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• Ideal Keyword Density For SEO Friendly Web Content

  A lot of people are looking to maximize the optimization of their web pages for the search engines and a constant question is. What is the ideal keyword density for SEO friendly web content? So let's take a look.

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• Check Keyword Density - A Secret to the First Page of Google

  Want to get to the first page of Google for your keywords? Then you have to know about keyword density. In this article you're going to learn what it is and how to use it.

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• No apparent reason for high load average

  - by Oz.

  We have several web servers running on Amazon (ec2) c1.xlarge, over Amazon AMI. The servers are duplicates of each other, running the exact same hardware and software. Each server spec is: 7 GB of memory 20 EC2 Compute Units (8 virtual cores with 2.5 EC2 Compute Units each) 1690 GB of instance storage 64-bit platform I/O Performance: High API name: c1.xlarge A couple of weeks ago we have run a yum upgrade on one of the servers. Starting on this upgrade the upgraded server started showing a high load average. Needless to say, we did not update the other servers and we can not do so until we understand the reason for this behavior. The strange thing is that when we compare the servers using top or iostat, we can not find the reason for the high load. Note that we have moved traffic from the "problematic" server to the others, which have made the "problematic" server less crowded in terms of requests, and still his load is higher. Do you have any idea what could it be, or where else can we check? Many thanks for the help! Oz. # # proper server # w command # 00:42:26 up 2 days, 19:54, 2 users, load average: 0.41, 0.48, 0.49 USER TTY FROM LOGIN@ IDLE JCPU PCPU WHAT pts/1 82.80.137.29 00:28 14:05 0.01s 0.01s -bash pts/2 82.80.137.29 00:38 0.00s 0.02s 0.00s w # # proper server # iostat command # Linux 3.2.12-3.2.4.amzn1.x86_64 _x86_64_ (8 CPU) avg-cpu: %user %nice %system %iowait %steal %idle 9.03 0.02 4.26 0.17 0.13 86.39 Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn xvdap1 1.63 1.50 55.00 367236 13444008 xvdfp1 4.41 45.93 70.48 11227226 17228552 xvdfp2 2.61 2.01 59.81 491890 14620104 xvdfp3 8.16 14.47 94.23 3536522 23034376 xvdfp4 0.98 0.79 45.86 192818 11209784 # # problematic server # w command # 00:43:26 up 2 days, 21:52, 2 users, load average: 1.35, 1.10, 1.17 USER TTY FROM LOGIN@ IDLE JCPU PCPU WHAT pts/0 82.80.137.29 00:28 15:04 0.02s 0.02s -bash pts/1 82.80.137.29 00:38 0.00s 0.05s 0.00s w # # problematic server # iostat command # Linux 3.2.20-1.29.6.amzn1.x86_64 _x86_64_ (8 CPU) avg-cpu: %user %nice %system %iowait %steal %idle 7.97 0.04 3.43 0.19 0.07 88.30 Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn xvdap1 2.10 1.49 76.54 374660 19253592 xvdfp1 5.64 40.98 85.92 10308946 21612112 xvdfp2 3.97 4.32 93.18 1087090 23439488 xvdfp3 10.87 30.30 115.14 7622474 28961720 xvdfp4 1.12 0.28 65.54 71034 16487112

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• High quality / high speed dvd reader for Mac Pro

  - by deadprogrammer

  I have a high end Mac pro, but one thing in is that I'm unhappy with is a DVD drive. It's a Hitachi GH41N. Apple calls it a "superdrive", but it's anything but. The damn thing makes an amazing amount of noise, and isn't too fast either. What I want is a state of the art, fast, quiet DVD reader, preferably not even a burner. What should I get?

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• High server load - [jbd2/md1-8] using 99.99% IO

  - by Alex

  I've been having spike in load over the last week. This usually occurs once or twice a day. I've managed to identify from iotop that [jbd2/md1-8] is using 99.99 % IO. During the high load times there is no high traffic to the server. Server specs are: AMD Opteron 8 core 16 GB RAM 2x2.000 GB 7.200 RPM HDD Software Raid 1 Cloudlinux + Cpanel Mysql is properly tuned Apart from the spikes, the load usually is around 0.80 at most. I've searched around but can't find what [jbd2/md1-8] does exactly. Has anyone had this problem or does anyone know a possible solution? Thank you. UPDATE: TIME TID PRIO USER DISK READ DISK WRITE SWAPIN IO COMMAND 16:05:36 399 be/3 root 0.00 B/s 38.76 K/s 0.00 % 99.99 % [jbd2/md1-8]

