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• Session serialization in JavaEE environment

  - by Ionut

  Please consider the following scenario: We are working on a JavaEE project for which the scalability starts to become an issue. Up until now, we were able to scale up but this is no longer an option. Therefore we need to consider scaling out and preparing the App for a clustered environment. Our main concern right now is serializing the user sessions. Sadly, we did not consider from the beginning the issue and we are encountering the following excetion: java.io.WriteAbortedException: writing aborted; java.io.NotSerializableException: org.apache.catalina.session.StandardSessionFacade I did some research and this exception is thrown because there are objects stored on the session which does not implement the Serializable interface. Considering that all over the app there are quite a few custom objects which are stored on the session without implementing this interface, it would require a lot of tedious work and dedication to fix all these classes declaration. We will fix all this declarations but the main concern is that, in the future, there may be a developer which will add a non Serializable object on the session and break the session serialization & replication over multiple nodes. As a quick overview of the project, we are developing using a home grown framework based on Struts 1 with the Servlet 3.0 API. This means that at this point, we are using the standard session.getAttribute() and session.setAttribute() to work with the session and the session handling is scattered all over the code base. Besides updating the classes of the objects stored on session and making sure that they implement the Serializable interface, what other measures of precaution should we take in order to ensure a reliable Session replication capability on the Application layer? I know it is a little bit late to consider this but what would be the best practice in this case? Furthermore, are there any other issues we should consider regarding this transition? Thank you in advance!

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• April 25th Online Forum -- Oracle Solaris 11: What's New Since the Launch

  - by Larry Wake

  It's been a few months since we released Oracle Solaris 11, so we thought it was time to check in and let you know how things are going. On April 25th, at 9:00 PT, we'll host an online forum, featuring Markus Flierl, the VP for Solaris core engineering, as well as engineers, customers and partners. During the forum, Markus and his crew will give an update on the release, recap Oracle's OS strategy, and give you a peek at what the engineers are working on for future updates. I think one of the more interesting parts of this event will be the chance for some of our customers to share why they've moved to Oracle Solaris 11 and what benefits it has already given them.  We'll also have an online chat, so you can ask Solaris engineers any questions about what you've heard, or other thoughts you've had.  It should be a worthwhile event -- hope you can join us. Online Forum: Oracle Solaris 11: What’s New Since the LaunchApril 25th 9:00 a.m. PDT – 11:30 a.m. PDTRegister today!

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• No proper kmeans clustering of images in matlab

  - by user3237134

  I am having 1200 face images in my training set.There are 2989 test face images. I am using eigen faces (PCA) for feature extraction. I am using kmeans clustering. Source code I tried: IDX = kmeans(z,5); clustercount=accumarray(IDX, ones(size(IDX))); disp(clustercount); Problem: Images are not clustered properly. Same faces should be clustered. But different faces are being clustered. Questions: Should I have to use still more face images for training? How accuracy of clustering can be achieved? What is the solution?

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• Monitoring folder diffs across servers with zabbix

  - by Marcus

  Problem: I want to make sure that a certain folder is equal regarding it's contents across my servers. I do not want an automatic filesync to keep them equal, changing is done manually. My initial thought was to once a day calculate some crc/hash on folder and send to Zabbix, and trigger when values differ. Is there any good tools out there that can calculate crc or similar of a folder? Anyone know of another solution that solves my problem?

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• Collaborative Filtering Techniques

  - by user95261

  Good Day! I am in need of help about collaborative filtering techniques implementation in predicting psychopathy of twitter users. I have two data set, training set and test set. Training set users have already scores in psychopathy, I need any collaborative filtering techniques to predict scores of test set users. Collaborative Filtering such as Item/User-Based CF, Bayesian Belief Nets, Clustering, Latent Semantic, etc. Please help me. :( I am very confused on how to implement any of these. Thank you!

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• hyperv machine guest loads slow

