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• Best CPUs for speeding up compiling times of C++ w/ DistGCC

  - by Jay

  I'm putting together a distributed build farm with DistGCC to speed up our teams compile times and just looking for thoughts on which processors to use in the hosts. Are we going to get a noticeable decrease in time using 8 cores vs. 4-hyperthreaded cores? Big difference in time between i7 and Xeon? etc, etc. Just need advice from people who've put together kick-a build clusters. We've got a majority of the normal things to speed up builds in place (pre-compiled headers, ccache, local gigabit connections between them, tons of ram, etc) so please just give advice on the best processor to use. And money is a factor, but anythings doable if the performance increase is noticeable. Thanks. Jay EDIT: Although any advice IS welcome, please refrain from "Do this first" posts as we're not planning on skimping on things like SSD, maxed out RAM, etc. My personal system is a iMac Quad-core i5 with 8GB of RAM. When I build our project locally, my processor floats around 99-100% a majority of the time, which makes me assume it is a bottleneck, even if you made everything else faster. My ram on the other hand doesn't even get close to maxing out. It's also worth noting that I did research this, however every discussion I could find was primarily for gaming machines, which is obviously a different beast in usage. These machines won't even have monitors or anything but integrated graphics since they have one purpose: Build freakin fast. (hopefully)

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• Best CPUs for speeding up compiling times of C++ w/ DistGCC

  - by Jay

  I'm putting together a distributed build farm with DistGCC to speed up our teams compile times and just looking for thoughts on which processors to use in the hosts. Are we going to get a noticeable decrease in time using 8 cores vs. 4-hyperthreaded cores? Big difference in time between i7 and Xeon? etc, etc. Just need advice from people who've put together kick-a build clusters. We've got a majority of the normal things to speed up builds in place (pre-compiled headers, ccache, local gigabit connections between them, tons of ram, etc) so please just give advice on the best processor to use. And money is a factor, but anythings doable if the performance increase is noticeable. Thanks. Jay EDIT: Although any advice IS welcome, please refrain from "Do this first" posts as we're not planning on skimping on things like SSD, maxed out RAM, etc. My personal system is a iMac Quad-core i5 with 8GB of RAM. When I build our project locally, my processor floats around 99-100% a majority of the time, which makes me assume it is a bottleneck, even if you made everything else faster. My ram on the other hand doesn't even get close to maxing out. It's also worth noting that I did research this, however every discussion I could find was primarily for gaming machines, which is obviously a different beast in usage. These machines won't even have monitors or anything but integrated graphics since they have one purpose: Build freakin fast. (hopefully)

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• Finding cause of TCP retransmission within a LAN

  - by Surreal

  Hello denizens of Server Fault I have an irritating problem with a LAN of about 100 computers, 2 Windows domain servers, and 12 VoIP phones. Since their installation around a year ago, every week or so, we notice a VoIP phone resetting itself - occasionally in the middle of a call. Simultaneously there are often signs of temporary loss of connection on computers: freezes in explorer while accessing network shares, errors in our administration software due to loss of connection to the database server. I have been doing some Wireshark monitoring on the connection between the VoIP PBX and the rest of the network. Wireshark picks up a clump of retransmitted TCP packets at the times when we record phone restarts. The Wireshark log shows about 2 clusters of retransmissions a day ranging from 5 packets to hundreds. Those in each cluster are mainly between the PBX and some set of the VoIP phones, but not always the same set. Often retransmissions at the same time are to phones connected to the same switch, but sometimes retransmissions occur together to phones at opposite ends of the network. There are usually some coincident retransmissions in passing TCP traffic, for example between client machines and the file servers. The spikes in retransmissions and phone resets do not correlate well with when the network is heavily loaded. They seem to occur slightly more during the day, but most in the evening, when traffic should be decreasing. They occur reasonably often late at night when most computers are turned off and traffic should be lowest. Do you have any ideas that might help diagnose the cause of problems like this? One thing I have not yet tried, but should have, is updating the firmware of all the switches.

