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  • Varnish returning 503, FetchError (could not get storage)

    - by Archan
    On the current setup we're running into a problem with Varnish, we're running a CentOS 5.7 x86_64 xenpv, with Cpanel WHM, hosted at VPS.net. Sometimes we will recieve a Guru Meditation from Varnish, and when we look in the varnishlog with the following command varnishlog -d -c -m TxStatus:503 it returns output similar to the following: 15 VCL_call c recv 15 VCL_acl c NO_MATCH devs 15 VCL_return c pass 15 VCL_call c hash 15 Hash c **** 15 Hash c ************* 15 VCL_return c hash 15 VCL_call c pass pass 15 Backend c 12 default default 15 TTL c 1835862523 RFC 0 -1 -1 1332454056 0 1332454055 375007920 0 15 VCL_call c fetch hit_for_pass 15 ObjProtocol c HTTP/1.1 15 ObjResponse c OK 15 ObjHeader c Date: Thu, 22 Mar 2012 22:07:35 GMT 15 ObjHeader c Server: Apache/2.2.21 (Unix) mod_ssl/2.2.21 OpenSSL/0.9.8e-fips-rhel5 mod_bwlimited/1.4 mod_fcgid/2.3.6 15 ObjHeader c X-Powered-By: PHP/5.3.9 15 ObjHeader c Expires: Thu, 19 Nov 1981 08:52:00 GMT 15 ObjHeader c Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0 15 ObjHeader c Pragma: no-cache 15 ObjHeader c Content-Type: text/html; charset=utf-8 15 ObjHeader c X-Cacheable: NO:Cache-Control=private 15 FetchError c chunked read_error: 12 (Could not get storage) 15 VCL_call c error deliver 15 VCL_call c deliver deliver As far as I have could gather, we could try increasing the nuke_limit, but currently we have a nuke_limit of 500, and when running varnishstat -1 -f n_lru_nuked we "only" get a total of 1031, even though we have seen the error happen on several pages. When we then run top to see how much memory Varnish is using, it only shows that it is using 763m, although we've set it to be allowed to use 1200m. Any ideas of what the problem can be?

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  • Need a recommendation for shared storage on auto-scaling ec2 w/ scalr

    - by john h.
    I have come across so many answers to this question that I am completely lost! I am moving our 2 sites to a load balanced ec2 system with scalr as our cloud manager. Now the question is coming up about persistent storage for the user's uploaded content and other files. Could someone please give me a suggestion and possible a link to a tutorial for the following setup and goals. 2 websites (1 Forum, 1 ecommerce). 1 LB 1 App server (to scale out to as many as needed) 1 DB server (to scale out to as many as needed) Our sites will need to autoscale and according to what I am learning about scalr, that means as new instances load up, I need to run a script to set the basics up on that server (git,php mods, pull site from git, move keys, etc) What I don't understand is how should I handle user uploaded content like profile pictures, avatars, product images, themes, etc... Do I mount an EBS or s3fs folder to hold the websites (maybe /var/www/websitefolder) or do I do something like mount the avatar folders /var/www/websitefolder/images/avatars) I am not sure where to go with this. Could someone give me some detailed help? -John

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  • GlusterFS as elastic file storage?

    - by Christopher Vanderlinden
    Is there any way to run GlusterFS in a replicated mode, but with the ability to dynamically scale the volume up and down? Say you have 3 servers all running glusterd. your Gluster volume would have to be setup with replica 3 gluster volume create test-volume replica 3 192.168.0.150:/test-volume 192.168.0.151:/test-volume 192.168.0.152:/test-volume You would then mount it as say \mnt\gfs_test What happens when I want to add 2 more servers to the storage pool and then also use them in this volume? Is there any easy way to expand the volume AND increase that replica count to 5? My end goal is to run this on EC2 instances, say 3 Apache front ends, with the webroot setup on the gluster volume mount. My concern is that if I ever need to spin up a server, I would want the server to not only be an additional Apache front end, but also another server in the gluster file system, adding to fault tolerance as well as possibly giving a slight boost in read speed. Maybe there are better options that would fit the bill here? Thanks.