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• Cheapest High Available Web Server [closed]

  - by xyz

  I would like to create a high-available setup (e.g. a small cluster) for a webserver, i.e. it will run Apache, PHP and MySQL. There will be between 2-8 small websites running with only very little traffic and workload. High availability is however very important. I don't want to be dependent on 1 datacenter, so there must be a minimum of 2 servers placed in different datacenters, and if one server goes down, the user must experience no or only a minimum of downtime - and no data loss. I have considered Amazon AWS using their Elastic Load Balancing, since it is possible to buy 2 EC2 instances in 2 availability zones and set up load balancing and RDS (Multi-AZ). However this seems rather expensive. Using the AWS price calculator http://calculator.s3.amazonaws.com/calc5.html it totals to 185$/month the first year (including the free tier). Are my calculations incorrect or is there a cheaper way to make this HA setup? Best regards

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• How to setup Wordpress High Availability

  - by Ketam

  I have installed Galera Cluster on 3 cluster + 1 management. I wanted to make it like this, Server1: Home (www.domain.com) Server2: For BBpress/Forum (Forum Tab Menu will forward to forum.domain.com) Server3: BuddyPress Activity (Social Tab Menu will forward to social.domain.com) The purpose I am doing this is to distribute my resource and load balancing each other at same time. However, I have difficulty to setup Apache Load-Balancing/mod_proxy/clustering or any suitable to have high availability WordPress. Any best suggestion/solution to make high availability WordPress? Or how to? And another question is I tried to copy whole WordPress files & folders to Server2 connecting to local database (same data inside since it is already on Galera Cluster) but the page blank. Any advice? OS: Centos 6.2 Thanks in advanced.

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• No clue for high load average on top

  - by Oz.

  We have several machines on Amazon (ec2) of the type c1.xlarge with 16 cpus, running the Amazon AMI. Details on the machine: 7 GB of memory 20 EC2 Compute Units (8 virtual cores with 2.5 EC2 Compute Units each) 1690 GB of instance storage 64-bit platform I/O Performance: High API name: c1.xlarge One out of the several machines is showing a high load average, since we have run the last yum upgrade a couple of weeks a go. We did not yet update the other machines, and everything looks normal on them. The strange thing is that the top command not showing any hint for the cause of the load. CPUs are 4.8%us, 1.1%sy, 0.0%ni, 94.1%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st(see below). Mem is about 1.5GB free. Any idea what could it be, or where else can we check? Many thanks for the help. # # top # top - 07:57:42 up 4:18, 1 user, load average: 1.36, 1.45, 1.47 Tasks: 131 total, 1 running, 130 sleeping, 0 stopped, 0 zombie Cpu(s): 4.8%us, 1.1%sy, 0.0%ni, 94.1%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st Mem: 7120092k total, 5644920k used, 1475172k free, 532888k buffers Swap: 0k total, 0k used, 0k free, 3463936k cached PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 1557 mysql 20 0 1829m 374m 6448 S 14.3 5.4 11:15.09 mysqld 6655 apache 20 0 416m 49m 3744 S 9.3 0.7 0:04.85 httpd 27683 apache 20 0 421m 54m 3708 S 9.0 0.8 0:00.99 httpd 6682 apache 20 0 424m 57m 3788 S 8.3 0.8 0:03.81 httpd 16816 apache 20 0 419m 51m 3760 S 4.3 0.7 0:04.09 httpd 22182 apache 20 0 417m 50m 3756 S 1.7 0.7 0:06.34 httpd 219 root 20 0 0 0 0 S 0.3 0.0 0:00.34 kworker/7:1 699 root 20 0 0 0 0 S 0.3 0.0 0:00.40 kworker/3:1 1 root 20 0 19376 1508 1212 S 0.0 0.0 0:00.29 init 2 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kthreadd 3 root 20 0 0 0 0 S 0.0 0.0 0:00.71 ksoftirqd/0

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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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• High CPU from httpd process