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• Mysql cluster strange behaviour

  - by Champion

  Hi Guys, I have 2 mysql clusters on two different servers with management node on each of them. It went down someway. I ran following commands to start the cluster: Start the management node on srv1: srv1: mysqlc/bin/ndb_mgmd --initial -f my_cluster/conf/config.ini --configdir=/home/mysql_cluster/my_cluster/conf Start the management node on srv2: srv2: mysqlc/bin/ndb_mgmd --initial -f my_cluster/conf/config.ini --configdir=/home/mysql_cluster/my_cluster/conf Start the ndbd nodes on srv1: srv1: mysqlc/bin/ndbd --initial -c localhost:1186 Start the ndbd nodes on srv2: srv2: mysqlc/bin/ndbd --initial -c localhost:1186 Start mysqld server on srv1: srv1: mysqlc/bin/mysqld --defaults-file=my_cluster/conf/my.cnf --user=root & and here is the problem. mysql server not loading the data. Only database names are present. All the tables which are ENGINE=ndbcluster are not being loaded. Tables with ENGINE=myisam are being loaded. Backup scripts helped me load the data. But this way I can't use cluster setup. Similar issue appeared when i started srv2. How can I resolve this issue ?

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• Architecture for highly available MySQL with automatic failover in physically diverse locations

  - by Warner

  I have been researching high availability (HA) solutions for MySQL between data centers. For servers located in the same physical environment, I have preferred dual master with heartbeat (floating VIP) using an active passive approach. The heartbeat is over both a serial connection as well as an ethernet connection. Ultimately, my goal is to maintain this same level of availability but between data centers. I want to dynamically failover between both data centers without manual intervention and still maintain data integrity. There would be BGP on top. Web clusters in both locations, which would have the potential to route to the databases between both sides. If the Internet connection went down on site 1, clients would route through site 2, to the Web cluster, and then to the database in site 1 if the link between both sites is still up. With this scenario, due to the lack of physical link (serial) there is a more likely chance of split brain. If the WAN went down between both sites, the VIP would end up on both sites, where a variety of unpleasant scenarios could introduce desync. Another potential issue I see is difficulty scaling this infrastructure to a third data center in the future. The network layer is not a focus. The architecture is flexible at this stage. Again, my focus is a solution for maintaining data integrity as well as automatic failover with the MySQL databases. I would likely design the rest around this. Can you recommend a proven solution for MySQL HA between two physically diverse sites? Thank you for taking the time to read this. I look forward to reading your recommendations.

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• Shared firewall or multiple client specific firewalls?

  - by Tauren

  I'm trying to determine if I can use a single firewall for my entire network, including customer servers, or if each customer should have their own firewall. I've found that many hosting companies require each client with a cluster of servers to have their own firewall. If you need a web node and a database node, you also have to get a firewall, and pay another monthly fee for it. I have colo space with several KVM virtualization servers hosting VPS services to many different customers. Each KVM host is running a software iptables firewall that only allows specific ports to be accessed on each VPS. I can control which ports any given VPS has open, allowing a web VPS to be accessed from anywhere on ports 80 and 443, but blocking a database VPS completely to the outside and only allowing a certain other VPS to access it. The configuration works well for my current needs. Note that there is not a hardware firewall protecting the virtualization hosts in place at this time. However, the KVM hosts only have port 22 open, are running nothing except KVM and SSH, and even port 22 cannot be accessed except for inside the netblock. I'm looking at possibly rethinking my network now that I have a client who needs to transition from a single VPS onto two dedicated servers (one web and one DB). A different customer already has a single dedicated server that is not behind any firewall except iptables running on the system. Should I require that each dedicated server customer have their own dedicated firewall? Or can I utilize a single network-wide firewall for multiple customer clusters? I'm familiar with iptables, and am currently thinking I'll use it for any firewalls/routers that I need. But I don't necessarily want to use up 1U of space in my rack for each firewall, nor the power consumption each firewall server will take. So I'm considering a hardware firewall. Any suggestions on what is a good approach?

