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  • Generate or update a PDF to include an encrypted, hidden watermark?

    - by Dave Jarvis
    Background Using LaTeX to write a book. When a user purchases the book, the PDF will be generated automatically. Problem The PDF should have a watermark that includes the person's name and contact information. Question What software meets the following criteria: Applies encrypted, invisible watermarks to a PDF Open Source Platform independent (Linux, Windows) Fast (marks a 200 page PDF in under 1 second) Batch processing (exclusively command-line driven) Collusion-attack resistant Non-fragile (e.g., PDF - EPS - PDF still contains the watermark) Well documented (shows example usages) Ideas & Resources Some thoughts and findings: Natural language processing (NLP) watermarks. Apply steganography on a randomly selected image. http://openstego.sourceforge.net/cmdline.html The problem with NLP is that grammatical errors can be introduced. The problem with steganography is that the images are sourced from an image cache, and so recreating that cache with watermarked images will impart a delay when generating the PDF (I could just delete one image from the cache, but that's not an elegant solution). Thank you!

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  • Squid/Kerberos authentication with only Linux

    - by user28362
    Hi, I would like to know if it possible to let a Windows Xp machine authenticate to Squid (Linux) using Kerberos without the need of an Active Directory domain. I only want to create a Kerberos ticket on the client side, which should give the client access to squid (using I.E.). I only found tutorials about configuring A.D./Squid, not an environment with only Linux servers. Thanks Update: The kerberos setup is correctly done, the proxy and client can get tickets. As for the browser (FF/IE), I get: ERROR Cache Access Denied While trying to retrieve the URL: http://www.google.com/ The following error was encountered: * Cache Access Denied. Sorry, you are not currently allowed to request: http://www.google.com/ from this cache until you have authenticated yourself. In kerberos, I get: squid_kerb_auth: Got 'YR ElRNTVMTUABBAABAB4IIogAAAAAAAAAAAAAAAAAAAAAFASgDAAAADw==' from squid (length: 59). squid_kerb_auth: parseNegTokenInit failed with rc=101 squid_kerb_auth: received type 1 NTLM token This message is strange, as I didn't configure NTLM. It looks like the browser uses the wrong authentication methode.

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  • How to generate user-specific PDF with encrypted hidden watermark?

    - by Dave Jarvis
    Background Using LaTeX to write a book. When a user purchases the book, the PDF will be generated automatically. Problem The PDF should have a watermark that includes the person's name and contact information. Question What software meets the following criteria: Applies encrypted, undetectable watermarks to a PDF Open Source Platform independent (Linux, Windows) Fast (marks a 200 page PDF in under 1 second) Batch processing (exclusively command-line driven) Collusion-attack resistant Non-fragile (e.g., PDF - EPS - PDF still contains the watermark) Well documented (shows example usages) Ideas & Resources Some thoughts and findings: Natural language processing (NLP) watermarks. Apply steganography on a randomly selected image. http://openstego.sourceforge.net/cmdline.html The problem with NLP is that grammatical errors can be introduced. The problem with steganography is that the images are sourced from an image cache, and so recreating that cache with watermarked images will impart a delay when generating the PDF (I could just delete one image from the cache, but that's not an elegant solution). Thank you!

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  • How to combine wildcards and spaces (quotes) in an Windows command?

    - by Jan Fabry
    I want to remove directories of the following format: C:\Program Files\FogBugz\Plugins\cache\[email protected]_NN NN is a number, so I want to use a wildcard (this is part of a post-build step in Visual Studio). The problem is that I need to combine quotes around the path name (for the space in Program Files) with a wildcard to match the end of the path. I already found out that rd is the remove command that accepts wildcards, but where do I put the quotes? I have tried no ending quote (works for dir), ...example.com*", ...example.com"*, ...example.com_??", ...cache\"[email protected]*, ...cache"\[email protected]*, but none of them work. (How many commands to remove a file/directory are there in Windows anyway? And why do they all differ in capabilities?)

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  • Php template caching design

    - by Thomas
    Hello to all, I want to include caching in my app design. Caching templates for starters. The design I have used so far is very modular. I have created an ORM implementation for all my tables and each table is represented by the corresponding class. All the requests are handled by one controller which routes them to the appropriate webmethod functions. I am using a template class for handling UI parts. What I have in mind for caching includes the implementation of a separate Cache class for handling caching with the flexibility to either store in files, apc or memcache. Right now I am testing with file caching. Some thoughts Should I include the logic of checking for cached versions in the Template class or in the webmethods which handle the incoming requests and which eventually call the Template class. In the first case, things are pretty simple as I will not have to change anything more than pass the template class an extra argument (whether to load from cache or not). In the second case however, I am thinking of checking for a cached version immediately in the webmethod and if found return it. This will save all the processing done until the logic reaches the template (first case senario). Both senarios however, rely on an accurate mechanism of invalidating caches, which brings as to Invalidating caches As I see it (and you can add your input freely) a template cached file, becomes invalidate if: a. the expiration set, is reached. b. the template file itself is updated (ie by the developer when adding a new line) c. the webmethod that handles the request changes (ie the developer adds/deletes something in the code) d. content coming from the db and ending in the template file is modified I am thinking of storing a json encoded array inside the cached file. The first value will be the expiration timestamp of the cache. The second value will be the modification time of the php file with the code handling the request (to cope with option c above) The third will be the content itself The validation process I am considering, according to the above senarios, is: a. If the expiration of the cached file (stored in the array) is reached, delete the cache file b. if the cached file's mod time is smaller than the template's skeleton file mod time, delete the cached file c. if the mod time of the php file is greated than the one stored in the cache, delete the cached file. d. This is tricky. In the ORM implementation I ahve added event handlers (which fire when adding, updating, deleting objects). I could delete the cache file every time an object thatprovides content to the template, is modified. The problem is how to keep track which cached files correpond to each schema object. Take this example, a user has his shortprofile page and a full profile page (2 templates) These templates can be cached. Now, every time the user modifies his profile, the event handler would need to know which templates or cached files correspond to the User, so that these files can be deleted. I could store them in the db but I am looking for a beter approach

