Directory explorer from Sysinternals that allows me to browse through Active Directory, and I found all the information that I need there (username, real name, date when it was created, privileges, company, etc.). Unfortunately I'm unable to export the data to a human readable format. I'm just able to take a snapshot of the whole database in a machine-readable format. Doing the snapshot takes hours and I'm afraid that the infrastructure guys won't like me doing entire snapshots on a regular basis. Do you know of any tool (command-line is preferable) that would allow me to retrieve the values of the keys or export it to XML, CSV, etc?

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• Very fast document similarity

  - by peyton

  Hello, I am trying to determine document similarity between a single document and each of a large number of documents (n ~= 1 million) as quickly as possible. More specifically, the documents I'm comparing are e-mails; they are grouped (i.e., there are folders or tags) and I'd like to determine which group is most appropriate for a new e-mail. Fast performance is critical. My a priori assumption is that the cosine similarity between term vectors is appropriate for this application; please comment on whether this is a good measure to use or not! I have already taken into account the following possibilities for speeding up performance: Pre-normalize all the term vectors Calculate a term vector for each group (n ~= 10,000) rather than each e-mail (n ~= 1,000,000); this would probably be acceptable for my application, but if you can think of a reason not to do it, let me know! I have a few questions: If a new e-mail has a new term never before seen in any of the previous e-mails, does that mean I need to re-compute all of my term vectors? This seems expensive. Is there some clever way to only consider vectors which are likely to be close to the query document? Is there some way to be more frugal about the amount of memory I'm using for all these vectors? Thanks!

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• What techniques can I employ to create a series of UI Elements from a collection of objects using WP

  - by elggarc

  I'm new to WPF and before I dive in solving a problem in completely the wrong way I was wondering if WPF is clever enough to handle something for me. Imagine I have a collection containing objects. Each object is of the same known type and has two parameters. Name (a string) and Picked (a boolean). The collection will be populated at run time. I would like to build up a UI element at run time that will represent this collection as a series of checkboxes. I want the Picked parameter of any given object in the collection updated if the user changes the selected state of the checkbox. To me, the answer is simple. I iterate accross the collection and create a new checkbox for each object, dynamically wiring up a ValueChanged event to capture when Picked should be changed. It has occured to me, however, that I may be able to harness some unknown feature of WPF to do this better (or "properly"). For example, could data binding be employed here? I would be very interested in anyone's thoughts. Thanks, E FootNote: The structure of the collection can be changed completely to better fit any chosen solution but ultimately I will always start from, and end with, some list of string and boolean pairs.

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• What's the safest way to kick off a root-level process via cgi on an Apache server?

  - by MartyMacGyver

  The problem: I have a script that runs periodically via a cron job as root, but I want to give people a way to kick it off asynchronously too, via a webpage. (The script will be written to ensure it doesn't run overlapping instances or such.) I don't need the users to log in or have an account, they simply click a button and if the script is ready to be run it'll run. The users may select arguments for the script (heavily filtered as inputs) but for simplicity we'll say they just have the button to choose to press. As a simple test, I've created a Python script in cgi-bin. chown-ing it to root:root and then applying "chmod ug+" to it didn't have the desired results: it still thinks it has the effective group of the web server account... from what I can tell this isn't allowed. I read that wrapping it with a compiled cgi program would do the job, so I created a C wrapper that calls my script (its permissions restored to normal) and gave the executable the root permissions and setuid bit. That worked... the script ran as if root ran it. My main question is, is this normal (the need for the binary wrapper to get the job done) and is this the secure way to do this? It's not world-facing but still, I'd like to learn best practices. More broadly, I often wonder why a compiled binary is more "trusted" than a script in practice? I'd think you'd trust a file that was human-readable over a cryptic binaryy. If an attacker can edit a file then you're already in trouble, more so if it's one you can't easily examine. In short, I'd expect it to be the other way 'round on that basis. Your thoughts?

