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  • Distributed website server redundancy

    - by Keith Lion
    Assume a website infrastructure is very complicated and is fully distributed (probably like most large web companies). Am I right in thinking that although there are all these extra web servers to handle multiple client requests, there is still a single "machine" whereby users must enter? I am guessing this machine will be the one physically associated to the IP address? I ask because I need to know whether, in places where distributed systems exist, there is still a single point of failure- usually the control node or, in this example, the machine connected to the public internet? Surely there cannot be two machines connected to the internet, as they would have to have different IP addresses? This "machine" may not be a server per se, but maybe it is a piece of cisco equipment. I just need to know whether, in the real world, these distributed systems still have a particular section where they depend on the integrity of one electronic device?

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  • web.config caching differences

    - by Ivanhoe123
    What are the differences between these two approaches of caching (set up through web.config file)? <caching> <profiles> <add extension=".php" policy="DisableCache" kernelCachePolicy="DisableCache" /> <add extension=".html" policy="CacheForTimePeriod" kernelCachePolicy="CacheForTimePeriod" duration="7:00:00" /> </profiles> </caching> and: <staticContent> <clientCache cacheControlMode="UseMaxAge" cacheControlMaxAge="7.00:00:00" /> </staticContent> If the first one has img/css/js extensions added, would both work the same way? Thank you!

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  • What are the functionalities of Distributed File systems and Distributed Storage Systems?

    - by Berkay
    i'm reading cloud vendors solutions for the distributed storage systems such as Amazon Dynamo and Google Big Table. and really confused in two terms : what is Distrubuted file systems for in cloud ? what is Distributed storage systems for? what are differences of these terms and functionalities ? if i understand these terms i will create the general architecture of the cloud vendors, any good tutorial or web page will be appreciated. Thanks

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  • Caching Profiles web.config vs IIS

    - by Lieven Cardoen
    What is the difference between configuring a Caching Profile in Web.Config and configuring it in IIS? If you have this in Web.Config <caching> <outputCache enableOutputCache="true" /> <outputCacheSettings> <outputCacheProfiles> <add duration="14800" enabled="true" varyByParam="*" name="AssetCacheProfile" /> </outputCacheProfiles> </outputCacheSettings> </caching> And nothing configured in IIS in the Output Caching, will it work? And what if you add all the extensions I use in Output Caching in IIS, what does that change? It's a aspx page RetrieveBlob.aspx that uses this Caching Profile: <%@ OutputCache CacheProfile="AssetCacheProfile" %> <%@ Page Language="C#" AutoEventWireup="true" CodeFile="RetrieveBlob.aspx.cs" Inherits="RetrieveBlob" %>

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  • WCF Caching Solution - Need Advice

    - by Brandon
    The company I work for is looking to implement a caching solution. We have several WCF Web Services hosted and we need to cache certain values that can be persisted and fetched regardless of a client's session to a service. I am looking at the following technologies: Caching Application Block 4.1 WCF TCP Service using HttpRuntime Caching Memcached Win32 and Client Microsoft AppFabric Caching Beta 2 Our test server is a Windows Server 2003 with IIS6, but our production server is Windows Server 2008, so any of the above options would work (except for AppFabric Caching on our test server). Does anyone have any experience with any of these? This caching solution will not be used to store a lot of data, but it will need to be fetched from frequently and fast. Thanks in advance.

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  • Extending ASP.NET Output Caching

    One of the most sure-fire ways to improve a web application's performance is to employ caching. Caching takes some expensive operation and stores its results in a quickly accessible location. Since it's inception, ASP.NET has offered two flavors of caching:<ul><li><b>Output Caching</b> - caches the entire rendered markup of an ASP.NET page or <a href="http://www.asp101.com/lessons/usercontrols.asp">User Control</a> for a specified duration.</li><li><b>Data Caching</b> - a API for caching objects. Using the data cache you can write code to add, remove, and retrieve items from the cache.</li></ul>Until recently, the underlying functionality of these two caching mechanisms was fixed - both cached data

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  • Distributed Database Services?

    - by Cameron
    I'm working on a database-driven web service with clients in the US and Australia. We're currently hosted in the US, however our Australian clients are experiencing lag. The lag is primarily due to the fact that the pages launch AJAX queries which require some db work to be done on our database in the US and these take a while to perform a round trip. Ideally, we're looking for some kind of distributed database system which replicates our main US database in Australia (and possibly other locations if we choose to expand later on). Does anyone have any suggestions for services which offer something like this? Something like a CDN (CacheFly etc), which is web-based, simple to set up etc but for databases instead of static files. Ideally it would be completely transparent to the application and abstract away all the distributed database management, syncs etc.