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• CHKDSK is unable to fix NTFS errors

  - by HackToHell

  After my PC shutdown due to power failure, I noticed several errors in EventViewer. The file system structure on the disk is corrupt and unusable. Please run the chkdsk utility on the volume \Device\HarddiskVolume2. and The file system structure on the disk is corrupt and unusable. Please run the chkdsk utility on the volume C:. So I forced a chkdsk check at startup, and it finds a stream of error, here is the output, it is smaller than the actual log, because, Event Viewer only seems to have this much, the same line was repeated thousands of times.Here is that line. Some clusters occupied by attribute of type 0x80 and instance tag 0x4 in file 0x198f2 is already in use. Deleting corrupt attribute record (128, "") from file record segment 104690. Attribute record of type 0x80 and instance tag 0x0 is cross linked Also, even after running CHKDSK, the same errors were being reported again so I ran CHKDSK another time and it still loops the same line above, without fixing the error. Can anyone tell me how to fix it?

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• SQL cluster instance names for large project

  - by Sam

  We're setting up two clusters. One dev and one prod. The Production will host two SQL instances - a OLTP and a DW. The development will host 4 OLTP non-production environments and at least one DW non-production. We're working on getting more DW non-prods and possibly more OLTP systems. I'm considering a naming scheme like this, where PROJ would be 3 initials for the project name. Dev Cluster MSSQLPROJD1\D1 (DEV) MSSQLPROJD2\D2 (TEST) MSSQLPROJD3\D3 (QA) MSSQLPROJD4\D4 (STAGE) MSSQLPROJD5\D5 (DW) Prd Cluster MSSQLPROJP1\P1 (PRD) MSSQLPROJP2\P2 (DW) To the left of the slash, each name must be unique network wide. On each server, the instance name, to the right of the slash, must be unique. Any thoughts on this? I'm trying to avoid having instance names drifting from reality as the project progresses - say we change what we call a certain environment or want to repurpose one. Then we can update a listing of the purposes for the instances and be done with it. How has a scheme like this worked out for you? Maybe you do things another way in your shop - tell me about it. Thanks.

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• Installing and running two postgresql versions on different ports (or two instances of same server)

  - by Andrius

  I have postgresql 9.1 installed on my machine (Ubuntu). I need another postgresql server that would run next to the old one. Exact version does not matter, but I'm thinking of using 9.2 version. How could I properly install and run another postgresql version without screwing old one (like upgrading). So those versions would run independently on different ports. Old one on 5432 and new one on 5433 for example. The reason I need this is for two OpenERP versions databases. If I run two OpenERP servers (with different versions) on single postgresql port, it crashes because new OpenERP version detects old versions database and tries to run it, but it crashes because it uses another schemes. P.S or maybe I could just run same postgresql server on two ports? Update So far I tried this: /usr/lib/postgresql/9.1/bin/pg_ctl initdb -D main2 It created new cluster. I changed port to 5433 in new clusters directory postgresql.conf file. Then ran this: /usr/lib/postgresql/9.1/bin/pg_ctl -D main2 -l logfile start I got response server starting. But when I tried to enter new cluster's template database with: psql template1 -p 5433 I got this error: psql: could not connect to server: No such file or directory Is the server running locally and accepting connections on Unix domain socket "/var/run/postgresql/.s.PGSQL.5433"? Also now when I try to stop server with: /usr/lib/postgresql/9.1/bin/pg_ctl -D main2 -l logfile start I get this error: pg_ctl: PID file "main2/postmaster.pid" does not exist Is server running? So I don't understand if server is running and what I'm missing here? Update Found what was wrong. Stupid me. I didn't notice that when I changed port in .conf file, that line was commented already. So actually I didn't change anything first time, but thought I did and it used default 5432 port.

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• Creating a Jenkins build farm in a hands-off manner?

  - by user183394

  My colleague and I have set up and run Jenkins on a KVM guest running Ubuntu 12.04 with good results for a while now. We are thinking about deploying a cluster of Jenkins CI hosts in master/slave configuration, with the libvirt slave plugin to keep our hardware count low. Our environment is strictly Linux (CentOS, Scientific Linux, Fedora, and Ubuntu). Both of us are competent in setting up large clusters. We typically use tools like cobbler + a configuration management tool (Puppet, Chef, and alike) to set up a large number of machines (physical and/or virtual) hands off (hundreds of nodes in less than an hour typical). We would like to do the same for nodes running Jenkins. But the step by step guide doesn't give us any clues in this regard. I did see a Multi-slave config plugin. But, being used to dealing with hundreds or more machines completely hands-off, clicking the UI for many machines just doesn't feel right. Can someone point to us a reference that talks about how to set up large cluster of Jenkins CI hosts more in the hands-off way?