  - by KHWeb

  I am currently getting high CPU on a server that is just running a couple of sites with very low traffic. One of the sites is in still development going live soon. However, this site is very very slow...When browsing through its pages I can see that the CPU goes from 30% to 100% for httpd (see top output below). I have tuned httpd & MySQL, Apache Solr, Tomcat for high performance, and I am using APC. Not sure what to do from here or how to find the culprit as I have a bunch of messages on the httpd log and have been chasing dead ends for some time...any help is greatly appreciated. Server: AuthenticAMD, Quad-Core AMD Opteron(tm) Processor 2352, RAM 16GB Linux 2.6.27 64-bit, Centos 5.5 Plesk 9.5.4, MySQL 5.1.48, PHP 5.2.17 Apache/2.2.3 (CentOS) DAV/2 mod_jk/1.2.15 mod_ssl/2.2.3 OpenSSL/0.9.8e-fips-rhel5 PHP/5.2.17 mod_perl/2.0.4 Perl/v5.8.8 Tomcat6-6.0.29-1.jpp5, Tomcat-native-1.1.20-1.el5, Apache Solr top 17595 apache 20 0 1825m 507m 10m R 100.4 3.2 0:17.50 httpd 17596 apache 20 0 1565m 247m 9936 R 83.1 1.5 0:10.86 httpd 17598 apache 20 0 1430m 110m 6472 S 54.5 0.7 0:08.66 httpd 17599 apache 20 0 1438m 124m 12m S 37.2 0.8 0:11.20 httpd 16197 mysql 20 0 13.0g 2.0g 5440 S 9.6 12.6 297:12.79 mysqld 17617 root 20 0 12748 1172 812 R 0.7 0.0 0:00.88 top 8169 tomcat 20 0 4613m 268m 6056 S 0.3 1.7 6:40.56 java httpd error_log [debug] prefork.c(991): AcceptMutex: sysvsem (default: sysvsem) [info] mod_fcgid: Process manager 17593 started [debug] proxy_util.c(1854): proxy: grabbed scoreboard slot 0 in child 17594 for worker proxy:reverse [debug] proxy_util.c(1967): proxy: initialized single connection worker 0 in child 17594 for (*) [debug] proxy_util.c(1854): proxy: grabbed scoreboard slot 0 in child 17595 for worker proxy:reverse [debug] proxy_util.c(1873): proxy: worker proxy:reverse already initialized [notice] child pid 22782 exit signal Segmentation fault (11) [error] (43)Identifier removed: apr_global_mutex_lock(jk_log_lock) failed [debug] util_ldap.c(2021): LDAP merging Shared Cache conf: shm=0x7fd29a5478c0 rmm=0x7fd29a547918 for VHOST: example.com [info] APR LDAP: Built with OpenLDAP LDAP SDK [info] LDAP: SSL support available [info] Init: Seeding PRNG with 256 bytes of entropy [info] Init: Generating temporary RSA private keys (512/1024 bits) [info] Init: Generating temporary DH parameters (512/1024 bits) [debug] ssl_scache_shmcb.c(374): shmcb_init allocated 512000 bytes of shared memory [debug] ssl_scache_shmcb.c(554): entered shmcb_init_memory() [debug] ssl_scache_shmcb.c(576): for 512000 bytes, recommending 4265 indexes [debug] ssl_scache_shmcb.c(619): shmcb_init_memory choices follow [debug] ssl_scache_shmcb.c(621): division_mask = 0x1F [debug] ssl_scache_shmcb.c(623): division_offset = 96 [debug] ssl_scache_shmcb.c(625): division_size = 15997 [debug] ssl_scache_shmcb.c(627): queue_size = 2136 [debug] ssl_scache_shmcb.c(629): index_num = 133 [debug] ssl_scache_shmcb.c(631): index_offset = 8 [debug] ssl_scache_shmcb.c(633): index_size = 16 [debug] ssl_scache_shmcb.c(635): cache_data_offset = 8 [debug] ssl_scache_shmcb.c(637): cache_data_size = 13853 [debug] ssl_scache_shmcb.c(650): leaving shmcb_init_memory()

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• High Availability with 2 servers?

  - by Tom R

  Is it possible to have a high availability setup with 2 servers? Running Windows Web Server 2008 and MSSQL Web Edition (as I know Express isn't supported)? Getting to the point where our one dedicated server needs scaled out and going to a second server already more than doubles the cost as need to use Web Edition rather than Express (db is only 500MB).

