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• JavaScript distributed computing project

  - by Ben L.

  I made a website that does absolutely nothing, and I've proven to myself that people like to stay there - I've already logged 11+ hours worth of cumulative time on the page. My question is whether it would be possible (or practical) to use the website as a distributed computing site. My first impulse was to find out if there were any JavaScript distributed computing projects already active, so that I could put a piece of code on the page and be done. Unfortunately, all I could find was a big list of websites that thought it might be a cool idea. I'm thinking that I might want to start with something like integer factorization - in this case, RSA numbers. It would be easy for the server to check if an answer was correct (simply test for modulus equals zero), and also easy to implement. Is my idea feasible? Is there already a project out there that I can use?

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• Ceph: open-source petabyte scale distributed storage

  - by Gregory Burd

  You might want to read this interesting research paper titled "Object Storage on Berkeley DB". The Ceph project is a distributed network file system designed to provide excellent performance, reliability, and scalability... and it uses Oracle Berkeley DB for storage.

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• Enabling Http caching and compression in IIS 7 for asp.net websites

  - by anil.kasalanati

  Caching – There are 2 ways to set Http caching 1-      Use Max age property 2-      Expires header. Doing the changes via IIS Console – 1.       Select the website for which you want to enable caching and then select Http Responses in the features tab       2.       Select the Expires webcontent and on changing the After setting you can generate the max age property for the cache control    3.       Following is the screenshot of the headers   Then you can use some tool like fiddler and see 302 response coming from the server. Doing it web.config way – We can add static content section in the system.webserver section <system.webServer>   <staticContent>             <clientCache cacheControlMode="UseMaxAge" cacheControlMaxAge="365.00:00:00" />   </staticContent> Compression - By default static compression is enabled on IIS 7.0 but the only thing which falls under that category is CSS but this is not enough for most of the websites using lots of javascript.  If you just thought by enabling dynamic compression would fix this then you are wrong so please follow following steps –   In some machines the dynamic compression is not enabled and following are the steps to enable it – Open server manager Roles > Web Server (IIS) Role Services (scroll down) > Add Role Services Add desired role (Web Server > Performance > Dynamic Content Compression) Next, Install, Wait…Done!   ?  Roles > Web Server (IIS) ?  Role Services (scroll down) > Add Role Services     Add desired role (Web Server > Performance > Dynamic Content Compression)     Next, Install, Wait…Done!     Enable  - ?  Open server manager ?  Roles > Web Server (IIS) > Internet Information Services (IIS) Manager   Next pane: Sites > Default Web Site > Your Web Site Main pane: IIS > Compression         Then comes the custom configuration for encrypting javascript resources. The problem is that the compression in IIS 7 completely works on the mime types and by default there is a mismatch in the mime types Go to following location C:\Windows\System32\inetsrv\config Open applicationHost.config The mimemap is as follows  <mimeMap fileExtension=".js" mimeType="application/javascript" />   So the section in the staticTypes should be changed          <add mimeType="application/javascript" enabled="true" />     Doing the web.config way –   We can add following section in the system.webserver section <system.webServer> <urlCompression doDynamicCompression="false"  doStaticCompression="true"/> More Information/References – ·         http://weblogs.asp.net/owscott/archive/2009/02/22/iis-7-compression-good-bad-how-much.aspx ·         http://www.west-wind.com/weblog/posts/98538.aspx  

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• Disable eclipselink caching and query caching - not working?

