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• Amazon EC2: Instances, IPs and a wordpress blog (LAMP)

  - by JustinXXVII

  I had a link to my blog posted on Reddit yesterday and MySQL crashed on my EC2 Micro instance. I know I didn't have that many visitors because I used a marketing link that tracks hits. The link got 167 hits over the course of the last 18 hours, and MySQL crashed twice. So anyway, 167 visits is not a lot, so I've done some short term optimizations like restricting the number of Apache threads to limit the MySQL calls. I also set up WP Super Cache to serve static content. Soon I'm going to offload all of my images to S3 or CloudFront. So this leads me to my question. If this doesn't seem to help, and if i have another traffic "spike", how do AMIs work when you have a MySQL database? I think I understand that if you have more than one instance and assign the same Elastic IP to both of them, the incoming traffic gets distributed among both. But what happens when the MySQL database gets updated on one of the instances? I just need to wrap my mind around what happens when I create an AMI and then launch a new instance to help with traffic. Thanks for your suggestions.

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• How can I use HAproxy with SSL and get X-Forwarded-For headers AND tell PHP that SSL is in use?

  - by Josh

  I have the following setup: (internet) ---> [ pfSense Box ] /-> [ Apache / PHP server ] [running HAproxy] --+--> [ Apache / PHP server ] +--> [ Apache / PHP server ] \-> [ Apache / PHP server ] For HTTP requests this works great, requests are distributed to my Apache servers just fine. For SSL requests, I had HAproxy distributing the requests using TCP load balancing, and it worked however since HAproxy didn't act as a proxy, it didn't add the X-Forwarded-For HTTP header, and the Apache / PHP servers didn't know the client's real IP address. So, I added stunnel in front of HAproxy, reading that stunnel could add the X-Forwarded-For HTTP header. However, the package which I could install into pfSense does not add this header... also, this apparently kills my ability to use KeepAlive requests, which I would really like to keep. But the biggest issue which killed that idea was that stunnel converted the HTTPS requests into plain HTTP requests, so PHP didn't know that SSL was enabled and tried to redirect to the SSL site. How can I use HAproxy to load balance across a number of SSL servers, allowing those servers to both know the client's IP address and know that SSL is in use? And if possible, how can I do it on my pfSense server? Or should I drop all this and just use nginx?

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• Systemd Service Start With Dynamic Port Value From Docker

  - by Sheriffen

  Using CoreOS, Docker and systemd to manage my services I want to properly perform service discovery. Since CoreOS utilizes etcd (distributed key-value) there is a very convenient way to do this. On systemd's ExecStartPost I can just insert the started service into etcd without problems. My usecase needs something like this: ExecStartPost=/usr/bin/etcdctl set /services/myServiceName '{ \"host\": \"%H\", \"port\": 5555 }' which works like a charm. But this is where my idea popped up. Docker has the power to randomly assign a port if I just run docker run -p 5555 which is awesome since I don't have to set it statically in the *.service file and I could possibly run multiple instances on the same host. What if I could get the randomly assigned port and insert instead of the static 5555? Turns out I can use the docker port command to get the port and with some formatting we can get just the port with $(echo $(/usr/bin/docker port my-container-name 5555) | cut -d':' -f2) which works if I set it (using bash) like this: /usr/bin/etcdctl set /services/myServiceName '{ \"host\": \"%H\", \"port\": '$(echo $(/usr/bin/docker port my-container-name 5555) | cut -d':' -f2)' }' but using systemd I just can't get it to work. This is the code I'm using: ExecStartPost=/usr/bin/etcdctl set /services/myServiceName '{ \"host\": \"%H\", \"port\": '$(echo $(/usr/bin/docker port my-container-name 5555) | cut -d':' -f2)'}' Somehow I got something wrong but it's hard to debug since it works when typed in the terminal.

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• Use autocomplete in dropdown cells with Excel 2007?

