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• Monitoring disk block access in Linux

  - by VoidPointer

  Is there a way to gather statistics about blocks being accessed on a disk? I have a scenario where a task is both memory and I/O intensive and I need to find a good balance as to how much of the available RAM I can assign to the process and how much I should leave for the system for building its I/O cache for the block device being used. I suspect that most of the I/O that is currently happening is accessing a rather small subset of the device and that performance could be optimized by increasing the RAM that is available for I/O buffering. Ideally, I would be able to create something like a "heat-map" that shows me which parts of the disk are accessed most of the time.

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• Computers with Small Capacity SSD - For caching?

  - by RXC

  Recently, in newsletters from websites, I have been seeing computers for sale from manufacturers that include an HDD and an SSD but the SSD has a small capacity like 24 GBs. I don't know if this still holds true, but I learned that when building a computer, you would want to install your OS on your fastest hard drive. I do a lot of PC gaming, so I install my OS and games on my SSD, because I learned that games and many applications make lots of system calls to the OS and performance can only be as fast as the slowest piece. Why these computers come with small capacity SSDs? Most OS's take up around 20 to 30 GBs of space, so what are the benefits of such a small SSD? Are these small size SSDs for caching? and what exactly does caching mean (what does it do and how does it help)?

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• How does Google manage to serve results so fast?

  - by Quintin Par

  I am building an autocomplete functionality for my site and the Google instant results are my benchmark. When I look at Google, the 50-60 ms response time baffle me. They look insane. In comparison here’s how mine looks like. To give you an idea my results are cached on the load balancer and served from a machine that has httpd slowstart and initcwnd fixed. My site is also behind cloudflare From a server side perspective I don’t think I can do anything more. Can someone help me take this 500 ms response time to 60ms? What more should I be doing to achieve Google level performance?

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• Have programmers at your work not taken up or been averse to an offer of a second monitor?

  - by Chris Knight

  I'm putting together a business case for the developers in my company to get a second monitor. After my own experiences and research, this seems a no-brainer to me in terms of increasing productivity and morale/happiness. One question which has niggled me is if I should be pushing to get all developers onto a second monitor or let folk opt-in (i.e. they get one if they want one). Thoughts on this are welcome, but my specific question relates to a snippet on this site: But when the IT manager at Thibeault's company asked other employees if they wanted dual monitors last year, few jumped at the offer. Blinded by my own pre-judgement, this surprised me. Has anyone else experienced this? I fully appreciate that some people prefer a single larger monitor, but my general experience of researching the web suggests that most programmers prefer a dual (or more) setup. I'm guessing this should be tempered with the thought that those developers who contribute to such discussions might not be considered your average developer who might not care one way or the other. Anyway, if you have experienced the above have you tried to sell the concept of dual monitors to the masses? If everyone just got 2 monitors regardless if they wanted it or not, were there adverse reactions or negative effects? UPDATE: The developers are on a mixture of 17", 22", or 24" single monitors. The desks should be able to accommodate dual 22" monitors as I am proposing, though this will take some getting used to I imagine.

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• Can T520+Bumblebee run an external monitor via DisplayPort?

  - by Fen

  Using 64-bit Ubuntu 11.10 and integrated (Intel) graphics, I can run the 1600x900 laptop display plus a 1600x1200 external monitor connected to the VGA adapter. But my external monitor is 1920x1200 so I have black stripes on each side. I believe the resolution is limited like this as the maximum resolution available from the Intel GPU is 2560x1600 = 4,096,000 pixels and I'm asking for a 3520x1200 = 4,224,000 display (with 1200x300 lost above the laptop screen). At 3200x1200 = 3,840,000 pixels, the Intel GPU seems happy. Under Windows, the same limit exists when using the VGA adapter, but if I turn Optimus on then I can connect the external monitor to the DisplayPort and get its full resolution and an extended desktop. I've seen that Bumblebee can run apps on the DisplayPort using the 'optirun' command. My question is: can Bumblebee run the DisplayPort in concert with the Intel card running the laptop screen creating a large virtual desktop (as on Windows)? If so, are there any pointers to how to do this? I tried once, failed, and dropped back to Integrated Graphics (and black stripes) as I could find no reports of this configuration working.

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• How can I get my monitor's maximum resolution without the proprietary AMD graphic driver installed?