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• Asp.net MVC - Model binding image button

  - by big dave

  I've got a very complex form and i'm using the MVC model binding to capture all the information I've got it set up to capture all the different submissions that can happen as there are about 10 different submit buttons on the form, and there are also 2 image buttons I tried to get a bit clever (or so i thought) with capturing the image button submissions, and have created a child class so that i can capture the x value that's returned public class ImageButtonViewData { public int x { get; set; } public string Value { get; set; } } The parent class looks something like this public class ViewDataObject { public ImageButtonViewData ImageButton { get; set; } public ViewDataObject(){ this.ImageButton = new ImageButton(); } } The html for the image button then looks like <input type="image" id="ViewDataObject_ImageButton" name="ViewDataObject.ImageButton" /> This works fine in all browsers except for Chrome. When i debug it in chrome, the Request.Form object contains the values that i would expect, but after the model binding has occurred, the ImageButton property on the ViewDataObject has been set to null The only difference that i can see between the submission values is that Chrome passes the x as lower case (ViewDataObject.ImageButton.x) and IE passes it as upper case (ViewDataObject.ImageButton.X) but i didn't think that model binding took any notice of casing on property names Does anyone have any ideas ?

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• Deployment and monitoring tools for java/tomcat/linux environment

  - by Ran

  I'm a developer for many years, but don't have tons of experience in ops, so apology if this is a newbe question. In my company we run a web service written in Java mainly based on a Tomcat web server. We have two datacenters with about 10 hosts each. Hosts are of several types: Dababase, Tomcats, some offline java processes, memcached servers. All hosts are Linux CentOS Up until now, when releasing a new version to production we've been using a set of inhouse shell script that copy jars/wars and restart the tomcats. The company has gotten bigger so it has become more and more difficult operating all this and taking code from development, through QA, staging and to production. A typical release many times involves human errors that cost us precious uptime. Sometimes we need to revert to last known good and this isn't easy to say the least... We're looking for a tool, a framework, a solution that would provide the following: Supports the given list of technology (java, tomcat, linux etc) Provides easy deployment through different stages, including QA and production Provides configuration management. E.g. setting server properties (what's the connection URL of each host etc), server.xml or context configuration etc Monitoring. If we can get monitoring in the same package, that'll be nice. If not, then yet another tool we can use to monitor our servers. Preferably, open source with tons of documentation ;) Can anyone share their experience? Suggest a few tools? Thanks!

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• Trying to diagnose network problem: ping 127.0.0.1 (or any address) results in error code 1

  - by Mnebuerquo

  NIC seems to be working, as windows detects the hardware and has a driver and reports success. DHCP seems to have gotten an ip address, 192.168.1.101. I released and renewed it and it seemed to work normally. I tried ping 127.0.0.1 as first step of testing network configuration. Pinging 127.0.0.1 with 32 bytes of data: PING: transmit failed, error code 1. I read somewhere that net helpmsg [error code] would give a human readable name for the error code. net helpmsg 1 says "Incorrect function" I've tried disabling the firewall and antivirus in McAfee SecurityCenter and I still get the same error. Could the firewall/antivirus be breaking it even if disabled? Broadcom Advanced Control Suite 2 is installed, and its network test passes all tests, including ping 192.168.1.1 which is the default gateway. If I try ping 192.168.1.1 from the command prompt I get the error code 1 again. So does anyone have any theories that would explain this problem? Other tests I should try? Thanks!

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• Firing PropertyChanged event in a complex, nested type in WPF

  - by John

  Hey I have a question about the PropertyChanged vent firing in WPF whne it is used in a complex type. I have a class called DataStore and a list of Departments (an ObservableCollection), and each department again has a list of Products. Properties in the Product class that are changed also affect properties in the Department and DataStore class. How does each Product notify the Department it belongs to, and the DataStore (which is the mother class of all) that one or more of its properties have changed their values? Example: a product has a property NumberSoldToday and is bound. The Department has a property called TotalNumberOfProductsSold: public int TotalNumberOfProductsSold { get { int result = 0; foreach(Product p in this.products) result += p.NumberSoldToday; return result; } } And the data store has a property TotalProductsSold (for all departments): public int TotalProductsSold { get { int result = 0; foreach(Product p in this.deparments) result += p.TotalNumberOfProductsSold; return result; } } If all these properties are bound, and the innermost property changes, it must somehow notify that the value of the other 2 changed as well. How? The only way I can see this happening is to hook up the PropertyChanged event in each class. Th event must also fire when deleting, adding to the collection of products and deparments, respectively. Is there a better, more clever way to do this?

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• jQuery: Preventing an event from being attached more than once?