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  • PDF Encrypted, Hidden Watermark

    - by Dave Jarvis
    Background Using LaTeX to write a book. When a user purchases the book, the PDF will be generated automatically. Problem The PDF should have a watermark that includes the person's name and contact information. Question What software meets the following criteria: Applies encrypted, undetectable watermarks to a PDF Open Source Platform independent (Linux, Windows) Fast (marks a 200 page PDF in under 1 second) Batch processing (exclusively command-line driven) Collusion-attack resistant Non-fragile (e.g., PDF - EPS - PDF still contains the watermark) Well documented (shows example usages) Ideas & Resources Some thoughts and findings: Natural language processing (NLP) watermarks. Apply steganography on a randomly selected image. http://openstego.sourceforge.net/cmdline.html The problem with NLP is that grammatical errors can be introduced. The problem with steganography is that the images are sourced from an image cache, and so recreating that cache with watermarked images will impart a delay when generating the PDF (I could just delete one image from the cache, but that's not an elegant solution). Thank you!

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  • perfmon reporting higher IOPs than possible?

    - by BlueToast
    We created a monitoring report for IOPs on performance counters using Disk reads/sec and Disk writes/sec on four servers (physical boxes, no virtualization) that have 4x 15k 146GB SAS drives in RAID10 per server, set to check and record data every 1 second, and logged for 24 hours before stopping reports. These are the results we got: Server1 Maximum disk reads/sec: 4249.437 Maximum disk writes/sec: 4178.946 Server2 Maximum disk reads/sec: 2550.140 Maximum disk writes/sec: 5177.821 Server3 Maximum disk reads/sec: 1903.300 Maximum disk writes/sec: 5299.036 Server4 Maximum disk reads/sec: 8453.572 Maximum disk writes/sec: 11584.653 The average disk reads and writes per second were generally low. I.e. for one particular server it was like average 33 writes/sec, but when monitoring in real-time it would often spike up to several hundreds and also sometimes into the thousands. Could someone explain to me why these numbers are significantly higher than theoretical calculations assuming each drive can do 180 IOPs? Additional details (RAID card): HP Smart Array P410i, Total cache size of 1GB, Write cache is disabled, Array accelerator cache ratio is 25% read and 75% write

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  • How does MySQL 5.5 and InnoDB on Linux use RAM?

    - by Loren
    Does MySQL 5.5 InnoDB keep indexes in memory and tables on disk? Does it ever do it's own in-memory caching of part or whole tables? Or does it completely rely on the OS page cache (I'm guessing that it does since Facebook's SSD cache that was built for MySQL was done at the OS-level: https://github.com/facebook/flashcache/)? Does Linux by default use all of the available RAM for the page cache? So if RAM size exceeds table size + memory used by processes, then when MySQL server starts and reads the whole table for the first time it will be from disk, and from that point on the whole table is in RAM? So using Alchemy Database (SQL on top of Redis, everything always in RAM: http://code.google.com/p/alchemydatabase/) shouldn't be much faster than MySQL, given the same size RAM and database?

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  • Is there a way i can see why Squid (Proxy Server) determines why a resources should be a MISS?

    - by Pure.Krome
    Hi folks, I'm using Fiddler/FireBug to debug some of our live server web content. We're getting a lot of :- X-Cache: MISS from X-Cache-Lookup: MISS from :8080 Via: 1.1 :8080 (squid/2.7.STABE3) I thought i knew a lot about cache-control / expires / last-modified / etags, etc.. but maybe not. So .. is there a way I can run squid in some verbose way to see why it thinks a resource which i request, is cached/is not getting cached, etc.. which is why we're getting MISSes back? cheers :)

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  • How to keep Varnish cached populate after backend down for an extended period?

    - by Nicholas Tolley Cottrell
    We have Varnish 3.0.2 running on Amazon's Linux and it works great. We have a ttl of 48 hours for most content pages and much longer for images, PDFs etc. This weekend we've taken the backend down for some maintenance, so I upped the ttl to 5 days earlier in the week. I had assumed that anything in cache would continue to be served for up to 5 days, but much to our disappointment we checked varnishstat this morning and the cache was almost completely empty and varnish was serving "page not found" messages. I know that this is not what Varnish is designed to do, but why would it reset its cache when the backend is down? And how can I prevent it for next time?

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  • Cron Script to Delete Folder Contents Every 5 Minutes on Media Temple

    - by Brian Iannone
    I'm not familiar with server-side scripting, but I'm currently using a PHP application on Media Temple to cache JPEGs from four webcams hosted on a server located in the middle of the Indian Ocean. (Hence my reason for caching them in the US.) The webcams are updated every five minutes. The PHP application stores the cached images in http://static.rigic.co/cache/. I would like to create a cron script to automatically delete the contents of "cache" (not the folder itself; just the files inside) at a regular interval.

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  • CSC folder data access AND roaming profiles issues (Vista with Server 2003, then 2008)

