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  • Linux servers seeing bad download performance behind Sonicwall firewall

    - by Joshua Penix
    I'm working with a pair of co-located CentOS Linux servers sitting behind a Sonicwall PRO 2040 Enhanced firewall running in transparent bridge mode. These servers are having a strange problem downloading files more than a few megabytes in size. For example, if I try to wget or FTP a copy of the Linux kernel from kernel.org, the first ~1-2MB will download at 600+K/s, and then throughput will drop off a cliff to 1K/s. I've reviewed all the firewall configuration settings for anything suspicious, but found nothing. More interestingly, I performed the same download with a Windows server sitting behind the same firewall, and it sailed right through at 600+K/s the whole way. Has anyone seen this? Where should I start looking to troubleshoot this problem?

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  • How should I use my new SSD drive?

    - by jasondavis
    I just built a new PC the other day. Specs... Processor: Intel i7-930 quad core CPU CPU Cooler: COOLER MASTER Hyper 212 Motherboard: AsRock X58 Extreme 3 RAM/Memory: 6gb G-Skill tripple channel DDR3 memory (3 sticks of 2gb planning to get another kit to make it 12gb total soon) Operating System Hard drive: Intel X25-M 80GB Mainstream SATA2 Solid State Drive Video Cards: 2 XFX ATI Redeon HD 4650 cards to run 3-4 monitors Case: Lian Li PC-B10 Midtower case Power Supply: Antec TruePower New TP-750 Blue 750W Operating System Windows 7 Pro 64bit Not sure if the specs are helpful at all but I posted them just in case. So I got everything put together and running great so far but I need some advice/ideas/help/tips. I got the SSD drive in hopes of using it strictly for my windows 7 install along with all my other programs I install. I am then going to get another drive or 2 just for data (video,music,photos, etc). So my plan is to just install the new data drives and then in windows 7 I will change my "My documents" "My Music" "My Video" "MY Photos" library's to be located on the data drives instead of the OS SSD drive. I would ultimately like to install all my programs with my windows install on the SSD drive and then create an IMAGE of the drive and then 6 months down the road if things are sluggish I can just wipe the drive and restore my IMAGE with all my programs and settings in tact still. So here are some questions now. 1) How can I verify that TRIM is working on my new SSD? 2) Is there anything above that I missed that I should be doing? I think I once read that there is a page file or some sort of file that windows changes a lot and that it should be moved off f an SSD an onto my data drives. DOes anyone know what I might of heard? If you do can you explain the pros and cons of doing such a thing as well as how to possibly? 3) Any tips or advice to get the best performance from all this, I built a pretty nice system and I just want to make it stay that way as long as I can.

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  • Logitech Performance MX Mouse Jumps on OS X Lion (10.7.4)

    - by Adam Thompson
    I have a Logitech MX Revolution wireless mouse that I am trying to use with OS X Lion. Everything is working except for one problem... there is a small, but quite noticeable, jump when the mouse cursor is moved. The problem is mostly prevalent when dragging and dropping files or trying to highlight items. It makes performing any task with the mouse accurately next to impossible. I did quite a bit of looking and found that all kinds of people have had mouse issues with OS X. I've tried all of the following with absolutely no success: Using the official drivers from Logitech (these performed worse than the default mouse drivers in OS X) Using SteerMouse as a third party mouse driver. This worked ever so slightly better than the default driver, but still suffered quite frequently from the skipping problem Cleaning the sensor on the mouse and ensuring it's not the result of the surface that it's being used on. Tested the mouse on a Windows machine. The mouse worked absolutely flawlessly on the other machine. Changed the channel that my wireless router operates on by the off chance my problems were the result of interference. This also had no effect. I can't think of anything else that could possibly interfere with the mouse. I'm am out of ideas on what to try, so I would really appreciate if anyone has any suggestions. I should also mention that an old wired mouse I had laying around worked just fine when I plugged it in. This really isn't the best solution, however, as I really prefer the MX Revolution.