  - by Evan Carroll

  Essentially, I have an element FOO that I want when clicked to attach a click event to a completely separate set of elements BAR, so that when they're clicked they can revert FOO to its previous content. I only want this event attached once. When FOO is clicked, its content is cached away in $back_up, and a trigger is added on the BAR set so that when clicked they can revert FOO back to its previous state. Is there a clever way to do this? Like to only .bind() if the event doesn't already exist? $('<div class="noprint little check" />').click( function () { var $warranty_explaination = $(this).closest('.page').children('.warranty_explaination'); var $back_up = $warranty_explaination.clone(true); $(this).closest('.page').find('.warranties .check:not(.noprint)').click( function () { /* This is the code I don't want to fire more than once */ /*, I just want it to be set to whatever is in the $back_up */ alert('reset'); $warranty_explaination.replaceWith( $back_up ) } ); $warranty_explaination.html('asdf') } ) Currently, the best way I can think to do this is to attach a class, and select where that class doesn't exist.

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• Lucene raise document score if sibling entity matches query

  - by Pitagoras

  I have the following design situation. I use hibernate search (lucene in the back). Tha application manages ITEMs which have title, description and tags. These are full text indexed. On the other hand, we have COLLECTION of ITEMs. The user can create a COLLECTION and add as many ITEMs as she wants. ITEMs can also belong to many COLLECTIONs. I have a boosted query so that search terms that appear in the tags are more important than in the title, and lastly in the description. But I need an additional matching criteria: for a given ITEM, it whould rank better if other documents in some COLLECTION where the ITEM belongs, also match the query. This is like to say: the title/tags/description of "fellow" items (i.e. items in some shared collection) make the item rank better. I was thinking that adding an ITEM to a COLLECTION would add something like "extra tags" to every other ITEM in the collection, being these extra tags the elements to match in the added ITEM. I feel a more clever solution lucene-wise should exists. Any ideas/pointers are welcome. Thanks.

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• Identifying test machines in analytics logs

  - by RTigger

  We're just beginning to add analytics to our SaaS application, to begin (among other things) billing clients based on usage. The problem we're running into is there's a few circumstances where our support team will simulate a log in into production to try to reproduce reported issues with a client's configuration. When they log in, an entry will be made into our analytics logs that their specific account has logged in, which we use to calculate billing. A few ideas we had to solve this: 1) We log IP addresses as well as machine keys for each PC that logs in - we could filter out known IP addresses and/or machine keys belonging to support. The drawback is we have to maintain a list of keys / addresses manually. 2) If support (or anyone else internal) runs our application in debug mode (as opposed to release), it will not report analytics. This is fine, as long as support / anyone else remembers to switch to debug mode. 3) Include some sort of reg key / similar setting required to be set when configuring a production system in order to send analytics. Again, fine, as long as our infrastructure team remembers to set the reg key or setting. All of these approaches require some sort of human involvement, which we all know can be iffy at best. Has anyone run into a similar situation? Is there an automated approach to this problem? (PS Of course, we shouldn't be testing in production, but there are a few one-off instances with customer set up that we can't reproduce without logging in as them in production. This is the only time we do so, and this is the case I'm talking about in this question.)

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• Why doesn't the value in /proc/meminfo seem to map exactly to the system RAM?

  - by Eric Asberry

  The values in /proc/meminfo for MemTotal don't make sense. As a human, eyeballing it, it seems to roughly correspond to the installed RAM, but for using it to display the installed RAM from an automated utility it appears to be inexact, and inconsistent. For a system with 1G of RAM, I would expect the MemTotal line to have a value of 1048576 - 1024*1024. But instead, I'm seeing 1029392. On another 4G box, I'm seeing 3870172, which is not a multiple of 1024, and it's not even close to 1029392*4. On an 8G box, I get 8128204, which again seems to have no correlation to the other values, nor is it a multiple of 1024. I'm trying to use this information to report the RAM on a status web page. My work-around is to just "round" it to the nearest 1G multiple, but I'd like to understand why these values seem inconsistent and don't match my expectations. Can somebody fill me in on what I'm missing here? EDIT: To expand on the accepted answer below.... The reference can be found here. Also of interest to me from that page, which explains the inconsistency, is this bit: meminfo: Provides information about distribution and utilization of memory. This varies by architecture and compile options. ...