  - by Martin

  I want to make a survey with Excel and I therefore have defined the cells for the answers as a dropdown cell which only accepts answers from a certain list, e. g.: The two Lists List1 and List2 (yellow cells) are the possible answers for the questions in Block 1.x resp. 2.x (blue) . There might be a block 4 with more questions, which again use List1 for their possible answers. My problem is: I'd like to be able to use the autocompleate feature to fill in the blue cells with the dropdown menu, so that the user only types 5 and it automatically expands to "5: extremely important" or "5: extremely difficult". According to my research on the www, this should be possible if I add the list with possible answers directly above the cells where autocomplete should work (I did this with the green helper cells which could be hidden) . But I have to enter at least 4 characters 5: e to get the autocompleted suggestion. Is there a way to make autocomplete already replace a "5" by the corresponding valid term? As the survey file shall be distributed to a lot of people "outside", I can not use VBA magic because it may be blocked on their computer and might not work. EDIT: it seems to have to do with the numbers I use: If I'd start my List items with A, B, C instead of 1, 2, 3, it would work perfectly. Excel seems to ignore the pure numbers when they are entered and does not try to autocomplete them.. is there a workaround? (I hope it is clear what I want, it seems a little difficult to explain.)

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• How to display/define Mirror/Stripping pairs with mdadm

  - by Chris

  I want to make a standard linux software Raid10 over 4 HDD. The server has 4HDDs, 2 pairs from different vendors in order to avoid batch problems. I want to have the mirror over two different Vendors, and then the Stripe over the mirror pairs. I could do that by manually creating Raid1/0, but mdadm supports Raid level 10. I just cant figure out how the Raid10 is then handled and how the data is distributed. mdadm --detail /dev/md10 /dev/md10: Version : 1.2 Creation Time : Wed May 28 11:06:23 2014 Raid Level : raid10 Array Size : 1953260544 (1862.77 GiB 2000.14 GB) Used Dev Size : 976630272 (931.39 GiB 1000.07 GB) Raid Devices : 4 Total Devices : 4 Persistence : Superblock is persistent Update Time : Wed May 28 11:06:23 2014 State : clean, resyncing (PENDING) Active Devices : 4 Working Devices : 4 Failed Devices : 0 Spare Devices : 0 Layout : near=2 Chunk Size : 512K Name : pdwhost:10 (local to host pdwhost) UUID : a3de0ad5:9e694ee1:addc6786:c4449e40 Events : 0 Number Major Minor RaidDevice State 0 8 1 0 active sync /dev/sda1 1 8 81 1 active sync /dev/sdf1 2 8 97 2 active sync /dev/sdg1 3 8 113 3 active sync /dev/sdh1 does not really give any information about that. How it should be: Raid 1 / Mirror over /dev/sda1 /dev/sdf1 and /dev/sdg1 /dev/sdh1 Raid 0 over the two Raid 1 pairs Is it possible to do that with the built in "level=10", how can I see what pairs are mirrored? Thanks a lot for you help

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• Internet setup for my office

  - by prakash

  We have two internet connections to our office and our current setup is like this.. The internet connections require pppoe log in so i take each cable and plug it into a wifi router and configure the router to log in to the pppoe and then plug in a cable from the router to a switch and distribute the internet throughout my office. The problem with this setup is it is really hard to monitor and im not able to monitor who is hogging internet usage and what he or she is actually using it for. apart from this we also have a nas setup which is routed through another switch . Could someone please throw a little light on how i can restructure this setup for easy monitoring and better transparency... ? each wan router is connected to a different switch and is distributed to users accordingly.. we have around 40 users in the office.. we want to setup a single linux box to which i want to connect the two wan connections and from there distribute it to all our users.... im looking for a solution where we do not have to invest more that buying a single pc and a couple of nics

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• Installing Visual Studio Express on Windows 8.1

