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• O(log n) algorithm to find the element having rank i in union of pre-sorted lists

  - by Eternal Learner

  Given two sorted lists, each containing n real numbers, is there a O(log?n) time algorithm to compute the element of rank i (where i coresponds to index in increasing order) in the union of the two lists, assuming the elements of the two lists are distinct? I can think of using a Merge procedure to merge the 2 lists and then find the A[i] element in constant time. But the Merge would take O(n) time. How do we solve it in O(log n) time?

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• For distributed applications, which to use, ASIO vs. MPI?

  - by Rhubarb

  I am a bit confused about this. If you're building a distributed application, which in some cases may perform parallel operations (although not necessarily mathematical), should you use ASIO or something like MPI? I take it MPI is a higher level than ASIO, but it's not clear where in the stack one would begin.

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• How to investigate if opencl is possible for an algorithm

  - by Marnix

  I have a heavy-duty algorithm in C# that takes two large Bitmaps of about 10000x5000 and performs photo and ray collision operations on a 3D model to map photos on the 3D model. I would like to know if it is possible to convert such an algorithm to OpenCL to optimize parallel operations during the algorithm. But before asking you to go into the details of the algorithm, I would like to know how I can investigate if my algorithm is convertible to OpenCL. I am not experienced in OpenCL and I would like to know if it is worth it to get into it and learn how it works. Are there things I have to look for that will definitely not work on the graphics card? (for-loops, recursion) Update: My algorithm goes something like: foreach photo split the photo in 64x64 blocks foreach block cast a ray from the camera to the 3D model foreach triangle in 3D model perform raycheck

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• ideas for a distributed cache proxy server

  - by Neeraj

  Hi everyone! I am implementing, a distributed cache proxy server.I have an idea of the HTTP and related stuff, so i am rather concentrating on the sub part "Distributed data storage". From some search on web i found that this could be done using Distributed Hash Tables(DHT). I was wondering if there exists some kind of library for this preferably in C/C++. Any better suggestions for the same will also be appreciated.

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• What is distributed storage/cache?

  - by symfony

  What's the difference between distributed and cluster?

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• GRAPH PROBLEM: find an algorithm to determine the shortest path from one point to another in a recta

  - by newba

  I'm getting such an headache trying to elaborate an appropriate algorithm to go from a START position to a EXIT position in a maze. For what is worth, the maze is rectangular, maxsize 500x500 and, in theory, is resolvable by DFS with some branch and bound techniques ... 10 3 4 7 6 3 3 1 2 2 1 0 2 2 2 4 2 2 5 2 2 1 3 0 2 2 2 2 1 3 3 4 2 3 4 4 3 1 1 3 1 2 2 4 2 2 1 Output: 5 1 4 2 Explanation: Our agent looses energy every time he gives a step and he can only move UP, DOWN, LEFT and RIGHT. Also, if the agent arrives with a remaining energy of zero or less, he dies, so we print something like "Impossible". So, in the input 10 is the initial agent's energy, 3 4 is the START position (i.e. column 3, line 4) and we have a maze 7x6. Think this as a kind of labyrinth, in which I want to find the exit that gives the agent a better remaining energy (shortest path). In case there are paths which lead to the same remaining energy, we choose the one which has the small number of steps, of course. I need to know if a DFS to a maze 500x500 in the worst case is feasible with these limitations and how to do it, storing the remaining energy in each step and the number of steps taken so far. The output means the agent arrived with remaining energy= 5 to the exit pos 1 4 in 2 steps. If we look carefully, in this maze it's also possible to exit at pos 3 1 (column 3, row 1) with the same energy but with 3 steps, so we choose the better one. With these in mind, can someone help me some code or pseudo-code? I have troubles working this around with a 2D array and how to store the remaining energy, the path (or number of steps taken)....