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• Retrieve POST data without knowing exact number of fields

  - by James

  Hi all! I'm creating an online poll from scratch which will be held in a database. I'm working on getting a system set up so someone can create a new poll. I will be having the user fill out a simple HTML form with the Questions and Answers (there may be several answers). The user will be able to add multiple questions and multiple answers for each question. As the total number of questions and answers will be decided by the user, I need to create some clever PHP to cater for this - however many there are. When dealing with a static number of questions, it's simple. But I'm having trouble thinking of a way to get all the POST data into individual PHP variables so I can process them. I was thinking of using a foreach loop, anyone got any ideas? Sorry for the long winded description! If anyone needs anything clarified, I'd be happy to do so. My problem is that I can't get my head around how to deal with the POST values when I don't know exactly which element of the array will contain what. If things were static with a set number of questions and answers, I'd know $_POST[0] was Question1, etc Thank you! =)

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• Accepting a socket on Windows 7 takes more than a second

  - by eburger

  Here's what I've done: I wrote a minimal web server (using Qt, but I don't think it's relevant here). I'm running it on a legal Windows 7 32-bit. The problem: If I make a request with Firefox, IE, Chrome or Safari it takes takes about one second before my server sees that there is a new connection to be accepted. Clues: Using other clients (wget, own test client that just opens a socket) than Firefox, IE, Chrome, Safari seeing the new connection is matter of milliseconds. I installed Apache and tried the clients mentioned above. Serving the request takes ~50ms as expected. The problem isn't reproducible when running Windows XP (or compiling and running the same code under Linux) The problem seems to present itself only when connecting to localhost. A friend connected over the Internet and serving the connection was a matter of milliseconds. Running the server in different ports has no effect on the 1 second latency Here's what I've tried without luck: Stopped the Windows Defender service Stopped the Windows Firewall service Any ideas? Is this some clever 'security feature' in Windows 7? Why isn't Apache affected? Why are only the browsers affected?

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• Firefox "intelligently" and silently fixes incorrect file references in CSS and Scripts at runtime.

  - by bobsoap

  Well this is a really weird issue, I really didn't find anything on this elsewhere so I thought I'd address it here. Say I have an "image.jpg" and accidentally reference it in the CSS like so: url(imag.jpg) Note the missing "e". Now for me, Firefox is so incredibly clever that it will still find the correct image, but NOT SPIT OUT A WARNING. So I assume that everything is ok. But later, when I test the page in any other browser, all of a sudden the image doesn't display (and rightly so). That's because Firefox thought it was a good idea to correct my error without telling me. This becomes more critical with scripts. Firefox will also auto-correct a typo in a reference. I just wasted a whole hour scratching my head and trying to debug an ajax function in Webkit - turns out, I just had a typo where I included the file. Why on earth does Firefox do this without telling, and where the heck can I turn this off? This has first occured somewhere around FF 3.0 and still persists in 3.6.3. /rant an thank fo any inpu ;)

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• Customer wants some data to appear after you later delete rows. System giant / not my creation. Fast

  - by John Sullivan

  This is a fairly common problem, it probably has a name, I just don't know what it is. A.) User sees obscure piece of information in Row B of L_OBSCURE_INFO displayed on some screen at a certain point. It is in table L_Obscure_info. B.) Under certain circumstances we want to correctly delete data in L_OBSCURE_INFO. Unfortunately, nobody accounted for the fact that the user might want to backtrack and see some random piece of information that was most recently in L_OBSCURE_INFO. C.) The system is enormous and L_OBSCURE_INFO is used all the time. You have no idea what the ramifications are of implementing some kind of hack and whatever you do, you don't want to introduce more bugs. I think the best approach would be to create an L_OBSCURE_INFO_HISTORY table and record a record in there every time you change data. But god help your ensuring it's accurate in this system where L_OBSCURE_INFO is being touched everywhere and you don't have time to implement L_OBSCURE_INFO_HISTORY. Is there a particularly easy, clever design solution for this kind of problem -- basically an elegant database hack? If not, is this kind of design problem under a particular class of problems or have a name?