    - by Alex Jones
    I'm a junior sysadmin for an IT contractor that helps small, local government agencies, like little towns and the like. One of our clients, a public library with ~ 50 staff users, was recently migrated from Server 2003 Standard to Server 2008 R2 Standard in a very short timeframe; our senior employee, the only network engineer, had suddenly put in his two weeks notice, so management pushed him to do this project before quitting. A bit hasty on management's part? Perhaps. Could we do anything about that? Nope. Do I have to fix this all by myself? Pretty much. The network is set up like this: a) 50ish staff workstations, all running Vista Business SP2. All staff use MS Outlook, which uses RPC-over-HTTPS ("Outlook Anywhere") for cached Exchange access to an offsite location. b) One new (virtualized) Server 2008 R2 Standard instance, running atop a Server 2008 R2 host via Hyper-V. The VM is the domain's DC, and also the site's one and only file server. Let's call that VM "NEWBOX". c) One old physical Server 2003 Standard server, running the same roles. Let's call it "OLDBOX". It's still on the network and accessible, but it's been demoted, and its shares have been disabled. No data has been deleted. c) Gigabit Ethernet everywhere. The organization's only has one domain, and it did not change during the migration. d) Most users were set up for a combo of redirected folders + offline files, but some older employees who had been with the organization a long time are still on roaming profiles. To sum up: the servers in question handle user accounts and files, nothing else (eg, no TS, no mail, no IIS, etc.) I have two major problems I'm hoping you can help me with: 1) Even though all domain users have had their redirected folders moved to the new server, and loggin in to their workstations and testing confirms that the Documents/Music/Whatever folders point to the new paths, it appears some users (not laptops or anything either!) had been working offline from OLDBOX for a long time, and nobody realized it. Here's the ugly implication: a bunch of their data now lives only in their CSC folders, because they can't access the share on OLDBOX and sync with it finally. How do I get this data out of those CSC folders, and onto NEWBOX? 2) What's the best way to migrate roaming profile users to non-roaming ones, without losing vital data like documents, any lingering PSTs, etc? Things I've thought about trying: For problem 1: a) Reenable the documents share on OLDBOX, force an Offline Files sync for ALL domain users, then copy OLDBOX's share's data to the equivalent share on NEWBOX. Reinitialize the Offline Files cache for every user. With this: How do I safely force a domain-wide Offline Files sync? Could I lose data by reenabling the share on OLDBOX and forcing the sync? Afterwards, how can I reinitialize the Offline Files cache for every user, without doing it manually, workstation by workstation? b) Determine which users have unsynced changes to OLDBOX (again, how?), search each user's CSC folder domain-wide via workstation admin shares, and grab the unsynched data. Reinitialize the Offline Files cache for every user. With this: How can I detect which users have unsynched changes with a script? How can I search each user's CSC folder, when the ownership and permissions set for CSC folders are so restrictive? Again, afterwards, how can I reinitialize the Offline Files cache for every user, without doing it manually, workstation by workstation? c) Manually visit each workstation, copy the contents of the CSC folder, and manually copy that data onto NEWBOX. Reinitialize the Offline Files cache for every user. With this: Again, how do I 'break into' the CSC folder and get to its data? As an experiment, I took one workstation's HD offsite, imaged it for safety, and then tried the following with one of our shop PCs, after attaching the drive: grant myself full control of the folder (failed), grant myself ownership of the folder (failed), run chkdsk on the whole drive to make sure nothing's messed up (all OK), try to take full control of the entire drive (failed), try to take ownership of the entire drive (failed) MS KB articles and Googling around suggests there's a utility called CSCCMD that's meant for this exact scenario...but it looks like it's available for XP, not Vista, no? Again, afterwards, how can I reinitialize the Offline Files cache for every user, without doing it manually, workstation by workstation? For problem 2: a) Figure out which users are on roaming profiles, and where their profiles 'live' on the server. Create new folders for them in the redirected folders repository, migrate existing data, and disable the roaming. With this: Finding out who's roaming isn't hard. But what's the best way to disable the roaming itself? In AD Users and Computers, or on each user's workstation? Doing it centrally on the server seems more efficient; that said, all of the KB research I've done turns up articles on how to go from local to roaming, not the other way around, so I don't have good documentation on this. In closing: we have good backups of NEWBOX and OLDBOX, but not of the workstations themselves, so anything drastic on the client side would need imaging and testing for safety. Thanks for reading along this far! Hopefully you can help me dig us out of this mess.

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  • how to obtain the relative path of a resource in a j2ee project

    - by Neeraj
    I have a Dynamic Web Project having a flat file (or say text file). I have created a servlet in which I need to use this file. My code is as following: protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // String resource = request.getParameter ("json") ; if ( resource != null && !resource.equals ( "" ) ) { //use getResourceAsStream ( ) to properly get the file. InputStream is = getServletContext ().getResourceAsStream ("rateJSON") ; if ( is != null ) { // the resource exists response.setContentType("application/json"); response.setHeader("Pragma", "No-cache"); response.setDateHeader("Expires", 0); response.setHeader("Cache-Control", "no-cache"); StringWriter sw = new StringWriter ( ) ; for ( int c = is.read ( ) ; c != -1; c = is.read ( ) ) { sw.write ( c ) ; } PrintWriter out = response.getWriter(); out.print (sw.toString ()) ; out.flush(); } } } The problem is that the InputStream is has null value. I'm not sure how to get the correct relative path. I'm using JBOSS as the app server. I have added the resource file in the WebContent directory of a Dynamic Web Project. As a different approch, I tried this: protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // TODO Auto-generated method stub ServletConfig config = getServletConfig(); String contextName = config.getInitParameter("ApplicationName"); System.out.println("context name"+ contextName); String contextPath = config.getServletContext().getRealPath(contextName); System.out.println("context Path"+contextPath); //contextPath = contextPath.substring(0, contextPath.indexOf(contextName)); contextPath += "\\rateJSON.txt"; System.out.println(contextPath); String resource = request.getParameter ("json") ; System.out.println("Hi there1"+resource); if ( resource != null && !resource.equals ( "" ) ) { System.out.println("Hi there"); //use getResourceAsStream ( ) to properly get the file. //InputStream is = getServletContext ().getResourceAsStream (resource) ; InputStream is = getServletConfig().getServletContext().getResourceAsStream(contextPath); if ( is != null ) { // the resource exists System.out.println("Hi there2"); response.setContentType("application/json"); response.setHeader("Pragma", "No-cache"); response.setDateHeader("Expires", 0); response.setHeader("Cache-Control", "no-cache"); StringWriter sw = new StringWriter ( ); for ( int c = is.read ( ) ; c != -1; c = is.read ( ) ) { sw.write ( c ) ; System.out.println(c); } PrintWriter out = response.getWriter(); out.print (sw.toString ()) ; System.out.println(sw.toString()); out.flush(); } } } The value of contextPath is now: C:\JBOSS\jboss-5.0.1.GA\server\default\tmp\4p72206b-uo5r7k-g0vn9pof-1-g0vsh0o9-b7\Nationwide.war\WEB-INF\rateJSON But at this location the rateJSON file is not there? It seems JBOSS is not putting this file in the App.war or doesn't deploy it??? Could someone please help me?