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  • Turn computer into DAS (Direct Attached Storage)

    - by Damon
    Can we build a direct attached storage by taking a computer/server, adding an HBA, and installing some appropriate software? We would use Debian as a host OS for both the DAS and the server. If so, what software do we use? And do we simply need a HBA for the DAS and the Server? Or do we need more hardware? The goal is to use an older server that does not have enough room for drives but does have ECC memory, server processors, redundant power supplies, dual nics, etc. Then find any boxes, server or not, the key being having enough room for 8-12 drives, fans, etc. and turning them into a DAS; build two of these DAS's and have them connected to the server. Eventually we want to have two servers using DRBD and associated services like heartbeat and pace maker to create an HA setup for our server(s) but that will take a long time to configure since I have no experience with anything related to DRBD (yet) and have a learning curve I have to get past, not to mention the additional cost of more hardware (two servers vs one).

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  • Need a place to store a few bytes of meta information on storage media

    - by Jason C
    I'm working on an embedded project. I need a place to store some filesystem-independent meta information on a storage device. The device has an MSDOS partition table. The device also may have unallocated space (depending on its size) but it will be TRIMmed (and also may be blown away by new partitions in the future). I need a location on the device that is not unallocated and that has a low risk of being touched (outside of completely erasing the device). The device is only guaranteed to have an MBR at the point the meta data needs to first be written; meaning there are no EBRs/VBRs present that I could use. There are 446 bytes at the very start of the device available for MBR bootstrap code. Currently my only idea is to store data at the end of this block. However, the device is bootable and I have no way of knowing if I'd be blowing away bootstrap code or not. The sector size is 512 bytes and the MBR is the first sector, I'm pretty sure (correct me if I'm wrong) that that means the second sector is available for use by partition data, so I can't use that either. Does anybody have any ideas? I need 4 bytes of space.

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  • Industrial strength cloud file storage

    - by ArthurG
    I'm looking for an industrial strength cloud file storage system. It will be used by multiple people in a startup. Our requirements: Transparent file system access: files and folders in the file system must be able transparently access (read and write) files in the cloud; files must be synchronized whenever network access is available and buffered otherwise. The system must be usable by non-technical people. Access control: we need to control who can access which files, at least on a very coarse basis. e.g., the developers will be able to access the system design documents, only the corporate folks can access recruiting documents, and only management can access certain corporate documents. Dropbox provides this via Sharing folders, but that's not adequate, if I understand it correctly, because there's no authentication of the sharing user. so the cloud service should have a notion of an account (our startup) with multiple users with distinct credentials and rights for each user Clients: it must be accessible from Macs and PCs; I would hope that it supports Linux (e.g., Ubuntu) too Security: it must provide robust security Backup: the cloud service must reliably backup the files Versioning: change version history, is a big plus, but not required Not free: we're willing to pay for the service So far, we've reviewed the following, albeit not completely thoroughly: Dropbox: has all except 1) Access control, which is provided via Sharing folders, but that's not adequate, if I understand it correctly, because there's no authentication of the sharing user. and 2) Security, as discussed here http://www.economist.com/blogs/babbage/2011/05/internet_security and here http://blog.dropbox.com/?p=821. Windows Live Mesh, has all except 1) Clients, only supporting Windows 7 and OS X. SpiderOak has all, except 1) Transparent file system access, which is only available for 1 user. Amazon Cloud, doesn't offer 1) Transparent file system access Rackspace Cloud Drive has all except 1) Access control and 2) Versioning I'll gladly include any clarifications or additional systems the community provides. Arthur

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  • Mounting an Azure blob container in a Linux VM Role