  - by James

  I am using eclipselink JPA with a database which is also being updated externally to my application. For that reason there are tables I want to query every few seconds. I can't get this to work even when I try to disable the cache and query cache. For example: EntityManagerFactory entityManagerFactory = Persistence.createEntityManagerFactory("default"); EntityManager em = entityManagerFactory.createEntityManager(); MyLocation one = em.createNamedQuery("MyLocation.findMyLoc").getResultList().get(0); Thread.sleep(10000); MyLocation two = em.createNamedQuery("MyLocation.findMyLoc").getResultList().get(0); System.out.println(one.getCapacity() + " - " + two.getCapacity()); Even though the capacity changes while my application is sleeping the println always prints the same value for one and two. I have added the following to the persistence.xml <property name="eclipselink.cache.shared.default" value="false"/> <property name="eclipselink.query-results-cache" value="false"/> I must be missing something but am running out of ideas. James

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• hibernate distributed 2nd level cache options

  - by ishmeister

  Not really a question but I'm looking for comments/suggestions from anyone who has experiences using one or more of the following: EhCache with RMI EhCache with JGroups EhCache with Terracotta Gigaspaces Data Grid A bit of background: our applications is read only for the most part but there is some user data that is read-write and some that is only written (and can also be reasonably inaccurate). In addition, it would be nice to have tools that enable us to flush and fill the cache at intervals or by admin intervention. Regarding the first option - are there any concerns about the overhead of RMI and performance of Java serialization?

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• Scalable distributed file system for blobs like images and other documents

  - by Pinnacle

  Cassandra & HBase both do not efficiently support storage of blobs like images. Storing directly on HDFS stresses the Namenode because of huge number of files. Facebook uses Haystack for images and attachments storage, but this is not open source. So is Lustre a good choice for distributed blob storage? I have read that Amazon S3 is used by many, but this would cost money and personally, I would not like to rely on third party system. What are other suggestions?

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• Helper library for distributed algorithms programming?

  - by anon

  When you code a distributed algorithm, do you use any library to model abstract things like processor, register, message, link, etc.? Is there any library that does that? I'm thinking about e.g. self-stabilizing algorithms, like self-stabilizing minimum spanning-tree algorithms.

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• ASP:NET :Problem in DoNut Caching

  - by Shyju

  I have an ASP.NET page where i am trying to do some output caching.But ran into a problem. My ASPX page has <%@ Page Language="C#" AutoEventWireup="true" CodeBehind="Default.aspx.cs" Inherits="MYProject._Default" %> <%@ OutputCache Duration="600" VaryByParam="None" %> <%@ Register TagPrefix="MYProjectUC" TagName="PageHeader" Src="~/Lib/UserControls/PageHeader.ascx" %> <%@ Register TagPrefix="MYProjectUC" TagName="PageFooter" Src="~/Lib/UserControls/PageFooter.ascx" %> and i have used the User control called "PageHeader" in the aspx page. In PageHeader.ascx, i have an asp.net substitution control, where i want to show some links based on the logged in user. <%@ Control Language="C#" AutoEventWireup="true" CodeBehind="PageHeader.ascx.cs" Inherits="MyProject.Lib.UserControls.PageHeader1" %> <div class="headerRow"> <div class="headerLogo"> <a href="Default.aspx"><img src="Lib/Images/header.gif" alt=""></a> </div> <div id="divHeaderMenu" runat="server"> <asp:Substitution ID="subLinks" runat="server" MethodName="GetUserProfileHeaderLinks" /> </div> </div><!--headerRow--> In my ascx.cs file,i have a static method which will return a string based on whether the used logged in or not using session public static string GetUserProfileHeaderLinks(HttpContext context) { string strHeaderLinks = string.Empty; // check session and return string return strHeaderLinks; } But Still the page shows the same content for both logged in user and Guest user. My objective is to to have the Page being cached except the content inside the substitution control. Any idea how to achieve this ? Thanks in advance

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• Caching large amount of ajax returned objects

  - by ofcapl

  I'm building an application which fetches large amount of items with ajax requests via other application API. It returns me 6k - 30k js objects which are used multiple times across various application views (sorting, filtering etc.). I would like to avoid querying API every time for such big list so I decided to cache this data somehow. I was thinking about various solutions: saving it to localstorage, using some caching library (e.g. locachejs), storing in js var. I'm not an expert so I would like to hear Your suggestions about each (or one of these) solution, about its pros and cons. Every help will be very appreciated.