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  • Websocket handshake response not forwarded from TCP to client

    - by Saharsh
    I am trying to create a websocket server. I can see the websocket client's opening handhshake. My response to it is received by the client laptop (I can see this on wireshark). So the TCP connection has been established. But the client (a chrome websocket client extension) does not receive the handshake packet. What could be a possible reason for TCP to not forward the handshake to the client or for the client to not be able to read the TCP message? Client handshake: GET HTTP/1.1 Upgrade: websocket Connection:Upgrade Cache-Control:no-cache Host:192.168.0.101 Origin:http://www.websocket.org Pragma:no-cache Sec-WebSocket-Extensions:permessage-deflate; client_max_window_bits, x-webkit-deflate-frame Sec-WebSocket-Key: qrmw/m+BoZije6h9HYKmVw== Sec-WebSocket-Version:13 Upgrade:websocket Server Response: HTTP/1.1 101 Switching Protocols Upgrade: websocket Connection: Upgrade Sec-WebSocket-Accept: jj1g5Io57m9ks8cme3jkbyo2asc= Access-Control-Allow-Origin: http://www.websocket.org Server: xyz Sec-WebSocket-Extensions: Thanks!

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  • Configuring memcached for a particular scenario

    - by pradeepchhetri
    I have a web application which queries opentsdb server(which in backend using Hbase cluster) for the datapoints of different metrics and using dygraph javascript graphing library, I am plotting those metrics. Since getting all the datapoints of past one day from opentsdb for a particular metric is itself taking nearly 2 seconds, my application which is plotting nearly 25 metrics is becoming very slow. In order to reduce this latency, I am thinking of using memcached module of php5 for caching all the queries. But I have few questions regarding memcached. Is there any way I can configure memcache to keep on updating its cache in the background by running some command line queries after particular interval of time. Is there any way I can configure memcache to always reply for a query using cache instead of first updating its cache because my application just plots datapoints for past one day. Missing out some datapoints is not that critical.

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  • High-End Gaming Desktop PC in France [closed]

    - by Lerikunus
    Hello, I was looking to buy an ALIENWARE AREA 51, as my Desktop crashed some days ago. But the Preliminary Ship date is 03.01.11 and I need the new PC until Friday next week =( Does someone know a(n) (online)-store where Build&Shipping time is quite low so I can get it until next Friday? I am living in France (Nice). Or any place I can ask fot his kind of advice? This is my desired configuration: Overclocked Intel® Core™ i7 980x Extreme Six Core Processor (4.0GHz, 12MB Cache) 12GB Triple Channel 1600MHz DDR3 Dual 2GB ATI Radeon™ HD 6950 2TB RAID 1+0 (4x 1TB SATA-II, 7,200 RPM, 32MB Cache HDDs) 2TB RAID 1 (2x2TB SATA-II, 7,200 RPM, 32MB Cache HDDs) Thank you very much!

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  • How to combine wildcards and spaces (quotes) in an Windows command?

    - by Jan Fabry
    I want to remove directories of the following format: C:\Program Files\FogBugz\Plugins\cache\[email protected]_NN NN is a number, so I want to use a wildcard (this is part of a post-build step in Visual Studio). The problem is that I need to combine quotes around the path name (for the space in Program Files) with a wildcard to match the end of the path. I already found out that rd is the remove command that accepts wildcards, but where do I put the quotes? I have tried no ending quote (works for dir), ...example.com*", ...example.com"*, ...example.com_??", ...cache\"[email protected]*, ...cache"\[email protected]*, but none of them work. (How many commands to remove a file/directory are there in Windows anyway? And why do they all differ in capabilities?)

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  • What is excessive swapping.

    - by amateur barista
    This post led me to ask that question. Cache contention On a large site, if you are using MyISAM, contention occurs in the database tables when the cache is forced to clear after a node or a comment is added. With tens of thousands of filter text snippets needing to be deleted, the table will be locked for a long period, and any accesses to it will be queued pending the purge of the data in it. The same is true for the page cache as well. This often causes a "site hang" for a minute or two. During that time new requests keep piling up, and if you do not have the MaxClients parameter in Apache setup correctly, the system can go into thrashing because of excessive swapping.

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  • Run script when Varnish starts

    - by kipusoep
    I'd like to run a script when Varnish starts. This script should execute a webrequest to a webserver (its backend), which then makes sure Varnish's cache gets filled with all pages residing on this webserver. So this script makes sure everyting is in Varnish's cache when Varnish (re)starts, because we're using Varnish as cache and fail-over (the webserver should be able to be down for let's say a week for example, without any consequences). What are the possibilities to do this? We can't just edit /etc/init.d/varnish and /usr/sbin/varnishd because they can het overwritten when updating varnish? Thanks!

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  • Override `drop` for a custom sequence