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  • Distributed file systems

    - by Neeraj
    I need to implement a distributed storage system for a set of nodes(devices) connected in a mesh network. So what basically my design goals are: The storage system should be capable of handling dynamic entry and exit of nodes. Replication (for fault tolerance). For this i am thinking of using a Distributed file system. Every node could access data in the other nodes in a transparent manner. Are there some simple, easily pluggable opensource implementations? Thanks for your thoughts!

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  • Distributed filesystem for automated offline data mirroring

    - by Petr Pudlák
    I'd like to achieve the following setup: Every time I connect my laptop to a local network, my partition gets automatically mirrored to a partition on my local server. I only want to mirror what has changed from the last time. (I understand that it is not a proper backup solution since there is no history of the changes, it'd be more like a non-persistent network RAID.) Is there a distributed file system that allows such a setup? I've done some searching and it seems to me that most distributed file-systems are focused on data availability and distribution, not duplicating them. I'd be thankful for suggestions. Edit: Sorry, I forgot to mention: I'm using Linux.

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  • Client side caching in GWT

    - by Silfverstrom
    We have a gwt-client, which recieves quite a lot of data from our servers. Logically, i want to cache the data on the client side, sparing the server from unnecessary requests. As of today i have let it up to my models to handle the caching of data, which doesn't scale very well. It's also become a problem since different developers in our team develop their own "caching" functionality, which floods the project with duplications. I'm thinking about how one could implement a "single point of entry", that handles all the caching, leaving the models clueless about how the caching is handled. Does anyone have any experience with client side caching in GWT? Is there a standard approach that can be implemented?

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  • Rails 3 functional optionally testing caching

    - by Stephan
    Generally, I want my functional tests to not perform action caching. Rails seems to be on my side, defaulting to config.action_controller.perform_caching = false in environment/test.rb. This leads to normal functional tests not testing the caching. So how do I test caching in Rails 3. The solutions proposed in this thread seem rather hacky or taylored towards Rails 2: How to enable page caching in a functional test in rails? I want to do something like: test "caching of index method" do with_caching do get :index assert_template 'index' get :index assert_template '' end end Maybe there is also a better way of testing that the cache was hit?

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  • ideas for a distributed cache proxy server

    - by Neeraj
    Hi everyone! I am implementing, a distributed cache proxy server.I have an idea of the HTTP and related stuff, so i am rather concentrating on the sub part "Distributed data storage". From some search on web i found that this could be done using Distributed Hash Tables(DHT). I was wondering if there exists some kind of library for this preferably in C/C++. Any better suggestions for the same will also be appreciated.

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  • VLC Caching levels

    - by Svish
    When I open the Preferences of VLC and go to Input & Codecs, I have a setting called Default Caching Level. I can choose between Cusom Lowest latency Low latency Normal High latency Higher latency I'm used to caching being set in seconds or something like that. So, more seconds/higher buffer means less chane of buffer underrun while streaming. What is latency? What does it mean to set it lower or higher? In what cases should I go in what direction? If I'm struggling with buffer underruns, should I set it to lower or higher latency?

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  • Fast distributed filesystem for a large amounts of data with metadata in database

    - by undefined hero
    My project uses several processing machines and one storage machine. Currently storage organized with a MSSQL filetable shared folder. Every file in storage have some metadata in database. Processing machines executes tasks for which they needed files from storage and their metadata. After completing task, processing machine puts resulting data back in storage. From there its taken by another processing machine, which also generates some file and put it back in storage. And etc. Everything was fine, but as number of processing machines increases, I found myself bottlenecked myself with storage machines hard drive performance. So I want processing machines to put files in distributed FS. to lift load from storage machines, from which they can take data from each other, not only storage machine. Can You suggest a particular distributed FS which meets my needs? Or there is another way to solve this problem, without it? Amounts of data in FS in one time are like several terabytes. (storage can handle this, but processors cannot). Data consistence is critical. Read write policy is: once file is written - its constant and may be only removed, but not modified. My current platform is Windows, but I'm ready to switch it, if there is a substantially more convenient solution on another one.

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  • Implementing Model-level caching

    - by Byron
    I was posting some comments in a related question about MVC caching and some questions about actual implementation came up. How does one implement a Model-level cache that works transparently without the developer needing to manually cache, yet still remains efficient? I would keep my caching responsibilities firmly within the model. It is none of the controller's or view's business where the model is getting data. All they care about is that when data is requested, data is provided - this is how the MVC paradigm is supposed to work. (Source: Post by Jarrod) The reason I am skeptical is because caching should usually not be done unless there is a real need, and shouldn't be done for things like search results. So somehow the Model itself has to know whether or not the SELECT statement being issued to it worthy of being cached. Wouldn't the Model have to be astronomically smart, and/or store statistics of what is being most often queried over a long period of time in order to accurately make a decision? And wouldn't the overhead of all this make the caching useless anyway? Also, how would you uniquely identify a query from another query (or more accurately, a resultset from another resultset)? What about if you're using prepared statements, with only the parameters changing according to user input? Another poster said this: I would suggest using the md5 hash of your query combined with a serialized version of your input arguments. This would require twice the number of serialization options. I was under the impression that serialization was quite expensive, and for large inputs this might be even worse than just re-querying. And is the minuscule chance of collision worth worrying about? Conceptually, caching in the Model seems like a good idea to me, but it seems in practicality the developer should have direct control over caching and write it into the controller. Thoughts/ideas? Edit: I'm using PHP and MySQL if that helps to narrow your focus.