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• Syncing objects to a remote server, and caching on local storage

  - by Harry

  What's the best method of sycing objects (as JSON) to a remote server, with local caching? I have some objects that will pretty much just be plain-text with some extra meta-data. I was thinking of perhaps including a "last modified date" for both Local storage and Remote storage. This could then be used to determine which object is the most recent. For example, even though objects will be saved to both local and remote when they are saved, sometimes the user may not have internet access, or the server may be down, or any other number of things. In this case, the last modified date for remote storage would be reverted to its previous date. Local storage would remain as it is. At this point, the user could exit the application, and when they reload the application would then look at the last modified dates of the local and remote storages, and decide. Is there anything I'm missing with this? Is there a better method that I could use?

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• Distributed transactions

  - by javi

  Hello! I've a question regarding distributed transactions. Let's assume I have 3 transaction programs: Transaction A begin a=read(A) b=read(B) c=a+b write(C,c) commit Transaction B begin a=read(A) a=a+1 write(A,a) commit Transaction C begin c=read(C) c=c*2 write(A,c) commit So there are 5 pairs of critical operations: C2-A5, A2-B4, B4-C4, B2-C4, A2-C4. I should ensure integrity and confidentiality, do you have any idea of how to achieve it? Thank you in advance!

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• Memcached and Rails Fragment Caching Issue

  - by Michael Waxman

  When I have 2 views that fragment cache the same query BUT display them differently, there is only one fragment and they both display it the same way. Is there any way around this? For example... #views/posts/list - cache(@posts) do - for p in @posts = p.title #views/posts/list_with_images - cache(@posts) do - for p in @posts = p.title = p.content = image_tag(p.image_url) #controllers/posts_controller def list ... @posts = Post.all end def list_with_images ... @posts = Post.all end

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• IE7 not Caching CSS Image over SSL

  - by Alex

  Hello, I'm using the WebDevHelper toolbar for Internet Explorer to troubleshoot HTTP requests/roundtrips on my SSL site and noticed that IE re-downloads my CSS :hover images every time they are triggered. This causes a huge amount of roundtrips. How can I prevent this from happening? Edit: All static content is served with cache-control: public, so images, javascript etc. are cached in Firefox and Chrome. This problem is IE specific.

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• Rails page caching and flash messages

  - by KJF

  I'm pretty sure I can page cache the vast majority of my site but the one thing preventing me from doing so is that my flash messages will not show, or they'll show at the wrong time. One thing I'm considering is writing the flash message to a cookie, reading it and displaying it via javascript and clearing the cookie once the message has been displayed. Has anyone had any success doing this or are there better methods? Thanks.

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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: Output Caching - caches the entire rendered markup of an ASP.NET page or User Control for a specified duration.Data Caching - a API for caching objects. Using the data cache you can write code to add, remove, and retrieve items from the cache.Until recently, the underlying functionality of these two caching mechanisms was fixed - both cached data in the web server's memory. This has its drawbacks. In some cases, developers may want to save output cache content to disk. When using the data cache you may want to cache items to the cloud or to a distributed caching architecture like memcached. The good news is that with ASP.NET 4 and the .NET Framework 4, the output caching and data caching options are now much more extensible. Both caching features are now based upon the provider model, meaning that you can create your own output cache and data cache providers (or download and use a third-party or open source provider) and plug them into a new or existing ASP.NET 4 application. This article focuses on extending the output caching feature. We'll walk through how to create a custom output cache provider that caches a page or User Control's rendered output to disk (as opposed to memory) and then see how to plug the provider into an ASP.NET application. A complete working example, available in both VB and C#, is available for download at the end of this article. Read on to learn more! Read More >