    - by Bruno Reis
    In short: in Clojure, is there a way to redefine a function from the standard sequence API (which is not defined on any interface like ISeq, IndexedSeq, etc) on a custom sequence type I wrote? 1. Huge data files I have big files in the following format: A long (8 bytes) containing the number n of entries n entries, each one being composed of 3 longs (ie, 24 bytes) 2. Custom sequence I want to have a sequence on these entries. Since I cannot usually hold all the data in memory at once, and I want fast sequential access on it, I wrote a class similar to the following: (deftype DataSeq [id ^long cnt ^long i cached-seq] clojure.lang.IndexedSeq (index [_] i) (count [_] (- cnt i)) (seq [this] this) (first [_] (first cached-seq)) (more [this] (if-let [s (next this)] s '())) (next [_] (if (not= (inc i) cnt) (if (next cached-seq) (DataSeq. id cnt (inc i) (next cached-seq)) (DataSeq. id cnt (inc i) (with-open [f (open-data-file id)] ; open a memory mapped byte array on the file ; seek to the exact position to begin reading ; decide on an optimal amount of data to read ; eagerly read and return that amount of data )))))) The main idea is to read ahead a bunch of entries in a list and then consume from that list. Whenever the cache is completely consumed, if there are remaining entries, they are read from the file in a new cache list. Simple as that. To create an instance of such a sequence, I use a very simple function like: (defn ^DataSeq load-data [id] (next (DataSeq. id (count-entries id) -1 []))) ; count-entries is a trivial "open file and read a long" memoized As you can see, the format of the data allowed me to implement count in very simply and efficiently. 3. drop could be O(1) In the same spirit, I'd like to reimplement drop. The format of these data files allows me to reimplement drop in O(1) (instead of the standard O(n)), as follows: if dropping less then the remaining cached items, just drop the same amount from the cache and done; if dropping more than cnt, then just return the empty list. otherwise, just figure out the position in the data file, jump right into that position, and read data from there. My difficulty is that drop is not implemented in the same way as count, first, seq, etc. The latter functions call a similarly named static method in RT which, in turn, calls my implementation above, while the former, drop, does not check if the instance of the sequence it is being called on provides a custom implementation. Obviously, I could provide a function named anything but drop that does exactly what I want, but that would force other people (including my future self) to remember to use it instead of drop every single time, which sucks. So, the question is: is it possible to override the default behaviour of drop? 4. A workaround (I dislike) While writing this question, I've just figured out a possible workaround: make the reading even lazier. The custom sequence would just keep an index and postpone the reading operation, that would happen only when first was called. The problem is that I'd need some mutable state: the first call to first would cause some data to be read into a cache, all the subsequent calls would return data from this cache. There would be a similar logic on next: if there's a cache, just next it; otherwise, don't bother populating it -- it will be done when first is called again. This would avoid unnecessary disk reads. However, this is still less than optimal -- it is still O(n), and it could easily be O(1). Anyways, I don't like this workaround, and my question is still open. Any thoughts? Thanks.

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  • Varnishhist x- and y-axis

    - by pst
    In varnishhist the x-axis shows the time varnish took between getting the request from the kernel and sending it back to kernel. The y-axis shows the number of requests. | => cache hit # => cache miss That is what I understood from the manpage. Correct me if I'm wrong. Yet there is one thing I'm unsure about. The pipes (|) on the far left side, do they also stand for cache hits or are they just there to print the y-axis? I'm voting for the latter, but would like to be sure.

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  • ASP.NET GZip Encoding Caveats

