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  • Weighted round robins via TTL - possible?

    - by Joe Hopfgartner
    I currently use DNS round robin for load balancing, which works great. The records look like this (I have a ttl of 120 seconds) ;; ANSWER SECTION: orion.2x.to. 116 IN A 80.237.201.41 orion.2x.to. 116 IN A 87.230.54.12 orion.2x.to. 116 IN A 87.230.100.10 orion.2x.to. 116 IN A 87.230.51.65 I learned that not every ISP / device treats such a response the same way. For example some DNS servers rotate the addresses randomly or always cycle them through. Some just propagate the first entry, others try to determine which is best (regionally near) by looking at the ip address. However if the userbase is big enough (spreads over multiple ISPs etc) it balances pretty well. The discrepancies from highest to lowest loaded server hardly every exceeds 15%. However now I have the problem that I am introducing more servers into the systems, that not all have the same capacities. I currently only have 1gbps servers, but I want to work with 100mbit and also 10gbps servers too. So what I want is I want to introduce a server with 10 GBps with a weight of 100, a 1 gbps server with a weight of 10 and a 100 mbit server with a weight of 1. I used to add servers twice to bring more traffic to them (which worked nice. the bandwidth doubled almost.) But adding a 10gbit server 100 times to DNS is a bit rediculous. So I thought about using the TTL. If I give server A 240 seconds ttl and server B only 120 seconds (which is about about the minimum to use for round robin, as a lot of dns servers set to 120 if a lower ttl is specified.. so i have heard) I think something like this should occour in an ideal scenario: first 120 seconds 50% of requests get server A -> keep it for 240 seconds. 50% of requests get server B -> keep it for 120 seconds second 120 seconds 50% of requests still have server A cached -> keep it for another 120 seconds. 25% of requests get server A -> keep it for 240 seconds 25% of requests get server B -> keep it for 120 seconds third 120 seconds 25% will get server A (from the 50% of Server A that now expired) -> cache 240 sec 25% will get server B (from the 50% of Server A that now expired) -> cache 120 sec 25% will have server A cached for another 120 seconds 12.5% will get server B (from the 25% of server B that now expired) -> cache 120sec 12.5% will get server A (from the 25% of server B that now expired) -> cache 240 sec fourth 120 seconds 25% will have server A cached -> cache for another 120 secs 12.5% will get server A (from the 25% of b that now expired) -> cache 240 secs 12.5% will get server B (from the 25% of b that now expired) -> cache 120 secs 12.5% will get server A (from the 25% of a that now expired) -> cache 240 secs 12.5% will get server B (from the 25% of a that now expired) -> cache 120 secs 6.25% will get server A (from the 12.5% of b that now expired) -> cache 240 secs 6.25% will get server B (from the 12.5% of b that now expired) -> cache 120 secs 12.5% will have server A cached -> cache another 120 secs ... i think i lost something at this point but i think you get the idea.... As you can see this gets pretty complicated to predict and it will for sure not work out like this in practice. But it should definitely have an effect on the distribution! I know that weighted round robin exists and is just controlled by the root server. It just cycles through dns records when responding and returns dns records with a set propability that corresponds to the weighting. My DNS server does not support this, and my requirements are not that precise. If it doesnt weight perfectly its okay, but it should go into the right direction. I think using the TTL field could be a more elegant and easier solution - and it deosnt require a dns server that controls this dynamically, which saves resources - which is in my opinion the whole point of dns load balancing vs hardware load balancers. My question now is... are there any best prectices / methos / rules of thumb to weight round robin distribution using the TTL attribute of DNS records? Edit: The system is a forward proxy server system. The amount of Bandwidth (not requests) exceeds what one single server with ethernet can handle. So I need a balancing solution that distributes the bandwidth to several servers. Are there any alternative methods than using DNS? Of course I can use a load balancer with fibre channel etc, but the costs are rediciulous and it also increases only the width of the bottleneck and does not eliminate it. The only thing i can think of are anycast (is it anycast or multicast?) ip addresses, but I don't have the means to set up such a system.