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• Centering Divisions Around Zero

  - by Mark

  I'm trying to create something that sort of resembles a histogram. I'm trying to create buckets from an array. Suppose I have a random array doubles between -10 and 10; this is very simplified. I then want to specify a center point, in this case 0 and the number of buckets. If I want 4 buckets the division would be -10 to -5, -5 to 0, 0 to 5 and 5 to 10. Not that complicated right. Now if I change the min and max to -12 and -9 and as for 4 divisions its more complicated. I either want a division at -3 and 3; it is centered around 0 ; or one at -6 to 0 and 0 to 6. Its not that hard to find the division size = Math.Ceiling((Abs(Max) + Abs(Min)) / Divisions) Then you would basically have an if statement to determine whether you want it centered on 0 or on an edge. You then iterate out from either 0 or DivisionSize/2 depending on the situation. You may not ALWAYS end up with the specified number of divisions but it will be close. Then you iterate through the array and increment the bin count. Does this seem like a good way to go about this? This method would surely work but it does not seem to be the most elegant. I'm curious as to whether the creation of the bins and the counting from the list could be done in a clever class with linq in a more elegant way? Something like creating the bins and then having each bin be a property {get;} that returns list.Count(x=> x >= Lower && x < Upper).

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• php / phpDoc - @return instance of $this class ?

  - by searbe

  How do I mark a method as "returns an instance of the current class" in my phpDoc? In the following example my IDE (Netbeans) will see that setSomething always returns a foo object. But that's not true if I extent the object - it'll return $this, which in the second example is a bar object not a foo object. class foo { protected $_value = null; /** * Set something * * @param string $value the value * @return foo */ public function setSomething($value) { $this->_value = $value; return $this; } } $foo = new foo(); $out = $foo->setSomething(); So fine - setSomething returns a foo - but in the following example, it returns a bar..: class bar extends foo { public function someOtherMethod(){} } $bar = new bar(); $out = $bar->setSomething(); $out->someOtherMethod(); // <-- Here, Netbeans will think $out // is a foo, so doesn't see this other // method in $out's code-completion ... it'd be great to solve this as for me, code completion is a massive speed-boost. Anyone got a clever trick, or even better, a proper way to document this with phpDoc?

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• Browser: Randomly Opens Pages in New Windows Without Reason?

  - by Mark R

  This is a very strange thing I've noticed on my computer and past computers over this past year or more. I know when page are meant to open in a new Window and know which settings to use on my browser for this. But on both my browsers Chrome and Firefox, I have this really strange issue. I'm starting to think it's a hacker. When I right click links and select Open Link in New Tab, sometimes they will randomly open in a new window and today it is happening a lot. Like lots and lots. I'm getting really creeped out by it and YES I understand when a link opens in a new window and when it isn't supposed to. And none of these links are meant to open in a new Window. Let me give you an example: I searched Google about my issue and clicked on the result that I thought good. It opened in a new tab but half way through loading in new tab it opens into a new window. Recently, I decided to record my screen and while recording my screen using Camtasia, the issue stops. When I stop recording it starts again, as if it's a human operated issue. VERY strange. This has been going on for months on my old and new computer and on both Firefox and Chrome. Is there something I can do to fix this intermittent problem?

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• Strategy for animation a lot of LED's - thread?, UIView animations? NSOperation? (iPhone)

  - by RickiG

  Hi I have to do some different views containing 72 LED lights. I built an LED Class so I can loop through the LED's and set them to different colors (Green, Red, Orange, Blue None etc.). The LED then loads the appropriate .png. This works fine, I loop over the LED's and set them. Now I know that at some time they will need to not just turn on/off change color, but will have to turn on with a small delay. Like an equalizer. I have a 5-10 views containing the 72 LED's and I would like to achieve the above with the minimum amount of memory/CPU strain. for(LED *l in self.ledArray) { [l display:Green]; } I simply loop as shown above and inside the LED is a switch case that does the correct logic. If this were actual LED's and a microController I would use sleep(100) or similar in the loop, but I would really like to avoid stuff like that for obvious reasons. I was thinking that doing a performOnThread withDelay would really be consuming, so would UIView animation changing the alpha and NSOperation would also be a lot of lifting for a small feature. Is there a both efficient and clever way to go around this? Thanks for any inspiration given:)

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• How can I document and automate a system's configuration?

