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• Choosing a distributed shared memory solution

  - by mindas

  I have a task to build a prototype for a massively scalable distributed shared memory (DSM) app. The prototype would only serve as a proof-of-concept, but I want to spend my time most effectively by picking the components which would be used in the real solution later on. The aim of this solution is to take data input from an external source, churn it and make the result available for a number of frontends. Those "frontends" would just take the data from the cache and serve it without extra processing. The amount of frontend hits on this data can literally be millions per second. The data itself is very volatile; it can (and does) change quite rapidly. However the frontends should see "old" data until the newest has been processed and cached. The processing and writing is done by a single (redundant) node while other nodes only read the data. In other words: no read-through behaviour. I was looking into solutions like memcached however this particular one doesn't fulfil all our requirements which are listed below: The solution must at least have Java client API which is reasonably well maintained as the rest of app is written in Java and we are seasoned Java developers; The solution must be totally elastic: it should be possible to add new nodes without restarting other nodes in the cluster; The solution must be able to handle failover. Yes, I realize this means some overhead, but the overall served data size isn't big (1G max) so this shouldn't be a problem. By "failover" I mean seamless execution without hardcoding/changing server IP address(es) like in memcached clients when a node goes down; Ideally it should be possible to specify the degree of data overlapping (e.g. how many copies of the same data should be stored in the DSM cluster); There is no need to permanently store all the data but there might be a need of post-processing of some of the data (e.g. serialization to the DB). Price. Obviously we prefer free/open source but we're happy to pay a reasonable amount if a solution is worth it. In any way, paid 24hr/day support contract is a must. The whole thing has to be hosted in our data centers so SaaS offerings like Amazon SimpleDB are out of scope. We would only consider this if no other options would be available. Ideally the solution would be strictly consistent (as in CAP); however, eventual consistence can be considered as an option. Thanks in advance for any ideas.

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• Are there any nasty side affects if i lock the HttpContext.Current.Cache.Insert method

  - by Ekk

  Apart from blocking other threads reading from the cache what other problems should I be thinking about when locking the cache insert method for a public facing website. The actual data retrieval and insert into the cache should take no more than 1 second, which we can live with. More importantly i don't want multiple thread potentially all hitting the Insert method at the same time. The sample code looks something like: public static readonly object _syncRoot = new object(); if (HttpContext.Current.Cache["key"] == null) { lock (_syncRoot) { HttpContext.Current.Cache.Insert("key", "DATA", null, DateTime.Now.AddMinutes(5), Cache.NoSlidingExpiration, CacheItemPriority.Normal, null); } } Response.Write(HttpContext.Current.Cache["key"]);

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• Concurrent WCF calls via shared channel

  - by Kent Boogaart

  I have a web tier that forwards calls onto an application tier. The web tier uses a shared, cached channel to do so. The application tier services in question are stateless and have concurrency enabled. But they are not being called concurrently. If I alter the web tier to create a new channel on every call, then I do get concurrent calls onto the application tier. But I wanted to avoid that cost since it is functionally unnecessary for my scenario. I have no session state, and nor do I need to re-authenticate the caller each time. I understand that the creation of the channel factory is far more expensive than than the creation of the channels, but it is still a cost I'd like to avoid if possible. I found this article on MSDN that states: While channels and clients created by the channels are thread-safe, they might not support writing more than one message to the wire concurrently. If you are sending large messages, particularly if streaming, the send operation might block waiting for another send to complete. Firstly, I'm not sending large messages (just a lot of small ones since I'm doing load testing) but am still seeing the blocking behavior. Secondly, this is rather open-ended and unhelpful documentation. It says they "might not" support writing more than one message but doesn't explain the scenarios under which they would support concurrent messages. Can anyone shed some light on this?

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• Distributed, persistent cache using EHCache

  - by Richard

  I currently have a distributed cache using EHCache via RMI that works just fine. I was wondering if you can include persistence with the caches to create a distributed, persistent cache. Alongside this, if the cache was persistent, would it load from the file store, then bootstrap from the cache cluster? Basically, what I want is: Cache starts Cache loads persistent objects from the file store Cache joins the distruted cluster and bootstraps as normal The usecase behind this is having 2 identical components running on independent machines, distributing the cache to avoid losing data in the event that one of the components fails. The persistence would guard against losing all data on the rare occasion that both components fail. Would moving to another distribution method (such as Terracotta) support this?