    - by Rick Strahl
    GZip encoding in ASP.NET is pretty easy to accomplish using the built-in GZipStream and DeflateStream classes and applying them to the Response.Filter property.  While applying GZip and Deflate behavior is pretty easy there are a few caveats that you have watch out for as I found out today for myself with an application that was throwing up some garbage data. But before looking at caveats let’s review GZip implementation for ASP.NET. ASP.NET GZip/Deflate Basics Response filters basically are applied to the Response.OutputStream and transform it as data is written to it through the ASP.NET Response object. So a Response.Write eventually gets written into the output stream which if a filter is also written through the filter stream’s interface. To perform the actual GZip (and Deflate) encoding typically used by Web pages .NET includes the GZipStream and DeflateStream stream classes which can be readily assigned to the Repsonse.OutputStream. With these two stream classes in place it’s almost trivially easy to create a couple of reusable methods that allow you to compress your HTTP output. In my standard WebUtils utility class (from the West Wind West Wind Web Toolkit) created two static utility methods – IsGZipSupported and GZipEncodePage – that check whether the client supports GZip encoding and then actually encodes the current output (note that although the method includes ‘Page’ in its name this code will work with any ASP.NET output). /// <summary> /// Determines if GZip is supported /// </summary> /// <returns></returns> public static bool IsGZipSupported() { string AcceptEncoding = HttpContext.Current.Request.Headers["Accept-Encoding"]; if (!string.IsNullOrEmpty(AcceptEncoding) && (AcceptEncoding.Contains("gzip") || AcceptEncoding.Contains("deflate"))) return true; return false; } /// <summary> /// Sets up the current page or handler to use GZip through a Response.Filter /// IMPORTANT: /// You have to call this method before any output is generated! /// </summary> public static void GZipEncodePage() { HttpResponse Response = HttpContext.Current.Response; if (IsGZipSupported()) { string AcceptEncoding = HttpContext.Current.Request.Headers["Accept-Encoding"]; if (AcceptEncoding.Contains("deflate")) { Response.Filter = new System.IO.Compression.DeflateStream(Response.Filter, System.IO.Compression.CompressionMode.Compress); Response.Headers.Remove("Content-Encoding"); Response.AppendHeader("Content-Encoding", "deflate"); } else { Response.Filter = new System.IO.Compression.GZipStream(Response.Filter, System.IO.Compression.CompressionMode.Compress); Response.Headers.Remove("Content-Encoding"); Response.AppendHeader("Content-Encoding", "gzip"); } } } As you can see the actual assignment of the Filter is as simple as: Response.Filter = new DeflateStream(Response.Filter, System.IO.Compression.CompressionMode.Compress); which applies the filter to the OutputStream. You also need to ensure that your response reflects the new GZip or Deflate encoding and ensure that any pages that are cached in Proxy servers can differentiate between pages that were encoded with the various different encodings (or no encoding). To use this utility function now is trivially easy: In any ASP.NET code that wants to compress its Response output you simply use: protected void Page_Load(object sender, EventArgs e) { WebUtils.GZipEncodePage(); Entry = WebLogFactory.GetEntry(); var entries = Entry.GetLastEntries(App.Configuration.ShowEntryCount, "pk,Title,SafeTitle,Body,Entered,Feedback,Location,ShowTopAd", "TEntries"); if (entries == null) throw new ApplicationException("Couldn't load WebLog Entries: " + Entry.ErrorMessage); this.repEntries.DataSource = entries; this.repEntries.DataBind(); } Here I use an ASP.NET page, but the above WebUtils.GZipEncode() method call will work in any ASP.NET application type including HTTP Handlers. The only requirement is that the filter needs to be applied before any other output is sent to the OutputStream. For example, in my CallbackHandler service implementation by default output over a certain size is GZip encoded. The output that is generated is JSON or XML and if the output is over 5k in size I apply WebUtils.GZipEncode(): if (sbOutput.Length > GZIP_ENCODE_TRESHOLD) WebUtils.GZipEncodePage(); Response.ContentType = ControlResources.STR_JsonContentType; HttpContext.Current.Response.Write(sbOutput.ToString()); Ok, so you probably get the idea: Encoding GZip/Deflate content is pretty easy. Hold on there Hoss –Watch your Caching Or is it? There are a few caveats that you need to watch out for when dealing with GZip content. The fist issue is that you need to deal with the fact that some clients don’t support GZip or Deflate content. Most modern browsers support it, but if you have a programmatic Http client accessing your content GZip/Deflate support is by no means guaranteed. For example, WinInet Http clients don’t support GZip out of the box – it has to be explicitly implemented. Other low level HTTP clients on other platforms too don’t support GZip out of the box. The problem is that your application, your Web Server and Proxy Servers on the Internet might be caching your generated content. If you return content with GZip once and then again without, either caching is not applied or worse the wrong type of content is returned back to the client from a cache or proxy. The result is an unreadable response for *some clients* which is also very hard to debug and fix once in production. You already saw the issue of Proxy servers addressed in the GZipEncodePage() function: // Allow proxy servers to cache encoded and unencoded versions separately Response.AppendHeader("Vary", "Content-Encoding"); This ensures that any Proxy servers also check for the Content-Encoding HTTP Header to cache their content – not just the URL. The same thing applies if you do OutputCaching in your own ASP.NET code. If you generate output for GZip on an OutputCached page the GZipped content will be cached (either by ASP.NET’s cache or in some cases by the IIS Kernel Cache). But what if the next client doesn’t support GZip? She’ll get served a cached GZip page that won’t decode and she’ll get a page full of garbage. Wholly undesirable. To fix this you need to add some custom OutputCache rules by way of the GetVaryByCustom() HttpApplication method in your global_ASAX file: public override string GetVaryByCustomString(HttpContext context, string custom) { // Override Caching for compression if (custom == "GZIP") { string acceptEncoding = HttpContext.Current.Response.Headers["Content-Encoding"]; if (string.IsNullOrEmpty(acceptEncoding)) return ""; else if (acceptEncoding.Contains("gzip")) return "GZIP"; else if (acceptEncoding.Contains("deflate")) return "DEFLATE"; return ""; } return base.GetVaryByCustomString(context, custom); } In a page that use Output caching you then specify: <%@ OutputCache Duration="180" VaryByParam="none" VaryByCustom="GZIP" %> To use that custom rule. It’s all Fun and Games until ASP.NET throws an Error Ok, so you’re up and running with GZip, you have your caching squared away and your pages that you are applying it to are jamming along. Then BOOM, something strange happens and you get a lovely garbled page that look like this: Lovely isn’t it? What’s happened here is that I have WebUtils.GZipEncode() applied to my page, but there’s an error in the page. The error falls back to the ASP.NET error handler and the error handler removes all existing output (good) and removes all the custom HTTP headers I’ve set manually (usually good, but very bad here). Since I applied the Response.Filter (via GZipEncode) the output is now GZip encoded, but ASP.NET has removed my Content-Encoding header, so the browser receives the GZip encoded content without a notification that it is encoded as GZip. The result is binary output. Here’s what Fiddler says about the raw HTTP header output when an error occurs when GZip encoding was applied: HTTP/1.1 500 Internal Server Error Cache-Control: private Content-Type: text/html; charset=utf-8 Date: Sat, 30 Apr 2011 22:21:08 GMT Content-Length: 2138 Connection: close ?`I?%&/m?{J?J??t??` … binary output striped here Notice: no Content-Encoding header and that’s why we’re seeing this garbage. ASP.NET has stripped the Content-Encoding header but left our filter intact. So how do we fix this? In my applications I typically have a global Application_Error handler set up and in this case I’ve been using that. One thing that you can do in the Application_Error handler is explicitly clear out the Response.Filter and set it to null at the top: protected void Application_Error(object sender, EventArgs e) { // Remove any special filtering especially GZip filtering Response.Filter = null; … } And voila I get my Yellow Screen of Death or my custom generated error output back via uncompressed content. BTW, the same is true for Page level errors handled in Page_Error or ASP.NET MVC Error handling methods in a controller. Another and possibly even better solution is to check whether a filter is attached just before the headers are sent to the client as pointed out by Adam Schroeder in the comments: protected void Application_PreSendRequestHeaders() { // ensure that if GZip/Deflate Encoding is applied that headers are set // also works when error occurs if filters are still active HttpResponse response = HttpContext.Current.Response; if (response.Filter is GZipStream && response.Headers["Content-encoding"] != "gzip") response.AppendHeader("Content-encoding", "gzip"); else if (response.Filter is DeflateStream && response.Headers["Content-encoding"] != "deflate") response.AppendHeader("Content-encoding", "deflate"); } This uses the Application_PreSendRequestHeaders() pipeline event to check for compression encoding in a filter and adjusts the content accordingly. This is actually a better solution since this is generic – it’ll work regardless of how the content is cleaned up. For example, an error Response.Redirect() or short error display might get changed and the filter not cleared and this code actually handles that. Sweet, thanks Adam. It’s unfortunate that ASP.NET doesn’t natively clear out Response.Filters when an error occurs just as it clears the Response and Headers. I can’t see where leaving a Filter in place in an error situation would make any sense, but hey - this is what it is and it’s easy enough to fix as long as you know where to look. Riiiight! IIS and GZip I should also mention that IIS 7 includes good support for compression natively. If you can defer encoding to let IIS perform it for you rather than doing it in your code by all means you should do it! Especially any static or semi-dynamic content that can be made static should be using IIS built-in compression. Dynamic caching is also supported but is a bit more tricky to judge in terms of performance and footprint. John Forsyth has a great article on the benefits and drawbacks of IIS 7 compression which gives some detailed performance comparisons and impact reviews. I’ll post another entry next with some more info on IIS compression since information on it seems to be a bit hard to come by. Related Content Built-in GZip/Deflate Compression in IIS 7.x HttpWebRequest and GZip Responses © Rick Strahl, West Wind Technologies, 2005-2011Posted in ASP.NET   IIS7  

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  • Is recursion really bad?