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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: Output Caching - caches the entire rendered markup of an ASP.NET page or User Control for a specified duration.Data Caching - a API for caching objects. Using the data cache you can write code to add, remove, and retrieve items from the cache.Until recently, the underlying functionality of these two caching mechanisms was fixed - both cached data in the web server's memory. This has its drawbacks. In some cases, developers may want to save output cache content to disk. When using the data cache you may want to cache items to the cloud or to a distributed caching architecture like memcached. The good news is that with ASP.NET 4 and the .NET Framework 4, the output caching and data caching options are now much more extensible. Both caching features are now based upon the provider model, meaning that you can create your own output cache and data cache providers (or download and use a third-party or open source provider) and plug them into a new or existing ASP.NET 4 application. This article focuses on extending the output caching feature. We'll walk through how to create a custom output cache provider that caches a page or User Control's rendered output to disk (as opposed to memory) and then see how to plug the provider into an ASP.NET application. A complete working example, available in both VB and C#, is available for download at the end of this article. Read on to learn more! Read More >Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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• Caching factory design

  - by max

  I have a factory class XFactory that creates objects of class X. Instances of X are very large, so the main purpose of the factory is to cache them, as transparently to the client code as possible. Objects of class X are immutable, so the following code seems reasonable: # module xfactory.py import x class XFactory: _registry = {} def get_x(self, arg1, arg2, use_cache = True): if use_cache: hash_id = hash((arg1, arg2)) if hash_id in _registry: return _registry[hash_id] obj = x.X(arg1, arg2) _registry[hash_id] = obj return obj # module x.py class X: # ... Is it a good pattern? (I know it's not the actual Factory Pattern.) Is there anything I should change? Now, I find that sometimes I want to cache X objects to disk. I'll use pickle for that purpose, and store as values in the _registry the filenames of the pickled objects instead of references to the objects. Of course, _registry itself would have to be stored persistently (perhaps in a pickle file of its own, in a text file, in a database, or simply by giving pickle files the filenames that contain hash_id). Except now the validity of the cached object depends not only on the parameters passed to get_x(), but also on the version of the code that created these objects. Strictly speaking, even a memory-cached object could become invalid if someone modifies x.py or any of its dependencies, and reloads it while the program is running. So far I ignored this danger since it seems unlikely for my application. But I certainly cannot ignore it when my objects are cached to persistent storage. What can I do? I suppose I could make the hash_id more robust by calculating hash of a tuple that contains arguments arg1 and arg2, as well as the filename and last modified date for x.py and every module and data file that it (recursively) depends on. To help delete cache files that won't ever be useful again, I'd add to the _registry the unhashed representation of the modified dates for each record. But even this solution isn't 100% safe since theoretically someone might load a module dynamically, and I wouldn't know about it from statically analyzing the source code. If I go all out and assume every file in the project is a dependency, the mechanism will still break if some module grabs data from an external website, etc.). In addition, the frequency of changes in x.py and its dependencies is quite high, leading to heavy cache invalidation. Thus, I figured I might as well give up some safety, and only invalidate the cache only when there is an obvious mismatch. This means that class X would have a class-level cache validation identifier that should be changed whenever the developer believes a change happened that should invalidate the cache. (With multiple developers, a separate invalidation identifier is required for each.) This identifier is hashed along with arg1 and arg2 and becomes part of the hash keys stored in _registry. Since developers may forget to update the validation identifier or not realize that they invalidated existing cache, it would seem better to add another validation mechanism: class X can have a method that returns all the known "traits" of X. For instance, if X is a table, I might add the names of all the columns. The hash calculation will include the traits as well. I can write this code, but I am afraid that I'm missing something important; and I'm also wondering if perhaps there's a framework or package that can do all of this stuff already. Ideally, I'd like to combine in-memory and disk-based caching.

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• What is a good local Windows DNS Caching Server/Service?

  - by Jason Stevenson

  My ISP constantly has trouble keeping their DNS servers up (or so it seems). Does anyone have any good suggestions for a local caching server that can be installed on Windows Vista? Thanks.

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• Optimistic work sharing on sparsely distributed systems

  - by Asti

  What would a system like BOINC look like if it were written today? At the time BOINC was written, databases were the primary choice for maintaining a shared state and concurrency among nodes. Since then, many approaches have been developed for tasking with optimistic concurrency (OT, partial synchronization primitives, shared iterators etc.) Is there an optimal paradigm for optimistically distributing units of work on sparsely distributing systems which communicate through message passing? Sorry if this is a bit vague. P.S. The concept of Tuple-spaces is great, but locking is inherent to its definition. Edit: I already have a federation system which works very well. I have a reactive OT system is implemented on top of it. I'm looking to extend it to get clients to do units of work.