  - by Dani Avni

  this is by far one of the strangest things I have seen. I have a win 2008R2 cluster with a CSV. the CSV itself is on an iSCSI storage (hitachi HUS 110) basic config of the two hosts in the cluster is Dell R610 Win 2008 R2 with all patches 64GB 1 NIC for host access 2 NICs for guest access 2 NICs for iSCSI these machine work great and I can load a 2008R2 test guest machine on them in less than 90 seconds after the above config is running for over a year, I now need to add a new host. now the host is Dell R620 (Still intel but different CPU) Win 2008 R2 with all patches 64GB 1 NIC for host access 2 NICs for guest access 2 NICs for iSCSI I added this new host to the domain and to the cluster, I gave it access to the CSV and I tried loading the same guest machine that loads in 90 seconds in the other hosts. the machine loads in about 6 minutes. no matter how many times I try this the old hosts load the machine in about 90 seconds and this new host in around 6 minutes to eliminate any problems with the iSCSI connection, I added a new LUN and directly accessed it from the new host and I was working at around 300MB/s so no problem there. I also tested the connection between the other hosts and the new one and network is working fine there too. to eliminate problems in HyperV, I copied the machine to the local disk of the new host and it loaded in less than 20 seconds. now is the point were things get a lot stranger: in my tests I tried installing a fresh windows guest machine to the CSV from the new host. I noticed that while the fresh windows was installing, my test guest was loading in less than 90 seconds even on the new host (I repeated this a few times). If I paused the fresh install guest and tried loading the test guest again it loaded in 6 minutes. and again after I resumed the guest installation the test guest loaded fast. after the fresh windows was also loaded, I ran tests loading the fresh window and my test machine. each one of them loaded in about 5 minutes when I tried loading them separately. however when I started both of them in the same time they both loaded in around 2.5 minutes it seems that the iSCSI disk access is only working if it is under some load (although I never got to above 10% utilization according to the task manager) does anyone have any idea what could be the problem?

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• How to script printer creation on a Windows Server 2008 R2 clustered print server?

  - by Massimo

  As per subject. I've found some ways of scripting printer creation on Windows print servers using WMI, but it looks like WMI doesn't support clustered print servers (or clustered servers at all). The scripts in C:\Windows\System32\Printing_Admin_Scripts are useless because, they are not cluster-aware and end up creating the printers on the active cluster node (just like using WMI). The only tool I found that was able to work on a clustered print server is printui.exe (shortcut for rundll32 printui.dll, PrintUIEntry), but it can't create TCP printing ports: it can only add printers if the port already exists. How can I completely script printer creation (including TCP printing ports!) on a clustered Windows Server 2008 R2 print server?

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• Apache mod_wsgi elegant clustering method

  - by Dr I

  I'm currently trying to build a scalable infrastructure for my Python webservers. Actually, I'm trying to find the most elegant way to build a scalable cluster to host all my Python WebServices. For now, I'm using three servers like this: 1 x PuppetMaster to deploy my servers. 2 x Apache Reverse Proxy Front-end servers. 1 x Apache HTTPd Server which host the Python WSGI Applications and binded to using mod_wsgi. 4 x MongoDB Clustered server. Everything is OK concerning the Reverse proxy and the DB Backend, I'm able to easily add a new Reverse Proxy and a new DB Node, but my problem is about the Python WebServer. I thinked to just provision a new node with exactly the same configuration and a rsync replication between the two nodes, but It's not really usefull in term of deployement for my developpers etc. So if you have a solution which is as efficient and elegant that the Tomcat Cluster I'll be really happy to ear it ;-)

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• how to proxy sql queries (INSERT, UPDATE e.t.c.)

  - by XakRu

  I have installed cluster MYSQL (galley with mariadb) As an application server installed Apache. on a server with Apache installed haproxy which proxies requests from php in this case installed for zabbix server cluster. But faced with deadlocks, now I want to proxy requests WRITE, INSERT, UPDATE to the second server. SELECT queries to the second and third server. I would be happy to see your suggestions. Please do not write: use mysql - proxy. I want to see what program it may to proxy SQL requests. scheme: http://www.gliffy.com/pubdoc/4474830/L.png

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• Setting up Cluster Configuration using an existing web server as a Primary Node?

  - by RapidWebs

  Thanks in advance for any help which is issued! I am having a slight issue, and need help with the decision making process when it comes to setting up my Cluster Configuration, consisting on a line of Ubuntu Servers (12.04). We currently have a Primary node, which resides in the US within a Datacenter, but we are going to be using this for all serious bandwidth and resource intensive websites, and through a configuration of Virtualmin + Webmin, will be setup as a sort of pseudo-cluster, using Virtualmins Cluster Modules. Anyways, on to the issue: We also have a business line setup locally, with three servers. here are their specs: Intel P4 2.4 ghz, 1GB Ram, 110 gb sata, Ubuntu 12.04* AMD 1.3 ghz, 512MB Ram, 20 GB IDE P3 Xeon 800mhz (dual physical processors), 1GB Ram, 3 * 25 GB Raid Configuration (one in use for host operating system). The first machine is currently IN USE and is serving virtual hosts off a sub-domain. My question is this: How can I integrate the Secondary node (which will be the Primary node per say, in this smaller configuration...) which is currently in use, into the cluster configuration w/ the other two servers for: Sharing Resources Redundancy (HA?) NFS /w the two Raid Disks without having the FORMAT the secondary node, and start fresh moving all my services in to a DRBD network drive or something similar, and than restoring all active virtualmin's Virtual hosts. the idea is that I want minimal downtime to people currently being served from server2.mywebsite.com, and from what I understand, all services need to be on a NFS so that they can be mounted on demand and accessed from the other machine taking over (i.e. Heartbeat + DRBD Config.) but my issue is that i already have all these services installed to their default directory structure: how can i most easily setup this NFS and HA system, move all my desires services to this new drive, and do it with minimal down time, and without breaking Virtualmin and everything else on my server? even just some pointers, a thread i could read, or a step by step check list or run down of commands i could issue to get started would be great! thanks!