    - by djechelon
    I previously asked a question about this topic but now I prefer to rewrite it from scratch because I was very confused back then. I currently have a Linux XS VM Role in Azure. I basically want to create a self-managed and evoluted hosting service using VMs rather than Azure's more-expensive Web Roles. I also want to take advantage of load balancing (between VM Roles) and geo-replication (of Storage Roles), making sure that the "web files" of customers are located in a defined and manageable place. One way I found to "mount" a drive in Linux VM is described here and involves mounting a VHD onto the virtual machine. From what I could learn, the VHD is reliably-stored in a storage role, and is exclusively locked by the VM that uses it. Once the VM Role has its drive I can format the partition to any size I want. I don't want that!! I would like each hosted site to have its own blob directory, then each replicated/load-balanced VM Role to rw mount like in NFS that blob directory to read HTML and script files. The database is obviously courtesy of Microsoft :) My question is Is it possible to actually mount a blob storage into a directory in the Linux FS? Is it possible in Windows Server 2008?

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  • Understanding Linux SCSI queue depths

    - by Troels Arvin
    I'm experimenting with the effects of different SCSI queue depth values on a Dell server running CentOS Linux 5.4 (x86_64). The server has two QLogic QLE2560 FC HBAs connected via multipathing to a storage system. The storage system has allocated two LUNs to the server, each connected through four paths in an active-active-active-active round-robin configuration. All in all, the two LUNs exist as eight /dev/sdX devices, represented by two devices in /dev/mpath. I currently adjust the queue depth values in /etc/modprobe.conf and check the result (after rebooting) by looking in the seventh column of /proc/scsi/sg/devices. Two questions related to that: Is there a way to adjust queue depths without rebooting or unloading the qla2xxx kernel module? E.g., can I echo a new queue depth value into some /proc or /sys-like file to update the queue depth? If I set the queue depth to 128, is that 128 in total for all devices handled by the qla2xxx module?, or 128 for each HBA? (256 in total), or 128 for each of the eight /dev/sdX devices (1024 in toal)?, or 128 for each of the two /dev/mpath/... devices (256 in total)? This is important for me to know so that my server doesn't flood the storage system, affecting other servers connected to it.

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  • Probability of Blade Chassis Failure

    - by ChrisZZ
    In my organisation we are thinking about buying blade servers - instead of rack servers. Of course technology vendors also make them sound very nice. A concern, that I read very often in different forums, is, that there is a theoretical possibility of the server chassis going down - which would in consequence take all the blades down. That is due to shared infrastructure. My reaction on this probability would be to have redundancy and by two chassis instead of one (very costly of course). Some people (including e.g. HP Vendors) try to convince us, that the chassis is very very unlikely to fail, due to many redundancies (redundant power supply, etc.). Another concern on my side is, that if something goes down, spare parts might be required - which is difficult in our location (Ethiopia). So I would ask to experienced administrators, that have managed blade server: What is your experience? Do they go down as a whole - and what is the sensible shared infrastructure, that might fail? That question could be extended to shared storage. Again I would say, that we need two storage units instead of only one - and again the vendors say, that this things are so rock solid, that no failure is expected. Well - I can hardly believe, that such a critical infrastructure can be very reliable without redundancy - but maybe you can tell me, whether you have successfull blade-based projects, that work without redundancy in its core parts (chassis, storage...) At the moment, we look at HP - as IBM looks much to expensive... thanks a lot best regards Christian

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  • Linux - real-world hardware RAID controller tuning (scsi and cciss)