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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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  • Puzzling TCP performance over 3G / UMTS

    - by lemonsqueeze
    I'm using 3G as my primary internet connection, and TCP over this thing is getting more puzzling every day. For example: Downloading from kernel.org is crazy fast: $wget http://www.kernel.org/pub/linux/kernel/v3.0/linux-3.6.8.tar.bz2 increases to ~500kB/s after a few secs ! Some servers are incredibly slow, for instance www.graphic-pc.com:Same thing, downloading a big file with wget it starts at ~30kB/s for a split second, then collapses to 5-10k or even worse. Web browsing is decent but somewhat unreliable. Randomly, a page will take really long to load or even fail to load, but a reload can succeed almost immediately. Now, by chance i started playing with OpenVPN over UDP on top of the 3G connection, and OMG suddenly everything's extremely fast !Same www.graphic-pc.com now shoots at 100-200kB/s ! What's going on here ??? How come it is so much better with the VPN than without ?? And why does graphic-pc.com crawl when kernel.org flies ?Something to do with my tcp stack (or the server), or some buggy router in between ?? Notes: Setup is laptop running Ubuntu Lucid and a Huawei 3G dongle (So direct pppd connection). I can reproduce this pretty much any time during the day and I'm not moving, so it's clearly not cell environment or internet congestion. (although kernel.org without VPN sometimes does worse in the evening, 60kB or so - but still 500kB with VPN !) For 2) wireshark shows retransmitted packets, dup ack's, even out of order sometimes. I've tried playing with different /proc/sys/net/ipv4 parameters (tcp_rmem, window_scaling, tcp_congestion...) doesn't seem to make a difference. Update: Tried under windows 7 (no VPN) with some interesting results: tcp settings : default tcp_optimizer kernel.org : 10 kB/s 20 kB/s graphic-pc.com: 8 kB/s 70 kB/s ! tcp_optimizer turned on ctcp among other things. Have to check what os graphic-pc.com is running, my bet is linux's tcp_westwood and ms ctcp don't mix well here...

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  • How to prevent slow printer performance when AD is not available

    - by AKoran
    When I take a domain based computer (Windows XP) and plug it into a network that doesn't have access to the AD, the first time I select a local printer (printing directly to printer) on the current network it takes a good 20-30 seconds before I can select the printer. Doing a little investigating using wireshark I can see the computer is trying to hit AD for some reason and it just keeps timing out. I also tried the same experiment with just a plain workgroup computer and it was able to bring the printer up immediately. Does anyone know how to prevent the machine from trying to contact AD?

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  • Polling performance on shared host

    - by Azincourt
    I am planning on writing a small browser game. The webserver is a shared server, with no root / install possible. I want to use AJAX for client/server communication. There will be 12 players. So each player would be polling the server for the current game status every X milliseconds (let's say 200ms). So that would be 200ms x 12 players x 5 = 60 requests per second Can Apache handle those requests? What might be the bottlenecks when using this attempt?

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  • Measuring performance indicators on a cluster

    - by Aditya Singh
    My architecture is based on Amazon. A ELB load balancer balances POST requests among m1.large instances. Every instance has a nginx server on port 80 which distributes the requests to 4 python-tornado servers on backend which handle the request. These tornado servers are taking about 5 - 10ms to respond to one request but this is the internal compute time of every request. I want to put this thing on test and i want to measure the response time from ELB to upstream and back and how does it vary when the QPS throughput is increased and plot a graph of Time vs. QPS vs. Latency and other factors like CPU and Memory. Is there a software to do that or should i log everything somewhere with latency checks and then analyze the whole log to get the stuff out. I would also need to write a self-monitor which keeps checking the whole response time. Is it possible to do it with a script from within the server. If so, will it be accurate ?

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  • Bad IIS 7.5 performance on webserver

    - by Robert P.
    I have a webpage (ASP.NET 4.0 / MVC 4). On my development machine (i5-2500 3.3 8GB Win7 VS2010 SP1 Fujitsu Esprimo P700) the page performs with 160 requests/sec on devenv webserver on my machine. The page performs with 250 requests/sec on my local IIS 7.5. (uncompiled web) The page performs with 20 requests per second on a 16core 32gb ram production server (Fujitsu RX-300 w2k8 rc2 IIS 7.5). (compiled web) Why? I think it's the IIS configuration but i can't figure out whats the problem. The page runs with 1 worker process on both machines. Web garden is not an option (it helps but the app isnt compatible with)

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  • Super simple high performance http server

    - by masylum
    I´m building a url shortener web application and I would like to know the best architecture to do it in order to provide a fast and reliable service. I would like to have two separate servicies in different machines. The first machine will have the application itself with a apache, nginx, whatever.. The second one will contain the database. The third one will be the one that will be responsible to handle the short url petitions. For the third machine I just need to accept one kind of http petition (GET www.domain.com/shorturl), but it have to do it really fast and it should be stable enough. Which server do you recommend me? Thank's in advance and sorry for my english

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  • Does a USB hub affect performance?