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  • DNS Round-robin, Load Balancing, Load sharing, and failover in 2012

    - by user1089770
    I have been reading many posts on serverfault as well as on other sites regarding all these. What I understand is, Multiple A records(round-robin dns) can be used for both : Load sharing (round-robin, but NOT load-balancing). Many people say that “Load Balancing” but I think there will be no load-balancing because “Balance” means (literally) “compare two(or more) and adjust” (and that is what Real s/w or h/w Load balancers do) but Browsers never do this, instead they randomly select and IP and connect to it. It doesn't have any knowledge about the current load of that server (probably, the IP it picked had the highest load!). Automatic failover (latest browsers only). Yes, I think DNS can be used as a simple failover system (at least in 2012, I dont know when it actually "came in effect"). please refer to : http://webmasters.stackexchange.com/questions/10927/using-multiple-a-records-for-my-domain-do-web-browsers-ever-try-more-than-one and Browser-based DNS failover using multiple A records and http://www.nber.org/sys-admin/dns-failover.html I would like to make sure my assumptions/findings are right. So let me know please.....

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  • Ruby BigDecimal Round: Is this an error?

    - by peterdp
    While writing a test with a value that gets represented as a BigDecimal, I ran into something weird and decided to dig into it. In brief, '0.00009' when rounded to two decimal places is returned as 0.01 instead of 0.00. Really. Here's my script/console capture: >> bp = BigDecimal('0.09') => #<BigDecimal:210fe08,'0.9E-1',4(8)> >> bp.round(2,BigDecimal::ROUND_HALF_DOWN).to_f => 0.09 >> bp = BigDecimal('0.009') => #<BigDecimal:210bcf4,'0.9E-2',4(8)> >> bp.round(2,BigDecimal::ROUND_HALF_DOWN).to_f => 0.01 >> bp = BigDecimal('0.0009') => #<BigDecimal:2107a8c,'0.9E-3',4(12)> >> bp.round(2,BigDecimal::ROUND_HALF_DOWN).to_f => 0.0 >> bp = BigDecimal('0.00009') => #<BigDecimal:2103428,'0.9E-4',4(12)> >> bp.round(2,BigDecimal::ROUND_HALF_DOWN).to_f => 0.01 >> bp = BigDecimal('0.000009') => #<BigDecimal:20ff0f8,'0.9E-5',4(12)> >> bp.round(2,BigDecimal::ROUND_HALF_DOWN).to_f => 0.0 Oh, and I get the same results if I use the default mode, like so: >> bd = BigDecimal('0.00009') => #<BigDecimal:2152ed8,'0.9E-4',4(12)> >> bd.round(2).to_f => 0.01 Here are my versions: ruby 1.8.6 (2008-03-03 patchlevel 114) [i686-darwin9.2.2] Rails 2.3.4 Has anyone seen anything like this?

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  • Using Round Robin DNS on simple VPN setup

    - by dannymcc
    We have two internet connections which are load balanced to share the load between the two. We set this up after one of the internet provider proved to be less than reliable but great speed and latency wise when it is working. We'd rather utilise both connections as much as possible rather than leave one idle until the other drops out. We have a number of remote workers who occasionally need to connect via VPN from their laptops or iPads, we also have a small number of permanent LAN to LAN tunnels running from smaller branches. Originally we only had one internet connection and used one of our static IP addresses for all VPN users. Now that we have two internet connections running all of the time I am trying to make sure that the VPN is available to our team regardless of which connection drops. So my solution is to create two A records for our domain name with a value of vpn. and the two static IP addresses from each peer. Is this a sensible way of achieving this? Should I expect higher latency due to packets being lost if one peer fails and some packets still get routed to it anyway? A brief mockup of the setup I have:

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  • Is there a way to do 'correct' arithmetical rounding in .NET? / C#