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  • Rails' page caching vs. HTTP reverse proxy caches

    - by John Topley
    I've been catching up with the Scaling Rails screencasts. In episode 11 which covers advanced HTTP caching (using reverse proxy caches such as Varnish and Squid etc.), they recommend only considering using a reverse proxy cache once you've already exhausted the possibilities of page, action and fragment caching within your Rails application (as well as memcached etc. but that's not relevant to this question). What I can't quite understand is how using an HTTP reverse proxy cache can provide a performance boost for an application that already uses page caching. To simplify matters, let's assume that I'm talking about a single host here. This is my understanding of how both techniques work (maybe I'm wrong): With page caching the Rails process is hit initially and then generates a static HTML file that is served directly by the Web server for subsequent requests, for as long as the cache for that request is valid. If the cache has expired then Rails is hit again and the static file is regenerated with the updated content ready for the next request With an HTTP reverse proxy cache the Rails process is hit when the proxy needs to determine whether the content is stale or not. This is done using various HTTP headers such as ETag, Last-Modified etc. If the content is fresh then Rails responds to the proxy with an HTTP 304 Not Modified and the proxy serves its cached content to the browser, or even better, responds with its own HTTP 304. If the content is stale then Rails serves the updated content to the proxy which caches it and then serves it to the browser If my understanding is correct, then doesn't page caching result in less hits to the Rails process? There isn't all that back and forth to determine if the content is stale, meaning better performance than reverse proxy caching. Why might you use both techniques in conjunction?

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  • Serving and caching content from Amazon S3 with Tomcat

    - by Rob
    Hi all, We're looking to serve a range of content using Amazon S3 as a store for the content and Tomcat to host the web application. The content is divided into free and paid for content. We intend to authenticate the users when they access the web application running in Tomcat. Based around their authentication we are able to tell if the user has access to paid for content or simply free stuff. So I envision the flow of a request being something like this: Authenticated request to Tomcat If user is "paid" user, display links to premium content Direct requests for paid content back through Tomcat to prevent direct access to it by non-paying users. Tomcat makes request to S3 through a web cache to keep our costs down Content is returned to user. As we have to pay for each request to S3, I'd ideally like to cache content locally to the Tomcat instance after it has been requested for the first time to keep costs to a minimum and to speed things up. I would also like to be able to invalidate this cache if we publish fresh content to S3. So to confirm my proposal: Client Request - Tomcat - Web Cache - S3 To invalidate the cache, I was thinking of using something like PubSubHubbub with the cache waiting for updates to the feed for content that it should invalidate. I'd appreciate some general feedback on this approach as I've no real experience of caching and I'm sure I've made some invalid assumptions. I'd also appreciate any recommendations for caching technologies. Thanks.

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  • For distributed applications, which to use, ASIO vs. MPI?

    - by Rhubarb
    I am a bit confused about this. If you're building a distributed application, which in some cases may perform parallel operations (although not necessarily mathematical), should you use ASIO or something like MPI? I take it MPI is a higher level than ASIO, but it's not clear where in the stack one would begin.

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  • Unusual Apache->Tomcat caching issue.

