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• Is frameworks really necessary for this problem?

  - by The Elite Gentleman

  Hi Guys I'm creating an online music store application (in Java) for signed and unsigned artist for my client. I'm currently using Struts 1.3.10 (I was recommended Spring but Spring setup is sort of similar to Struts) for my Web application. My Database is currently a MySQL 5 (or higher) and I'm using a DAO pattern to talk to it. There are limitations to using Struts and DAO's (e.g. Multiple File upload in Struts is not implemented the same way as multiple String parameters, and for DAO's, there lacks a Publish-Subscribe feature). Is what I'm doing the best way forward or should I go straight Hibernate (or similar) and move out of Struts? What are the performance implications or technical issues that you've experienced with the same setup I have? The client doesn't care how I do it as long as it is done.

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• How do I check the validity of the Canadian Social Insurance Number in C#?

  - by user518307

  I've been given the assignment to write an algorithm in C# that checks the validity of a Canadian Social Insurance Number (SIN). Here are the steps to validate a SIN. Given an example Number: 123 456 782 Remove the check digit (the last digit): 123456782 Extract the even digits (2,4,6,8th digith): 12345678 Double them: 2 4 6 8 | | | | v v v v 4 8 12 16 Add the digits together: 4+8+1+2+1+6 = 22 Add the Odd placed digits: 1+3+5+7 = 16 Total : 38 Validity Algorithm If the total is a multiple of 10, the check digit should be zero. Otherwise, Subtract the Total from the next highest multiple of 10 (40 in this case) The check digit for this SIN must be equal to the difference of the number and the totals from earlier (in this case, 40-38 = 2; check digit is 2, so the number is valid) I'm lost on how to actually implement this in C#, how do I do this?

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• Is this a correct Interlocked synchronization design?

  - by Dan Bryant

  I have a system that takes Samples. I have multiple client threads in the application that are interested in these Samples, but the actual process of taking a Sample can only occur in one context. It's fast enough that it's okay for it to block the calling process until Sampling is done, but slow enough that I don't want multiple threads piling up requests. I came up with this design (stripped down to minimal details): public class Sample { private static Sample _lastSample; private static int _isSampling; public static Sample TakeSample(AutomationManager automation) { //Only start sampling if not already sampling in some other context if (Interlocked.CompareExchange(ref _isSampling, 0, 1) == 0) { try { Sample sample = new Sample(); sample.PerformSampling(automation); _lastSample = sample; } finally { //We're done sampling _isSampling = 0; } } return _lastSample; } private void PerformSampling(AutomationManager automation) { //Lots of stuff going on that shouldn't be run in more than one context at the same time } } Is this safe for use in the scenario I described?

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• Send a "304 Not Modified" for images stored in the datastore

  - by Emilien

  I store user-uploaded images in the Google App Engine datastore as db.Blob, as proposed in the docs. I then serve those images on /images/<id>.jpg. The server always sends a 200 OK response, which means that the browser has to download the same image multiple time (== slower) and that the server has to send the same image multiple times (== more expensive). As most of those images will likely never change, I'd like to be able to send a 304 Not Modified response. I am thinking about calculating some kind of hash of the picture when the user uploads it, and then use this to know if the user already has this image (maybe send the hash as an Etag?) I have found this answer and this answer that explain the logic pretty well, but I have 2 questions: Is it possible to send an Etag in Google App Engine? Has anyone implemented such logic, and/or is there any code snippet available?

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• Is it possible to have an out-of-process COM server where a separate O/S process is used for each ob

  - by Tom Williams

  I have a legacy C++ "solution engine" that I have already wrapped as an in-process COM object for use by client applications that only require a single "solution engine". However I now have a client application that requires multiple "solution engines". Unfortunately the underlying legacy code has enough global data, singletons and threading horrors that given available resources it isn't possible to have multiple instances of it in-process simultaneously. What I am hoping is that some kind soul can tell me of some COM magic where with the flip of a couple of registry settings it is possible to have a separate out-of-process COM server (separate operating system process) for each instance of the COM object requested. Am I in luck?

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• How to leverage Spring Integration in a real-world JMS distributed architecture?

