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• How to use a DHT for a social trading environment

  - by Lirik

  I'm trying to understand if a DHT can be used to solve a problem I'm working on: I have a trading environment where professional option traders can get an increase in their risk limit by requesting that fellow traders lend them some of their risk limit. The lending trader will can either search for traders with certain risk parameters which are part of every trader's profile, i.e. Greeks, or the lending trader can subscribe to requests from certain traders. I want this environment to be scalable and decentralized, but I don't know how traders can search for specific profile parameters when the data is contained in a DHT. Could anybody explain how this can be done?

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• users authentication and dht

  - by mtasic

  Lets say that I have only DHT (distributed hash table) implemented (in Python), and I want to build authentication service over P2P network, but without introducing centralized authentication server with such a service. Can it be done, and if so how can I achieve this? I'm familiar with how Skype and Wuala have done this, but I am looking for decentralized solution without single point of failure.

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• Which DHT algorithm to use (if I want to join two separate DHTs)?

  - by webdreamer

  I've been looking into some DHT systems, specially Pastry and Chord. I've read some concerns about Chord's reaction to churn, though I believe that won't be a problem for the task I have at hands. I'm implementing some sort of social network service that doesn't rely on any central servers for a course project. I need the DHT for the lookups. Now I don't know of all the servers in the network in the beginning. As I've stated, there's no main tracker server. It works this way: each client has three dedicated servers. The three servers have the profile of the client, and it's wall, it's personal info, replicated. I only get to know about other group of servers when the user adds a friend (inputing the client's address). So I would create two separate DHTs on the two groups of three servers and when they friend each other I would like to join the DHTs. I would like to this consistently. I haven't had a lot of time to get all that familiar with the protocols, so I would like to know which one is better if I want to join the two separate DHTs?

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• java distributed cache for low latency, high availability

  - by Shahbaz

  I've never used distributed caches/DHTs like memcached, jboss cache, ehcache, etc. I'm wondering which, if any, is appropriate for my use. First, I'm not doing web applications (as most of these project seem to be geared towards web apps). I write servers (Order Management Systems actually) for financial trading firms. The servers themselves are not too complicated. They need to receive information (market data, orders, executions, etc.) rout them to their destination while possibly transforming some of these messages. I am looking at these products to solve the following problems: * Safe repository of the state of the server. I'd rather build the logic of my application as a bunch of transformers (similar to Apache Camel) and store the state in a 'safe' place * This repository should be distributed: in case one of these data stores crashes, one or two more should be up and I should be able to switch to them seamlessly * This repository should be fast. Single digits milliseconds count here, in other words, systems which consume/process this data are automated systems, not humans clicking on links. This system needs to have high-throughput and low latency. By sending my data outside the process, I am necessarily slowing performance, but I am trying to balance absolute raw speed and absolute protection of data. * This repository should be safe. Similar to the point about several on-line backups, this system needs to write data to disk (potentially more than one disk). I'd really like to stop writing my own 'transaction servers.' Am I correct to be looking into projects such as jboss cache, ehcache, etc.? Thanks

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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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• Easiest way to find the correct kademlia bucket

  - by Martin

  In the Kademlia protocol node IDs are 160 bit numbers. Nodes are stored in buckets, bucket 0 stores all the nodes which have the same ID as this node except for the very last bit, bucket 1 stores all the nodes which have the same ID as this node except for the last 2 bits, and so on for all 160 buckets. What's the fastest way to find which bucket I should put a new node into? I have my buckets simply stored in an array, and need a method like so: Bucket[] buckets; //array with 160 items public Bucket GetBucket(Int160 myId, Int160 otherId) { //some stuff goes here } The obvious approach is to work down from the most significant bit, comparing bit by bit until I find a difference, I'm hoping there is a better approach based around clever bit twiddling. Practical note: My Int160 is stored in a byte array with 20 items, solutions which work well with that kind of structure will be preferred.

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• Torrent upload ratio not updated on Synology DS212+

  - by user179271

  I have a Synology DS212+ NAS running DSM 4.2-3211 (current version). I use it for several purposes including torrent download using Download Station and a tracker that needs authentication. My problem is that my download/upload ratio isn't updated, so it constantly falls down. My NAS is behind a router, and I configured the NAT to forward ports 6890 to 6999 to the internal IP address of the NAS. Here are the Download Station settings : TCP port : 6990, Sharing ratio : 900%, Sharing time : infinite, max download speed : 0 (no limit), max upload speed : 0 (no limit), BT protocol encryption : checked, max numbers of peers allowed by torrent file : 4000, DHT : checked, with port 6889. When the DHT option is not checked, the NAS doesn't upload any files. I don't know what is this option for. Can someone help me to solve this problem ? Did I miss any step, or does it come from the NAT ? How is the authentication managed by Dowload Station ? (Sorry for my english) Thanks.