    - by Markus
    I'm trying to round a number to it's first decimal place and, considering the different MidpointRounding options, that seems to work well. A problem arises though when that number has sunsequent decimal places that would arithmetically affect the rounding. An example: With 0.1, 0.11..0.19 and 0.141..0.44 it works: Math.Round(0.1, 1) == 0.1 Math.Round(0.11, 1) == 0.1 Math.Round(0.14, 1) == 0.1 Math.Round(0.15, 1) == 0.2 Math.Round(0.141, 1) == 0.1 But with 0.141..0.149 it always returns 0.1, although 0.146..0.149 should round to 0.2: Math.Round(0.145, 1, MidpointRounding.AwayFromZero) == 0.1 Math.Round(0.146, 1, MidpointRounding.AwayFromZero) == 0.1 Math.Round(0.146, 1, MidpointRounding.ToEven) == 0.1 Math.Round(0.146M, 1, MidpointRounding.ToEven) == 0.1M Math.Round(0.146M, 1, MidpointRounding.AwayFromZero) == 0.1M I tried to come up with a function that addresses this problem, and it works well for this case, but of course it glamorously fails if you try to round i.e. 0.144449 to it's first decimal digit (which should be 0.2, but results 0.1.) (That doesn't work with Math.Round() either.) private double round(double value, int digit) { // basically the old "add 0.5, then truncate to integer" trick double fix = 0.5D/( Math.Pow(10D, digit+1) )*( value = 0 ? 1D : -1D ); double fixedValue = value + fix; // 'truncate to integer' - shift left, round, shift right return Math.Round(fixedValue * Math.Pow(10D, digit)) / Math.Pow(10D, digit); } I assume a solution would be to enumerate all digits, find the first value larger than 4 and then round up, or else round down. Problem 1: That seems idiotic, Problem 2: I have no idea how to enumerate the digits without a gazillion of multiplications and subtractios. Long story short: What is the best way to do that?

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  • Is there a tool to do round trip software engineering between a sequence diagram and a group of objects that message back and forth?

    - by DeveloperDon
    Is there a tool to do round trip software engineering between a sequence diagram and a group of objects that message back and forth? Perhaps this seems a little exotic, but it seems like a function that includes message calls or even method invocations on other objects could be automatically converted to a sequence diagram given that it is not hard to do manually. Similarly, when a sequence diagram is modified, based on the message name and type of message, should it not be possible to add a message or method to the calling object?

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  • activemq round robin between queues or topics

    - by forkit
    I'm trying to achieve load balancing between different types of messages. I would not know in advance what the messages coming in might be until they hit the queue. I know I can try resequencing the messages, but I was thinking that maybe if there was a way to have the various consumers round robin between either queues or between topics, this would solve my problem. The main problem i'm trying to solve is that I have many services sending messages to one queue with many consumers feeding off one queue. I do not want one type of service monopolizing the entire worker cluster. Again I don't know in advance what the messages that are going to hit the queue are going to be. To try to clearly repeat my question: Is there a way to tell the consumers to round robin between either existing queues or topics? Thank you in advance.

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  • Implement Semi-Round-Robin file which can be expanded and saved on demand

    - by ircmaxell
    Ok, that title is going to be a little bit confusing. Let me try to explain it a little bit better. I am building a logging program. The program will have 3 main states: Write to a round-robin buffer file, keeping only the last 10 minutes of data. Write to a buffer file, ignoring the time (record all data). Rename entire buffer file, and start a new one with the past 10 minutes of data (and change state to 1). Now, the use case is this. I have been experiencing some network bottlenecks from time to time in our network. So I want to build a system to record TCP traffic when it detects the bottleneck (detection via Nagios). However by the time it detects the bottlenecking, most of the useful data has already been transmitted. So, what I'd like is to have a deamon that runs something like dumpcap all the time. In normal mode, it'll only keep the past 10 minutes of data (Since there's no point in keeping a boat load of data if it's not needed). But when Nagios alerts, I will send a signal in the deamon to store everything. Then, when Naigos recovers it will send another signal to stop storing and flush the buffer to a save file. Now, the problem is that I can't see how to cleanly store a rotating 10 minutes of data. I could store a new file every 10 minutes and delete the old ones if in mode 1. But that seems a bit dirty to me (especially when it comes to figuring out when the alert happened in the file). Ideally, the file that was saved should be such that the alert is always at the 10:00 mark in the file. While that is possible with new files every 10 minutes, it seems like a bit dirty to "repair" the files to that point. Any ideas? Should I just do a rotating file system and combine them into 1 at the end (doing quite a bit of post-processing)? Is there a way to implement the semi-round-robin file cleanly so that there is no need for any post-processing? Thanks Oh, and the language doesn't matter as much at this stage (I'm leaning towards Python, but have no objection to any other language. It's less of an issue than the overall design)...