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• high resolution on small screen size

  - by vishesh

  I have recently got an intel ultrabook,but its screen size is 13.3' and the native resolution is 1600X900.So the problem is that the letters that appear on screen are very small.Reducing resolution blurs the display and making everything bigger also doesn't feel very good.is there a way to get around this problem without changing hardware. I am even ok with this high resolution but I am concerned about the harmful effects it might have on my eyes in long term. Any advice will be very useful.Please help

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• Why not have a High Level Language based OS? Are Low Level Languages more efficient?

  - by rtindru

  Without being presumptuous, I would like you to consider the possibility of this. Most OS today are based on pretty low level languages (mainly C/C++) Even the new ones such as Android uses JNI & underlying implementation is in C In fact, (this is a personal observation) many programs written in C run a lot faster than their high level counterparts (eg: Transmission (a bittorrent client on Ubuntu) is a whole lot faster than Vuze(Java) or Deluge(Python)). Even python compilers are written in C, although PyPy is an exception. So is there a particular reason for this? Why is it that all our so called "High Level Languages" with the great "OOP" concepts can't be used in making a solid OS? So I have 2 questions basically. Why are applications written in low level languages more efficient than their HLL counterparts? Do low level languages perform better for the simple reason that they are low level and are translated to machine code easier? Why do we not have a full fledged OS based entirely on a High Level Language?

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• GlusterFs - high load 90-107% CPU

  - by Sara

  I try and try and try to performance and fix problem with gluster, i try all. I served on gluster webpages, php files, images etc. I have problem after update from 3.3.0 to 3.3.1. I try 3.4 when i think maybe fix it but still the same problem. I temporarily have 1 brick, but before upgrade will be fine. Config: Volume Name: ... Type: Replicate Volume ID: ... Status: Started Number of Bricks: 0 x 2 = 1 Transport-type: tcp Bricks: Brick1: ...:/... Options Reconfigured: cluster.stripe-block-size: 128KB performance.cache-max-file-size: 100MB performance.flush-behind: on performance.io-thread-count: 16 performance.cache-size: 256MB auth.allow: ... performance.cache-refresh-timeout: 5 performance.write-behind-window-size: 1024MB I use fuse, hmm "Maybe the high load is due to the unavailable brick" i think about it, but i cant find information on how to safely change type of volume. Maybe u know how?

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• Providing high availability and failover using MySQL on EC2

  - by crb

  I would like to have a highly-available MySQL system, with automatic failover, running on Amazon EC2 instances. The standard approach to solving this is problem Heartbeat + DRBD, but I've found a lot of posts suggesting DRBD doesn't work on EC2, though none saying exactly why. Obviously, a serial heartbeat or distinct network is out of the question in the virtualised environment. It would also be good to have the different servers be in different availability zones, but we're getting into a much harder problem there. What are peoples' opinion on having a high uptime solution in "the cloud"?

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• Most suitable high availability solution

  - by Alex Bagnolini

  My company is hosting a website in a server with IIS, SQL Server and a 3rd party windows service (written in C#, source code available for amendments). We bought a new identical server, composed by: 1x Quad Core, 12GB RAM, 4x160GB SATA Raid 5, Windows Server 2008 R2 Datacenter, Public IP. We aim to put all webpages and the 3rd party windows service in an high-availability state. After some lab-testing on how to configure Failover Clustering and Hyper-V, we have deep doubts on what the "best" solution would be, by "best" meaning maintainable and able to correctly handle a physical server failure. Any suggestion on how we should configure the two servers? We don't need all the configuration's step, just an hint on the right direction to follow.

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• Unable to watch a high resolution and high frame rate video

  - by Abhijith Madhav

  I have a video of a tennis match whose Resolution = 1280 * 720 Codec = H264 Frame rate = 50fps (Copy paste from info given by totem media player) My laptop is not powerful enough to play this video smoothly. How can I reduce the frame-rate of this video so that my laptop can play it? I have observed that my laptop can play videos with 25fps without an issue. I use ubuntu. I wouldn't mind using windows to edit/re-encode this video.