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• Get Json and output to text file undecoded

  - by Gary

  Hi, I want to fetch json script and write it to a txt file undecoded, exactly how it was originally. I do have a script that I use that I am modifying but unsure what to commands to use. This script decodes, which is what I want to advoid. //Get Age list($bstat,$bage,$bdata) = explode("\t",check_file('./advise/roadsnow.txt',60*2+15)); //Test Age if ( $bage > $CacheMaxAge ) { //echo "The if statement evaluated to true so get new file and reset $bage"; $bage="0"; $file = file_get_contents('http://somesite.jsontxt'); $out = (json_decode($file)); $report = wordwrap($out->mainText, 100, "\n"); //$valid = $out->validTo; //write the data to a text file called roadsnow.txt $myFile = "./advise/roadsnow.txt"; $fh = fopen($myFile, 'w') or die("can't open file"); $stringData = $report; fwrite($fh, $stringData); } else { //echo the test evaluated to false; file is not stale so read local cache //print "we are at the read local cache"; $stringData = file_get_contents("./advise/roadsnow.txt"); } // if/else is done carry on with processing //Format file $data = $stringData

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• Is there a client-side way to prevent an image from being cached?

  - by morgancodes

  Is it possible to control with javascript whether a browser goes to the server for an image or to the browser cache? Can I force the browser to make a server call when it would otherwise use a cached image? I know I can simply append a query string to my image url, but, if I understand correctly, that works because the browser sees that as a new image. I want the old image to be replaced in the cache.

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• iPhone: cached profile images from the web - how to find out that remote image changed?

  - by Stefan Klumpp

  I'm loading profile pictures from Facebook, cache them on disk and load them into cells of a UITableView. Now I'm wondering, how I can find out when someone has changed his/her profile picture on Facebook that I have to load the new image from the web instead of using the one cached disk. The url of the image is always the same. Is there a lightweight way of doing this without downloading the image and comparing it to the local file?

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• How do you set cache time lenght of memcache with Zend_cache?

  - by matt gardner

  I know that you can specify how long you want an object cached in memcache, however I setup memcache with Zend's Zend_Cache and there does not appear to be documentation related to how long the item stays in cache. Anyone know how to do this?

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• Load SQL query result data into cache in advance

  - by Marc

  I have the following situation: .net 3.5 WinForm client app accessing SQL Server 2008 Some queries returning relatively big amount of data are used quite often by a form Users are using local SQL Express and restarting their machines at least daily Other users are working remotely over slow network connections The problem is that after a restart, the first time users open this form the queries are extremely slow and take more or less 15s on a fast machine to execute. Afterwards the same queries take only 3s. Of course this comes from the fact that no data is cached and must be loaded from disk first. My question: Would it be possible to force the loading of the required data in advance into SQL Server cache? Note My first idea was to execute the queries in a background worker when the application starts, so that when the user starts the form the queries will already be cached and execute fast directly. I however don't want to load the result of the queries over to the client as some users are working remotely or have otherwise slow networks. So I thought just executing the queries from a stored procedure and putting the results into temporary tables so that nothing would be returned. Turned out that some of the result sets are using dynamic columns so I couldn't create the corresponding temp tables and thus this isn't a solution. Do you happen to have any other idea?

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• Auto-versioning of static content with JBoss

  - by Bears will eat you

  As per the Q&A here, I'd like to implement a similar auto-versioning system for a web app running in JBoss 5. Is there anything already out there to do this sort of thing, or will I need to write something myself? To be clear: I am not using PHP. Not knowing much about PHP, I'm not sure what the Tomcat/JBoss analogs of PHP's .htaccess, etc. are. If I do have to write my own auto-versioning, where would I start? The principle is clear to me - rewriting the URL using the file's timestamp, but I don't know much about URL rewriting with JBoss/Tomcat.