    - by iftrue
    Right now, I have an Apache setup sitting in front of Tomcat to handle caching. This setup has been given to an external service to manage, and since the transition, I've noticed odd behavior. Specifically, when I request a swf file from the web server, I hit the Apache cache (good), but occasionally I'll receive a truncated file. Once I receive this truncated file, the cache will NOT refresh until I manually delete the cache and let the swf pull down from tomcat again. The external service claims that the configuration is fine, but I don't see any way this could be happening aside from improper configuration. Now, there are two apache and two tomcat servers under a load balancer, and occasionally one apache cache will break while another does not (leading to 50% of all requests getting bad, truncated data). Where should I start looking to debug this issue? What could POSSIBLY be causing this odd behavior? Edit: Inspecting the logs, tomcat throws this: java.io.IOException: Bad file number at java.io.FileInputStream.readBytes(Native Method) at java.io.FileInputStream.read(FileInputStream.java:199) at java.io.BufferedInputStream.read1(BufferedInputStream.java:256) at java.io.BufferedInputStream.read(BufferedInputStream.java:317) at java.io.FilterInputStream.read(FilterInputStream.java:90) at org.apache.catalina.servlets.DefaultServlet.copyRange(DefaultServlet.java:1968) at org.apache.catalina.servlets.DefaultServlet.copy(DefaultServlet.java:1714) at org.apache.catalina.servlets.DefaultServlet.serveResource(DefaultServlet.java:809) at org.apache.catalina.servlets.DefaultServlet.doGet(DefaultServlet.java:325) at javax.servlet.http.HttpServlet.service(HttpServlet.java:690) at javax.servlet.http.HttpServlet.service(HttpServlet.java:803) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102) at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:568) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109) at org.apache.catalina.ha.session.JvmRouteBinderValve.invoke(JvmRouteBinderValve.java:209) at org.apache.catalina.ha.tcp.ReplicationValve.invoke(ReplicationValve.java:347) at org.terracotta.modules.tomcat.tomcat_5_5.SessionValve55.invoke(SessionValve55.java:57) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:286) at org.apache.jk.server.JkCoyoteHandler.invoke(JkCoyoteHandler.java:190) at org.apache.jk.common.HandlerRequest.invoke(HandlerRequest.java:283) at org.apache.jk.common.ChannelSocket.invoke(ChannelSocket.java:767) at org.apache.jk.common.ChannelSocket.processConnection(ChannelSocket.java:697) at org.apache.jk.common.ChannelSocket$SocketConnection.runIt(ChannelSocket.java:889) at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:690) at java.lang.Thread.run(Thread.java:619) followed by access_log.2009-12-14.txt:1.2.3.4 - - [14/Dec/2009:00:27:32 -0500] "GET /myApp/mySwf.swf HTTP/1.1" 304 - access_log.2009-12-14.txt:1.2.3.4 - - [14/Dec/2009:01:27:33 -0500] "GET /myApp/mySwf.swf HTTP/1.1" 304 - access_log.2009-12-14.txt:1.2.3.4 - - [14/Dec/2009:01:39:53 -0500] "GET /myApp/mySwf.swf HTTP/1.1" 304 - access_log.2009-12-14.txt:1.2.3.4 - - [14/Dec/2009:02:27:38 -0500] "GET /myApp/mySwf.swf HTTP/1.1" 304 - So apache is caching the bad file size. What could possibly be causing this, and possibly separate, how do I ensure that this exception does not get written to cache?

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  • HTTP caching headers: how should must-revalidate work?

    - by Bobby Jack
    Using trac, I'm getting a response with the following header: Cache-control: must-revalidate Moreover, no 'Expires' header is being sent. Our local proxy, however, is caching these responses, so when an edit is made, pages need to be 'hard refreshed' to update. Is the proxy misbehaving? Other headers that might be relevant: Connection Keep-Alive Proxy-Connection Keep-Alive Keep-Alive timeout=15, max=100

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  • How to enable caching on Apache / Ubuntu Linux?

    - by Jim Mischel
    I have a large (several megabytes) XML file that's updated rather frequently (every 10 minutes or less) and gets a lot of traffic. I'd like to implement some caching to reduce bandwidth and server load. Looking at the Apache documents, I see a dizzying array of configuration options that involve various combinations of mod_expires, mod_headers, and mod_cache (and variants). I end up running in circles and the results aren't what I expect. I'm comfortable editing the various configuration files if I have some idea what I'm supposed to change. But at the moment I'm poking around in the dark and that's never a comfortable feeling. So, perhaps if I describe what I want, somebody here can take me by the hand and say, "This is what you need to do." Periodically, this file, call it "stuff.xml" is updated and a new version copied to the directory. The external url would be, for example, http://example.com/stuff.xml. Understand, this part works. Whenever I request the file, I get the expected result. But the file is big and I want to save bandwidth, so first I'd like to implement conditional GET semantics with the If-Modified-Since header. How do I do this? I've enabled mod_headers and mod_expired and added the <FilesMatching> section in my httpd.conf as recommended in countless examples I've seen online, but that didn't change the behavior when made a conditional GET request. I always get a status 200 with the entire document. So how the heck do I implement this? That'll cut down on neeless transfers. I'd also like to limit the amount of data transferred. Seeing as this is XML, gzipping it should save me 50% or more. My next step would be to somehow gzip the file and, if it's not too difficult, store it in memory. That'll cut down on per-access data transfer, and also reduce disk transfers. So how do I implement this type of caching? Thanks in advance.

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  • Browser caching is generating hugo I/O to server

    - by Rime
    Our users My Documents are stored on a Emc NAS. I have noticed huge traffic coming from users and I see that most of it is coming to cache directories of Internet Explorer and other browsers. One thing i suspect is Adobe Flash caching streams. We have various Windows clients and no restrictions on browsers. Is there any way to remove this traffic from our NAS by a group policy or whatever? Thanks Rime

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