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• How can I automatically synchronize a directory tree on multiple machines?

  - by Blacklight Shining

  I have two Mac laptops and a Debian server, each with a directory that I would like to keep in sync between the three. The solution should meet the following criteria (in rough order of importance): It must not use any third-party service (e.g. Dropbox, SugarSync, Google whatever). This does not include installing additional software (as long as it's free). It must not require me to use specific directories or change my way of storing things. (Dropbox does this IIRC) It must work in all directions (changes made on /any/ machine should be pushed to the others) All data sent must be encrypted (I have ssh keypairs set up already) It must work even when not all machines are available (changes should be pushed to a machine when it comes back online) It must work even when the /directories/ on some machines are not available (they may be stored on disk images which will not always be mounted) This can be solved for Macs by using launchd to automatically launch and kill (or in some way change the behavior of) whatever daemon is used for syncing when the images are mounted and unmounted. It must be immediate (using an event-based system, not a periodic one like cron) It must be flexible (if more machines are added, I should be able to incorporate them easily) I also have some preferences that I would like to be fulfilled, but do not have to be: It should notify me somehow if there are conflicts or other errors. It should recognize symbolic and hard links and create corresponding ones. It should allow me to create a list of exceptions (subdirectories which will not be synced at all). It should not require me to set up port forwarding or otherwise reconfigure a network. This can be solved by using an ssh tunnel with reverse port forwarding. If you have a solution that meets some, but not all of the criteria, please contribute it in the comments as it might be useful in some way, and it might be possible to meet some of the criteria separately. What I tried, and why it didn't work: rsync and lsyncd do not support bidirectional synchronization csync2 is designed for server clusters and does not appear to work with machines with dynamic IPs DRBD (suggested by amotzg) involves installing a kernel module and does not appear to work on systems running OS X

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• What are good systems for managing PHP/MySQL infrastructure?

  - by sbrattla

  I work in a company which is about to migrate most applications from in-house custom built Java/Tomcat applications to Drupal. Due to company policies, applications and websites need to run on in-house servers. This means that we need infrastructure for Drupal (PHP/MySQL) applications. This must have been solved a million times already. I believe this is what web-hosting companies does every day. Even though we work on a much smaller scale than web-hosting companies, i assume it would make sense to look at the task as if we're going to have an internal small-scale web-hosting company. This means that the guys in IT operations could be "responsible" for "offering" web-hosting, while developers could use these "services". We have three environments; dev(elopment), test and prod(uction). It would make sense that developers could log in to a system and create/edit/delete dev and test sites as they'd like. Production sites should be available through the same system, but only available to IT ops. We need to work with clusters of web servers, meaning that an administration system should be capable of creating/editing/deleting sites across multiple servers. I know there's no "this is it" answer to my question; but what would be a good place to start to get going with this? Apart from the actual hardware, what would be a good administration system for this?

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• Restoring MBR, partition table, and boot sector of memory card without data loss ("USBC")