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• How to make Rails caches_page survive a capistrano deploy?

  - by aaronrussell

  Is it possible to configure Rails so caches created with caches_page survive a Capistrano deploy? Ie, can I configure the cache to be saved into a shared directory rather than in the public directory?

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• Is is better to store serialized data or raw html in mysql?

  - by Yegor

  I de-normalized my database, since the application was crawling otherwise, and Im storing a list of categories for each item in the DB as a raw html version, and simply echoing it out in my design. Each category is actually a link, which is include a tag. Naturally, this is abit of a pain, especially if I want to change the look of how the category links are displayed, since I gotta update all the old cached entries. What if I were to store this data as a serialized array instead, and simply unserialize it, and then apply formatting to it in php. Would there be a significant performance decrease over simply echoing out the raw html?

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• Hashing a python method to regenerate output when method is modified

  - by Seth Johnson

  I have a python method that has a deterministic result. It takes a long time to run and generates a large output: def time_consuming_method(): # lots_of_computing_time to come up with the_result return the_result I modify time_consuming_method from time to time, but I would like to avoid having it run again while it's unchanged. [Time_consuming_method only depends on functions that are immutable for the purposes considered here; i.e. it might have functions from Python libraries but not from other pieces of my code that I'd change.] The solution that suggests itself to me is to cache the output and also cache some "hash" of the function. If the hash changes, the function will have been modified, and we have to re-generate the output. Is this possible or a ridiculous idea? If this isn't a terrible idea, is the best implementation to write f = """ def ridiculous_method(): a = # # lots_of_computing_time return a """ , use the hashlib module to compute a hash for f, and use compile or eval to run it as code?

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• cached data base

  - by radi

  hi , in my project i need a tow tables each of it has about 2000 row , i want my application to be speed so my db should load into memory (cached) when the app start and before it close the db have to be saved on the disk . i am using java and i want to use sql

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• Squid server - multiple originservers with different domains

  - by jduncan

  I have 2 squid servers load-balanced with F5 LTMs set up as a reverse proxy. My problem: origin server A hosts domains 1, 2, and 3 origin server B hosts domains 4 and 5. how can I set up squid so that it will cache all vhosts for both servers? my current config: cache_peer serverA parent 80 0 round-robin no-query originserver login=PASS If I add a second line: cache_peer serverB parent 80 0 round-robin no-query originserver login=PASS it only caches domains on serverB, requests for serverA content generate 404 errors. I don't use squid a whole lot, and all help is appreciated. thanks.

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• What' the expected release date for Microsoft Velocity?

  - by Waleed Eissa

  CTP3 was released in March, is there any expected release date for v1?

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• Application_End() cannot access cache through HttpContext.Current.Cache[key]

  - by Carl J.

  I want to be able to maintain certain objects between application restarts. To do that, I want to write specific cached items out to disk in Global.asax Application_End() function and re-load them back on Application_Start(). I currently have a cache helper class, which uses the following method to return the cached value: return HttpContext.Current.Cache[key]; Problem: during Application_End(), HttpContext.Current is null since there is no web request (it's an automated cleanup procedure) - therefore, I cannot access .Cache[] to retrieve any of the items to save to disk. Question: how can I access the cache items during Application_End()?

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• Does the `Expires` HTTP header needs to be consistent across multiple cold-cache requests?

  - by chakrit

  I'm implementing a custom web server of a kind. And am looking into adding an Expires header support. However, I'm a little unsure of how exactly to implement it. If multiple cold-cache requests are being made to the same unchanged resource on the server and the server returned different Expires header (say it uses relative time to calculate the exact value of the Expires date e.g. +6 hours from the request time), does that invalidate the cache on all the proxy servers in-between as well? Or is it impossible to happen (per the spec)? Does the Expires HTTP header needs to be consistent across multiple cold-cache requests?