  - by Venki

  I am using Ubuntu 14.04. I have an AMD Radeon 5570 HD graphic card. Actually, the default open source REDWOOD drivers aren't allowing me to choose my monitor's maximum screen resolution(which is 1366 x 768). I just have two resolutions displayed which are 1024x768 and 800x600 . If I give the command : xrandr -s 1366x768 then the output is: Size 1366x768 not found in available modes So just for the sake of getting 1366x768 resolution I am forced to install the proprietary graphic driver that AMD gives me from its site. But if I install it(which itself is quite a problem-prone process), I undergo a lot of 'inconvenience'. Sometimes after an OS update, the driver crashes unity. Then I will have to uninstall that driver from a tty and google around for a solution. Also I encounter screen tearing problems occasionally. In addition I also cant see my login screen(See this question which states this particular problem). The main problem is AMD does not update its driver as quick as Ubuntu updates its OS. This is quite irritating. So, I want the maximum resolution(and performance) that my graphics card and monitor can give me without installing the 'problematic' proprietary graphic card driver that AMD gives. Is this possible? Suggestions please. Thanks in advance. PS :- More system specs details:- Intel i3 2100 processor AMD P8H61-M PLUS2 motherboard AMD Radeon 5570 HD graphic card DELL monitor (BTW, Thank you for reading through my elaborate description!)

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• Windows Spooler Events API doesn't generate events for network printers

  - by clyfe

  the context i use Spooler Events API to capture events generated by the spooler when a user prints a document ie. FindFirstPrinterChangeNotification FindNextPrinterChangeNotification the problem When I print a document on the network printers from my machine no events are captured by the monitor (uses the fuctions above) Notice Events ARE generated OK for local printers, only Network Printers are problematic!

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• How To Trace Win32 Socket Calls and Requests

  - by Olaseni

  How can I effectively trace the raw data sent to my socket server listening on a win32 machine? I want the trace to be specific to the port my server is listening on, so I can monitor only that traffic. I want to see how the data exchange works on the wire.

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• Visual studio has gone crazy trying to create files

  - by zachary

  I downloaded Process Monitor and began monitoring my project directory that I am writing code in. I see endless entries every couple seconds of: Operation: Create File C:\Inetpub\wwwroot\csharp C:\Inetpub\wwwroot\code C:\Inetpub\wwwroot\web and so on for the rest of the templates Then it says the result is PATH NOT FOUND. What is happening? Has Visual Studio GONE CRAZY?!?!?!?!?!?!?!

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• Stale statistics on a newly created temporary table in a stored procedure can lead to poor performance

  - by sqlworkshops

  When you create a temporary table you expect a new table with no past history (statistics based on past existence), this is not true if you have less than 6 updates to the temporary table. This might lead to poor performance of queries which are sensitive to the content of temporary tables.I was optimizing SQL Server Performance at one of my customers who provides search functionality on their website. They use stored procedure with temporary table for the search. The performance of the search depended on who searched what in the past, option (recompile) by itself had no effect. Sometimes a simple search led to timeout because of non-optimal plan usage due to this behavior. This is not a plan caching issue rather temporary table statistics caching issue, which was part of the temporary object caching feature that was introduced in SQL Server 2005 and is also present in SQL Server 2008 and SQL Server 2012. In this customer case we implemented a workaround to avoid this issue (see below for example for workarounds).When temporary tables are cached, the statistics are not newly created rather cached from the past and updated based on automatic update statistics threshold. Caching temporary tables/objects is good for performance, but caching stale statistics from the past is not optimal.We can work around this issue by disabling temporary table caching by explicitly executing a DDL statement on the temporary table. One possibility is to execute an alter table statement, but this can lead to duplicate constraint name error on concurrent stored procedure execution. The other way to work around this is to create an index.I think there might be many customers in such a situation without knowing that stale statistics are being cached along with temporary table leading to poor performance.Ideal solution is to have more aggressive statistics update when the temporary table has less number of rows when temporary table caching is used. I will open a connect item to report this issue.Meanwhile you can mitigate the issue by creating an index on the temporary table. You can monitor active temporary tables using Windows Server Performance Monitor counter: SQL Server: General Statistics->Active Temp Tables. The script to understand the issue and the workaround is listed below:set nocount onset statistics time offset statistics io offdrop table tab7gocreate table tab7 (c1 int primary key clustered, c2 int, c3 char(200))gocreate index test on tab7(c2, c1, c3)gobegin trandeclare @i intset @i = 1while @i <= 50000begininsert into tab7 values (@i, 1, ‘a’)set @i = @i + 1endcommit trangoinsert into tab7 values (50001, 1, ‘a’)gocheckpointgodrop proc test_slowgocreate proc test_slow @i intasbegindeclare @j intcreate table #temp1 (c1 int primary key)insert into #temp1 (c1) select @iselect @j = t7.c1 from tab7 t7 inner join #temp1 t on (t7.c2 = t.c1)endgodbcc dropcleanbuffersset statistics time onset statistics io ongo–high reads as expected for parameter ’1'exec test_slow 1godbcc dropcleanbuffersgo–high reads that are not expected for parameter ’2'exec test_slow 2godrop proc test_with_recompilegocreate proc test_with_recompile @i intasbegindeclare @j intcreate table #temp1 (c1 int primary key)insert into #temp1 (c1) select @iselect @j = t7.c1 from tab7 t7 inner join #temp1 t on (t7.c2 = t.c1)option (recompile)endgodbcc dropcleanbuffersset statistics time onset statistics io ongo–high reads as expected for parameter ’1'exec test_with_recompile 1godbcc dropcleanbuffersgo–high reads that are not expected for parameter ’2'–low reads on 3rd execution as expected for parameter ’2'exec test_with_recompile 2godrop proc test_with_alter_table_recompilegocreate proc test_with_alter_table_recompile @i intasbegindeclare @j intcreate table #temp1 (c1 int primary key)–to avoid caching of temporary tables one can create a constraint–but this might lead to duplicate constraint name error on concurrent usagealter table #temp1 add constraint test123 unique(c1)insert into #temp1 (c1) select @iselect @j = t7.c1 from tab7 t7 inner join #temp1 t on (t7.c2 = t.c1)option (recompile)endgodbcc dropcleanbuffersset statistics time onset statistics io ongo–high reads as expected for parameter ’1'exec test_with_alter_table_recompile 1godbcc dropcleanbuffersgo–low reads as expected for parameter ’2'exec test_with_alter_table_recompile 2godrop proc test_with_index_recompilegocreate proc test_with_index_recompile @i intasbegindeclare @j intcreate table #temp1 (c1 int primary key)–to avoid caching of temporary tables one can create an indexcreate index test on #temp1(c1)insert into #temp1 (c1) select @iselect @j = t7.c1 from tab7 t7 inner join #temp1 t on (t7.c2 = t.c1)option (recompile)endgoset statistics time onset statistics io ondbcc dropcleanbuffersgo–high reads as expected for parameter ’1'exec test_with_index_recompile 1godbcc dropcleanbuffersgo–low reads as expected for parameter ’2'exec test_with_index_recompile 2go

