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  • When DNS doesn't cache

    - by John Francis
    We've had some odd DNS problems over the past couple of days that I don't fully understand. Some of our DNS names stopped resolving for some of our customers due to some 'unknown' server reconfiguration at our DNS provider. The problem seemed to be intermittent i.e. stopped working and started working within a few minutes over a couple of days. I'm no expert on DNS, but I'd have expected DNS caches to prevent this sort of thing from happening - when we need to change an IP address for a DNS record, it can take 24 hours to propogate, so how can our DNS provider be breaking name resolution intermittently for our customers so easily? Shouldn't the DNS caches kick in here? We had a similar problem about a month ago when one of their nameservers 'decided to reload the DNS database from scratch' - this broke our name resolution too. Again, why didn't the caches satisfy the name resolution requests. Any guesses would be appreciated. John

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  • How does NFS read cache work on Debian?

    - by Ztyx
    I am planning to use NFS to serve out many small files. They will be read very often so client side caching is crucial. Does NFS handle this? Is there a way to increase the client side caching in some way? ...or should I look at another solution? Syncing using rsync or unison periodically is not an option since the files are modified on the client side from time to time.

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  • Centos swap cache memory leak

    - by user30008
    We have a image server that keeps running out of memory and crashing, we thought there was a hardware issue with the machine because the code base has not changed and this is a new issue. We brought a new machine online with newer kernel and fresh centos 5.4 install and just brought online one subdomain and the exact same error is occurring on the new machine. How should I try and troubleshoot this issue.

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  • Varnish : Non-Cache/Data Fetch + Load-Balance

    - by xperator
    Someone commented at my previous question and said it's possible to do this with Varnish: Instead of : Client Request Varnish LB Backend Varnish LB Client I want to have (Direct reply from backend to client, instead of going through the LB) : Client Request Varnish LB Backend Client This is not working : sub vcl_pass { if (req.http.host ~ "^(www.)?example.com$") { set req.backend = baz; return (pass); } }

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  • Disqus cache of unposted posts

    - by user129107
    Some webpages implement Disqus and also have the rather bad policy of adding auto refresh to the page. This result in for example one writing a long answer in a debate and then a refresh comes along – and everything is gone. Is the comments, written, but not posted, cached somewhere? Is it possible to retrieve? I have experienced this on various pages. In the current case the debate page was reloaded and a rather lengthy post with a lot of references and long thought out sentences vanished. This page closes the debate during night time, and do a auto refresh of the page when one pass midnight – as such I'm not able to retrieve the debate for another 8 hours. Other pages implement for example an auto refresh after 20 minutes. Linux, Google Chrome.

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  • How to utilize Varnish for A/B Testing and Feature Rollout?

    - by Ken
    Hi all, wasn't really sure if this should go here on or stackoverlow - admins, please move if i'm mistaken (and sorry). Today we have our web layer exposed to the world. We would like to add Varnish in front of our web layer to accelerate the site and reduce calls to the backend. However, we have some concerns and i was wondering how most people approach them: A/B Testing - How do you test two "versions" of each page and compare? I mean, how does varnish know which page to serve up? If and how do you save seperate versions on each page? Feature rollout - how would you set up a simple feature rollout mechanism? Let's say i want to open a new feature/page to just 10% of the traffic.. and then later increase that to 20%? How do you handle code deployments? Do you purge your entire varnish cache every deployment? (We have deployments on a daily basis). Or do you just let it slowly expire (using TTL)? Any ideas and examples regarding these issues is greatly appreciated! Thanks in advance. Ken.

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  • ZFS with L2ARC (SSD) slower for random seeks than without L2ARC