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• Open source Distributed computing tool

  - by Prasenjit Chatterjee

  I want to set up distributed computing on my Local Area Network consisting a bunch of PCs. Say for the time being each one has the same OS - Windows 7. Is there any opensource tool available so that I can share the resources of these PCs over the LAN and increase the speed of my applications and the memory space. I know that if its a graphics intensive application then, it is not very practical, because the speed of LAN is much slower than Graphics processors. But I only want to share general applications, some basic softwares, Programming language IDEs etc. Can anyone shed some light on it? Thanks in Advance..

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• distributed, fault-tolerant network block device

  - by gucki

  I'm looking for a distributed, fault-tolerant network storage system which exposes block devices (not filesystems) on the clients. A client's block device should write simultaneously to several storage nodes A client's block device should not fail as long as not all storage nodes backing it went down The master should automatically redistribute storages' data when a storage node fails or gets added/ removed A single master (which is for metadata only) is fine So ideally the architecture would be very similar to moosefs (http://www.moosefs.org/) but instead of exposing a real filesystem mounted using a fuse client it'd expose block devices on the clients. I know of iscsi and drbd but both don't seem to offer what I'm looking for. Or am I missing something?

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• Is there a distributed project management software like Redmine?

  - by Tobias Kienzler

  I am quite familiar with and love using git, among other reasons due to its distributed nature. Now I'd like to set up some similarly distributed (FOSS) Project Management software with features similar to what Redmine offers, such as Issue & time tracking, milestones Gantt charts, calendar git integration, maybe some automatic linking of commits and issues Wiki (preferably with Mathjax support) Forum, news, notifications Multiple Projects However, I am looking for a solution that does not require a permanently accesible server, i.e. like in git, each user should have their own copy which can be easily synchronized with others. However it should be possible to not have a copy of every Project on every machine. Since trac uses multiple instances for multiple projects anyway, I was considering using that, but I neither know how well it adapts to simply giting the database itself (which would be be easiest way to handle the distribution due to git being used anyway), nor does it include all of Redmine's feature. So, can you recommend me a distributed project management software? If your suggestion is a software that usually runs on a server please include a description of the distribution method (e.g. whether simply putting the data in a git repository would do the trick), and if it's e.g. trac, please mention plugins required to include the features mentioned.

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• Use a custom value object or a Guid as an entity identifier in a distributed system?

  - by Kazark

  tl;dr I've been told that in domain-driven design, an identifier for an entity could be a custom value object, i.e. something other than Guid, string, int, etc. Can this really be advisable in a distributed system? Long version I will invent an situation analogous to the one I am currently facing. Say I have a distributed system in which a central concept is an egg. The system allows you to order eggs and see spending reports and inventory-centric data such as quantity on hand, usage, valuation and what have you. There area variety of services backing these behaviors. And say there is also another app which allows you to compose recipes that link to a particular egg type. Now egg type is broken down by the species—ostrich, goose, duck, chicken, quail. This is fine and dandy because it means that users don't end up with ostrich eggs when they wanted quail eggs and whatnot. However, we've been getting complaints because jumbo chicken eggs are not even close to equivalent to small ones. The price is different, and they really aren't substitutable in recipes. And here we thought we were doing users a favor by not overwhelming them with too many options. Currently each of the services (say, OrderSubmitter, EggTypeDefiner, SpendingReportsGenerator, InventoryTracker, RecipeCreator, RecipeTracker, or whatever) are identifying egg types with an industry-standard integer representation the species (let's call it speciesCode). We realize we've goofed up because this change could effect every service. There are two basic proposed solutions: Use a predefined identifier type like Guid as the eggTypeID throughout all the services, but make EggTypeDefiner the only service that knows that this maps to a speciesCode and eggSizeCode (and potentially to an isOrganic flag in the future, or whatever). Use an EggTypeID value object which is a combination of speciesCode and eggSizeCode in every service. I've proposed the first solution because I'm hoping it better encapsulates the definition of what an egg type is in the EggTypeDefiner and will be more resilient to changes, say if some people now want to differentiate eggs by whether or not they are "organic". The second solution is being suggested by some people who understand DDD better than I do in the hopes that less enrichment and lookup will be necessary that way, with the justification that in DDD using a value object as an ID is fine. Also, they are saying that EggTypeDefiner is not a domain and EggType is not an entity and as such should not have a Guid for an ID. However, I'm not sure the second solution is viable. This "value object" is going to have to be serialized into JSON and URLs for GET requests and used with a variety of technologies (C#, JavaScript...) which breaks encapsulation and thus removes any behavior of the identifier value object (is either of the fields optional? etc.) Is this a case where we want to avoid something that would normally be fine in DDD because we are trying to do DDD in a distributed fashion? Summary Can it be a good idea to use a custom value object as an identifier in a distributed system (solution #2)?