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• Eclipse grinds to a halt when building workspace

  - by Chris Thompson

  Hi all, This is a bit of a vague question because, frankly, I don't even know where to begin diagnosing the issue. My eclipse (Galileo) installation grinds to a complete halt when it's building the workspace -- to the point where I can't even type. I know the Android SDK I have installed is a major culprit because I can watch the memory usage go through the roof (through the built-in heap monitor) when the Android SDK content loader starts up. Every time I save a file though, the program just stops. The message at the bottom of the screen says Building workspace (74%) and sits there for about 30 or so seconds before completing and returning the performance to normal. I have a few other plugins installed (Maven, SVN, etc) but I'm assuming the main issue is Android. Has anybody had similar issues or any luck correcting this sort of problem? If there's anymore information you think would be helpful, just let me know...I didn't want to do a core dump on this question... I'm running it on Windows 7 64-bit for what it's worth. Thanks! Chris

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• Request bursting from web application Load Tests

  - by MaseBase

  I'm migrating our web and database hosting to a new environment on all new machines. I've recently performed a Load Test using WAPT to generate load from multiple distributed clients. The server has plenty of room to handle the traffic load, but I'm seeing an odd pattern of incoming traffic during the load tests. Here is the gist of our setup: Firewall server running MS Forefront TMG 2010 on Win 2k8 server Request routing done by IIS Application Request Routing on firewall machine Web server is a Hyper-V VM on the Database server (which is the host OS) These machines are hefty with dual-CPU's with six cores (12 total procs) Web server running IIS 7.5 Web applications built in ASP.NET 2.0, with 1 ISAPI filter (Url Rewrite) in front What I'm seeing during the load tests is that the requests all come through in bursts. Even though I have 7 different distributed clients sending traffic loads, the requests come through about 300-500 requests at a time. The performance monitor shows nearly all of the counters moving through this pattern, where a burst of requests comes in the req/sec jumps to 70, the queued requests jumps to 500, the current requests jumps up, the CPU jumps up, everything. Then once it's handled that group of requests, it has a lull for nearly 10 seconds where nearly nothing is happening. 0-5 req/sec, 0 queued requests, minimal CPU usage. Then after 10 seconds of inactivity, another burst comes through, spiking all of the counters once again. What I can't figure out is why the requests are coming through in bursts when I know that the load being generated is not sent that way, especially considering the various load-generating clients sending traffic all in different intervals with random think time's between each request. Is there something in the layers between Hyper-V or perhaps in the hardware which might cause this coalesce of requests together? Here is what i'm looking at, the highlighted metric is Requests/sec, but the others critical counter go with it: Requests Queued (which I'd obviously like to keep as close to 0 as possible). Any ideas on this?