  - by Synetech

  Abstract I have a FAT32 memory card that when inserted into a computer causes Windows to prompt to format it. The card is definitely not supposed to be blank and has a bunch of files on it. Symptoms Using a hex-editor/disk-viewer, I examined the card and found that several sectors/clusters have been overwritten with something that has a signature of USBC at the start of the sector. Specifically, the master boot record (and partition table) is gone (hence Windows thinking the card is blank and needing to be formatted), as are the boot sectors (they have the USBC signature and a volume label of NO NAME and partition type of FAT32). Fortunately, it looks like both copies of the FAT are almost entirely intact (a few FAT entries at the start of a cluster here and there seem to be overwritten by USBC). The root directory is also nearly intact—I can see the volume label entry and subdirectory listings, but one sector is overwritten. (There are no more instances of USBC after the last one in the FAT2.) Hypothesis These observations seem to indicate some sort of virus that erases a few key filesystem structures, and then overwrites a few extra sectors here and there. Googling it seems to corroborate the idea of a virus, except that others report a file called USBC which does not apply here, and in fact, could not be possible since there is no filesystem to even see files. I cannot find any information about a virus with these symptoms, nor a removal tool. (I can't help but wonder if it is actually due to an autorun virus prevention tool.) Question I can likely fix the FAT corruption since they are mostly contiguous chains and maybe even the lost sector of the root directory, but does anyone know of a convenient way to restore or (re)create the MBR/partition table and boot sectors (without formatting or overwriting the data)?

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• How to allow users to transfer files to other users on linux

  - by Jon Bringhurst

  We have an environment of a few thousand users running applications on about 40 clusters ranging in size from 20 compute nodes to 98,000 compute nodes. Users on these systems generate massive files (sometimes 1PB) controlled by traditional unix permissions (ACLs usually aren't available or practical due to the specialized nature of the filesystem). We currently have a program called "give", which is a suid-root program that allows a user to "give" a file to another user when group permissions are insufficient. So, a user would type something like the following to give a file to another user: > give username-to-give-to filename-to-give ... The receiving user can then use a command called "take" (part of the give program) to receive the file: > take filename-to-receive The permissions of the file are then effectively transferred over to the receiving user. This program has been around for years and we'd like to revisit things from a security and functional point of view. Our current plan of action is to remove the bit rot in our current implementation of "give" and package it up as an open source app before we redeploy it into production. Does anyone have another method they use to transfer extremely large files between users when only traditional unix permissions are available?

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• Determining physical location of data on a disc

  - by Synetech

  Does anybody know of a way to find out where, physically on a CD or DVD a given piece of data would be located? I am trying to watch a DVD at the moment, and am about half-way through, but it keeps dying at a specific spot in the film, presumably because of a scratch. I have a repair kit, but I don’t know where to focus my repair because there are several scuffs and scratches on the disc and I have no way of knowing which one is causing the issue. Obviously, cleaning all of them is inadvisable because not only does it waste the consumable materials in the kit, but not all of them are a problem, and by working them, some may become unreadable. Moreover, just because I am half-way through the movie does not mean that it would be half-way from the hub to the edge for several reasons: Discs have more data towards the outer edge than the inner edge (circles are more mathematically complicated than rectangles) The disc is not completely filled up (and even if it were, the movie itself would be be using it all, there are extras and such) Because in this particular case it is a commercial DVD, it is also dual-layer which further complicates manual determination As such, I am trying to find a program that can let me identify a file (or part thereof), cluster, etc. and show me a picture of where on the CD/DVD it would be located. That way, I can look at the disc and fix any scratches that correspond to that distance from the hub. For example, the image below might indicate where on a disc a couple of files or range of clusters would be located, so by looking for anomalies in those areas (rotating as necessary), the correct one can be identified. I’m sure it can be done since at least one form of copy protection (DPM) uses it and DVD-lab Pro includes a “DVD Topology” feature to do this.

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• Deploying multiple identical copies of a virtual machine for compute tasks

  - by Reid

  I have a compute task which has a large number of library dependencies. I would like to deploy it on some of my company's large Linux clusters, where I do not have root. I could probably track down, compile, and install the right versions of all the libraries, but this looks to be quite tedious and would have to be repeated if I deployed it again somewhere else. On the other hand, it's pretty easy to install on current Ubuntu. This led me to wonder about a virtual machine approach. Could I put together a virtual machine which booted up, ran the computation (with parameters from and results to the host), and then shut down? In other words, I'd like a command like this that I could run on the host: $ ./run-vm --ram N --task /path/on/host/foo.sh --results /another/host/dir/ This would boot the VM, run foo.sh, and put the (relatively small) results of the computation in /another/host/dir/. It's important to start up many instances of the VM simultaneously, both on a single node and multiple nodes of the cluster. So it would be nice if I didn't have to make many copies of the VM virtual disk and metadata. As the task instances are completely independent, the VMs would not need any network support once deployed, or any outside communications beyond reading and writing the host filesystem. Is this possible, and if so, how might I go about doing it? Are there assumptions I've made above which are bogus?