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• Geographically distributed file system with preferred locality

  - by dpb

  Hi All -- I'm building a application that needs to distribute a standard file server across a few sites over a WAN. Basically, each site needs to write a lot of misc files of varying size (some in the 100s MB range, but most small), and the application is written such that collisions aren't a problem. I'd like to have a system set up that meets the following qualifications: Each site can store files in a shared "namespace". That is, all the files would show up in the same filesystem. Each site would not send data over the WAN unless necessary. I.e., there would be local storage on each side of the WAN that would be "merged" into the same logical filesystem. Linux & Free ($$$) is a must. Basically, something like a central NFS share would meet most of the requirements, however it would not allow the locally written data to stay local. All data from remote sides of the WAN would be copied locally all the time. I have looked into Lustre, and have run some successful tests with it, however, it appears to distribute files fairly uniformly across the distributed storage. I have dug through the documentation and have not found anything that automatically will "prefer" local storage over remote storage. Even something that went with the lowest latency storage would be fine. It would work most of the time, which would meet this application's requirements. Any ideas?

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• Distributed File Systems.

  - by GruffTech

  So, I've been reading several articles around ServerFault as well as google. (For Example, this link) My Requirements are very similar to the link above, however i'd like to also have dynamic or at least resizeable file volumes, so if necessary i can add 4-5 servers to the pool, and then expand the volume. Any Distributed File systems that support that, to save me some time? Thanks! LustreFS will be my next test cluster to build. GlusterFS I've build a 3-machine test GlusterFS cluster, However i quickly became aware of several of its limitations that it doesn't seem to make clearly public. One, i can't seem to resize a volume. Once a volume is created, its done. Which seems retarded, why have a fully scalable file system if i can't scale a volume? So maybe i'm doing something wrong. I'm not sure. AmazonS3 while gives the cheapest startup adds too much cost when broken down to per client per month, so its out. Building my own system when prorated over several years with no bandwidth costs makes it significantly cheaper. MogileFS isn't an option as we'd like this server to be a SAN-Replacement, for storing tons of media from a multitude of systems, which for us means it needs to be POSIX compliant so it can be remotely mounted via NFS or CIFS.

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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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• Fast block placement algorithm, advice needed?