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• Distributed Transaction Framework across webservices

  - by John Petrak

  I am designing a new system that has one central web service and several site web services which are spread across the country and some overseas. It has some data that must be identical on all sites. So my plan is to maintain that data in the central web service and then "sync" the data to sites. This includes inserts, edits and deletes. I see a problem when deleting, if one site has used the record, then I need to undo the delete that has happened on the other servers. This lead me to idea that I need some sort of transaction system that can work across different web servers. Before I design one from scratch, I would like to know if anyone has come across this sort of problem and if there are any frame works or even design patterns that might aid me?

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• Interconnect nodes in a Java distributed infrastructure for tweet processing

  - by David Moreno García

  I'm working in a new version of an old project that I used to download and process user statuses from Twitter. The main problem of that project was its infrastructure. I used multiple instances of a java application (trackers) to download from Twitter given an specific task (basically terms to search for), connected with a central node (a web application) that had to process all tweets once per day and generate a new task for each trackers once each 15 minutes. The central node also had to monitor all trackers and enable/disable them under user petition. This, as I said, was too slow because I had multiple bottlenecks, so in this new version I want to improve the infrastructure and isolate all functionalities in specific nodes. I also need a good notification system to receive notifications for any node. So, in the next diagram I show the components that I'll need in this new version: As you can see, there are more nodes. Here are some notes about them: Dashboard: Controls trackers statuses and send a single task to each of them (under user request). The trackers will use this task until replaced with a new one (if done, not each 15 minutes like before). Search engine: I need to store all the tweets. They are firstly stored in a local database for each tracker but after that I'm thinking on using something like Elasticsearch to be able to do fast searches. Tweet processor: Just and isolated component with its own database (maybe something like the search engine to have fast access to info generated by the module). In the future more could be added. Application UI: A web application with a shared database with the Dashboard (mainly to store users information and preferences). Indeed, both could be merged into a single web. The main difference with the previous version of the project is that now they will be isolated and they will only show information and send requests. I will not do any heavy task in them (like process tweets as I did before). So, having this components, my main headache is how to structure all to not have to rewrite a lot of code every time I need to access any new data. Another headache is how can I interconnect nodes. I could use sockets but that is a pain in the ass. Maybe a REST layer? And finally, if all the nodes are isolated, how could I generate notifications for each user which info is only in the database used by the Application UI? I'm programming this using Java and Spring (at least I used them in the last version) but I have no problems with changing the language if I can take advantage of a tool/library/engine to make my life easier and have a better platform. Any comment will be appreciated.

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• I've totally missed the point of distributed vcs [closed]

  - by NimChimpsky

  I thought the major benefit of it was that each developers code gets stored within each others repository. My impression was that each developer has their working directory, their own repository, and then a copy of the other developers repository. Removing the need for central server, as you have as many backups as you have developers/repositories Turns out this is nto the case, and your code is only backed up (somewhere other than locally) when you push, the same as a commit in subversions. I am bit disappointed ... hopefully I will be pleasantly surprised when it handles merges better and there are less conflicts ?

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• Building a Redundant / Distrubuted Application