    - by ewwhite
    Most of the Linux systems I manage feature hardware RAID controllers (mostly HP Smart Array). They're all running RHEL or CentOS. I'm looking for real-world tunables to help optimize performance for setups that incorporate hardware RAID controllers with SAS disks (Smart Array, Perc, LSI, etc.) and battery-backed or flash-backed cache. Assume RAID 1+0 and multiple spindles (4+ disks). I spend a considerable amount of time tuning Linux network settings for low-latency and financial trading applications. But many of those options are well-documented (changing send/receive buffers, modifying TCP window settings, etc.). What are engineers doing on the storage side? Historically, I've made changes to the I/O scheduling elevator, recently opting for the deadline and noop schedulers to improve performance within my applications. As RHEL versions have progressed, I've also noticed that the compiled-in defaults for SCSI and CCISS block devices have changed as well. This has had an impact on the recommended storage subsystem settings over time. However, it's been awhile since I've seen any clear recommendations. And I know that the OS defaults aren't optimal. For example, it seems that the default read-ahead buffer of 128kb is extremely small for a deployment on server-class hardware. The following articles explore the performance impact of changing read-ahead cache and nr_requests values on the block queues. http://zackreed.me/articles/54-hp-smart-array-p410-controller-tuning http://www.overclock.net/t/515068/tuning-a-hp-smart-array-p400-with-linux-why-tuning-really-matters http://yoshinorimatsunobu.blogspot.com/2009/04/linux-io-scheduler-queue-size-and.html For example, these are suggested changes for an HP Smart Array RAID controller: echo "noop" > /sys/block/cciss\!c0d0/queue/scheduler blockdev --setra 65536 /dev/cciss/c0d0 echo 512 > /sys/block/cciss\!c0d0/queue/nr_requests echo 2048 > /sys/block/cciss\!c0d0/queue/read_ahead_kb What else can be reliably tuned to improve storage performance? I'm specifically looking for sysctl and sysfs options in production scenarios.

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  • Encrypted off-site data storage

    - by Dan
    My business has a rather unique problem. We work in China and we want to implement a file server paradigm which does not store any files locally, but rather in a server overseas. Applications would be saved onto our local machines, but data would be loaded directly into memory from the cloud, e.g. I load a docx into word at the beginning of the day, saving periodically to the cloud as I work on it, and turn off my computer at night, with nothing saved locally. Considering recent events, we worry about being raided by the Chinese authorities, and although all our data is encrypted, it would not be hard for the authorities to force us to give up the keys. So the goal is not to have anything compromising physically in China. We have about 20 computers, and we need an authenticated, encrypted connection with this overseas file server. A system with Active-Directory-like permissions would be best, so that only management can read or write to certain files, or workers can only access files that relate to their projects, and to which all access can be cut off should the need arise. The file server itself would also need to be encrypted. And for convenience, it would be nice if this system was integrated with each computer's file explorer (like skydrive or dropbox does, but, again, without saving a copy locally), rather than through a browser. I can't find any solution online. Does anyone know of a service that does this? Otherwise I'll have to do it myself (which kinda sounds fun, but I don't really have the time), and I'm not sure where to start. Amazon maybe. But the protocols that offices would use on their intranet typically aren't encrypted; we need all traffic securely tunneled out of the country. Each computer already has a VPN to a server in California, but I'm unsure whether it would be efficient to pipe file transfers through it. Let me know if anyone has any ideas. And this is my first post; feel free say whether this question is inappropriate/needs to be posted elsewhere.

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  • Windows 2003 Storage Server Hanging on Large File Transfers

    - by user25272
    In one of our offices we have a Dell PowerVault 745N NAS device which acts as the main file server. Its running 32bit Windows 2003 Storage Server SP2 with 3GB RAM. The server holds around 60 users HOME folders, which are mapped via AD. The office clients are a mix of XP SP3, Vista and Windows 7. Occasionally the server will completely hang when transferring large files. When the hang happens the console becomes unresponsive with only the mouse active and blank wallpaper. Sometimes stopping the copy frees the server, sometimes not. The hanging can last around 20 minutes. During this time other servers also become unresponsive with blank wallpaper at the console. If you do manage to get onto another server the taskbar and run commands are unresponsive. This also transcends to the client computers sometimes with explorer crashing. I'm guessing this is due to the HOME folder mapping. Eventually the NAS server with free up and everything will be back to normal. The server is configured as follows: PERC 4/DC DATA 2 - 12 SCSI HDD - RAID5 SHADOWCOPY 2 SCSI HDD - RAID1 CERC SATA DATA 11 4 SATA HDD - RAID5 OS 4 SATA HDD - RAID5 All the drivers and firmware is up to date. I've been through all the diagnostics with Dell and the hardware has come up clean including full HDD tests on the arrays. The server has NOD32 installed as the AV, but the hanging happens when it is uninstalled. There are no errors in the event log when this happens and we don't have any errors logged on any of our ProCurve switches. DNS is fine on the domain and AD from what I can tell is running happily. There are no DFS or NFS shares setup either. All the shares are standard Windows. I've unchecked the allow the computer to turn off this device to save power box under Power Management on the NIC. "Set Link Speed and Duplex to Auto-negotiate 1000 " Increased Receive Descriptors buffer from 256 to 352 (reserves more CPU resource for handling data) I've run network traces using network monitor and have found the following: 417 8.078125 {SMB:192, NbtSS:25, TCP:24, IPv4:23} 192.168.2.244 192.168.5.35 SMB SMB:R; Nt Create Andx - NT Status: System - Error, Code = (52) STATUS_OBJECT_NAME_NOT_FOUND I've tried different cabling; NICs and switch ports all with the same result. Transferring files from other servers on the domain is fine. All I haven't done is run CHKDSK on the drives to look for any file system errors. On the Vista clients I have also run netsh interface tcp set global autotuning=disabled with no result. Could it be that the server has a faulty drive or that the I/O is too much for it to handle? Any ideas why would the hang cause issues with the other servers on the LAN? Many Thanks.