    - by Florian Kruse
    I am currently testing ZFS (Opensolaris 2009.06) in an older fileserver to evaluate its use for our needs. Our current setup is as follows: Dual core (2,4 GHz) with 4 GB RAM 3x SATA controller with 11 HDDs (250 GB) and one SSD (OCZ Vertex 2 100 GB) We want to evaluate the use of a L2ARC, so the current ZPOOL is: $ zpool status pool: tank state: ONLINE scrub: none requested config: NAME STATE READ WRITE CKSUM afstank ONLINE 0 0 0 raidz1 ONLINE 0 0 0 c11t0d0 ONLINE 0 0 0 c11t1d0 ONLINE 0 0 0 c11t2d0 ONLINE 0 0 0 c11t3d0 ONLINE 0 0 0 raidz1 ONLINE 0 0 0 c13t0d0 ONLINE 0 0 0 c13t1d0 ONLINE 0 0 0 c13t2d0 ONLINE 0 0 0 c13t3d0 ONLINE 0 0 0 cache c14t3d0 ONLINE 0 0 0 where c14t3d0 is the SSD (of course). We run IO tests with bonnie++ 1.03d, size is set to 200 GB (-s 200g) so that the test sample will never be completely in ARC/L2ARC. The results without SSD are (average values over several runs which show no differences) write_chr write_blk rewrite read_chr read_blk random seeks 101.998 kB/s 214.258 kB/s 96.673 kB/s 77.702 kB/s 254.695 kB/s 900 /s With SSD it becomes interesting. My assumption was that the results should be in worst case at least the same. While write/read/rewrite rates are not different, the random seek rate differs significantly between individual bonnie++ runs (between 188 /s and 1333 /s so far), average is 548 +- 200 /s, so below the value w/o SSD. So, my questions are mainly: Why do the random seek rates differ so much? If the seeks are really random, they should not differ much (my assumption). So, even if the SSD is impairing the performance it should be the same in each bonnie++ run. Why is the random seek performance worse in most of the bonnie++ runs? I would assume that some part of the bonnie++ data is in the L2ARC and random seeks on this data performs better while random seeks on other data just performs similarly like before.

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  • iptables secure squid proxy

    - by Lytithwyn
    I have a setup where my incoming internet connection feeds into a squid proxy/caching server, and from there into my local wireless router. On the wan side of the proxy server, I have eth0 with address 208.78.∗∗∗.∗∗∗ On the lan side of the proxy server, I have eth1 with address 192.168.2.1 Traffic from my lan gets forwarded through the proxy transparently to the internet via the following rules. Note that traffic from the squid server itself is also routed through the proxy/cache, and this is on purpose: # iptables forwarding iptables -A FORWARD -i eth1 -o eth0 -s 192.168.2.0/24 -m state --state NEW -j ACCEPT iptables -A FORWARD -m state --state ESTABLISHED,RELATED -j ACCEPT iptables -A POSTROUTING -t nat -j MASQUERADE # iptables for squid transparent proxy iptables -t nat -A PREROUTING -i eth1 -p tcp --dport 80 -j DNAT --to 192.168.2.1:3128 iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 80 -j REDIRECT --to-port 3128 How can I set up iptables to block any connections made to my server from the outside, while not blocking anything initiated from the inside? I have tried doing: iptables -A INPUT -i eth0 -s 192.168.2.0/24 -j ACCEPT iptables -A INPUT -i eth0 -j REJECT But this blocks everything. I have also tried reversing the order of those commands in case I got that part wrong, but that didn't help. I guess I don't fully understand everything about iptables. Any ideas?

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  • Caching/preloading files on Linux into RAM

    - by Andrioid
    I have a rather old server that has 4GB of RAM and it is pretty much serving the same files all day, but it is doing so from the hard drive while 3GBs of RAM are "free". Anyone who has ever tried running a ram-drive can witness that It's awesome in terms of speed. The memory usage of this system is usually never higher than 1GB/4GB so I want to know if there is a way to use that extra memory for something good. Is it possible to tell the filesystem to always serve certain files out of RAM? Are there any other methods I can use to improve file reading capabilities by use of RAM? More specifically, I am not looking for a 'hack' here. I want file system calls to serve the files from RAM without needing to create a ram-drive and copy the files there manually. Or at least a script that does this for me. Possible applications here are: Web servers with static files that get read alot Application servers with large libraries Desktop computers with too much RAM Any ideas? Edit: Found this very informative: The Linux Page Cache and pdflush As Zan pointed out, the memory isn't actually free. What I mean is that it's not being used by applications and I want to control what should be cached in memory.

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  • Would a PHP application benefit from being served from a RAM drive?

    - by Tom Marthenal
    I am in charge of hosting a PHP application that is large and slow, but easy to scale. The application is entirely static, with writable disk storage needed. We've profiled the application, and the main bottleneck appears to come from loading the application and not the work the application does. The application is not CPU-intensive, although it does use a fair amount of memory (think Magento). Currently we distribute it by having a series of servers with the same PHP files on their hard drive and a load balancer in front of them. Easy but expensive. I've been reading about RAM disks and the IO benefits they offer, and was wondering if they would be well-suited to PHP applications. Since PHP applications are loaded from disk for every request and often involve lots of different files (as opposed to being kept in memory like with a Java application), I would figure that disk performance can be a severe bottleneck. Would placing the PHP files on a RAM disk and using the mount point as Apache's document root offer performance benefits? A startup script could create the RAM drive and then copy the files (which are plain-text and small) from a permanent location to the temporary RAM drive. Does this make sense, or should I just trust the linux kernel to cache the appropriate files in memory by itself?