  - by robrene

  I've been trying to install the latest version of Microsoft Visual Studio Express from their website to toy around with the IDE and C# development in general. I have a relatively fresh and completely vanilla installation of Windows 8.1 Professional x64 for this purpose. I come from a Linux background, where installing software (especially software distributed by the maintainer of the OS) is usually done with package managers. First, I tried to look for Visual Studio in the Windows 8 Store. There was one entry, but it did not have an installation button. Instead, it redirected me to their website. From all the products listed under the "Download" section on their website, I decided Visual Studio 2013 Express for Windows Desktop was the best for me. I selected it and clicked on "Install now". An installer program downloaded, and I'm assuming that the installer downloaded the necessary files as it was running. When it was done, it asked for a reboot, to which I obliged. However, I can't seem to find the IDE installed anywhere? It doesn't show up anywhere in the Start menu interface. I can't find any executables that look like they might be the IDE in its installation folder. Running the installer again and selecting "Repair" does download some files, but after its requested reboot, nothing has changed. The only thing that I can find is an advertisement link to "Try other Visual Studio 2013 Products" in my start menu. I suppose my question is what I have to do to run Visual Studio 2013 Express on Windows 8.1? Am I not looking in the right places? Am I doing the installation process wrong? Thanks in advance

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• Azure Virtual Machines - what fault tolerance do they provide?

  - by Borek

  We are thinking about moving our virtual machines (Hyper-V VHDs) to Windows Azure but I haven't found much about what kind of fault tolerance that infrastructure provides. When I run VHD in Azure, I've got two questions: Is my VHD and all the data in it safe? I think that uploaded VHDs use the "Storage" infrastructure so they should be automatically replicated to multiple disks and geographically distributed but should I still make a full-image backup just to be safe? (Note that of course I will be backing up the actual data inside VMs that I care about; I just want to know if there is a chance greater than 0.0000001% that one day I will receive an email from Microsoft telling me that my VM is gone and that I should create or restore it from scratch). Do I need to worry about other things regarding the availability of my VMs? I mean, when I have an on-premise server I need to worry about the hardware itself, about the host operating system, what would happen if my router failed, if my Hyper-V's C: drive failed etc. Am I right in thinking that with Azure, their infrastructure takes care of all of this? Thanks.

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• Managed LAMP platform for maximizing availability and global reach, not scalability

  - by user66819

  Assume a Linux/Apache/MySQL/PHP application for a small base of registered users. With small userbase, there are no traffic peaks so the scalability that cloud platforms offer is not imperative. But the system is mission-critical, so availability is the primary goal. Users are also distributed across Asia, Europe, and US, so multiple server locations that minimize users' network hops would be highly desirable. The dream: a managed VPS platform where we would configure a single server (uploading PHP and other files, manipulating database, etc.), and the platform would automatically mirror the server in a handful of key places around the world (say one on each US coast, one in Europe, one in east Asia). File system synchronization and MySQL replication would happen automatically. Core operating system is managed, so we don't need to do full system administration and security, and low-level backups are also done by service provider, though we also do our own backups as well. Couple this with some sort of DNS geo-detection, so users are routed to the nearest operational server... with support for https, of course. Does such a dream exist? If not, what are some approaches to accomplish the same end with minimal time investment and minimal monthly hosting costs?

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• Why does Google Analytics use two domains?

  - by AKeller

  I'm building a distributed widget that is comparable to Google Analytics. Users will add a <script> tag to their site that references my widget's JavaScript file. The Google Analytics tracking code looks like this: var _gaq = _gaq || []; _gaq.push(['_setAccount', 'UA-XXXXXXXX-X']); _gaq.push(['_trackPageview']); (function () { var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s); })(); Can anyone explain the reasoning behind separate HTTP and HTTPS hostnames? My instinct is to just secure the www address and then use the protocol-less syntax, like //www.google-analytics.com/ga.js. But I'm sure the Google Analytics architects put a lot of thought into this approach. I'd love to understand their logic before I follow/ignore their model.