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• thought about shared storage (NFS, Lustre) [closed]

  - by user134880

  Possible Duplicate: Can you help me with my capacity planning? Now I habe small cluster with total of 8 nodes. 6 of them are computing nodes (apache and vmware) and 2 nodes are for storage. 2 storage nodes are identical. Each storage server is linux box with 8 x 1Tb WD RE4 in soft raid 10. 1st box is master and 2nd is slave. Data is mirrored with DRDB. We export NFSv4 shares to Apache (for document root) and iSCSI to Vmware. Now all is working pretty good and stable. But it will be soon time to upgrade our system. I have been thinking of Lustre. Does some one has any real experience with Lustre or NFS medium clusters? Will it be good idea just to upgrade server and change hdd's to 3Tb ? With NFS we will always have only 2 servers to maintain (one primary and one slave). Thanks. QUESTIONS: 1) Does some one used Lustre? In production? I have seen a lot of info about how it is hard to setup Lustre because you need to compile own kernel and patches. It's answers from newbies. Is there some one who has used Lustre for some period of time? 2) About disk upgrades - it's only description of strategy. I'm not asking if it is enough 3Tb or not. I just ask if it is right just to replace hdds instead of adding new server (like with Lustre) Thanks again.

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• Experience with asymmetrical (non-identical hardware) SQL Server 2005 / Win 2003 cluster

  - by user24161

  I am reasonably good at dealing with SQL Server clusters; I am wondering if folks have experience, good or bad, using a mix of different models of servers from the same vendor in one SQL 2005 cluster. Suppose: I have one more powerful, more RAM, more shizzle box and one less powerful, less memory, less shizzle box bound together in a 2-node cluster. These would be HP DL380 and 580 machines (not that it should matter) I understand AND automate the process of managing memory for each SQL instance, so there's no memory contention when SQL instances fail over. Basically I am thinking a CLR proc will monitor the instances and self-regulate memory caps on each instance, so that they won't page or step on one another. I get the fact the instances might be slower and or under memory pressure if they share a "lesser" node, and that's OK. The business can deal with a slower instance in a server-problem scenario. Reasonable? Any "gotchas" to watch out for? More info 10/28: doing some experiments with a test cluster I find that reconfiguring max/min memory is OK PROVIDED the instance isn't already under memory pressure. If I torture the system with a huge query that demands a big chunk of RAM, and simultaneously adjust the memory allocation to a smaller value than what is being actively used, it's possible to run the instance out of memory and have it halt and restart itself (unhappy situation). Many ugly out-of-memory messages in the error log, crashing, burning... It's an extreme case, but good to know. Seems, then, that it would only be really safe to set this on startup of the instance, as in have a startup script that says "I am on node1, so my RAM settings are X or I am on node two, so they are Y," like this: http://sqlblog.com/blogs/aaron_bertrand... Update: I am testing a SQL Agent + PowerShell solution described in more detail here.

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• Using Openfire for distributed XMPP-based video-chat

  - by Yitzhak

  I have been tasked with setting up a distributed video-chat system built on XMPP. Currently my setup looks like this: Openfire (XMPP server) + JingleNodes plugin for video chat OpenLDAP (LDAP server) for storing user information and allowing directory queries Kerberos server for authentication and passwords In testing with one set of machines (i.e. only three), everything works as expected: I can log in to Openfire and it looks up the user information in the OpenLDAP database, which in turn authenticates my user with Kerberos. Now, I want to have several clusters, so that there is a cluster on each continent. A typical cluster will probably contain 2-5 servers. Users logging in will be directed to the closest cluster based on geographical location. Something that concerns me particularly is the dynamic maintenance of contact lists. If a user is using a machine in Asia, for example, how would contact lists be updated around the world to reflect the current server he is using? How would that work with LDAP? Specific questions: How do I direct users based on geographical location? What is the best architecture for a cluster? -- would all traffic need to come into a load-balancer on each one, for example? How do I manage the update of contact lists across all these servers? In general, how do I go about setting this up? What are the pitfalls in doing this? I am inexperienced in this area, so any advice and suggestions would be appreciated.