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  • Memory efficient way of inserting an array of objects with Core Data

    - by randombits
    I'm working on a piece of code for an iPhone application that fetches a bunch of data from a server and builds objects from it on the client. It ends up creating roughly 40,000 objects. They aren't displayed to the user, I just need to create instances of NSManagedObject and store them to persistent storage. Am I wrong in thinking that the only way to do this is to create a single object, then save the context? is it best to create the objects all at once, then somehow save them to the context after they're created and stored in some set or array? If so, can one show some example code for how this is done or point me in the direction to code where this is done? The objects themselves are relatively straight forward models with string or integer attributes and don't contain any complex relationships.

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  • Efficient 4x4 matrix inverse (affine transform)

    - by Budric
    Hi, I was hoping someone can point out an efficient formula for 4x4 affine matrix transform. Currently my code uses cofactor expansion and it allocates a temporary array for each cofactor. It's easy to read, but it's slower than it should be. Note, this isn't homework and I know how to work it out manually using 4x4 co-factor expansion, it's just a pain and not really an interesting problem for me. Also I've googled and came up with a few sites that give you the formula already (http://www.euclideanspace.com/maths/algebra/matrix/functions/inverse/fourD/index.htm). However this one could probably be optimized further by pre-computing some of the products. I'm sure someone came up with the "best" formula for this at one point or another? Thanks.

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  • What is an efficient way to write password cracking algorithm (python)

    - by Luminance
    This problem might be relatively simple, but I'm given two text files. One text file contains all encrypted passwords encrypted via crypt.crypt in python. The other list contains over 400k+ normal dictionary words. The assignment is that given 3 different functions which transform strings from their normal case to all different permutations of capitalizations, transforms a letter to a number (if it looks alike, e.g. G - 6, B - 8), and reverses a string. The thing is that given the 10 - 20 encrypted passwords in the password file, what is the most efficient way to get the fastest running solution in python to run those functions on dictionary word in the words file? It is given that all those words, when transformed in whatever way, will encrypt to a password in the password file. Here is the function which checks if a given string, when encrypted, is the same as the encrypted password passed in: def check_pass(plaintext,encrypted): crypted_pass = crypt.crypt(plaintext,encrypted) if crypted_pass == encrypted: return True else: return False Thanks in advance.

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  • Efficient counting of an association’s association

    - by Matthew Robertson
    In my app, when a User makes a Comment in a Post, Notifications are generated that marks that comment as unread. class Notification < ActiveRecord::Base belongs_to :user belongs_to :post belongs_to :comment class User < ActiveRecord::Base has_many :notifications class Post < ActiveRecord::Base has_many :notifications I’m making an index page that lists all the posts for a user and the notification count for each post for just that user. # posts controller @posts = Post.where( :user_id => current_user.id ) .includes(:notifications) # posts view @posts.each do |post| <%= post.notifications.count %> This doesn’t work because it counts notifications for all users. What’s an efficient way to do this without running a separate query for each post?