    - by user1018733
    I have two devices I want maximum throughput and latency with. (Midi drums and midi keyboard for example) Would connecting both to the same USB port via a hub effectively limit the maximum data transfer rate to 1/2 to each of them? I am assuming yes, but I didn't know if USB hubs had a handshaking and priority giving protocol available (e.g. let the device with the longer built up buffer of data communicate first) Thanks

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  • Performance Bottleneck with Photoshop CS3 on XPSP3

    - by Doozer1979
    I have an intel core 2 4400, with 4GB of ram running on XP 32-BIT SP3. Photoshop CS3 becomes sluggish & unresponsive even after loading up small files, and this is with only Bridge open as well, plus McAffee AV. My photos are loaded in from a USB 2 external drive, and my c: drive is used only for programs and windows itself. Even with 4GB of RAM, i am seeing the pagefile increase to 1.6GB, whilst there appears to be 1.5GB of RAM free to use. I've defragged the drive, with defraggler, and after that the only file reported to be fragmented was the pagefile itself. Anyone have any ideas what i can do to improve/solve this?

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  • Oracle redo log performance degradation when inserting

    - by Aldarund
    I have a oracle 11g database. I'm testing in for inserts. The database running in noarchive mode. I have 3 redo log configured, each 2gb. I'm trying to insert data into test table. At begin it goes fine with 15k ins/second. I make a commit after 200 inserts. But after about 1.3m inserted records it become really slow, about 1-2k ins/second. As i noticed in resource explorer at this point we have filled all redo logs and so the inserts from this points work slow. So my question is why it become so slow when it fills redo logs, even if i commit each 200 records. And how this situation can be fixed ( except the turning off logging completely at inserts)

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  • Linux/Apache performance very slow even on local network