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  • Round-robin assignment

    - by Robert
    Hi, I have a Customers table and would like to assign a Salesperson to each customer in a round-robin fashion. Customers --CustomerID --FName --SalespersonID Salesperson --SalespersonID --FName So, if I have 15 customers and 5 salespeople, I would like the end result to look something like this: CustomerID -- FName -- SalespersonID 1 -- A -- 1 2 -- B -- 2 3 -- C -- 3 4 -- D -- 4 5 -- E -- 5 6 -- F -- 1 7 -- G -- 2 8 -- H -- 3 9 -- I -- 4 10 -- J -- 5 11 -- K -- 1 12 -- L -- 2 13 -- M -- 3 14 -- N -- 4 15 -- 0 -- 5 etc... I've been playing around with this for a bit and am trying to write some SQL to update my Customers table with the appropriate SalespersonID, but am having some trouble getting it to work. Any ideas are greatly appreciated!

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  • PHP - Math - Round Number Function

    - by aSeptik
    Hi All guys! this time i have a math question for you! Assuming we have three numbers one is the Number of Votes the second is the Total Values and the last is the Units Ratings. units_ratings can be a number from 1 to 10; if ( total_values / units_ratings != number_of_votes ) { //do something for let the "number_of_votes" fit the division! } I ask this to you, cause i want know the best (fastest) way of achieve this! Thanks!

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  • How to round current time in teradata and insert into timestamp(6) feilds

    - by user3471254
    I have a table with date fields of timestamp(6) fields . create table test_time ( t1 timestamp(6) format 'mm/dd/yyyy hh:mm:si' , ); I want to insert into this table with current date and time rounded. i.e. say for example if the current date time is 08/07/2014 10:34:56 then the value in the table should be 08/07/2014 10:00:00 . (or) if current data and time is 08/07/2014 10:54:56 then also the value should be 08/07/2014 10:34:56

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  • Loop append div and repeat

    - by Diego Vieira
    I have this code <div class="round-3-top"> <div class="round-2-top"> <div class="round-1-top"></div> <div class="round-1-bottom"></div> </div> <div class="round-2-bottom"> <div class="round-1-top"></div> <div class="round-1-bottom"></div> </div> </div> <div class="round-3-bottom"> <div class="round-2-top"> <div class="round-1-top"></div> <div class="round-1-bottom"></div> </div> <div class="round-2-bottom"> <div class="round-1-top"></div> <div class="round-1-bottom"></div> </div> </div> But i want generate dynamically, how i do that? Ex.: i have 4 rounds, this would be the generated code <div class="round-4-top"> <div class="round-3-top"> <div class="round-2-top"> <div class="round-1-top"></div> <div class="round-1-bottom"></div> </div> <div class="round-2-bottom"> <div class="round-1-top"></div> <div class="round-1-bottom"></div> </div> </div> <div class="round-3-bottom"> <div class="round-2-top"> <div class="round-1-top"></div> <div class="round-1-bottom"></div> </div> <div class="round-2-bottom"> <div class="round-1-top"></div> <div class="round-1-bottom"></div> </div> </div> </div> <div class="round-4-bottom"> <div class="round-3-top"> <div class="round-2-top"> <div class="round-1-top"></div> <div class="round-1-bottom"></div> </div> <div class="round-2-bottom"> <div class="round-1-top"></div> <div class="round-1-bottom"></div> </div> </div> <div class="round-3-bottom"> <div class="round-2-top"> <div class="round-1-top"></div> <div class="round-1-bottom"></div> </div> <div class="round-2-bottom"> <div class="round-1-top"></div> <div class="round-1-bottom"></div> </div> </div> </div> I try using TagBuilder in MVC C# but I can not do. What should happen is, if you are 3 rounds, adding he should go inside each div is like the example above. Any idea how can I develop it?

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  • How to round currency values [migrated]

    - by Kenny
    I already have several ways to solve this, but I am interested in whether there is a better solution to this problem. Please only respond with a pure numeric algorithm. String manipulation is not acceptable. I am looking for an elegant and efficient solution. Given a currency value (ie $251.03), split the value into two half and round to two decimal places. The key is that the first half should round up and the second should round down. So the outcome in this scenario should be $125.52 and $125.51.