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• AS3 and hashing

  - by gok

  Is it possible to hash flv videos so it is unplayable by itself and the format is unrecognizable by softwares, but i could actually de-hash them and play in my as3 script? This is going to be realized on a CD so I can't use server scripts.

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• Operations on Python hashes

  - by cdecker

  I've got a rather strange problem. For a Distributed Hash Table I need to be able to do some simple math operations on MD5 hashes. These include a sum (numeric sum represented by the hash) and a modulo operation. Now I'm wondering what the best way to implement these operations is. I'm using hashlib to calculate the hashes, but since the hashes I get are then string, how do I calculate with them?

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• Numeric operations over SHA-1 generated keys in C#

  - by webdreamer

  I'm trying to implement a Chord distributed hash table. I want to use SHA-1 as the hash function to generate node ids and map values to the DHT. However, I'll need to use numerical operations on the SHA-1 generated key, such as a modulo, for example. I wonder in which type of variable should I put the array of bytes I get, and how can I convert from one to another.

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• How does Microsoft generate the Event ID for winqual events?

  - by Tim

  I am curious about the IDs that are used to identify items in winqual. I assume it is some sort of hash. Is this published? Hash of the module name, its version and an offset? That seems appropriate but the size is too small to cover the possibilities unless some truncation/lossy algorithm is used. This seems to be generated with the minidump on the client machine.

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• Compile-time (preprocessor) hashing of string

  - by AshirusNW

  Is there any way to create a hash of string at compile time using the C/C++ preprocessor (or even template-metaprogramming)? e.g. UNIQUE_SALT("HelloWord", 3DES); The idea is that HelloWorld will not be present in the compiled binary, just a hash.

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• What's the big deal with brute force on hashes like MD5

  - by Jan Kuboschek

  I just spent some time reading http://stackoverflow.com/questions/2768248/is-md5-really-that-bad (I highly recommend!). In it, it talks about hash collisions. Maybe I'm missing something here, but can't you just encrypt your password using, say, MD5 and then, say, SHA-1 (or any other, doesn't matter.) Wouldn't this increase the processing power required to brute-force the hash and reduce the possibility of collision?

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• Hashing (hidding) strings in Python

  - by Lucas

  What I need is to hash a string. It doesn't really have to be secure because its just going to be a hidden pharse in the text file (simply it doesn't have to be recognizable for a human-eye). It should not be just a random string because when user will be typing the string I would like to hash it and compare it with already hashed one (in the text file). What would be the best for this purpose? Can it be done with the own class?

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• Rails - Why is HAML showing the full hash?

  - by Mr. Demetrius Michael

  View: !!! %html %head %title= full_title(yield(:title)) =stylesheet_link_tag "application", media: "all" =javascript_include_tag "application" =csrf_meta_tags =render 'layouts/shim' %body =render 'layouts/header' .container =flash.each do |key, value| %div{class: "alert alert-#{key}"} #{value} Controller def create @user = User.new(params[:user]) if @user.save flash[:success] = "This is Correct" redirect_to @user else flash[:wrong] = "no" render 'new' end end Regardless of the flash (:success or :wrong or otherwise) it always compiles the entire hash as html (below) Output: <!DOCTYPE html> .... <div class='container'> <div class='alert alert-wrong'>no</div> {:wrong=&gt;&quot;no&quot;} </div> </body> </html> I have no idea why {:wrong=&gt;&quot;no&quot;} is being displayed. I've been staring at this terminal for hours. What's interesting is that the hash is being outputted with the container id, but not in the alert class. It feels like an indentation problem, but I went through several permutations with no success.