    - by klausch
    I have an Ubuntu server machine running Apache and MYSQL. System and version info is as follows: Linux kernel 3.0.0.-12 Apache/2.2.20 MySQL Ver 14.14.Distrib 5.1.58 I am running a few websites on this server, some HTML only, some PHP/MySQL. THe [problem is that response time is very slow, both on static as well as the dynamic sites. Sometimes it takes more than 10 seconds before a response is given, this makes the sites very slow and almost unusable. The problem occurs even when requesting from the local network. I have added the involved subdomains to my /etc/hosts file, and abolve all the problem is not solved by using IP numbers instead of URL's. So there is no DNS lookup issue. I have modified the log format by showing the response times and sometimes a files takes 12 seconds to be served, see the jquery~.js file in the example screenshot. I have no explanation for this extremely long response time, but is is not even the only issue here, some other files takes a long time to be served too, but do not show a long response time in the log file. So probably different tissues are involved here. I cannot find a solution until now, any suggestions??? THanx in advance, Klaas link to screenshot picture from access logfile Some extra configuration info: apache2.conf (comment is removed) LockFile ${APACHE_LOCK_DIR}/accept.lock PidFile ${APACHE_PID_FILE} Timeout 300 KeepAlive On MaxKeepAliveRequests 100 KeepAliveTimeout 5 <IfModule mpm_prefork_module> StartServers 5 MinSpareServers 5 MaxSpareServers 10 MaxClients 150 MaxRequestsPerChild 0 </IfModule> <IfModule mpm_worker_module> StartServers 2 MinSpareThreads 25 MaxSpareThreads 75 ThreadLimit 64 ThreadsPerChild 25 MaxClients 150 MaxRequestsPerChild 0 </IfModule> <IfModule mpm_event_module> StartServers 2 MinSpareThreads 25 MaxSpareThreads 75 ThreadLimit 64 ThreadsPerChild 25 MaxClients 150 MaxRequestsPerChild 0 </IfModule> User ${APACHE_RUN_USER} Group ${APACHE_RUN_GROUP} AccessFileName .htaccess <Files ~ "^\.ht"> Order allow,deny Deny from all Satisfy all </Files> DefaultType text/plain HostnameLookups Off ErrorLog ${APACHE_LOG_DIR}/error.log LogLevel warn Include mods-enabled/*.load Include mods-enabled/*.conf Include httpd.conf Include ports.conf LogFormat "%v:%p %h %l %u %t \"%r\" %>s %O \"%{Referer}i\" \"%{User-Agent}i\"" vhost_combined LogFormat "%h %l %u %t \"%r\" %>s %O \"%{Referer}i\" \"%{User-Agent}i\" %T/%D" combined LogFormat "%h %l %u %t \"%r\" %>s %O" common LogFormat "%{Referer}i -> %U" referer LogFormat "%{User-agent}i" agent Include conf.d/ Include sites-enabled/ And the virtual hostfile for one of the slow sites, in fact it is pretty straightforward... <VirtualHost *:80> ServerAdmin [email protected] ServerSignature EMail ServerName toenjoy.drsklaus.nl DocumentRoot /var/www/toenjoy.drsklaus.nl <Directory /> Options FollowSymLinks AllowOverride None </Directory> <Directory /var/www/toenjoy.drsklaus.nl/> Options Indexes FollowSymLinks MultiViews AllowOverride AuthConfig AuthType Basic AuthName "To Enjoy" AuthUserFile /etc/.htpasswd Require user petraaa Order allow,deny allow from all </Directory> ScriptAlias /cgi-bin/ /usr/lib/cgi-bin/ <Directory "/usr/lib/cgi-bin"> AllowOverride None Options +ExecCGI -MultiViews +SymLinksIfOwnerMatch Order allow,deny Allow from all </Directory> ErrorLog /var/log/apache2/error.log # Possible values include: debug, info, notice, warn, error, crit, # alert, emerg. LogLevel warn CustomLog /var/log/apache2/access.log combined Alias /doc/ "/usr/share/doc/" <Directory "/usr/share/doc/"> Options Indexes MultiViews FollowSymLinks AllowOverride None Order deny,allow Deny from all Allow from 127.0.0.0/255.0.0.0 ::1/128 </Directory> </VirtualHost> And the output of free -m: klaas@ubuntu-server:/etc/apache2$ free -m total used free shared buffers cached Mem: 1997 1401 595 0 144 1017 -/+ buffers/cache: 238 1758 Swap: 2035 0 2035 and I have no indication that swapping occurs on the moments the site is slow. I have runned top and it does not appear to be a CPU issue. I have the impression that the spawning of a apache thread could maybe be the bottleneck but it is just a suggestion. Maybe this gives some extra information! EDIT: The problem seemed to be gone for some time but occurs again! And not only with Apache, also connecting using SSH takes a tremendous time, sometimes it takes up to 15 seconds before the keyphrase is asked for. Also scp works very slowly. The behavious is really unpredoctable and makes the server very hard to use. Any ideas...?

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  • Slow performance with WAMP localhost access from other devices

    - by Adam
    I setup a localhost WAMP server and other device can access my localhost site on my win8 laptop with computer name instead of IP (bc I have use DCIP so that the wireless router can assign me IP otherwise it will not work). However, problem is that the website (WordPress), access speed is extremely slow on other devices other than my localhost computer, usually a 3s task take at least 10 seconds. (i.e. view my localhost site with computer name in a phone within the same wireless network.) Is that normal? What could be the reason causing it? Thank You

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  • Query Performance Degrades with High Number of Logical Reads