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• what is best multi-server configuration with OpenVPN

  - by sebut

  We have a number of Database severs running MongoDB on Debian plus a number of Application servers also on Debian. The db servers hold replicating db clusters, so they need to talk to each other. Application servers need to talk to all db servers (for reasons of fault tolerance). The servers are potentially spread across multiple hosting centers, so we need secure channels between all servers. The number of servers is bound to grow, so we need a VPN solution that's easy to maintain and expand. This is why I feel that SSH that we use for testing might not be up to the task and OpenVPN seems the way to go. I have ruled out TAP, since I understand that this would mean all traffic going to all the servers - perhaps this is a misunderstanding and TAP acts more like a switch? With TUN devices I imagine that all DB servers would live in their own separate subnet, they would also need a client configured to be able to connect to each of their peers. The application servers could live in a common subnet range with a client config only. Does this sound like a reasonable setup? Strangely, on the web I did not find anything about multi-server with OpenVPN. Thanks for all insights and ideas!

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• Synchronizing Asynchronous request handlers in Silverlight environment

  - by Eric Lifka

  For our senior design project my group is making a Silverlight application that utilizes graph theory concepts and stores the data in a database on the back end. We have a situation where we add a link between two nodes in the graph and upon doing so we run analysis to re-categorize our clusters of nodes. The problem is that this re-categorization is quite complex and involves multiple queries and updates to the database so if multiple instances of it run at once it quickly garbles data and breaks (by trying to re-insert already used primary keys). Essentially it's not thread safe, and we're trying to make it safe, and that's where we're failing and need help :). The create link function looks like this: private Semaphore dblock = new Semaphore(1, 1); // This function is on our service reference and gets called // by the client code. public int addNeed(int nodeOne, int nodeTwo) { dblock.WaitOne(); submitNewNeed(createNewNeed(nodeOne, nodeTwo)); verifyClusters(nodeOne, nodeTwo); dblock.Release(); return 0; } private void verifyClusters(int nodeOne, int nodeTwo) { // Run analysis of nodeOne and nodeTwo in graph } All copies of addNeed should wait for the first one that comes in to finish before another can execute. But instead they all seem to be running and conflicting with each other in the verifyClusters method. One solution would be to force our front end calls to be made synchronously. And in fact, when we do that everything works fine, so the code logic isn't broken. But when it's launched our application will be deployed within a business setting and used by internal IT staff (or at least that's the plan) so we'll have the same problem. We can't force all clients to submit data at different times, so we really need to get it synchronized on the back end. Thanks for any help you can give, I'd be glad to supply any additional information that you could need!

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• Resources related to data-mining and gaming on social networks

  - by darren

  Hi all I'm interested in the problem of patterning mining among players of social networking games. For example detecting cheaters of a game, given a company's user database. So far I have been following the usual recipe for a data mining project: construct a data warehouse that aggregates significant information select a classifier, and train it with a subsectio of records from the warehouse validate classifier with another test set lather, rinse, repeat Surprisingly, I've found very little in this area regarding literature, best practices, etc. I am hoping to crowdsource the information gathering problem here. Specifically what I'm looking for: What classifiers have worked will for this type of pattern mining (it seems highly temporal, users playing games, users receiving rewards, users transferring prizes etc). Are there any highly agreed upon attributes specific to social networking / gaming data? What is a practical amount of information that should be considered? One problem I've run into is data overload, where queries and data cleansing may take days to complete. Related to point above, what hardware resources are required to produce results? I've found it difficult to estimate the amount of computing power I will require for production use. It has become apparent that a white box in the corner does not have enough horse-power for such a project. Are companies generally resorting to cloud solutions? Are they buying clusters? Basically, any resources (theoretical, academic, or practical) about implementing a social networking / gaming pattern-mining program would be very much appreciated. Thanks.

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• How are you taking advantage of Multicore?