  - by MattW

  This is more of a "point me in the right direction" question. I (and my team of 3) have built a hosted web app that queues and routes customer chat requests to available customer service agents (It does other things as well, but this is enough background to illustrate the issue). The basic dev architecture today is: a single page ajax web UI (ASP.NET MVC) with floating chat windows (think Gmail) a backend Windows service to queue and route the chat requests this service also logs the chats, calculates service levels, etc a Comet server product that routes data between the web frontend and the backend Windows service this also helps us detect which Agents are still connected (online) And our hardware architecture today is: 2 servers to host the web UI portion of the application a load balancer to route requests to the 2 different web app servers a third server to host the SQL Server DB and the backend Windows service responsible for queuing / delivering chats So as it stands today, one of the web app servers could go down and we would be ok. However, if something would happen to the SQL Server / Windows Service server we would be boned. My question - how can I make this backend Windows service logic be able to be spread across multiple machines (distributed)? The Windows service is written to accept requests from the Comet server, check for available Agents, and route the chat to those agents. How can I make this more distributed? How can I make it so that I can distribute the work of the backend Windows service can be spread across multiple machines for redundancy and uptime purposes? Will I need to re-write it with distributed computing in mind? I should also note that I am hosting all of this on Rackspace Cloud instances - so maybe it is something I should be less concerned about? Thanks in advance for any help!

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• open source gossip-based membership protocol?

  - by Aaron

  I am looking for a library which I can plug into a distributed application which implements any gossip-based membership protocol. Such a library would allow me to send/receive membership lists, merge received membership lists, etc... Even better would be if the library implemented a protocol with performance O(logn) performance guarantees. Does anyone know of any open source library like this? It doesn't need to meet all of the aforementioned requirements; even something partially implemented would be helpful.

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• Force caching of handler output which actively resists caching

  - by deceze

  I'm trying to force caching of a very obnoxious piece of PHP script which actively tries to resist caching for no good reason by actively setting all the anti-cache headers: Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0 Content-Type: text/html; charset=UTF-8 Date: Thu, 22 May 2014 08:43:53 GMT Expires: Thu, 19 Nov 1981 08:52:00 GMT Last-Modified: Pragma: no-cache Set-Cookie: ECSESSID=...; path=/ Vary: User-Agent,Accept-Encoding Server: Apache/2.4.6 (Ubuntu) X-Powered-By: PHP/5.5.3-1ubuntu2.3 If at all avoidable I do not want to have to modify this 3rd party piece of code at all and instead just get Apache to cache the page for a while. I'm doing this very selectively to only very specific pages which have no real impact on session cookies or the like, i.e. which do not contain any personalised information. CacheDefaultExpire 600 CacheMinExpire 600 CacheMaxExpire 1800 CacheHeader On CacheDetailHeader On CacheIgnoreHeaders Set-Cookie CacheIgnoreCacheControl On CacheIgnoreNoLastMod On CacheStoreExpired On CacheStoreNoStore On CacheLock On CacheEnable disk /the/script.php Apache is caching the page alright: [cache:debug] AH00698: cache: Key for entity /the/script.php?(null) is http://example.com:80/the/script.php? [cache_disk:debug] AH00709: Recalled cached URL info header http://example.com:80/the/script.php? [cache_disk:debug] AH00720: Recalled headers for URL http://example.com:80/the/script.php? [cache:debug] AH00695: Cached response for /the/script.php isn't fresh. Adding conditional request headers. [cache:debug] AH00750: Adding CACHE_SAVE filter for /the/script.php [cache:debug] AH00751: Adding CACHE_REMOVE_URL filter for /the/script.php [cache:debug] AH00769: cache: Caching url: /the/script.php [cache:debug] AH00770: cache: Removing CACHE_REMOVE_URL filter. [cache_disk:debug] AH00737: commit_entity: Headers and body for URL http://example.com:80/the/script.php? cached. However, it is always insisting that the "cached response isn't fresh" and is never serving the cached version. I guess this has to do with the Expires header, which marks the document as expired (but I don't know whether that's the correct assumption). I've tried to overwrite and unset headers using mod_headers, but this doesn't help; whatever combination I try the cache is not impressed at all. I'm guessing that the order of operation is wrong, and headers are being rewritten after the cache sees them. early header processing doesn't help either. I've experimented with CacheQuickHandler Off and trying to set explicit filter chains, but nothing is helping. But I'm really mostly poking in the dark, as I do not have a lot of experience with configuring Apache filter chains. Is there a straight forward solution for how to cache this obnoxious piece of code?

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