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• Re-packaging commercial software into RPM packages

  - by gac

  The situation is this - I have a small CentOS 5 "cluster" (currently 7 machines, but potential for more) which run a commercially available software package that's distributed essentially in tarball format (it's actually a zip file with a mixture of Windows/Linux binaries and an installation shell script with no potential for automation). I'd like to re-package this somehow into an RPM package (ideally that I can throw onto a self-hosted yum repository) in order to keep these "cluster" machines both up to date and consistent. I could do 7 manual installations, but there's scope for error. As I understand it, I'll need to accomplish the following tasks: add a non-privileged user to the target system for running the daemon without unnecessary root privileges package the binary files themselves up from the final installation location on a separate build machine (probably under /opt/package for sanity's sake). No source is available. add a firewall hole in order for the end-users to be able to communicate with the "cluster" nodes add a cron task which can start the daemon on @reboot I'm coming up with plenty of good packaging resources so far, but all are based on the traditional method (i.e. if I were the vendor packaging up my source files), rather than re-packaging a ton of binary files from an already-installed instance of the application, which is the only option available to me. Anyone have any good resources they can share for achieving this goal? Thanks!

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• Replicated filesystem and EC2 MySQL

  - by El Yobo

  I'm currently investigating migrating our infrastructure over to run on Amazon's EC2 and am trying to figure out the best way to set up a MySQL service. I'm leaning towards running our own MySQL instances, rather than going with Amazon's RDS, but am still considering the best approach for performance and cost on the instance itself. In order to have persistent data, the MySQL data needs to be on an EBS volume (with some form of striped RAID, e.g. RAID0 or RAID10) to improve persistence. However, EBS IO is limited by the network interface (gigabit, so a theoretical maximum of 128 MB/s), while the ephemeral volumes have no such problem. I did see a suggestion for running two MySQL servers on an instance, with a master running on the ephemeral disk (which we would also RAID) and a slave storing changes to an EBS volume, but this has some additional overhead and complexity (two servers). What I was imagining is using some form of replicated file system such that I could have a filesystem on top of a RAID0 of ephemeral volumes to maximise performance all changes from the above immediately replicated to another RAID1 volume backed by multiple EBS volumes to ensure no data loss The advantages of this would be best possible IO performance for the DB server; no network delay in IO decreased IO on EBS volumes (as all read IO will be done on the ephemeral volumes) so decreased cost good data security, as it's backed onto redundant EBS volumes However, I haven't seen an appropriate system to replicate all changes from one volume to the other; is there a filesystem, or any other approach, which will do this? The distributed file systems, e.g. GlusterFS, DRBD etc seem to focus on replicating disks between servers, can they be set up to do what I'm interested in here? I also haven't seen anything about other's taking this approach. Do I have a solution in need of a problem here (i.e. is performance good enough, so this whole idea is redundant)? Is there some flaw in the plan?

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• Possible Hack with FTP - What are the solutions?

  - by iamrohitbanga

  I was reading the FTP rfc and hence had this idea. Suppose there are several public ftp servers that allow anonymous user login. I open a control connection on port 21 to each of these servers. Now suppose there is a web server a.com with ip address x.y.z.w listening on port 80. FTP allows a user to specify the host on which the data connection is to be setup. So a user specifies the host and port number of a.com web server. Now the ftp server starts sending data to a.com for which it is not a valid HTTP request and hence it is rejected. But a.com notes that the invalid http request came from a public ftp server and not my ip address. Can this not lead to a distributed attack by utilizing all public ftp servers. worse still the the data being sent by ftp server could be a valid http request which could trigger a.com to send a file back to the ftp server. Is there a solution for this or is it no problem at all.

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• Network using only switches

  - by mschultz

  So I'm not a network guy - but here's what I want to do - I have an existing network using wifi, which I like, and which is used to connect several computers to the internet. It is headed up by a router, which is in another part of the building. Three of those computers are in my office. All three have gigabit wired ethernet. I have a gigabit switch. Here's what I want to do: Build a 2nd network, out of just that switch, which allows all 3 computers to connect to each other (just to each other is fine, for this purpose, they need no internet). I have a distributed computing task (rendering high-quality fractal artwork, as it were), that requires the best connection speed to all 3 computers. I want them to be able to "talk to each other" as quickly as possible, with the fewest dropped packets (the dataflow over this network will be quite high). So how do I do this. I'm not a networking guy at all - I tried connecting them all, and nobody got an IP address (which I assume is because nobody is running a DNS server?). What all do I need to do to make this work? PS - two are running windows, one is running ubuntu.