  - by tgamblin

  As someone in the world of HPC who came from the world of enterprise web development, I'm always curious to see how developers back in the "real world" are taking advantage of parallel computing. This is much more relevant now that all chips are going multicore, and it'll be even more relevant when there are thousands of cores on a chip instead of just a few. My questions are: How does this affect your software roadmap? I'm particularly interested in real stories about how multicore is affecting different software domains, so specify what kind of development you do in your answer (e.g. server side, client-side apps, scientific computing, etc). What are you doing with your existing code to take advantage of multicore machines, and what challenges have you faced? Are you using OpenMP, Erlang, Haskell, CUDA, TBB, UPC or something else? What do you plan to do as concurrency levels continue to increase, and how will you deal with hundreds or thousands of cores? If your domain doesn't easily benefit from parallel computation, then explaining why is interesting, too. Finally, I've framed this as a multicore question, but feel free to talk about other types of parallel computing. If you're porting part of your app to use MapReduce, or if MPI on large clusters is the paradigm for you, then definitely mention that, too. Update: If you do answer #5, mention whether you think things will change if there get to be more cores (100, 1000, etc) than you can feed with available memory bandwidth (seeing as how bandwidth is getting smaller and smaller per core). Can you still use the remaining cores for your application?

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• subgraph cluster ranking in dot

  - by Chris Becke

  I'm trying to use graphviz on media wiki as a documentation tool for software. First, I documented some class relationships which worked well. Everything was ranked vertically as expected. But, then, some of our modules are dlls, which I wanted to seperate into a box. When I added the nodes to a cluster, they got edged, but clusters seem to have a LR ranking rule. Or being added to a cluster broke the TB ranking of the nodes as the cluster now appears on the side of the graph. This graph represents what I am trying to do: at the moment, cluster1 and cluster2 appear to the right of cluster0. I want/need them to appear below. <graphviz> digraph d { subgraph cluster0 { A -> {B1 B2} B2 -> {C1 C2 C3} C1 -> D; } subgraph cluster1 { C2 -> dll1_A; dll1_A -> B1; } subgraph cluster2 { C3 -> dll2_A; } dll1_A -> dll2_A; } </graphviz>

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• Problem with JMX query of Coherence node MBeans visible in JConsole

  - by Quinn Taylor

  I'm using JMX to build a custom tool for monitoring remote Coherence clusters at work. I'm able to connect just fine and query MBeans directly, and I've acquired nearly all the information I need. However, I've run into a snag when trying to query MBeans for specific caches within a cluster, which is where I can find stats about total number of gets/puts, average time for each, etc. The MBeans I'm trying to access programatically are visible when I connect to the remote process using JConsole, and have names like this: Coherence:type=Cache,service=SequenceQueue,name=SEQ%GENERATOR,nodeId=1,tier=back It would make it more flexible if I can dynamically grab all type=Cache MBeans for a particular node ID without specifying all the caches. I'm trying to query them like this: QueryExp specifiedNodeId = Query.eq(Query.attr("nodeId"), Query.value(nodeId)); QueryExp typeIsCache = Query.eq(Query.attr("type"), Query.value("Cache")); QueryExp cacheNodes = Query.and(specifiedNodeId, typeIsCache); ObjectName coherence = new ObjectName("Coherence:*"); Set<ObjectName> cacheMBeans = mBeanServer.queryMBeans(coherence, cacheNodes); However, regardless of whether I use queryMBeans() or queryNames(), the query returns a Set containing... ...0 objects if I pass the arguments shown above ...0 objects if I pass null for the first argument ...all MBeans in the Coherence:* domain (112) if I pass null for the second argument ...every single MBean (128) if I pass null for both arguments The first two results are the unexpected ones, and suggest a problem in the QueryExp I'm passing, but I can't figure out what the problem is. I even tried just passing typeIsCache or specifiedNodeId for the second parameter (with either coherence or null as the first parameter) and I always get 0 results. I'm pretty green with JMX — any insight on what the problem is? (FYI, the monitoring tool will be run on Java 5, so things like JMX 2.0 won't help me at this point.)

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