    - by dotneteer
    After my previous post about the stack space, it appears that there is perception from the feedback that recursion is bad and we should avoid deep recursion. After writing a compiler, I know that the modern computer and compiler are complex enough and one cannot automatically assume that a hand crafted code would out-perform the compiler optimization. The only way is to do some prototype to find out. So why recursive code may not perform as well? Compilers place frames on a stack. In additional to arguments and local variables, compiles also need to place frame and program pointers on the frame, resulting in overheads. So why hand-crafted code may not performance as well? The stack used by a compiler is a simpler data structure and can grow and shrink cleanly. To replace recursion with out own stack, our stack is allocated in the heap that is far more complicated to manage. There could be overhead as well if the compiler needs to mark objects for garbage collection. Compiler also needs to worry about the memory fragmentation. Then there is additional complexity: CPUs have registers and multiple levels of cache. Register access is a few times faster than in-CPU cache access and is a few 10s times than on-board memory access. So it is up to the OS and compiler to maximize the use of register and in-CPU cache. For my particular problem, I did an experiment to rewrite my c# version of recursive code with a loop and stack approach. So here are the outcomes of the two approaches:   Recursive call Loop and Stack Lines of code for the algorithm 17 46 Speed Baseline 3% faster Readability Clean Far more complex So at the end, I was able to achieve 3% better performance with other drawbacks. My message is never assuming your sophisticated approach would automatically work out better than a simpler approach with a modern computer and compiler. Gage carefully before committing to a more complex approach.

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  • In Which We Demystify A Few Docupresentment Settings And Learn the Ethos of the Author