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• HREF link that targets nothing, does not want to use hash or void(0)

  - by Mattis

  I have a link that I want to be able to click to trigger a piece of jQuery code. Currently I have <a href="#" id="foo">Link</a> and $('#foo').click(function(){ // Do stuff }); which works well. But, I have always hated using hash in this way. The page flickers and the hash is added to the page url. One alternative is to use <a href="javascript:void(0);" id="foo">Link</a> but I also dislike seeing that piece of code in the browser status bar. It looks tacky. What I'd rather have is an explanatory javascript placeholder that does nothing, like <a href="javascript:zoom();" id="foo">Link</a> which actually works, but throws an ReferenceError in the javascript console since there are no such function. What's the minimum definition of a function that does nothing? Are there any other alternatives? Should I just skip the link and use something like <span id="foo" style="cursor:pointer;cursor:hand;">Link</span> instead?

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• Prevent hash navigation url

  - by Koningh

  I have the following problem: I'm using a slider (coda) to let people navigate trough some 'pages'. The slider uses hash links to navigate to the next page/slide. If a user is at page one (#page1), there is a link which will lead the user to page 2 (#page2) and so on. At the top of the slider the numbers of the pages appear as a link, but only when the page is visited. So if there are six pages and the user navigates from the first to the second and then the third one, there are only three links at the top of the slider (to page one, two and three). The problem is that a user can navigate to page five (or any page actually) without first visiting the pages previous to page five by just using the hash URL and typing the whole link in their address bar. For example if I would type www.mydomain.com/slider/index.php#page5 the slider automatically navigates to the fifth slide/page of the slider and thereby skipping the first four. I want to allow users to navigate to #page5 only if they have visited the first four (So by clicking trough the slides). This means that if they would go to #page5 directly by typing the URL in the address bar, I would like them to be send to the first page (#page1). Does anyone have any idea on solving this?

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• Perl help dereferencing a reference to an array of hash references, containing record set data

  - by user1724150

  I'm using the a Amazon Perl module that returns a reference to an array of hash references as $record_sets, containing record set data and I'm having a hard time dereferencing it. I can print the data using data dumper but I need to be able to manipulate the data. Below is the documentation provided for the module Thanks In Advance: #list_resource_record_sets #Lists resource record sets for a hosted zone. #Called in scalar context: $record_sets = $r53->list_resource_record_sets(zone_id => '123ZONEID'); #Returns: A reference to an array of hash references, containing record set data. Example: $record_sets = [ { name => 'example.com.', type => 'MX' ttl => 86400, records => [ '10 mail.example.com' ] }, { name => 'example.com.', type => 'NS', ttl => 172800, records => [ 'ns-001.awsdns-01.net.', 'ns-002.awsdns-02.net.', 'ns-003.awsdns-03.net.', 'ns-004.awsdns-04.net.' ]

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• Storing large json strings to database + hash

  - by Guy

  I need to store quiete large JSON data strings to the database. I am using gzip to compress the string and therefore BLOB MySQL data type to store it. However, only 5% of all the requests contain unique data and only unique data ought to be stored to the database. My approach is as follows. array_multisort data (array [a, b, c] is virtually the same as [a, c, b]). json_encode data (json_encode is faster than serialize; we need string array representation for the step 3). sha1 data (slower than md5, though less possible the collisions). Check if the hash exists in the database. 5.1 yes – do not insert the data. 5.2. no – gzip the data and store it along the hash. Is there anything about this (apart from storing JSON data to the database in the first place) that sounds fishy or should be done a different way? p.s. We are talking about a database with roughly 1kk unique records being created every month.

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• hash tables and 2d vectors

  - by Sunil

  I want to push a 2d vector into a hash table row by row and later search for a row (vector) in the hash table and want to be able to find it. I want to do something like #include <iostream> #include <set> #include <vector> using namespace std; int main(){ std::set < vector<int> > myset; vector< vector<int> > v; int k = 0; for ( int i = 0; i < 5; i++ ) { v.push_back ( vector<int>() ); for ( int j = 0; j < 5; j++ ) v[i].push_back ( k++ ); } for ( int i = 0; i < 5; i++ ) { std::copy(v[i].begin(),v[i].end(),std::inserter(myset)); // This is not correct but what is the right way ? // and also here, I want to search for a particular vector if it exists in the table. for ex. the second row of vector v. } return 0; } I'm not sure how to insert and look up a vector in a set. So if nybody could guide me, it will be helpful. Thanks

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• OPTICS Clustering algorithm. How to get the best epsilon