    - by electricsk8
    I'm using Confio Ignite8 to derive this information, and monitor waits. I have one query that runs frequently, and I notice that on some days there is an extremely high number of logical reads incurred, +300,000,000 for 91,000 executions. On a good day, the logical reads are much lower, 18,000,000 for 94,000 executions. The execution plan for the query utilizes clustered index seeks, and is below. StmtText |--Nested Loops(Inner Join, OUTER REFERENCES:([f].[ParentId])) |--Clustered Index Seek(OBJECT:([StructuredFN].[dbo].[Folder].[PK_Folders] AS [f]), SEEK:([f].[FolderId]=(8125)), WHERE:([StructuredFN].[dbo].[Folder].[DealId] as [f].[DealId]=(300)) ORDERED FORWARD) |--Clustered Index Seek(OBJECT:([StructuredFN].[dbo].[Folder].[PK_Folders] AS [p]), SEEK:([p].[FolderId]=[StructuredFN].[dbo].[Folder].[ParentId] as [f].[ParentId]), WHERE:([StructuredFN].[dbo].[Folder].[DealId] as [p].[DealId]=(300)) ORDERED FORWARD) Output from showstatistics io ... Table 'Folder'. Scan count 0, logical reads 4, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. Any ideas on how to troubleshoot where these high logical reads come from on certain days, and others nothing?

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  • On ESXi, guest machines hang for significant intervals compared to real machines. How can I fix this?

    - by Tarbox
    This is ESXi version 5.0.0. We plan on upgrading to 5.5 eventually. I have four code profiles, two taken on a real, unvirtualized machine, two taken on a virtual machine. Ordering the list of subroutines by time spent in each one, the two real profiles are practically identical. The two virtual profiles are different from each other and from the real profiles: a subset of subroutines are taking a lot more time on the virtual machines, and the subset is different for each run. The two virtual profiles take a similar amount of time, which is 3 times the amount of time the real profiles take. This gross "how long does it take?" result is consistent after hundreds of tests across three different virtual machines on two different host machines -- the virtual machine is just slower. I've only the code profiling on the four, however. Here's the most guilty set of lines: This is the real machine: 8µs $text = '' unless defined $text; 1.48ms foreach ( split( "\n", $text ) ) { This is the first run on the virtual machine: 20.1ms $text = '' unless defined $text; 1.49ms foreach ( split( "\n", $text ) ) { This is the second run on the virtual machine: 6µs $text = '' unless defined $text; 21.9ms foreach ( split( "\n", $text ) ) { My WAG is that the VM is swapping out the thread and then swapping it back in, destroying some level of cache in the process, but these code profiles were taken when the vm in question was the only active vm on the host, so... what? What does that mean? The guest itself is under light load, this is a latency problem for my users rather than throughput. The host is also under a light load, if I knew what resources to assign where, I could do it without worrying about the cost. I've attempted to lock memory, reserve cpu, assign a restrictive affinity, and disable hyperthread sharing. They don't help, it still takes the VM 2-4x the amount of time to do the same thing as the real machine. The host the tests were run on is 6x2.50GHz, Intel Xeon E5-26400 w/ 16gigs of ram. The guest exhibits the same performance under a wide combination of settings. The real machine is 4x2.13GHz, Xeon E5506 w/ 2 gigs of ram. Thank you for all advice.

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  • Prioritize file sharing performance in Windows Server 2008

    - by cmbrnt
    I've got a server running Windows Server 2008, and use it mainly for sharing files throughout the domain from a number of disks. It's running on VMware ESXi 4.0, in case that matters. My problem is that when I log in to the server to check user permissions etc, the access speed the files on the remote disks almost grinds to a halt. I havn't been able to measure the speeds, but I would guess it slows down to about 100kB/s as soon as I log in. This is on a gigabit network and the problems are equal for all users, even the ones connected to the same switch as the server. I've assigned 2 GB RAM to the server, and reserved it 1,5Ghz processor power. I don't have to do anything special on the server for this halt to occur. How can I make sure file sharing is prioritized on the server, so no matter what applications I'm using it will always make sure file sharing works properly? Could this be a VMware issue?

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  • Site's performance slows over time until Apache is restarted

    - by udbhav
    I'm running a Django app w/ Nginx and Apache. All our static media is stored on S3, and basically it takes a while for the app to check if thumbnails have been created every time a page is loaded. To alleviate this problem, I'm caching the output of the templates w/ memcached. Over the course of an hour or two, the site's speed goes down significantly, until I restart apache, and then all is good for a little while. I have very little sysadmin experience, and was hoping somebody could at least point me in the right direction.