  - by James Morris

  I need to emulate the window placement strategy of the Fluxbox window manager. As a rough guide, visualize randomly sized windows filling up the screen one at a time, where the rough size of each results in an average of 80 windows on screen without any window overlapping another. It is important to note that windows will close and the space that closed windows previously occupied becomes available once more for the placement of new windows. The window placement strategy has three binary options: Windows build horizontal rows or vertical columns (potentially) Windows are placed from left to right or right to left Windows are placed from top to bottom or bottom to top Why is the algorithm a problem? It needs to operate to the deadlines of a real time thread in an audio application. At this moment I am only concerned with getting a fast algorithm, don't concern yourself over the implications of real time threads and all the hurdles in programming that that brings. So far I have two choices which I have built loose prototypes for: 1) A port of the Fluxbox placement algorithm into my code. The problem with this is, the client (my program) gets kicked out of the audio server (JACK) when I try placing the worst case scenario of 256 blocks using the algorithm. This algorithm performs over 14000 full (linear) scans of the list of blocks already placed when placing the 256th window. 2) My alternative approach. Only partially implemented, this approach uses a data structure for each area of rectangular free unused space (the list of windows can be entirely separate, and is not required for testing of this algorithm). The data structure acts as a node in a doubly linked list (with sorted insertion), as well as containing the coordinates of the top-left corner, and the width and height. Furthermore, each block data structure also contains four links which connect to each immediately adjacent (touching) block on each of the four sides. IMPORTANT RULE: Each block may only touch with one block per side. The problem with this approach is, it's very complex. I have implemented the straightforward cases where 1) space is removed from one corner of a block, 2) splitting neighbouring blocks so that the IMPORTANT RULE is adhered to. The less straightforward case, where the space to be removed can only be found within a column or row of boxes, is only partially implemented - if one of the blocks to be removed is an exact fit for width (ie column) or height (ie row) then problems occur. And don't even mention the fact this only checks columns one box wide, and rows one box tall. I've implemented this algorithm in C - the language I am using for this project (I've not used C++ for a few years and am uncomfortable using it after having focused all my attention to C development, it's a hobby). The implementation is 700+ lines of code (including plenty of blank lines, brace lines, comments etc). The implementation only works for the horizontal-rows + left-right + top-bottom placement strategy. So I've either got to add some way of making this +700 lines of code work for the other 7 placement strategy options, or I'm going to have to duplicate those +700 lines of code for the other seven options. Neither of these is attractive, the first, because the existing code is complex enough, the second, because of bloat. The algorithm is not even at a stage where I can use it in the real time worst case scenario, because of missing functionality, so I still don't know if it actually performs better or worse than the first approach. What else is there? I've skimmed over and discounted: Bin Packing algorithms: their emphasis on optimal fit does not match the requirements of this algorithm. Recursive Bisection Placement algorithms: sounds promising, but these are for circuit design. Their emphasis is optimal wire length. Both of these, especially the latter, all elements to be placed/packs are known before the algorithm begins. I need an algorithm which works accumulatively with what it is given to do when it is told to do it. What are your thoughts on this? How would you approach it? What other algorithms should I look at? Or even what concepts should I research seeing as I've not studied computer science/software engineering? Please ask questions in comments if further information is needed. [edit] If it makes any difference, the units for the coordinates will not be pixels. The units are unimportant, but the grid where windows/blocks/whatever can be placed will be 127 x 127 units.

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• Distributed and/or Parallel SSIS processing