  - by ngeek

  For the following scenario I am looking for your advices and tips on best practices: In a distributed (mainly Java-based) system with: many (different) client applications (web-app, command-line tools, REST API) a central JMS message broker (currently in favor of using ActiveMQ) multiple stand-alone processing nodes (running on multiple remote machines, computing expensive operations of different types as specified by the JMS message payload) How would one best apply the JMS support provided by the Spring Integration framework to decouple the clients from the worker nodes? When reading through the reference documentation and some very first experiments it looks like the configuration of an JMS inbound adapter inherently require to use a subscriber, which in a decoupled scenario does not exist. Small side note: communication should happen via JMS text messages (using a JSON data structure for future extensibility).

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• Retrieve the CAKeyframeAnimationKey's key in AnimationDidStop

  - by JacktheSparrow

  I have multiple CAKeyframeAnimation objects, each with a unique key like the following: ..... [myAnimation setValues:images]; [myAnimation setDuration:1]; .... [myLayer addAnimation:myAnimation forKey:@"unique key"]; My question is, if I have multiple animation like this and each with a unique key, how do I retrieve their keys in the method AnimationDidStop? I want to be able to do something like this: -(void)animationDidStop:(CAAnimation*)animation finished:(BOOL)flag{ if(..... ==@"uniquekey1"){ //code to handle this specific animation here: }else if(.... ==@"uiquekey2"){ //code to handle this specific animation here: } }

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• communication between two JVMs without RMI?

  - by JavaUser

  Hi, How can two/multiple JVMs running in a same machine communicate without RMI?. Thx

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• Network access lags for Win7 when server network utilization is high

  - by Jeff Miles

  We have a Dell PE2950 file server running Windows 2008, hosting a DFS namespace of ~1.2 TB. This server has two Broadcom 1Gbps NICs teamed together. When there is high traffic going to the server across the network (greater than 200 Mbps), any Windows 7 client accessing a DFS share at the time experiences severe performance problems. For example: Computer A has an AutoCAD drawing opened directly from the DFS share. Performance is normal, not causing any issues. Computer B begins a file transfer, putting a 11GB file onto a different DFS namespace, on the same server Computer A immediately notices lag while using AutoCAD. The cursor momentarily freezes within AutoCAD every 10 seconds or so, and any browsing of the DFS share is extremely slow. Computer B completes file transfer, and performance resumes to normal for Computer A. This is only affecting Windows 7 clients, using a variety of hardware (desktop + laptop). All of our Windows XP clients see no performance impact during the file transfer. Things I have tried with no change: Had Computer A work from an entirely different RAID array from the file transfer destination Updated NIC drivers on clients and server Enabled TCP offload and receive side scaling on the server NIC (previously disabled when the issue began) Antivirus disabled during file transfer I am currently having a user test applications other than AutoCAD when the file transfer occurs, and will update the question with that result. Does anyone have any recommendations for resolution or additional troubleshooting steps?

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• How sophisticated should be DAL?

  - by Andrew Florko

  Basically, DAL (Data Access Layer) should provide simple CRUD (Create/Read/Update/Delete) methods but I always have a temptation to create more sophisticated methods in order to minimize database access roundtrips from Business Logic Layer. What do you think about following extensions to CRUD (most of them are OK I suppose): Read: GetById, GetByName, GetPaged, GetByFilter... e.t.c. methods Create: GetOrCreate methods (model entity is returned from DB or created if not found and returned), Create(lots-of-relations) instead of Create and multiple AssignTo methods calls Update: Merge methods (entities list are updated, created and deleted in one call) Delete: Delete(bool children) - optional children delete, Cleanup methods Where do you usually implement Entity Cache capabilities? DAL or BLL? (My choice is BLL, but I have seen DAL implementations also) Where is the boundary when you decide: this operation is too specific so I should implement it in Business Logic Layer as DAL multiple calls? I often found insufficient BLL operations that were implemented in dozen database roundtrips because developer was afraid to create a bit more sophisticated DAL. Thank you in advance!

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• 10GE network: Is it still deadly expensive? Any options?

  - by BarsMonster

  Hi! I am building home cluster where I going to have about 16 nodes which can live with 1G ports, but I really want to have 10GE on file server & central node. It's all local, so no need for cabels longer than 3-5m. And ofcourse I want to spend as little money as possible (not going to spend more than whole cluster costs) :-) What are my options? 1) Legacy solution is to take some 24-48 port 1GE switch, and connect to file/central nodes via 4-8 aggregated links. This will work I guess, cost is very acceptable, but I am not sure if it's ok to use that much aggregated links. And ofcourse it would be hard to double bandwidth when needed... :-D 2) Switch with several 10GE uplink 'ports'. As far as I see, they all require modules which costs about 1000$, so I will need 4 10G modules, and 2 10GE cards... Smells like way more than 5000$+... 3) Connect file & central node via 2 10G cards directly, and put 4 quadport 1GE NICs on fileserver. I am saving on 2 10G modules and a switch, fileserver will have to do packet routing, but it's still gonna have alot of CPU's left :-) 4) Any other options? Infiniband? 5) Are MyriNet adaptors works fine? I guess there are no cheaper options? 6) Hmm... Scrap fileserver, put it all on central node and provide dedicated 1GE port for each of the nodes... This is sad...