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• DES3 decryption in Ruby on Rails

  - by AntonAL

  My RoR server receives a string, that was encrypted in C++ application using des3 with base64 encoding The cipher object is created so: cipher = OpenSSL::Cipher::Cipher::new("des3") cipher.key = key_str cipher.iv = iv_str key_str and iv_str: are string representations of key and initialization vector for encryption algorithm. They are the same for RoR and C++ application. The code on the RoR side is following: result = "" result << cipher.update( Base64.decode64(message) ) result << cipher.final After executing the last line of code, i get an exception OpenSSL::CipherError (bad decrypt) What is wrong here ? Any ideas ?

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• How to convert DATETIME to FILETIME value in T-SQL?

  - by Alek Davis

  I need to convert a SQL Server DATETIME value to FILETIME in a T-SQL SELECT statement (on SQL Server 2000). Is there a built-in function to do this? If not, can someone help me figure out how to implement this conversion routine as a UDF (or just plain Transact-SQL)? Here is what I know: FILETIME is 64-bit value representing the number of 100-nanosecond intervals since January 1, 1601 (UTC) (per MSDN: FILETIME Structure). SQL Server time era starts on 1900-01-01 00:00:00 (per SELECT CAST(0 as DATETIME). I found several examples showing how to convert FILETIME values to T-SQL DATETIME (I'm not 100% sure they are accurate, though), but could not find anything about reverse conversion. Even the general idea (or algorithm) would help.

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• Is Programming == Math?

  - by moffdub

  I've heard many times that all programming is really a subset of math. Some suggest that OO, at its roots, is mathematically based. I don't get the connection. Aside from some obvious examples: using induction to prove a recursive algorithm formal correctness proofs functional languages lambda calculus asymptotic complexity DFAs, NFAs, Turing Machines, and theoretical computation in general the fact that everything on the box is binary In what ways is programming really a subset of math? I'm looking for an explanation that might have relevance to enterprise/OO development (if there is a strong enough connection, that is). Thanks in advance. Edit: as I stated in a comment to an answer, math is uber important to programming, but what I struggle with is the "subset" argument.

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• Generating a KML heatmap from given data set of [lat, lon, density]

  - by Will Croft

  I am looking to build a static KML (Google Earth markup) file which displays a heatmap-style rendering of a few given data sets in the form of [lat, lon, density] tuples. A very straightforward data set I have is for population density. My requirements are: must be able to feed in data for a given lat, lon must be able to specific the given density of the data at that lat, lon must export to KML The requirements are language agnostic for this project as I will be generating these files offline in order to build the KML used elsewhere. I have looked at a few projects, most notably heatmap.py, which is a port of gheat in Python with KML export. I have hit a brick wall in the sense that the projects I have found to date all rely on building the heatmap from the density of [lat, lon] points fed into the algorithm. If I am missing an obvious way to adapt my data set to feed in just the [lat, lon] tuples but adjusting how I feed them using the density values I have, I would love to know!

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• Drawing a clamped uniform cubic B-spline using Cairo

  - by Tamás

  I have a bunch of coordinates which are the control points of a clamped uniform cubic B-spline on the 2D plane. I would like to draw this curve using Cairo calls (in Python, using Cairo's Python bindings), but as far as I know, Cairo supports Bézier curves only. I also know that the segments of a B-spline between two control points can be drawn using Bézier curves, but I can't find the exact formulae anywhere. Given the coordinates of the control points, how can I derive the control points of the corresponding Bézier curves? Is there any efficient algorithm for that?