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  • Apache FilesMatch regexp: Can it match by the cache buster 10 digit (rails generated) following the filename?

    - by ynkr
    According to the apache FilesMatch docs: The FilesMatch directive provides for access control by filename Basically, I only want to set an expires header for resources that have a 10 digit "cache buster" id appended to the name. So, here is my attempt at such a thing in my httpd.conf <FilesMatch "(jpg|jpeg|png|gif|js|css)\?\d{10}$"> ExpiresActive On ExpiresDefault "now plus 5 minutes" </FilesMatch> And here is an example of a resource I want to match: http://localhost:3000/images/of/elvis/eating-a-bacon-sandwich.png?1306277384 Now obviously my FilesMatch regexp is not matching so I am guessing 1 of 2 things is happening. Either my regexp is wonky or the '?1231231231' cache busting part of the file is not part of what apache considers part of the filename. Can anybody confirm and/or give me a way to cache only those resources that will not persist beyond the next deploy?

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  • Myths: Does Deleting the Cache Actually Speed Up Your PC?

    - by The Geek
    Every time you ask somebody with a reasonable level of tech skills what you should do to speed up your PC, they start jabbering on about running ccleaner and clearing the cache. But does the act of clearing a cache really speed things up? Nope. Most people assume that all temporary files are just clutter created by lousy applications, but that isn’t actually the truth. Cache files are created by apps to store commonly used information so it doesn’t have to be generated or downloaded again.    

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  • how to add a url cache to ASIHttpRequest

    - by smokey_the_bear
    I'm using ASIHttpRequests and an ASINetworkQueue in an iphone app to retrieve some 100k XML files and a lot of thumbnails from a web service. I'd like to cache the requests in the style of NSURLCache. ASI doesn't seem to support caching as is, and I looked at the code and it drops to C to create the requests, so inserting the NSURLCache layer seemed tricky. What's the best way to implement this?

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  • Cache invalidation between two web applications

    - by Muxa
    I need to invalidate cache in a web application when related data is updated in another application (running on the same machine). Both applications use the same database. I know there's SqlCacheDependency. How do is it in terms of performance? Is interprocess communication (e.g. using name pipes) an option in web applications? Does it outperform SqlCacheDependency?

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  • Why is the HttpContext.Cache count always zero?

    - by jjr2527
    I set up a few pages with OutputCache profiles and confirmed that they are being cached by using multiple browsers and requests to retrieve the page with a timestamp which matched across all requests. When I try to enumerate the HttpContect.Cache it is always empty. Any ideas what is going on here or where I should be going for this information instead?

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  • Access Google Chrome's cache

    - by jldupont
    Is it possible to access Google Chrome's cache from within an extension? I'd like to write an extension that loads a cached version of a page when the online one can't be accessed (e.g. Internet connectivity issue). Updated: I know I could write an NPAPI plugin accessible through an extension to accomplish this but I'd rather not suffer writing one... I am after a solution without resorting to NPAPI, please.

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  • Cache SHA1 digest result?

    - by johnathan
    I'm storing several versions of a file based on a digest of the original filename and its version, like this: $filename = sha1($original . ':' . $version); Would it be worth it to cache the digest ($filename) in memcache as a key/value pair (the key being the original + version and value the sha1 hash), or is generating the digest quick enough (for a high traffic php web app)? Thanks, Johnathan

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  • Cache in iphone

    - by venkat
    hello friends i am new to networking in iphone.i would like to see some sample code for cache its not based on image.i need for complete url. thanks in advance.

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  • Caching and cache invalidation in user controls?

    - by Rishabh Ohri
    HI, In our .aspx pages we have many user controls. each user control executes a sql query. The caching mechanism to be followed is to fragment cache each user control on the page and add the query dependency to the respective queries of the user controls. How to achieve query dependency on fragment cached data for invalidation?

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  • Squid change cache key

    - by Ken Struys
    Lets say you want to serve different content from the same url but still want to be able to use squid caching. For example caching a logged in users homepage vs another user. Is there anyway to append a cookie to the request url before throwing it into the squid's cache?

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