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  • Round Table - Minimum Cost Algorithm

    - by 7Aces
    Problem Link - http://www.iarcs.org.in/zco2013/index.php/problems/ROUNDTABLE It's dinner time in Castle Camelot, and the fearsome Knights of the Round Table are clamouring for dessert. You, the chef, are in a soup. There are N knights, including King Arthur, each with a different preference for dessert, but you cannot afford to make desserts for all of them. You are given the cost of manufacturing each Knight's preferred dessert-since it is a round table, the list starts with the cost of King Arthur's dessert, and goes counter-clockwise. You decide to pick the cheapest desserts to make, such that for every pair of adjacent Knights, at least one gets his dessert. This will ensure that the Knights do not protest. What is the minimum cost of tonight's dinner, given this condition? I used the Dynamic Programming approach, considering the smallest of i-1 & i-2, & came up with the following code - #include<cstdio> #include<algorithm> using namespace std; int main() { int n,i,j,c,f; scanf("%d",&n); int k[n],m[n][2]; for(i=0;i<n;++i) scanf("%d",&k[i]); m[0][0]=k[0]; m[0][1]=0; m[1][0]=k[1]; m[1][1]=1; for(i=2;i<n;++i) { c=1000; for(j=i-2;j<i;++j) { if(m[j][0]<c) { c=m[j][0]; f=m[j][1];} } m[i][0]=c+k[i]; m[i][1]=f; } if(m[n-2][0]<m[n-1][0] && m[n-2][1]==0) printf("%d\n",m[n-2][0]); else printf("%d\n",m[n-1][0]); } I used the second dimension of the m array to store from which knight the given sequence started (1st or 2nd). I had to do this because of the case when m[n-2]<m[n-1] but the sequence started from knight 2, since that would create two adjacent knights without dessert. The problem arises because of the table's round shape. Now an anomaly arises when I consider the case - 2 1 1 2 1 2. The program gives an answer 5 when the answer should be 4, by picking the 1st, 3rd & 5th knight. At this point, I started to doubt my initial algorithm (approach) itself! Where did I go wrong?

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  • Has programming ruined your perception of round numbers?

    - by Jon Purdy
    Most of the world works in base 10 nowadays, but as programmers working on binary systems, we constantly find ourselves working with powers of 2. While most people consider integer multiples of powers of 10 "nice and round" and somehow aesthetically superior, I found early on in my programming adventures that multiples of powers of 2 feel much more intuitively round to me: fewer factors, of course. I'm much more likely to lay out a Web site using, say, 8- or 16-pixel margins rather than 10 or 20, and when someone remarks that 128 is an insanely arbitrary number of ounces to be in a gallon, I have to smile a little inside at how, just perhaps, the U.S. system might be superior to metric in one small way. I'm just curious: has programming ruined (read: altered) your perception of the roundness of a number?

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  • How to make my simple round sprite look right in XNA

    - by Joshua Perina
    Ok, I'm very new to graphics programming (but not new to coding). I'm trying to load a simple image in XNA which I can do fine. It is a simple round circle which I made in photoshop. The problem is the edges show up rough when I draw it on the screen even with the exact size. The anti-aliasing is missing. I'm sure I'm missing something very simple: GraphicsDevice.Clear(Color.Black); // TODO: Add your drawing code here spriteBatch.Begin(); spriteBatch.Draw(circle, new Rectangle(10, 10, 10, 10), Color.White); spriteBatch.End(); Couldn't post picture because I'm a first time poster. But my smooth png circle has rough edges. So I found that if I added: spriteBatch.Begin(SpriteSortMode.FrontToBack, BlendState.NonPremultiplied); I can get a smooth image when the image is the same size as the original png. But if I want to scale that image up or down then the rough edges return. How do I get XNA to smoothly resize my simple round image to a smaller size without getting the rough edges?