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  • Efficient Search function with Linq to SQL

    - by Bayonian
    Hi, I'm using VB.NET and Linq to SQL. I have a table with thousands of rows and growing. Right now I'm using .Contains() in the Where clause to perform the query. Below is my search function : Public Shared Function DemoSearchFunction(ByVal keyword As String) As DataTable Dim db As New BibleDataClassesDataContext() Dim query = From b In db.khmer_books _ From ch In db.khmer_chapters _ From v In db.testing_khmers _ Where v.t_v.Contains(keyword) And ch.kh_book_id = b.kh_b_id And v.t_chid = ch.kh_ch_id _ Select b.kh_b_id, b.kh_b_title, ch.kh_ch_id, ch.kh_ch_number, v.t_id, v.t_vn, v.t_v Dim dtDataTableOne = New DataTable("dtOne") dtDataTableOne.Columns.Add("bid", GetType(Integer)) dtDataTableOne.Columns.Add("btitle", GetType(String)) dtDataTableOne.Columns.Add("chid", GetType(Integer)) dtDataTableOne.Columns.Add("chn", GetType(Integer)) dtDataTableOne.Columns.Add("vid", GetType(Integer)) dtDataTableOne.Columns.Add("vn", GetType(Integer)) dtDataTableOne.Columns.Add("verse", GetType(String)) For Each r In query dtDataTableOne.Rows.Add(New Object() {r.kh_b_id, r.kh_b_title, r.kh_ch_id, r.kh_ch_number, r.t_id, r.t_vn, r.t_v}) Next Return dtDataTableOne End Function I would like to know other methods for doing efficient search using Linq to SQL. Thanks.

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  • Memory efficient import many data files into panda DataFrame in Python

    - by richardh
    I import into a panda DataFrame a directory of |-delimited.dat files. The following code works, but I eventually run out of RAM with a MemoryError:. import pandas as pd import glob temp = [] dataDir = 'C:/users/richard/research/data/edgar/masterfiles' for dataFile in glob.glob(dataDir + '/master_*.dat'): print dataFile temp.append(pd.read_table(dataFile, delimiter='|', header=0)) masterAll = pd.concat(temp) Is there a more memory efficient approach? Or should I go whole hog to a database? (I will move to a database eventually, but I am baby stepping my move to pandas.) Thanks! FWIW, here is the head of an example .dat file: cik|cname|ftype|date|fileloc 1000032|BINCH JAMES G|4|2011-03-08|edgar/data/1000032/0001181431-11-016512.txt 1000045|NICHOLAS FINANCIAL INC|10-Q|2011-02-11|edgar/data/1000045/0001193125-11-031933.txt 1000045|NICHOLAS FINANCIAL INC|8-K|2011-01-11|edgar/data/1000045/0001193125-11-005531.txt 1000045|NICHOLAS FINANCIAL INC|8-K|2011-01-27|edgar/data/1000045/0001193125-11-015631.txt 1000045|NICHOLAS FINANCIAL INC|SC 13G/A|2011-02-14|edgar/data/1000045/0000929638-11-00151.txt

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  • Do you know a good and efficient FFT?

    - by yan bellavance
    Hi, I am trying to find a very fast and efficient Fourier transform (FFT). Does anyone know of any good ones. I need to run it on the iPhone so it must not be intensive. Instead, maybe you know of one that is wavelet like, i need frequency resolution but only a narrow band (vocal audio range up to 10khz max...even 10Khz might be too high). Im thinking also of truncating this FFT to keep the frequency resolution while eliminating the unwanted frequency band. This is for an iphone ...I have taken a look at the FFT in Aurio touch but it seems this is an int FFT but my app uses floats.....would it give a big performance increase to try and adapt program to an int FFT or not(which i really dont feel like doing...plus aurio touch uses a radix 2 FFT which is not that great).