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  • windows 8 on macbook locks after 2 mins despite high performance settings

    - by Mark
    I am running my Macbook Prop as a Windows 8 machine using bootcamp and for some reason, when I leave the keyboard/mouse alone for 2 mins it locks the PC (i.e. goes to the lock screen). I have (of course) checked the power settings and I can assure you that it is not set to these settings. I did notice that when I added my work's Mail Account the computer asked me to accept some group policy settings, which I did, so I suspect that this is a group policy setting, but I cannot find it. Can someone help? P.S. I have searched these forums first, and this is different to the PC going to sleep once locked, this is locking while logged in after 2 mins. Thanks.

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  • Solr performance (tomcat) - High load

    - by Ward Loockx
    I'm relatively new to solr. I have a production site running on a VPS, but now I'm having serious load issues. I don't know where to start in order to get the load down... VPS specs (linode.com 512) 512 MB RAM 4 CPU (1x priority) Looks like my solr server (tomcat) is using a lot of CPU power You can find my solrconfig.xml on http://pastebin.com/qdfi8Med and my schema.xml on http://pastebin.com/rRusDP8b I've tried to increaese the cache size, but this didn't do anything on the load. You can see the stats page below. EDIT - Because the screenshot was unclear, I took smaller screenshots if what (I think) is important. Dismax query handler stats Caches stats Thanks for the help!

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  • db2 tablespace size and performance impact

    - by jrhickey
    Originally when we began moving to db2 LUW we ran into some issues where our tables were too big to fit into the default 4K table space. As a result of "pressure" to get it done we just went with a 32K default table space and put ALL of our tables there. What impact would that have if any? I talked to one person who said that it would possible make out database MUCH larger than it needed to be. Is that true? What about memory? Would there be any benefit to moving the smaller tables back to a 4K table space? I have looked around in forums and what not but cannot seem to find a good answer.

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  • Accessing local variable doesn't improve performance

    - by NicMagnier
    The short version Why is this code: var index = (Math.floor(y / scale) * img.width + Math.floor(x / scale)) * 4; More performant than this one? var index = Math.floor(ref_index) * 4; The long version This week, the author of Impact js published an article about some rendering issue: http://www.phoboslab.org/log/2012/09/drawing-pixels-is-hard In the article there was the source of a function to scale an image by accessing pixels in the canvas. I wanted to suggest some traditional ways to optimize this kind of code so that the scaling would be shorter at loading time. But after testing it my result was most of the time worst that the original function. Guessing this was the JavaScript engine that was doing some smart optimization I tried to understand a bit more what was going on so I did a bunch of test. But my results are quite confusing and I would need some help to understand what's going on. I have a test page here: http://www.mx981.com/stuff/resize_bench/test.html jsPerf: http://jsperf.com/local-variable-due-to-the-scope-lookup To start the test, click the picture and the results will appear in the console. There are three different versions: The original code: for( var y = 0; y < heightScaled; y++ ) { for( var x = 0; x < widthScaled; x++ ) { var index = (Math.floor(y / scale) * img.width + Math.floor(x / scale)) * 4; var indexScaled = (y * widthScaled + x) * 4; scaledPixels.data[ indexScaled ] = origPixels.data[ index ]; scaledPixels.data[ indexScaled+1 ] = origPixels.data[ index+1 ]; scaledPixels.data[ indexScaled+2 ] = origPixels.data[ index+2 ]; scaledPixels.data[ indexScaled+3 ] = origPixels.data[ index+3 ]; } } jsPerf: http://jsperf.com/so-accessing-local-variable-doesn-t-improve-performance One of my attempt to optimize it: var ref_index = 0; var ref_indexScaled = 0 var ref_step = 1 / scale; for( var y = 0; y < heightScaled; y++ ) { for( var x = 0; x < widthScaled; x++ ) { var index = Math.floor(ref_index) * 4; scaledPixels.data[ ref_indexScaled++ ] = origPixels.data[ index ]; scaledPixels.data[ ref_indexScaled++ ] = origPixels.data[ index+1 ]; scaledPixels.data[ ref_indexScaled++ ] = origPixels.data[ index+2 ]; scaledPixels.data[ ref_indexScaled++ ] = origPixels.data[ index+3 ]; ref_index+= ref_step; } } jsPerf: http://jsperf.com/so-accessing-local-variable-doesn-t-improve-performance The same optimized code but with recalculating the index variable each time (Hybrid) var ref_index = 0; var ref_indexScaled = 0 var ref_step = 1 / scale; for( var y = 0; y < heightScaled; y++ ) { for( var x = 0; x < widthScaled; x++ ) { var index = (Math.floor(y / scale) * img.width + Math.floor(x / scale)) * 4; scaledPixels.data[ ref_indexScaled++ ] = origPixels.data[ index ]; scaledPixels.data[ ref_indexScaled++ ] = origPixels.data[ index+1 ]; scaledPixels.data[ ref_indexScaled++ ] = origPixels.data[ index+2 ]; scaledPixels.data[ ref_indexScaled++ ] = origPixels.data[ index+3 ]; ref_index+= ref_step; } } jsPerf: http://jsperf.com/so-accessing-local-variable-doesn-t-improve-performance The only difference in the two last one is the calculation of the 'index' variable. And to my surprise the optimized version is slower in most browsers (except opera). Results of personal testing (not the jsPerf tests): Opera Original: 8668ms Optimized: 932ms Hybrid: 8696ms Chrome Original: 139ms Optimized: 145ms Hybrid: 136ms Safari Original: 433ms Optimized: 853ms Hybrid: 451ms Firefox Original: 343ms Optimized: 422ms Hybrid: 350ms After digging around, it seems an usual good practice is to access mainly local variable due to the scope lookup. Because The optimized version only call one local variable it should be faster that the Hybrid code which call multiple variable and object in addition to the various operation involved. So why the "optimized" version is slower? I thought that it might be because some JavaScript engine don't optimize the Optimized version because it is not hot enough but after using --trace-opt in chrome, it seems all version are properly compiled by V8. At this point I am a bit clueless and wonder if somebody would know what is going on? I did also some more test cases in this page: http://www.mx981.com/stuff/resize_bench/index.html