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• Adding subnet to a vsphere with single vcenter and esxi host

  - by Ilya Rakhlin

  Let me start of by saying that I do not specialize in networking, I am in the process of adding additional VMs to a testing environment and wanted some recommendations. In this case I am running a single ESXI 5.1 host and a single Vcenter management server. The problem is, I need another range of IP addresses added to the existing setup; hopefully without reconfiguring everything. Currently the esxi host is configured to IP: 192.168.100.200, gateway: 192.168.100.1 and subnet: 255.255.255.0. All of the VMs are running some version of linux with hard coded IP addresses in that range, and using that subnet. The VMs I am about to deploy I want to be on the 192.168.101.X network. Is it possible to add an additional subnet to this existing system that will also communicate with the current subnet? The esxi host has 6 physical NICs but only one connected as it is only a testing system; not sure if that matters. Are there any other ways to accomplish this hopefully without restarting or at least reconfiguring the IP addresses for each VM? Reason: Due to the configuration of the VMs to run the applications that we need I am using a large amount of the current IPs in the potential range (mostly VIPs). I will be setting up a new version of this “environment” while keeping the old one, thus potentially running out of IP addresses.

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• How to place a virtual machine in DMZ?

  - by Giordano

  I have an Ubuntu 12.04 server running few virtual machines with KVM. I would like to expose some of these virtual machines on the internet, to make it possible for customers to test the products we're developing and make available other products for demo purposes. One of the server NICs is configured with a public IP. However before exposing anything on the web I would like to be sure that if one of the virtual machines get compromised, the attacker doesn't reach the rest of the hosts. What I would like to do is to put these virtual machines into a DMZ. These are the steps I'm planning to do: Create a tap interface in the virtualization host (let's say tap1) Create a bridge using tap1 and give it an IP in a subnet separate from the other hosts. Let's say 10.0.0.1 Attach the DMZ virtual machines to the bridge and configure their IP statically (10.0.0.2, 10.0.0.3, etc...) Using UFW, forbid any traffic from 10.0.0.0/24 to any of the internal hosts, allow the traffic from the internal hosts towards 10.0.0.0/24 and expose the virtual machines on the web using port forwarding. Do you think this setup is safe? Can you suggest any improvement or a better/safer approach? Thanks in advance!

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• Safe HttpContext.Current.Cache Usage

  - by Burak SARICA

  Hello there, I use Cache in a web service method like this : var pblDataList = (List<blabla>)HttpContext.Current.Cache.Get("pblDataList"); if (pblDataList == null) { var PBLData = dc.ExecuteQuery<blabla>( @"SELECT blabla"); pblDataList = PBLData.ToList(); HttpContext.Current.Cache.Add("pblDataList", pblDataList, null, DateTime.Now.Add(new TimeSpan(0, 0, 15)), Cache.NoSlidingExpiration, CacheItemPriority.Normal, null); } I wonder is it thread safe? I mean the method is called by multiple requesters And more then one requester may hit the second line at the same time while the cache is empty. So all of these requesters will retrieve the data and add to cache. The query takes 5-8 seconds. May a surrounding lock statement around this code prevent that action? (I know multiple queries will not cause error but i want to be sure running just one query.)

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• Are concurrency issues possible when using the WCF Service Behavoir attribute set to ConcurrencyMode

  - by Brandon Linton

  We have a WCF service that makes a good deal of transactional NHibernate calls. Occasionally we were seeing SQL timeouts, even though the calls were updating different rows and the tables were set to row level locking. After digging into the logs, it looks like different threads were entering the same point in the code (our transaction using block), and an update was hanging on commit. It didn't make sense, though, because we believed that the following service class attribute was forcing a unique execution thread per service call: [ServiceBehavior(ConcurrencyMode = ConcurrencyMode.Multiple, InstanceContextMode = InstanceContextMode.PerCall)] We recently changed the concurrency mode to ConcurrencyMode.Single and haven't yet run into any issues, but the bug was very difficult to reproduce (if anyone has any thoughts on flushing a bug like that out, let me know!). Anyway, that all brings me to my question: shouldn't an InstanceContextMode of PerCall enforce thread-safety within the service, even if the ConcurrencyMode is set to multiple? How would it be possible for two calls to be serviced by the same service instance? Thanks!