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  • Efficient JSON encoding for data that may be binary, but is often text

    - by Evgeny
    I need to send a JSON packet across the wire with the contents of an arbitrary file. This may be a binary file (like a ZIP file), but most often it will be plain ASCII text. I'm currently using base64 encoding, which handles all files, but it increases the size of the data significantly - even if the file is ASCII to begin with. Is there a more efficient way I can encode the data, other than manually checking for any non-ASCII characters and then deciding whether or not to base64-encode it? I'm currently writing this in Python, but will probably need to do the same in Java, C# and C++, so an easily portable solution would be preferable.

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  • Please for efficient query

    - by user278618
    I want to have efficient query to get some rows from my table. Here is I think the best presentation of my table. -Somedate is not duplicated - it is date of modifiedon -a,b,c are parent ids, let say countryCode -1,2,3,4 are subparent, let say citycode -guids are id of rows -true, false are values of rows - one can name this column - freshAir a 1 GUID somedate true a 1 GUID somedate true a 2 GUID somedate false a 2 GUID somedate false b 3 GUID somedate false b 3 GUID somedate false b 3 GUID somedate false b 4 GUID somedate false c 5 GUID somedate true c 6 GUID somedate true c 6 GUID somedate false c 6 GUID somedate false c 7 GUID somedate false I want the most recent rows MAX(modifiedon) grouped by countrycode and citycode and in this groups I need elements which have another values (true, false). And in result I want: a 1 GUID somedate true a 2 GUID somedate false c 5 GUID somedate true c 6 GUID somedate false c 7 GUID somedate false Look that in result I don't want to have records with "b", because all rows have the same value (false). Best regards

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  • Struct in C, are they efficient?

    - by pygabriel
    I'm reading some C code like that: double function( int lena,double xa,double ya, double za, double *acoefs, ..., int lenb,double xb,double yb, double zb, double *bcoefs, ..., same for c, same for d ) This function is called in the code mor than 100.000 times so it's performance-critical. I'm trying to extend this code but I want to know if it's efficient or not (and how much this influences the speed) to encapsulate all the parameters in a struct like this struct PGTO { int len; double x,y,z ; double *acoefs } and then access the parameters in the function.

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  • Efficient heaps in purely functional languages

    - by Kim
    As an exercise in Haskell, I'm trying to implement heapsort. The heap is usually implemented as an array in imperative languages, but this would be hugely inefficient in purely functional languages. So I've looked at binary heaps, but everything I found so far describes them from an imperative viewpoint and the algorithms presented are hard to translate to a functional setting. How to efficiently implement a heap in a purely functional language such as Haskell? Edit: By efficient I mean it should still be in O(n*log n), but it doesn't have to beat a C program. Also, I'd like to use purely functional programming. What else would be the point of doing it in Haskell?

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  • Most efficient way to create and nest divs with appendChild using *plain* javascript (no libraries)

    - by Matrym
    Is there a more efficient way to write the following appendChild / nesting code? var sasDom, sasDomHider; var d = document; var docBody = d.getElementsByTagName("body")[0]; var newNode = d.createElement('span'); var secondNode = d.createElement('span'); // Hider dom newNode.setAttribute("id", "sasHider"); docBody.appendChild(newNode); sasDomHider = d.getElementById("sasHider"); // Copyier dom secondNode.setAttribute("id", "sasText"); sasDomHider.appendChild(secondNode); sasDom = d.getElementById("sasText"); Thanks in advance for your time :)

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  • Are large include files like iostream efficient? (C++)

    - by Keand64
    Iostream, when all of the files it includes, the files that those include, and so on and so forth, adds up to about 3000 lines. Consider the hello world program, which needs no more functionality than to print something to the screen: #include <iostream> //+3000 lines right there. int main() { std::cout << "Hello, World!"; return 0; } this should be a very simple piece of code, but iostream adds 3000+ lines to a marginal piece of code. So, are these 3000+ lines of code really needed to simply display a single line to the screen, and if not, do they create a less efficient program than if I simply copied the relevant lines into the code?

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