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• VMware Virtual vCenter and High Availability

  - by rufo

  To continue with this question: Should be Vmware vCenter server high available? According to the response there even if vCenter is down HA will continue to work. So, if my vCenter is a VM, using the express sql edition in the same VM, and that VM is hosted in the same cluster it manages (and the cluster is setup for HA): Am I correct to assume that if the host that hosts the vCenter goes down HA will vmotion the vCenter VM to another host and it will continue to function? BTW: my environment is small, two ESXi 5.0 hosts, with about 50 VMs, using iSCSI shared storaged for everything.

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• High availability for Windows Service under Windows Server 2003

  - by empi

  Hi. I have a following situation: I need to deploy a windows service that listens for incoming request on tcp port (basically WCF service). I have a High Availability requirement - the service must be deployed on two servers and if the service stops (only the service, not the whole server) on one server, all the requests must be redirected to the second one. For me it looks like a basic failover scenario. How can I achieve this on Windows Server 2003? Should I use Microsoft Cluster Service or Network Load Balancing? The important part is that the process of swapping the servers should not concern the clients (the client must see only single address / single host or domain name). Thanks in advance for help.

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• Very fast Laptop Heating due to very high CPU usage by dwm.exe

  - by Sushan Shrestha

  My laptop gets heated very fast and when I check the task manager, I find dwm.exe consuming very high CPU (mostly 100%). In the beginning I found the message "The graphic adapter has been stopped and recovered".Also I am getting one error message "Cidaemon.exe has stopped working" very frequently. During this period also, cpu usage is 100% which is consumed by dwm.exe. I have run ccleaner and Kingsoft PC doctor monitor to fix the register problem but the problem has not been solved. My display adaptor is : NVIDIA NVS 5200M. After the driver update, I am not getting "The graphic adapter has been stopped and recovered" but dwm.exe is still consuming 100% CPU one time in about 5 mins. Multiple restarts has not helped. Laptop Model: Dell Latitude E6430. Thanks in advance.

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• Providing high availability and failover using MySQL on EC2

  - by crb

  I would like to have a highly-available MySQL system, with automatic failover, running on Amazon EC2 instances. The standard approach to solving this is problem Heartbeat + DRBD, but I've found a lot of posts suggesting DRBD doesn't work on EC2, though none saying exactly why. Obviously, a serial heartbeat or distinct network is out of the question in the virtualised environment. It would also be good to have the different servers be in different availability zones, but we're getting into a much harder problem there. What are peoples' opinion on having a high uptime solution in "the cloud"? Note: This question was asked before RDS with multi-AZ was announced, which is the nice automatic answer for today's modern IT professional. :)

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• Matlab - binary vector with high concentration of 1s (or 0s)

  - by JohnIdol

  What's the best way to generate a number X of random binary vectors of size N with concentration of 1s (or, simmetrically, of 0s) that spans from very low to very high? Using randint or unidrnd (as in this question) will generate binary vectors with uniform distributions, which is not what I need in this case. Any help appreciated!

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• Linux Tuning for High Traffic JBoss Server with LDAP Binds

  - by Levi Stanley

  I'm configuring a high traffic Linux server (RedHat) and running into a limit I haven't been able to track down. I need to be able to handle sustained 300 requests per second throughput using Nginx and JBoss. The point of this server is to run checks on a user's account when that user signs in. Each request goes through Nginx to JBoss (specifically Torquebox with JBoss A7 with a Sinatra app) and then makes an LDAP request to bind that user and retrieve several attributes. It is during the bind that these errors occur. I'm able to reproduce this going directly to JBoss, so that rules out Nginx at least. I get a variety of error messages, though oddly JBoss stopped writing to the log file recently. It used to report errors about creating native threads. Now I just see "java.net.SocketException: Connection reset" and "org.apache.http.conn.HttpHostConnectException: Connection to http://my.awesome.server:8080 refused" as responses in jmeter. To the best of my knowledge, I have plenty of available file handles, processes, sockets, and ports, yet the issue persists. Unfortunately, I have very little experience tuning servers. I've found a couple useful documents - Ipsysctl tutorial 1.0.4 and Linux Tuning - but those documents are a bit over my head (and just entering the the configuration described in Linux Tuning doesn't fix my issue. Here are the configuration changes I've tried (webproxy is the user that runs Nginx and JBoss): /etc/security/limits.conf webproxy soft nofile 65536 webproxy hard nofile 65536 webproxy soft nproc 65536 webproxy hard nproc 65536 root soft nofile 65536 root hard nofile 65536 root soft nproc 65536 root hard nofile 65536 First attempt /etc/sysctl.conf sysctl net.core.somaxconn = 8192 sysctl net.ipv4.ip_local_port_range = 32768 65535 sysctl net.ipv4.tcp_fin_timeout = 15 sysctl net.ipv4.tcp_keepalive_time = 1800 sysctl net.ipv4.tcp_keepalive_intvl = 35 sysctl net.ipv4.tcp_tw_recycle = 1 sysctl net.ipv4.tcp_tw_reuse = 1 Second attempt /etc/sysctl.conf net.core.rmem_max = 16777216 net.core.wmem_max = 16777216 net.ipv4.tcp_rmem = 4096 87380 16777216 net.ipv4.tcp_wmem = 4096 65536 16777216 net.core.netdev_max_backlog = 30000 net.ipv4.tcp_congestion_control=htcp net.ipv4.tcp_mtu_probing=1 Any ideas what might be happening here? Or better yet, are there some good documentation resources designed for beginners?