  - by Jeff

  Background: Our company hosts SaaS DSS applications, where clients provide us data Daily and/or Weekly, which we process & merge into their existing database. During business hours, load in the servers are pretty minimal as it's mostly users running simple pre-defined queries via the website, or running drill-through reports that mostly hit the SSAS OLAP cube. I manage the IT Operations Team, and so far this has presented an interesting "scaling" issue for us. For our daily-refreshed clients, the server is only "busy" for about 4-6 hrs at night. For our weekly-refresh clients, the server is only "busy" for maybe 8-10 hrs per week! We've done our best to use some simple methods of distributing the load by spreading the daily clients evenly among the servers such that we're not trying to process daily clients back-to-back over night. But long-term this scaling strategy creates two notable issues. First, it's going to consume a pretty immense amount of hardware that sits idle for large periods of time. Second, it takes significant Production Support over-head to basically "schedule" the ETL such that they don't over-lap, and move clients/schedules around if they out-grow the resources on a particular server or allocated time-slot. As the title would imply, one option we've tried is running multiple SSIS packages in parallel, but in most cases this has yielded VERY inconsistent results. The most common failures are DTExec, SQL, and SSAS fighting for physical memory and throwing out-of-memory errors, and ETLs running 3,4,5x longer than expected. So from my practical experience thus far, it seems like running multiple ETL packages on the same hardware isn't a good idea, but I can't be the first person that doesn't want to scale multiple ETLs around manual scheduling, and sequential processing. One option we've considered is virtualizing the servers, which obviously doesn't give you any additional resources, but moves the resource contention onto the hypervisor, which (from my experience) seems to manage simultaneous CPU/RAM/Disk I/O a little more gracefully than letting DTExec, SQL, and SSAS battle it out within Windows. Question to the forum: So my question to the forum is, are we missing something obvious here? Are there tools out there that can help manage running multiple SSIS packages on the same hardware? Would it be more "efficient" in terms of parallel execution if instead of running DTExec, SQL, and SSAS same machine (with every machine running that configuration), we run in pairs of three machines with SSIS running on one machine, SQL on another, and SSAS on a third? Obviously that would only make sense if we could process more than the three ETL we were able to process on the machine independently. Another option we've considered is completely re-architecting our SSIS package to have one "master" package for all clients that attempts to intelligently chose a server based off how "busy" it already is in terms of CPU/Memory/Disk utilization, but that would be a herculean effort, and seems like we're trying to reinvent something that you would think someone would sell (although I haven't had any luck finding it). So in summary, are we missing an obvious solution for this, and does anyone know if any tools (for free or for purchase, doesn't matter) that facilitate running multiple SSIS ETL packages in parallel and on multiple servers? (What I would call a "queue & node based" system, but that's not an official term). Ultimately VMWare's Distributed Resource Scheduler addresses this as you simply run a consistent number of clients per VM that you know will never conflict scheduleing-wise, then leave it up to VMWare to move the VMs around to balance out hardware usage. I'm definitely not against using VMWare to do this, but since we're a 100% Microsoft app stack, it seems like -someone- out there would have solved this problem at the application layer instead of the hypervisor layer by checking on resource utilization at the OS, SQL, SSAS levels. I'm open to ANY discussion on this, and remember no suggestion is too crazy or radical! :-) Right now, VMWare is the only option we've found to get away from "manually" balancing our resources, so any suggestions that leave us on a pure Microsoft stack would be great. Thanks guys, Jeff

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• Cross-platform distributed fault-tolerant (disconnected operation/local cache) filesystem

  - by Adrian Frühwirth

  We are facing a design "challenge" where we are required to set up a storage solution with the following properties: What we need HA a scalable storage backend offline/disconnected operation on the client to account for network outages cross-platform access client-side access from certainly Windows (probably XP upwards), possibly Linux backend integrates with AD/LDAP (permission management (user/group management, ...)) should work reasonably well over slow WAN-links Another problem is that we don't really know all possible use cases here, if people need to be able to have concurrent access to shared files or if they will only be accessing their own files, so a possible solution needs to account for concurrent access and how conflict management would look in this case from a user's point of view. This two years old blog posts sums up the impression that I have been getting during the last couple of days of research, that there are lots of current übercool projects implementing (non-Windows) clustered petabyte-capable blob-storage solutions but that there is none that supports disconnected operation nicely and natively, but I am hoping that we have missed an obvious solution. What we have tried OpenAFS We figured that we want a distributed network filesystem with a local cache and tested OpenAFS (which, as the only currently "stable" DFS supporting disconnected operation, seemed the way to go) for a week but there are several problems with it: it's a real pain to set up there are no official RHEL/CentOS packages the package of the current stable version 1.6.5.1 from elrepo randomly kernel panics on fresh installs, this is an absolute no-go Windows support (including the required Kerberos packages) is mystical. The current client for the 1.6 branch does not run on Windows 8, the current client for the 1.7 does but it just randomly crashes. After that experience we didn't even bother testing on XP and Windows 7. Suffice to say, we couldn't get it working and the whole setup has been so unstable and complicated to setup that it's just not an option for production. Samba + Unison Since OpenAFS was a complete disaster and no other DFS seems to support disconnected operation we went for a simpler idea that would sync files against a Samba server using Unison. This has the following advantages: Samba integrates with ADs; it's a pain but can be done. Samba solves the problem of remotely accessing the storage from Windows but introduces another SPOF and does not address the actual storage problem. We could probably stick any clustered FS underneath Samba, but that means we need a HA Samba setup on top of that to maintain HA which probably adds a lot of additional complexity. I vaguely remember trying to implement redundancy with Samba before and I could not silently failover between servers. Even when online, you are working with local files which will result in more conflicts than would be necessary if a local cache were only touched when disconnected It's not automatic. We cannot expect users to manually sync their files using the (functional, but not-so-pretty) GTK GUI on a regular basis. I attempted to semi-automate the process using the Windows task scheduler, but you cannot really do it in a satisfactory way. On top of that, the way Unison works makes syncing against Samba a costly operation, so I am afraid that it just doesn't scale very well or even at all. Samba + "Offline Files" After that we became a little desparate and gave Windows "offline files" a chance. We figured that having something that is inbuilt into the OS would reduce administrative efforts, helps blaming someone else when it's not working properly and should just work since people have been using this for years. Right? Wrong. We really wanted it to work, but it just doesn't. 30 minutes of copying files around and unplugging network cables/disabling network interfaces left us with (silent! there is only a tiny notification in Windows explorer in the statusbar, which doesn't even open Sync Center if you click on it!) undeletable files on the server (!) and conflicts that should not even be conflicts. In the end, we had one successful sync of a tiny text file, everything else just exploded horribly. Beyond that, there are other problems: Microsoft admits that "offline files" in Windows XP cannot cope with "large files" and therefore does not cache/sync them at all which would mean those files become unavailable if the connection drop In Windows 7 the feature is only available in the Professional/Ultimate/Enterprise editions. Summary Unless there is another fault-tolerant DFS that supports Windows natively I assume that stacking a HA Samba cluster on top of something like GlusterFS/Lustre/whatnot is the only option, but I hope that I am wrong here. How do other companies allow fault-tolerant network access to redundant storage in a heterogeneous environment with Windows?