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• How to route broadcast packets from machine with two network interfaces on same subnet

  - by Syam

  I run RHEL 5 and have two NICs on one machine connected to the same subnet: eth0 192.168.100.10 eth1 192.168.100.11 My application needs to receive and transmit UDP packets (both unicast & broadcast) via these interfaces. I've found the way to handle the ARP problem and I've added routes to handle the routing problem: ip rule add from 192.168.100.10 lookup 10 ip route add table 10 default src 192.168.100.10 dev eth0 (and similarly, table 11 for eth1) The problem is that only unicast packets gets routed properly. Broadcast packets always go out through eth0. I tried removing the rule for 192.168.100.0 & 192.168.100.255 from table 255 and adding them to my tables. But then I see ARP requests being given out for packets to 192.168.100.255 (obviously, no nodes respond and nobody gets any data). Due to several techno-political issues, I'm stuck with this configuration and can't change subnets or try something different. I've tried SO_BINDTODEVICE and it works, but I'd prefer a solution that doesn't need my application to run as root. Is there a way to get this working? Any help is highly appreciated.

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• Dealing w/ Sqlite Join results in a cursor

  - by Bill

  I have a one-many relationship in my local Sqlite db. Pretty basic stuff. When I do my left outer join I get back results that look like this: the resulting cursor has multiple rows that look like this: A1.id | A1.column1 | A1.column2 | B1.a_id_fk | B1.column1 | B1.column2 A1.id | A1.column1 | A1.column2 | B2.a_id_fk | B2.column1 | B2.column2 and so on... Is there a standard practice or method of dealing with results like this ? Clearly there is only A1, but it has many B-n relationships. I am coming close to using multiple queries instead of the "relational db way". Hopefully I am just not aware of the better way to do things. I intend to expose this query via a content provider and I would hate for all of the consumers to have to write the same aggregation logic.

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• restful way for deleting a bunch of items

  - by keisimone

  In wiki article for REST it is indicated that if you use http://example.com/resources DELETE, that means you are deleting the entire collection. If you use http://example.com/resources/7HOU57Y DELETE, that means you are deleting that element. I am doing a WEBSITE, note NOT WEB SERVICE. I have a list that has 1 checkbox for each item on the list. Once i select multiple items for deletion, i will allow users to press a button called DELETE SELECTION. If user presses the button, a js dialog box will popup asking user to confirm the deletion. if user confirms, all the items are deleted. So how should i cater for deleting multiple items in a RESTFUL way? NOTE, currently for DELETE in a webpage, what i do is i use FORM tag with POST as action but include a _method with the value DELETE since this is what was indicated by others in SO on how to do RESTful delete for webpage.

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• Proxmox drbd configuration split brain [on hold]

  - by AudioDan

  I am planning a proxmox HA configuration with two Dell R710 machines (dual 6 core processors in each) with enterprise level drive raid arrays. I would be using DRBD with a quorum disk on a third machine. I would dedicate two 1GB nics on each server to the DRBD communications. We would have approximately 12 to 14 Virtual Machines running on this pair of servers. The proxmox manual recommends creating two DRBD resources - one for the Virtual Machines that normally run on ServerA and one for the Virtual Machines that normally run on ServerB. This is because of the Primary/Primary state in which this configuration runs. If both servers have VMs talking to the same DRBD resource and a split brain situation occurs, there is potential for data corruption that must be resolved. While I understand it would take more effort to create new virtual machines, can anybody foresee any potential problems with running a separate DRBD resource for each VM instead? Does anyone have experience running a setup that way and has it worked well? It seems to me that would allow more flexibility in moving machines back and forth.

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• Linking Excel and Access

  - by Mel

  I run a sports program where i have a master roll of who is in which class in excel. I want to link this to a database in access that stores the other information about each athlete, e.g. address, parents name, school, medical details. I want to be able to add names to class in the excel speadsheet and have this automatically generate a record for that person in access. There also needs to be some failsafe for athletes that are in multiple classes. I was also doing class roles as pivot tables out of the access database so i need to code for classes and also have this allow for athletes in multiple classes/disciplines.

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• Using Entity Framework, how do I specify a sort on a navagation property?