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• Large, high performance object or key/value store for HTTP serving on Linux

  - by Tommy

  I have a service that serves images to end users at a very high rate using plain HTTP. The images vary between 4 and 64kbytes, and there are 1.300.000.000 of them in total. The dataset is about 30TiB in size and changes (new objects, updates, deletes) make out less than 1% of the requests. The number of requests pr. second vary from 240 to 9000 and is dispersed pretty much all over, with few objects being especially "hot". As of now, these images are files on a ext3 filesystem distributed read only across a large amount of mid range servers. This poses several problems: Using a fileysystem is very inefficient since the metadata size is large, the inode/dentry cache is volatile on linux and some daemons tend to stat()/readdir() it's way through the directory structure, which in my case becomes very expensive. Updating the dataset is very time consuming and requires remounting between set A and B. The only reasonable handling is operating on the block device for backup, copying, etc. What I would like is a deamon that: speaks HTTP (get, put, delete and perhaps update) stores data it in an efficient structure. The index should remain in memory, and considering the amount of objects, the overhead must be small. The software should be able to handle massive connections with slow (if any) time needed to ramp up. Index should be read in memory at startup. Statistics would be nice, but not mandatory. I have experimented a bit with riak, redis, mongodb, kyoto and varnish with persistent storage, but I haven't had the chance to dig in really deep yet.

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• SQL Server High Availability - Mirroring with MSCS?

  - by David

  I'm looking at options for high-availability for my SQL Server-powered application. The requirements are: HA protection from storage failure. Data accessibility when one of the DB servers is undergoing software updates (e.g. planned outage for Windows Update / SQL Server service-packs). Must not involve much in the way of hardware procurement. The application is an ASP.NET web application. The web application's users have their own database instances. I've seen two main options: SQL Server failover clustering, and SQL Server mirroring. I understand that SQL Server Failover Clustering requires the purchasing of a shared disk array and doesn't offer any protection if the shared storage goes down (so the documentation recommends to set up a Mirroring between two clusters). Database Mirroring seems the cheaper option (as it only requires two database servers and a simple witness box) - but I've heard it doesn't work well when you have a large number of databases. The application I'm developing involves giving each client their own database for their application - there could be hundreds of databases. Setting up the mirroring is no problem thanks to the automation systems we have in place. My final point concerns how failover works with respect to client connections - SQL Server Failover Clustering uses MSCS which means that the cluster is invisible to clients - a connection attempt might fail during the failover, but a simple reconnect will have it working again. However mirroring, as far as I know, requires that the client be aware of the mirrored partners: if the client cannot connect to the primary server then it tries the secondary server. I'm wondering how this work with respect to Connection Pooling in ASP.NET applications - does the client connection failovering mean that there's a potential 2-second (assuming 2000ms TCP timeout policy) pause when the connection pool tries the primary server on every connection attempt? I read somewhere that Mirroring can be used on top of MSCS which means that the client does not need to be aware of mirroring (so there wouldn't be any potential delays during connection, and also that no changes would need to be made to the client, not even the connection string) - however I'm finding it hard to get documentation or white papers on this approach. But if true, then it means the best method is then Mirroring (for HA) with MSCS (for client ignorance and connection performance). ...but how does this scale to a server instance that might contain hundreds of mirrored databases?

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