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• Algorithm design, "randomising" timetable schedule in Python although open to other languages.

  - by S1syphus

  Before I start I should add I am a musician and not a native programmer, this was undertook to make my life easier. Here is the situation, at work I'm given a new csv file each which contains a list of sound files, their length, and the minimum total amount of time they must be played. I create a playlist of exactly 60 minutes, from this excel file. Each sample played the by the minimum number of instances, but spread out from each other; so there will never be a period where for where one sound is played twice in a row or in close proximity to itself. Secondly, if the minimum instances of each song has been used, and there is still time with in the 60 min, it needs to fill the remaining time using sounds till 60 minutes is reached, while adhering to above. The smallest duration possible is 15 seconds, and then multiples of 15 seconds. Here is what I came up with in python and the problems I'm having with it, and as one user said its buggy due to the random library used in it. So I'm guessing a total rethink is on the table, here is where I need your help. Whats is the best way to solve the issue, I have had a brief look at things like knapsack and bin packing algorithms, while both are relevant neither are appropriate and maybe a bit beyond me.

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• What is a good genetic algorithm (GA) or particle swarm optimisation (PSO) framework to use for .NET

  - by Luke Machowski

  I would like to know what is a good, stable, framework that you guys suggest for implementing evolutionary optimisation techniques like PSO or GA? I have written my own ones and I like them, I would be interested in comparing or adding to existing stable ones (or just using them if they are solid and extensible).

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• Diff Algorithm

  - by Daniel Magliola

  I've been looking like crazy for an explanation of a diff algorithm that works and is efficient. The closest I got is this link to RFC 3284 (from several Eric Sink blog posts), which describes in perfectly understandable terms the data format in which the diff results are stored. However, it has no mention whatsoever as to how a program would reach these results while doing a diff. I'm trying to research this out of personal curiosity, because I'm sure there must be tradeoffs when implementing a diff algorithm, which are pretty clear sometimes when you look at diffs and wonder "why did the diff program chose this as a change instead of that?"... Does anyone know where I can find a description of an efficient algorithm that'd end up outputting VCDIFF? By the way, if you happen to find a description of the actual algorithm used by SourceGear's DiffMerge, that'd be even better. NOTE: longest common subsequence doesn't seem to be the algorithm used by VCDIFF, it looks like they're doing something smarter, given the data format they use. Thanks!