  - by Jared

  I have two tables: [Category], [Item]. They are connected by a join table: [CategoryAndItem]. It has two primary key fields: [CategoryKey], [ItemKey]. Foreign keys exist appropriately and Entity has no problem pulling this in and creating the correct navigation properties that connect the entity objects. Basically each category can have multiple items, and items can be in multiple categories. The problem is that the order of items is specified per category, so that a particular item might be third in one category but fifth in another. In the past, I have added a [Sequence] field to the join table and modified the stored procedure to handle it. But since Entity is replacing my stored procedures, I need to figure out how to make Entity handle the sequence. Any suggestions?

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• How to deal with many to many relationships with NSFetchedResultsController?

  - by Phil Yates

  OK so I have two entities in my data model (let's say entityA and entityB), both of these entities have a to-many relationship to each other. I have setup a NSFetchedResultsController to fetch a bunch of entityA. Now I'm trying to have the section names for the tableview be the title of entityB. sectionNameKeyPath:@"entityB.title" Now this causes a problem, where by the section name returned from that relationship appears to be ({title1}) or ({title1,title2...titleN}) obviously depending on how many different entityB's are involved. This doesn't look great in a tableview and doesn't group the objects as I would like. What I would like is a section per entityB title with entityA appearing under each section, under multiple sections if necessary. I'm at a loss as how I am supposed to achieve this whether I need to update the predicate to get the entity to appear multiple times or whether I need to update the section and header functions to do some processing as the controller loops through the objects. Any help is appreciated :) Thanks

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• google docs + web app

  - by King

  Hi Guys I am trying to create a web app to share docs with all editor features (just like google docs). My main requirements for this app are as follows: 1. Should have all editor features (can be done using open office api, google docs api, Microsoft office web apps api) 2. Should be shared between multiple users and can be edited by multiple users and other sync features (can be done using google docs api, Microsoft office web apps) 3. Can save the document created and edited on my own/ custom server addr. (Which api can support this??? I know open office can support this) Guys can you please suggest me one api which can be used to do all the above. Also please suggest if I am underestimating any API above regarding any functionality that i thing is not supported. Thanks King

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• Virtualize SBS 2003 - P2V vs migrating to new VM

  - by jlehtinen

  I need to virtualize a SBS 2003 server in my work environment. I need some tips on what people think is the best way to proceed. Background: The SBS 2003 server is the primary DC for the domain and also hosts FTP, RRAS(VPN), DNS, and file shares. Exchange is NOT used, neither is SQL server. DHCP is done via a firewall appliance. I have added a Server 2003 VM to the domain and promoted it to the DC role. AD/DNS is replicating here correctly. This was mainly done to provide fault-tolerance to the domain, I was not intending to make this VM the primary DC. I've already asked about buying upgraded licensing for Server 2008/2012 but was refused due to cost. Options: I see (at least) two routes I could take to complete this. From what I've read option 2 is the "preferred" method, but there's a few steps where I'm not clear on what to expect. Option 1.) P2V the primary DC Power off primary DC Power off secondary DC (to prevent USN rollback in case P2V has issue) P2V (cold clone) primary DC Boot new PDC VM Allow new hardware to detect Remove old NIC hardware from device manager Assign old IPs to new virtual NICs Reboot PDC VM, confirm connectivity and no major issues Power on secondary DC, confirm replication Option 2.) Create new VM, transfer roles, remove original DC from domain Create new VM, install SBS 2003 Do I need the original SBS install discs for this? MS migration doc mentions this. Add VM to domain, promote to DC role Does this start 7 day timer where two SBS servers can be in same domain? Set up RRAS on new VM Set up IIS/FTP on new VM Move file shares to new VM Transfer FSMO roles to new VM DC dcpromo original primary DC out of domain

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• Database storage for high sample rate data in web app

  - by Jim

  I've got multiple sensors feeding data to my web app. Each channel is 5 samples per second and the data gets uploaded bundled together in 1 minute json messages (containing 300 samples). The data will be graphed using flot at multiple zoom levels from 1 day to 1 minute. I'm using Amazon SimpleDB and I'm currently storing the data in the 1 minute chunks that I receive it in. This works well for high zoom levels, but for full days there will be simply be too many rows to retrieve. The idea I've currently got is that every hour I can crawl through the data and collect together 300 samples for the last hour and store them in an hour Domain (table if you like). Does this sound like a reasonable solution? How have others implemented the same sort of systems?

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