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  • Storage of leftover values in a situation of having to round down

    - by jt0dd
    I'm writing an app (client and server side) where the number of sales required by each employee must be kept track of in round-number form. Each month, the employees are required to sell a certain number, and this app needs to keep track of how many sales must be made for each 12 hour interval during the work week. Because I have to round the values down to a whole number, I must keep track of leftovers in the rounding process and ensure that they are always carried over. My method must ensure the storage of the leftover value even when client and server side crash, restart, close, etc. Right now, I'm working on doing this by storing the leftovers in a field in the user's account row in the database each time a value is rounded, reading the stored value, removing any portion that is used (when a whole number is reached, most of the leftover is used up), and storing the new value. This practice seems weird because while the leftovers are calculated on the client side, it's the same number for each employee, and every employee using the app is storing a copy of the same leftover data. Alternatively, I could have all clients store the data at once into the same data field on a general table, but this is just as weird. Is there a better way that this can be handled or is my method correct?

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  • Shouldn't recruitment be the other way round?

    - by Fanatic23
    I really don't know why nobody's thought of this so far, but recruitment should be the other way round. Engineers should have some sort of a common platform where they register skills or domains they are interested in, demonstrate their capabilities and companies should take it up from there. I think this is way more effective since if you are paid well to do work that you love doing, you will generally make a fine job out of it. Does anybody know of some recruitment platform like this?

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  • Google Maps API Round-up

    Google Maps API Round-up This week, Mano Marks and Paul Saxman go over recent launches and things you might have missed with the Google Maps APIs, including the new Google Time Zone API, traffic estimates with the Directions API (for enterprise customers), and the Places Autocomplete API query results and data service enhancements. From: GoogleDevelopers Views: 0 0 ratings Time: 00:00 More in Education

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  • Fast Data Executive Round Table FY14 event kit

    - by JuergenKress
    We are very interested to run joint marketing events jointly with you as our partners! At our SOA Community Workspace (SOA Community membership required) you can find a new Fast Data Executive Round Table FY14 event kit. This event is designed at senior IT and executives level for the purposes of education, awareness, and thought leadership around the subject of big data; and a specific flavor of big data - Fast Data - that has begun to spark the imagination of many Oracle customers. Fast Data is not new. It’s a term that was invented initially by Ovum’s Tony Baer as a way to represent the collection of ‘high velocity’ solutions with respect to the big data. For Oracle, the Fast Data campaign in FY13 began as a way to tie a broader set of solutions together (SOA/Business Process Management, Data Integration and Business Analytics) under a set of use cases focused on real-time, high velocity data. It has helped to give Oracle a leap-frog advantage over many of the niche integration vendors (i.e. Informatica, Pega, Tibco, Software AG, Terracotta) who haven’t been able to address these types of end-to-end use cases which rely on the combination of filtering, in-memory data processing, correlation, real-time data movement and transformation, end-to-end analytics, and business process management. Only Oracle can address all the dimensions of fast data, and only Oracle can provide a set of engineered solutions to address this space. This event is designed to continue that thought leadership momentum and raise the awareness about what Oracle Fast Data solutions are designed to solve. It’s designed to highlight real customer solutions and articulate the business benefits that fast data can address. This is not an event that gets into the esoteric technical standards of Hadoop, NoSQL, and in-memory data grids. This is an event that instead gets into the heart of business problems that big data has left un-addressed and charts the path for next steps in fast data. Get the Fast Data Executive Round Table FY14 event kit here. Support marketing campaigns We can support such events by: Oracle speakers - contact your partner manager Marketing budget - contact your A&C marketing manager Event location - free use of Oracle Customer Visitor Centers conference rooms Promote your event at events.oracle.com: http://tinyurl.com/eventspecialized E-Blast: invite customers to your event – contact your A&C marketing manager For additional marketing kits e.g for Business Process Managementplease visit our SOA Community Workspace. SOA & BPM Partner Community For regular information on Oracle SOA Suite become a member in the SOA & BPM Partner Community for registration please visit www.oracle.com/goto/emea/soa (OPN account required) If you need support with your account please contact the Oracle Partner Business Center. Blog Twitter LinkedIn Facebook Wiki Mix Forum Technorati Tags:

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  • Silverlight - round doubles away from zero

    - by Cornel
    In Silverlight the Math.Round() method does not contain an overload with 'MidpointRounding' parameter. What is the best approach to round a double away from zero in Silverlight in this case? Example: Math.Round(1.4) = 1 Math.Round(1.5) = 2 Math.Round(1.6) = 2

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