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• problem of setting cache as datatable and reading it

  - by MyHeadHurts

  and this is how i see if my cache is empty all my syntax errors are coming when i am trying to see if the cache is null and if it is to run the stored procedure If RadioButtonList1.SelectedIndex = 0 Then If Cache["netcache"] = null Then bcmd.CommandText = "yearlynetsales" Else btable = cache["netcache"] end if If RadioButtonList1.SelectedIndex = 1 Then If Cache["salescache"] = null Then bcmd.CommandText = "yearlysales" Else btable = cache["salescache"] end if end if this is how i set my cache If RadioButtonList1.SelectedIndex = 0 Then Cache.Insert("netcache", bTable) ElseIf RadioButtonList1.SelectedIndex = 1 Then Cache.Insert("salescache", bTable) ElseIf RadioButtonList1.SelectedIndex = 2 Then Cache.Insert("cxsalescache", bTable) ElseIf RadioButtonList1.SelectedIndex = 3 Then Cache.Insert("cxvaluecache", bTable) ElseIf RadioButtonList1.SelectedIndex = 4 Then Cache.Insert("othersalescache", bTable) ElseIf RadioButtonList1.SelectedIndex = 5 Then Cache.Insert("inssalescache", bTable) End If

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• Detect IE setting: check for newer versions of stored pages "never"

  - by xx

  I understand there isn't a way to interrogate a users IE settings directly due to security reasons, but is there a way to derive this answer with some other mechanism? I would like to stop a user from using my site if the setting "Check for newer versions of stored pages" is set to "Never". Any suggestions? Is there a way I could test for this using javascript? An example of what I am trying to accomplish is this: While it is not possible to check IE settings to see if you are running a popup blocker, that is a way to "test" for a popup blocker via javascript. I am looking for something similiar but for the cache setting, not the popup blocker.

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• Can we view objects in the JVM memory?

  - by Sebastien Lorber

  Hey, At work we found that on some instances (particulary the slow ones) we have a different behaviour, acquired at the reboot. We guess a cache is not initialized correctly, or maybe a concurrency problem... Anyway it's not reproductible in any other env than production. We actually don't have loggers to activate... it's an old component... Thus i'd like to know if there are tools that can help us to see the different objets present in the JVM memory in order to check the content of the cache... Thank you!

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• My iphone mobile safari does not cache , but i have a manifest file,...

  - by Ploetzeneder

  Hello, i have now put the site on: http://www.ploetzeneder.eu/Dateien/test/index4.html the manifest is there: http://www.ploetzeneder.eu/Dateien/test/app-cache-demo.manifest Why does it not work? The Webserver where the relevant problem has this url: http://www.pharao.mobi/WebAppproblem/ Username is the Username Passwort is the Password the problem is on index4.html where all images should be cached but are not

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• How does the proc in the caches_action if clause get execute

  - by Sid

  I have a newbie kind of question which I cant get my head around. How does the Proc in the if condition of the caches_action get executed for the caches_action method. for example caches_action :show, :if=Proc.new{|x| something} what i dont get its how does this get called. I know i can execute a proc defined as proc= Proc.new by proc.call so i dont understand how this gets called. Second how do I pass conditions like if logged_in? I'd appreciate any help on this

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• How to flush output after each `echo` call?

  - by CuSS

  Hi all! I've a php script that only produces logs to the client. When I echo something, i wan't it to be transfered to client on-the-fly. (Because while the script is processing, the page is blank) I had already played arround with ob_start() and ob_flush(), but they didn't worked. What's the best solution? PS: it is a little dirty to put a flush at the end of the echo call... EDIT: Neither the Answers worked, PHP or Apache Fault? Thanks in advance, José Moreira Sorry for my bad English. ;)

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• How I can use the HTTP headers to indicate in the Response that possibility?

  - by Cris Hong Kong CRISHK

  Finally I accomplished to cache dynamic images, css, and javascript files using HTTP headers BUT I have a problem now: I have specific dynamic images that are equal but has different URL's. For example: http://example.com/image/src/the-same-image.jpg http://example.com/image/custom/src/the-same-image2.jpg 1 and 2 has the same file content but different URL. This is a problem now because the navigator assumes that the file are different and need to be cached (due to the URL), when the real cached file is only one. I have the possibility to know if the file at the URL's are the same. How I can use the headers to indicate in the Response that possibility, and the navigator will cache only one file?

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