  - by Diomidis Spinellis

  Having a system's configuration represented by its current state is risky, inefficient, and opaque. At some point you may be left with an unsupported system and no upgrade path. Then configuring a new system compatible with the old is a process or trial and error. Furthermore, if at some point the system is damaged the only option is to go back to the most recent full backup, and try to remember what changes followed from that point. Also, the only way to create a system compatible with the original is through a complete dump/restore. Finally, in such a setup there's no way to know how you solved a particular problem; the only thing you can do is to look at the corresponding configuration files and try to guess what you changed to achieve the desired effect. Currently for each system I maintain, I keep a log file where I record all system administration activity, starting from the installation: installation options, added packages, changes in configuration files, updates, problem fixes etc. In theory this allows me to (manually) replay all changes to arrive at the current state, or to unroll an erroneous change by executing the reverse commands. However, this process is also inefficient, error-prone, and relies on human judgment. Another thing I've tried is to put /etc configuration files under version control with git. This helps me document the changes automatically and also apply them on a clean setup. But it's not without problems: git has to run under sudo, passwords and private keys may be stored in the repository, installed packages can't be meaningfully tracked, and git will have a fit if I try to extend this approach to all the system's directories. I've also thought about performing all changes through shell scripts or makefiles, but I think this process will require a lot of effort and will be fragile. Are there some better methods or tools that I'm missing?

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• dm_exec_query_stats returning stale data?

  - by VoiceOfUnreason

  I've been testing my app on a SQL Server 2005 database, and am trying to establish a preliminary picture of the query performance using sys.dm_exec_query_stats. Problem: there's a particular query that I'm interested in, because total_elapsed_time and last_elapsed_time are both large numbers. When I tickle my app to invoke that query (this runs successfully), then refresh my view of the stats, I find that 1) execution_count has incremented (expected) 2) last_execution_time has updated to now (expected) 3) last_elapsed_time is still a large value (not expected - I anticipated a new value) 4) total_elapsed_time is unchanged (contradiction?) If last_elapsed_time refers to the execution that happened @ last_execution_time, then the total_elapsed_time should have increased? This documentation: http://msdn.microsoft.com/en-us/library/ms189741(SQL.90).aspx tells me that last_execution_time is the last time the plan was executed, and last_elapsed_time comes from the "most recently executed plan", but doesn't tell me why those might be different. The query itself is uncomplicated (SELECT/WHERE/ORDER BY - parameters appearing in the where clause, but no clever operations), the table has maybe 25 rows in it right now. Questions: 1) What's the real relationship between execution_count, last_execution_time, and last_elapsed_time? 2) Where is the documentation of this relationship (manual, third party book, blog, bug ticket, stone tablets...) ?

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• Querying for a unique value based on the aggregate of another value while grouping on a third value

  - by Justin Swartsel

  So I know this problem isn't a new one, but I'm trying to wrap my head around it and understand the best way to deal with scenarios like this. Say I have a hypothetical table 'X' that looks like this: GroupID ID (identity) SomeDateTime -------------------------------------------- 1 1000 1/1/01 1 1001 2/2/02 1 1002 3/3/03 2 1003 4/4/04 2 1004 5/5/05 I want to query it so the result set looks like this: ---------------------------------------- 1 1002 3/3/03 2 1004 5/5/05 Basically what I want is the MAX SomeDateTime value grouped by my GroupID column. The kicker is that I DON'T want to group by the ID column, I just want to know the 'ID' that corresponds to the MAX SomeDateTime. I know one pseudo-solution would be: ;WITH X1 as ( SELECT MAX(SomeDateTime) as SomeDateTime, GroupID FROM X GROUP BY GroupID ) SELECT X1.SomeDateTime, X1.GroupID, X2.ID FROM X1 INNER JOIN X as X2 ON X.DateTime = X2.DateTime But this doesn't solve the fact that a DateTime might not be unique. And it seems sloppy to join on a DateTime like that. Another pseudo-solution could be: SELECT X.GroupID, MAX(X.ID) as ID, MAX(X.SomeDateTime) as SomeDateTime FROM X GROUP BY X.GroupID But there are no guarantees that ID will actually match the row that SomeDateTime comes from. A third less useful option might be: SELECT TOP 1 X.GroupID, X.ID, X.SomeDateTime FROM X WHERE X.GroupID = 1 ORDER BY X.SomeDateTime DESC But obviously that only works with a single, known, GroupID. I want to be able to join this result set on GroupID and/or ID. Does anyone know of any clever solutions? Any good uses of windowing functions? Thanks!

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