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• Alternative to distributed caching

  - by Chen

  Hi, There is a technical requirement to scale a new system easily. This new system consists of three tiered applications (as a batch processors). Each tier will contains at least 2 servers with the same application resides on each server. So, when one of the tier reaches peak performance, we could extend the scalability easily by adding a new server and the same application to off-load some of the processing loads. The problem is that one or two of the three tiers require heavy caching (about 3 million records and increasing). I'm thinking of using distributed caching system to overcome this problem but the new distributed caching system will means an additional point of failure as applications now need to interact with additional caching systems for processing. I'm currently looking at ncache but just wondering if there is an alternatives to this problem? or is there any other comparable distributed caching system that maybe similar or better than ncache and provide enterprise supports too? Thanks, Chen

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• Is there a secure p2p distributed database?

  - by p2pgirl

  I'm looking for a distributed hash table to store and retrieve values securely. These are my requirements: It must use an existing popular p2p network (I must guarantee my key/value will be stored and kept in multiple peers). None but myself should be able to edit or delete the key/value. Ideally an encryption key that only I have access to would be required to edit my key value. All peers would be able to read the key value (read-only access, only the key holder would be able to edit the value) Is there such p2p distributed hash table? Would the bittorrent distributed hash table meet my requirements?' Where could I find documentation?

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• How are distributed services better than distributed objects?

  - by Gabriel Šcerbák

  I am not interested in the technology e.g. CORBA vs Web Services, I am interested in principles. When we are doing OOP, why should we have something so procedural at higher level? Is not it the same as with OOP and relational databases? Often services are supported through code generation, apart from boilerplate, I think it is because we new SOM - service object mapper. So again, what are the reasons for wervices rather than objects?

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• Distributed, Parallel, Fault-tolerant File System

  - by Eddified

  There are so many choices that it's hard to know where to start. My requirements are these: Runs on Linux Most of the files will be between 5-9 MB in size. There will also be a significant number of small-ish jpgs (100px x 100px). All of the files need to be available over http. Redundancy -- ideally it would provide the space efficiency similar to RAID 5 of 75% (in RAID 5 this would be calculated thus: with 4 identical disks, 25% of the space is used for parity = 75% efficent) Must support several petabytes of data scalable runs on commodity hardware In addition, I look for these qualities, though they are not "requirements": Stable, mature file system Lots of momentum and support etc I would like some input as to which file system works best for the given requirements. Some people at my organization are leaning towards MogileFS, but I'm not convinced of the stability and momentum of that project. GlusterFS and Lustre, based on my limited research, appear to be better supported... Thoughts?

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• Web application design with distributed servers

  - by Bonn

  I want to build a web application/server with this structure: main-server sub-server transaction-server (create, update, delete) view-server (view, search) authentication-server documents-server reporting-server library-server e-learning-server The main-server acts as host server for sub-server. I can add many sub-servers and connect it to main-server (via plug-play interface maybe), then it can begin querying data from another sub-servers (which has been connected to the main-server). The sub-servers can be anywhere as long as connected to internet. The main-server can manage all sub-servers which are connected to it (query data, setting permission between sub-servers, etc). The purpose is simple, the web application will be huge as the company grows, so I want to distribute it into small connected plug-able servers. My question is, does the structure above already have a standardized method? or are there any different views? what are the technologies needed? I need a lot of researches before the execution plan begin. thanks a lot.

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• Distributed filesystem across a slow link

  - by Jeff Ferland

  I have an image in my head where a link is too slow to realize the real-time transfer of files, but fast enough to catch up every day. What I'd like to see is a master <- master setup where when I write a file to Server A, the metadata will transfer to Server B immediately and the file will transfer at idle or immediately when Server B's client tries to read the file before Server A has sent it. It seems that there are many filesystems which can perform well over fast links, but I don't know of any that do well with a big bottle neck and a few hours of latency.

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