  - by Marco Galassi

  I am implementing a project which needs to cluster geographical points. OPTICS algorithm seems to be a very nice solution. It needs just 2 parameters as input(MinPts and Epsilon), which are, respectively, the minimum number of points needed to consider them as a cluster, and the distance value used to compare if two points are in can be placed in same cluster. My problem is that, due to the extreme variety of the points, I can't set a fixed epsilon. Just look at the image below. The same points structure but in a different scale would result very different. Suppose to set MinPts=2 and epsilon = 1Km. On the left, the algorithm would create 2 clusters(red and blue), but on the right it would create one single cluster containing all of the points(red), but I would like to obtain 2 clusters even on the right. So my question is: is there any kind of way to calculate dynamically the epsilon value to get this result? Thank you very much and excuse my for my poor english. Marco

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• apache mod_jk loadbalancing issue for glassfish cluster instances

  - by SibzTer

  I have a JEE ear application deployed on 2 clusters with 2 instances each on Glassfish v3.1. These are load balanced by an Apache server running on the same machine. My problem is that I am frequently seeing the following error messages frequently in the mod_jk.log file. Can you help me understand what the issue is? [Mon Jun 13 09:37:51 2011] [7116:7852] [info] ajp_process_callback::jk_ajp_common.c (1885): Writing to client aborted or client network problems [Mon Jun 13 09:37:51 2011] [7116:7852] [info] ajp_service::jk_ajp_common.c (2543): (viewerLocalInstance4) sending request to tomcat failed (unrecoverable), because of client write error (attempt=1) [Mon Jun 13 09:37:51 2011] loadbalancerLocal myServer 0.062500 [Mon Jun 13 09:37:51 2011] [7116:6512] [info] ajp_process_callback::jk_ajp_common.c (1885): Writing to client aborted or client network problems [Mon Jun 13 09:37:51 2011] [7116:6512] [info] ajp_service::jk_ajp_common.c (2543): (viewerLocalInstance4) sending request to tomcat failed (unrecoverable), because of client write error (attempt=1) [Mon Jun 13 09:37:52 2011] [7116:3080] [info] ajp_process_callback::jk_ajp_common.c (1885): Writing to client aborted or client network problems [Mon Jun 13 09:37:52 2011] [7116:3080] [info] ajp_service::jk_ajp_common.c (2543): (viewerLocalInstance4) sending request to tomcat failed (unrecoverable), because of client write error (attempt=1) [Mon Jun 13 09:38:21 2011] [7116:6512] [info] service::jk_lb_worker.c (1388): service failed, worker viewerLocalInstance4 is in local error state [Mon Jun 13 09:38:21 2011] [7116:7852] [info] service::jk_lb_worker.c (1388): service failed, worker viewerLocalInstance4 is in local error state [Mon Jun 13 09:38:21 2011] [7116:6512] [info] service::jk_lb_worker.c (1407): unrecoverable error 200, request failed. Client failed in the middle of request, we can't recover to another instance. [Mon Jun 13 09:38:21 2011] [7116:7852] [info] service::jk_lb_worker.c (1407): unrecoverable error 200, request failed. Client failed in the middle of request, we can't recover to another instance. [Mon Jun 13 09:38:21 2011] loadbalancerLocal myServer 29.046875 [Mon Jun 13 09:38:21 2011] loadbalancerLocal myServer 29.171875 [Mon Jun 13 09:38:21 2011] [7116:6512] [info] jk_handler::mod_jk.c (2620): Aborting connection for worker=loadbalancerLocal [Mon Jun 13 09:38:21 2011] [7116:7852] [info] jk_handler::mod_jk.c (2620): Aborting connection for worker=loadbalancerLocal [Mon Jun 13 09:38:21 2011] [7116:7852] [info] ajp_process_callback::jk_ajp_common.c (1885): Writing to client aborted or client network problems [Mon Jun 13 09:38:21 2011] [7116:7852] [info] ajp_service::jk_ajp_common.c (2543): (viewerLocalInstance4) sending request to tomcat failed (unrecoverable), because of client write error (attempt=1) [Mon Jun 13 09:38:21 2011] loadbalancerLocal myServer 0.156250 [Mon Jun 13 09:38:21 2011] loadbalancerLocal myServer 0.062500 [Mon Jun 13 09:38:22 2011] [7116:3080] [info] service::jk_lb_worker.c (1388): service failed, worker viewerLocalInstance4 is in local error state [Mon Jun 13 09:38:22 2011] [7116:3080] [info] service::jk_lb_worker.c (1407): unrecoverable error 200, request failed. Client failed in the middle of request, we can't recover to another instance.

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