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• glusterfs mounts get unmounted when 1 of the 2 bricks goes offline

  - by Shiquemano

  I have an odd case where 1 of the 2 replicated glusterfs bricks will go offline and take all of the client mounts down with it. As I understand it, this should not be happening. It should fail over to the brick that is still online, but this hasn't been the case. I suspect that this is due to configuration issue. Here is a description of the system: 2 gluster servers on dedicated hardware (gfs0, gfs1) 8 client servers on vms (client1, client2, client3, ... , client8) Half of the client servers are mounted with gfs0 as the primary, and the other half are pointed at gfs1. Each of the clients are mounted with the following entry in /etc/fstab: /etc/glusterfs/datavol.vol /data glusterfs defaults 0 0 Here is the content of /etc/glusterfs/datavol.vol: volume datavol-client-0 type protocol/client option transport-type tcp option remote-subvolume /data/datavol option remote-host gfs0 end-volume volume datavol-client-1 type protocol/client option transport-type tcp option remote-subvolume /data/datavol option remote-host gfs1 end-volume volume datavol-replicate-0 type cluster/replicate subvolumes datavol-client-0 datavol-client-1 end-volume volume datavol-dht type cluster/distribute subvolumes datavol-replicate-0 end-volume volume datavol-write-behind type performance/write-behind subvolumes datavol-dht end-volume volume datavol-read-ahead type performance/read-ahead subvolumes datavol-write-behind end-volume volume datavol-io-cache type performance/io-cache subvolumes datavol-read-ahead end-volume volume datavol-quick-read type performance/quick-read subvolumes datavol-io-cache end-volume volume datavol-md-cache type performance/md-cache subvolumes datavol-quick-read end-volume volume datavol type debug/io-stats option count-fop-hits on option latency-measurement on subvolumes datavol-md-cache end-volume The config above is the latest attempt at making this behave properly. I have also tried the following entry in /etc/fstab: gfs0:/datavol /data glusterfs defaults,backupvolfile-server=gfs1 0 0 This was the entry for half of the clients, while the other half had: gfs1:/datavol /data glusterfs defaults,backupvolfile-server=gfs0 0 0 The results were exactly the same as the above configuration. Both configs connect everything just fine, they just don't fail over. Any help would be appreciated.

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• Why is Transmission constantly active?

  - by Dov

  I am using Transmission (1.92, the latest version) in Mac OS X 10.6.2 Snow Leopard, and have noticed that, without any torrents (at all, not even paused), Little Snitch reports constant activity from it. What's going on? I'd always assumed when I saw that with Torrents loaded but inactive, it had to do with the DHT, or some such kind of scanning activity. But what could it be doing when no torrents are loaded at all?

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• Even distribution through a chain of resources

  - by ClosetGeek

  I'm working on an algorithm which routes tasks through a chain of distributed resources based on a hash (or random number). For example, say you have 10 gateways into a service which distribute tasks to 1000 handlers through 100 queues. 10,000 connected clients are expected to be connected to gateways at any given time (numbers are very general to keep it simple). Thats 10,000 clients 10 gateways (producers) 100 queues 1000 workers/handlers (consumers) The flow of each task is client-gateway-queue-worker Each client will have it's own hash/number which is used to route each task from the client to the same worker each time, with each task going through the same gateway and queue each time. Yet the algorithm handles distribution evenly, meaning each gateway, queue, and worker will have an even workload. My question is what exactly would this be called? Does such a thing already exist? This started off as a DHT, but I realized that DHTs can't do exactly what I need, so I started from scratch.

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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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• 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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• Can we increase Torrent share ratio using Local Peer Discovery?

  - by Jagira

  I just want to know whether this is a flaw or not in Bittorrent system. Let us assume that I am member of a Private Torrent site which requires me to maintain a specific upload to download ratio. Will this work: I create a torrent of a large file say [ Fedora Linux ~ 4 GB ] and upload it to the tracker I download the same torrent using my ID and start it on another machine on LAN or a Virtual machine Both clients have Local Peer Discovery enabled, so they will find 'em [ not via DHT ] and start x'ferring data using LAN bandwidth at LAN speeds. Though both uploads and downloads will increase, my ratio will also increase If I reiterate the entire process 'n' times, the numerator in the "RATIO" i.e Upload will become so large that the effect of downloads on ratio will become less. I want to know whether this is legitimate???

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• uTorrent error: Access is denied

  - by Ben Franchuk

  When I booted my computer today and opened up uTorrent it went on, as usual, to check the torrents that I had been running before. On one it returned an "Access is denied" error after it had been checked. I have absolutely no idea why this is happening as I was downloading the same torrent just the night before, and additionally because I have other torrents going in the same downloads folder and they do not have any such errors. It may be worth noting that on said defective torrent, there appear to be no seeds and no connected peers (of the 33 available) and three of the trackers appear to be inactive as well (those being Peer Exchange, Local Peer Discovery and DHT). I have rebooted a few times in an attempt to fix this problem, but to no success. I also tried a few times force rechecking / force starting but neither of those worked either. edit I booted today and it was working for whatever reason. thanks for all of the help anyways guys!

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• Designing DAL in .NET to be "data-source independent" and not just "database independent" ?

  - by Munish Goyal

  How to design such flexible DAL (specifically in .NET) ? What interfaces .NET provides and what should be done on my own ? Its a greenfield project starting with SQL Server as data source but in future, parts of it will move to different NoSQL type of datastores. Also, we may need to experiment with lot of different datastores (like some data may have to go with Cassandra, some with RDBMS, some to other DHT etc.) Therefore easily switchable access layer will be needed. All i know right now is the 'data' and 'operations needed on that data'.

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• How do I choose a database?

  - by liamzebedee

  I need a comparison table of some sort for database varieties (MySQL, SQLite etc.). I can't find one. My use case is, I am implementing storage of objects in a distributed hash table. I need a database solution that is: Fast for sorting Simplistic (no users, preferably no additional structures like multiple tables etc.) Concurrent (if possible) Multi-platform File based (not stored in memory primarily) Centralized I will be programming in Go. As I understand, I believe I need what is called a Document Orientated Database, because I am storing objects, identified by keys. EDIT: While I am implementing a DHT, I will also be storing metadata about the objects, such as access counts etc. It would also be preferable to have TLL (time to live)

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