    - by Andy Little
    It's no secret that Docupresentment (part of the Oracle Documaker suite) is powerful tool for integrating on-demand and interactive applications for publishing with the Oracle Documaker framework.  It's also no secret there are are many details with respect to the configuration of Docupresentment that can elude even the most erudite of of techies.  To be sure, Docupresentment will work for you right out of the box, and in most cases will suit your needs without toying with a configuration file.  But, where's the adventure in that?   With this inaugural post to That's The Way, I'm going to introduce myself, and what my aim is with this blog.  If you didn't figure it out already by checking out my profile, my name is Andy and I've been with Oracle (nee Skywire Software nee Docucorp nee Formmaker) since the formative years of 1998.  Strangely, it doesn't seem that long ago, but it's certainly a lifetime in the age of technology.  I recall running a BBS from my parent's basement on a 1200 baud modem, and the trepidation and sweaty-palmed excitement of upgrading to the power and speed of 2400 baud!  Fine, I'll admit that perhaps I'm inflating the experience a bit, but I was kid!  This is the stuff of War Games and King's Quest I and the demise of TI-99 4/A.  Exciting times.  So fast-forward a bit and I'm 12 years into a career in the world of document automation and publishing working for the best (IMHO) software company on the planet.  With That's The Way I hope to shed a little light and peek under the covers of some of the more interesting aspects of implementations involving the tech space within the Oracle Insurance Global Business Unit (IGBU), which includes Oracle Documaker, Rating & Underwriting, and Policy Administration to name a few.  I may delve off course a bit, and you'll likely get a dose of humor (at least in my mind) but I hope you'll glean at least a tidbit of usefulness with each post.  Feel free to comment as I'm a fairly conversant guy and happy to talk -- it's stopping the talking that's the hard part... So, back to our regularly-scheduled post, already in progress.  By this time you've visited Oracle's E-Delivery site and acquired your properly-licensed version of Oracle Documaker.  Wait -- you didn't find it?  Understandable -- navigating the voluminous download library within Oracle can be a daunting task.  It's pretty simple once you’ve done it a few times.  Login to the e-delivery site, and accept the license terms and restrictions.  Then, you’ll be able to select the Oracle Insurance Applications product pack and your appropriate platform. Click Go and you’ll see a list of applicable products, and you’ll click on Oracle Documaker Media Pack (as I went to press with this article the version is 11.4): Finally, click the Download button next to Docupresentment (again, version at press time is 2.2 p5). This should give you a ZIP file that contains the installation packages for the Docupresentment Server and Client, cryptically named IDSServer22P05W32.exe and IDSClient22P05W32.exe. At this time, I’d like to take a little detour and explain that the world of Oracle, like most technical companies, is rife with acronyms.  One of the reasons Skywire Software was a appealing to Oracle was our use of many acronyms, including the occasional use of multiple acronyms with the same meaning.  I apologize in advance and will try to point these out along the way.  Here’s your first sticky note to go along with that: IDS = Internet Document Server = Docupresentment Once you’ve completed the installation, you’ll have a shiny new Docupresentment server and client, and if you installed the default location it will be living in c:\docserv. Unix users, I’m one of you!  You’ll find it by default in  ~/docupresentment/docserv.  Forging onward with the meat of this post is learning about some special configuration options.  By now you’ve read the documentation included with the download (specifically ids_book.pdf) which goes into some detail of the rubric of the configuration file and in fact there’s even a handy utility that provides an interface to the configuration file (see Running IDSConfig in the documentation).  But who wants to deal with a configuration utility when we have the tools and technology to edit the file <gasp> by hand! I shall now proceed with the standard Information Technology Under the Hood Disclaimer: Please remember to back up any files before you make changes.  I am not responsible for any havoc you may wreak! Go to your installation directory, and locate your docserv.xml file.  Open it in your favorite XML editor.  I happen to be fond of Notepad++ with the XML Tools plugin.  Almost immediately you will behold the splendor of the configuration file.  Just take a moment and let that sink in.  Ok – moving on.  If you reviewed the documentation you know that inside the root <configuration> node there are multiple <section> nodes, each containing a specific group of settings.  Let’s take a look at <section name=”DocumentServer”>: There are a few entries I’d like to discuss.  First, <entry name=”StartCommand”>. This should be pretty self-explanatory; it’s the name of the executable that’s run when you fire up Docupresentment.  Immediately following that is <entry name=”StartArguments”> and as you might imagine these are the arguments passed to the executable.  A few things to point out: The –Dids.configuration=docserv.xml parameter specifies the name of your configuration file. The –Dlogging.configuration=logconf.xml parameter specifies the name of your logging configuration file (this uses log4j so bone up on that before you delve here). The -Djava.endorsed.dirs=lib/endorsed parameter specifies the path where 3rd party Java libraries can be located for use with Docupresentment.  More on that in another post. The <entry name=”Instances”> allows you to specify the number of instances of Docupresentment that will be started.  By default this is two, and generally two instances per CPU is adequate, however you will always need to perform load testing to determine the sweet spot based on your hardware and types of transactions.  You may have many, many more instances than 2. Time for a sidebar on instances.  An instance is nothing more than a separate process of Docupresentment.  The Docupresentment service that you fire up with docserver.bat or docserver.sh actually starts a watchdog process, which is then responsible for starting up the actual Docupresentment processes.  Each of these act independently from one another, so if one crashes, it does not affect any others.  In the case of a crashed process, the watchdog will start up another instance so the number of configured instances are always running.  Bottom line: instance = Docupresentment process. And now, finally, to the settings which gave me pause on an not-too-long-ago implementation!  Docupresentment includes a feature that watches configuration files (such as docserv.xml and logconf.xml) and will automatically restart its instances to load the changes.  You can configure the time that Docupresentment waits to check these files using the setting <entry name=”FileWatchTimeMillis”>.  By default the number is 12000ms, or 12 seconds.  You can save yourself a few CPU cycles by extending this time, or by disabling  the check altogether by setting the value to 0.  This may or may not be appropriate for your environment; if you have 100% uptime requirements then you probably don’t want to bring down an entire set of processes just to accept a new configuration value, so it’s best to leave this somewhere between 12 seconds to a few minutes.  Another point to keep in mind: if you are using Documaker real-time processing under Docupresentment the Master Resource Library (MRL) files and INI options are cached, and if you need to affect a change, you’ll have to “restart” Docupresentment.  Touching the docserv.xml file is an easy way to do this (other methods including using the RSS request, but that’s another post). The next item up: <entry name=”FilePurgeTimeSeconds”>.  You may already know that the Docupresentment system can generate many temporary files based on certain request types that are processed through the system.  What you may not know is how those files are cleaned up.  There are many rules in Docupresentment that cause the creation of temporary files.  When these files are created, Docupresentment writes an entry into a properties file called the file cache.  This file contains the name, creation date, and expiration time of each temporary file created by each instance of Docupresentment.  Periodically Docupresentment will check the file cache to determine if there are files that are past the expiration time, not unlike that block of cheese festering away in the back of my refrigerator.  However, unlike my ‘fridge cleaning tendencies, Docupresentment is quick to remove files that are past their expiration time.  You, my friend, have the power to control how often Docupresentment inspects the file cache.  Simply set the value for <entry name=”FilePurgeTimeSeconds”> to the number of seconds appropriate for your requirements and you’re set.  Note that file purging happens on a separate thread from normal request processing, so this shouldn’t interfere with response times unless the CPU happens to be really taxed at the point of cache processing.  Finally, after all of this, we get to the final setting I’m going to address in this post: <entry name=”FilePurgeList”>.  The default is “filecache.properties”.  This establishes the root name for the Docupresentment file cache that I mentioned previously.  Docupresentment creates a separate cache file for each instance based on this setting.  If you have two instances, you’ll see two files created: filecache.properties.1 and filecache.properties.2.  Feel free to open these up and check them out. I hope you’ve enjoyed this first foray into the configuration file of Docupresentment.  If you did enjoy it, feel free to drop a comment, I welcome feedback.  If you have ideas for other posts you’d like to see, please do let me know.  You can reach me at [email protected]. ‘Til next time! ###

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  • Flash Technology Can Revolutionize your IT Infrastructure

    - by kimberly.billings
    A recent article in the Data Center Journal written by Mark Teter outlines how flash is becoming a disruptive technology in the data center and how it will soon replace HDDs in the storage hierarchy. As Teter explains, the drivers behind this trend are lower cost/performance and power savings; flash is over 100x faster for reads than the fastest HDD, and while it is expensive, it can produce dramatic reductions in the cost of performance as measured in Input/Outputs per second (IOPS). What's more, flash consumes 1/5th the power of HDD, so it's faster AND greener. Teter writes, "when appropriately used, flash turns the current economics of IT performance on its head. That's disruptive." Exadata Smart Flash Cache in the Sun Oracle Database Machine makes intelligent use of flash storage to deliver extreme performance for OLTP and mixed workloads. It intelligently caches data from the Oracle Database replacing slow mechanical I/O operations to disk with very rapid flash memory operations. Exadata Smart Flash Cache is the fundamental technology of the Sun Oracle Database Machine that enables the processing of up to 1 million random I/O operations per second (IOPS), and the scanning of data within Exadata storage at up to 50 GB/second. Are you incorporating flash into your storage strategy? Let us know! Read more: "Flash technology can revolutionize your IT infrastructure", The Data Center Journal, March 30, 2010. Exadata Smart Flash Cache and the Sun Oracle Database Machine white paper var gaJsHost = (("https:" == document.location.protocol) ? "https://ssl." : "http://www."); document.write(unescape("%3Cscript src='" + gaJsHost + "google-analytics.com/ga.js' type='text/javascript'%3E%3C/script%3E")); try { var pageTracker = _gat._getTracker("UA-13185312-1"); pageTracker._trackPageview(); } catch(err) {}

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