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• Genetic algorithms

  - by daniels

  I'm trying to implement a genetic algorithm that will calculate the minimum of the Rastrigin functon and I'm having some issues. I need to represent the chromosome as a binary string and as the Rastrigin's function takes a list of numbers as a parameter, how can decode the chromosome to a list of numbers? Also the Rastrigin's wants the elements in the list to be -5.12<=x(i)<=5.12 what happens if when i generate the chromosome it will produce number not in that interval? I'm new to this so help and explanation that will aid me in understanding will be highly appreciated. Thanks.

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• Matlab 3d volume visualization and 3d overlay

  - by inf.ig.sh

  Hi, so the question ist pretty much the title. I have a 3d volume loaded as raw data [256, 256, 256] = size(A). It contains only values of zero's and ones, where the 1's represent the structure and 0's the "air". I want to visualize the structure in matlab and then run an algorithm on it and put an overlay on it, let's say in the color red. So to be more precise: How do i visualize the 3d volume. 0's transparent, 1's semitransparent? Plot a line in the 3 d vis as an overlay? I already read the mathworks tutorials and they didn't help. I tried using the set command, but it fails completly saying for every property i try "invalid root property". I hope someone can help.

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• Design for a machine learning artificial intelligence framework

  - by Lirik

  This is a community wiki which aims to provide a good design for a machine learning/artificial intelligence framework (ML/AI framework). Please contribute to the design of a language-agnostic framework which would allow multiple ML/AI algorithms to be plugged into a single framework which: runs the algorithms with a user-specified data set. facilitates learning, qualification, and classification. allows users to easily plug in new algorithms. can aggregate or create an ensemble of the existing algorithms. can save/load the progress of the algorithm (i.e. save the network and weights of a neural network, save the tree of a decision tree, etc.). What is a good design for this sort of ML/AI framework?

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• Translation of clustering problem to graph theory language

  - by honk

  I have a rectangular planar grid, with each cell assigned some integer weight. I am looking for an algorithm to identify clusters of 3 to 6 adjacent cells with higher-than-average weight. These blobs should have approximately circular shape. For my case the average weight of the cells not containing a cluster is around 6, and that for cells containing a cluster is around 6+4, i.e. there is a "background weight" somewhere around 6. The weights fluctuate with a Poisson statistic. For small background greedy or seeded algorithms perform pretty well, but this breaks down if my cluster cells have weights close to fluctuations in the background. Also, I cannot do a brute-force search looping through all possible setups because my grid is large (something like 1000x1000). I have the impression there might exist ways to tackle this in graph theory. I heard of vertex-covers and cliques, but am not sure how to best translate my problem into their language.

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• Sorting eigenvectors by their eigenvalues (associated sorting)

  - by fbrereto

  I have an unsorted vector of eigenvalues and a related matrix of eigenvectors. I'd like to sort the columns of the matrix with respect to the sorted set of eigenvalues. (e.g., if eigenvalue[3] moves to eigenvalue[2], I want column 3 of the eigenvector matrix to move over to column 2.) I know I can sort the eigenvalues in O(N log N) via std::sort. Without rolling my own sorting algorithm, how do I make sure the matrix's columns (the associated eigenvectors) follow along with their eigenvalues as the latter are sorted?

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• Java: ArrayList bottleneck

  - by Jack

  Hello, while profiling a java application that calculates hierarchical clustering of thousands of elements I realized that ArrayList.get occupies like half of the CPU needed in the clusterization part of the execution. The algorithm searches the two more similar elements (so it is O(n*(n+1)/2) ), here's the pseudo code: int currentMax = 0.0f for (int i = 0 to n) for (int j = i to n) get content i-th and j-th if their similarity > currentMax update currentMax merge the two clusters So effectively there are a lot of ArrayList.get involved. Is there a faster way? I though that since ArrayList should be a linear array of references it should be the quickest way and maybe I can't do anything since there are simple too many gets.. but maybe I'm wrong. I don't think using a HashMap could work since I need to get them all on every iteration and map.values() should be backed by an ArrayList anyway.. Otherwise should I try other collection libraries that are more optimized? Like google's one, or apache one.. Thanks

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