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  • Is HTML5/WebGL performance bad on low-end Android tablets and phones?

    - by Boris van Schooten
    I've developed a couple of WebGL games, and am trying them out on Android. I found that they run very slowly on my tablet, however. For example, a game with 10 sprites or so runs as 5fps. I tried Chrome and CocoonJS, but they are comparably slow. I also tried other games, and even games with only 5 or so moving sprites are this slow. This seems inconsistent with reports from others, such as this benchmark. Typically, when people talk about HTML5 game performance, they mention well-known and higher-end phones and tables. While my 7" tablet is cheap (I believe it's a relabeled Allwinner tablet, apparently with the Mali 400 GPU), I found it generally has a good gaming performance. All the games I tried run smoothly. I also developed an OpenGL ES 2 demo with 200 shaded 3D objects, and it ran at 50fps. My suspicion is that many low-end and white-label devices may have unacceptable HTML5/WebGL support, which means there may be a large section of gamers you will not reach when you choose this as your platform. I've heard rumors about inconsistent performance of HTML5 and WebGL on different devices, but no clear picture emerges. I would like to hear if any of you have had similar experiences with HTML5 or WebGL, or whether I can find information about the percentage of devices I can expect to have decent performance.

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  • Is HTML5/WebGL performance unreliable on low-end Android tablets and phones?

    - by Boris van Schooten
    I've developed a couple of WebGL games, and am trying them out on Android. I found that they run very slowly on my tablet, however. For example, a game with 10 sprites or so runs as 5fps. I tried Chrome and CocoonJS, but they are comparably slow. I also tried other games, and even games with only 5 or so moving sprites are this slow. This seems inconsistent with reports from others, such as this benchmark. Typically, when people talk about HTML5 game performance, they mention well-known and higher-end phones and tables. While my 7" tablet is cheap (I believe it's a relabeled Allwinner tablet, apparently with the Mali 400 GPU), I found it generally has a good gaming performance. All the games I tried run smoothly. I also developed an OpenGL ES 2 demo with 200 shaded 3D objects, and it ran at 50fps. My suspicion is that many low-end and white-label devices may have unacceptable HTML5/WebGL support, which means there may be a large section of gamers you will not reach when you choose this as your platform. I've heard rumors about inconsistent performance of HTML5 and WebGL on different devices, but no clear picture emerges. I would like to hear if any of you have had similar experiences with HTML5 or WebGL, or whether I can find information about the percentage of devices I can expect to have decent performance.

    Read the article

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