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• Win 2008 R2 - copying TO disk is very slow, copying FROM is more or less okay

  - by avs099

  I have Windows 2008 R2 SP1 with 4 identical SATA disks (Seagate Barracude 7200) in RAID 5 array. It has 4Gb of memory; all recent updates are installed. Problem: when I copy large file from one folder to another, I get about 10MB/s average speed. When I read this file from network share via 1Gbps connection - I get about 25-30 MB/s. Both numbers seems to be low for me - but specifically I'm very frustrated with low write speed. there is no antivirus, no hyper-v, it's just a fileserver - i when i do my tests nobody else reads/write from it (we have only 4 people in a team, so I'm sure). Not sure if that matters, but there is only 1 logic disk "C" with all available space (1400 GB). I'm not an admin at all, so I have no idea where to look and what other information to provide. I did run performance monitor with "% idle time", "avg bytes read", "avg byte write" - here is the screenshot: I'm not sure why there are such obvious spikes. Any idea? Please let me know if you need me to provide more information - what counters should I check, etc. I'm very eager to get this solved. Thank you. UPDATE: we have another Windows 2008 R2 SP1 server with 2 RAID1 arrays - one is disk C (where windows is installed, another one is disk E). It is running Hyper-V and does not have antivirus. I noticed the following behavior when I copy large file (few GBs): C - C: about 50MB/sec C - E: about 55MB/sec E - E: 8MB/sec!!! E - C: 8MB/sec!!! what could cause this?? E drive is RAID1 array from same Seagate Barracuda 1TB drives..

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• Server nearly unusable when doing disk writes

  - by Wikser

  My question closely relates to my last question here on serverfault. I was copying about 5GB from a 10 year old desktop computer to the server. The copy was done in Windows Explorer. In this situation I would assume the server to be bored by the dataflow. But as usual with this server, it really slowed down. At least I could work with the remote session, even there was some serious latency. The copy took its time (20min?). In this time I went to a colleague and he tried to log in in the same server via remote desktop (for some other reason). It took about a minute to get to the login screen, a minute to open the control panel, a minute to open the performance monitor, ... Icons were loading maybe one per second. We saw the following (from memory): CPU: 2% Avg. Queue Length: 50 Pages/sec: 115 (?) There was no other considerable activity on the server. The server seldom serves some ASP.NET pages, which became also very slow in this time. The relevant configuration is as follows: Windows 2003 SEAGATE ST3500631NS (7200 rpm, 500 GB) LSI MegaRAID based RAID 5 4 disks, 1 hot spare Write Through No read-ahead Direct Cache Mode Harddisk-Cache-Mode: off Is this normal behaviour for such a configuration? What measurements could give further clues? Is it reasonable to reduce the priority of such copy I/O and favour other processes like the remote desktop? How would you do that? Many thanks!

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• Windows Server 2012 Hyper-V very slow

  - by Matt Taylor

  I have been running several Hyper-V VMs on Windows Server 2008 R2 for the past couple of years and enjoying perfectly adequate performance for my testing/development/r&d environments. I'm a software developer so my hardware knowledge is basic however I built the rig using: •Gigabyte GA-X58A-UD3R Intel X58 (Socket 1366) DDR3 Motherboard •Intel Core i7 960 3.20GHz (Bloomfield) (Socket LGA1366) •24GB triple channel RAM The host OS is running on an OCZ SSD and all the VMs are running on a 2TB Marvell SATA3 RAID 0 array consisting of 2 Western Digital Caviar Black 7,200rpm drives. I have tested the speed of the 2TB drive and appear to be getting less than 3Mbs but it can adequately run a 4 VM farm including a DC, (SQL) database and IIS application servers. I recently upgraded the SSD on which the host runs to a 256GB OCZ Vertex 4 and took the opportunity to upgrade to Windows Server 2012 and installed the Hyper-V role. I tried importing one of my existing Windows Server 2008 R2 VMs (and converted it to .vhdx) plus I have tried creating a brand new Windows Server 2008 R2 VM but both are running extremely slowly and I can see nothing obvious using the host and guest Task Manager/Resource Monitor tools. In both cases the VM has 8GB RAM (fixed), 4 CPUs, fixed size HD (not expanding) and is using an external virtual network running on a separate NIC to the host. I have upgraded the BIOS to the latest available version and checked the virtualization settings. I have run out of "obvious" (to a developer) things to check/configure and my next option will be to re-install the host OS but before I do I would very much appreciate any advice from any experts out there. Thanks

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• How to stop Firefox on an SSD from freezing when using the search box or submitting a form?

  - by sblair

  Firefox usually freezes for about a second whenever I search for something from the toolbar search box, when submitting a form, or when clearing the search box history. I suspect it has something to do with the auto-complete feature. Using Windows 7's Resource Monitor, the problem seems to be from the file: C:\Users\<username>\AppData\Roaming\Mozilla\Firefox\Profiles\<profile>\formhistory.sqlite-journal I believe this is a temporary file which caches database writes. The following screenshot shows the very high response times from six different searches, and that the queue length on drive C shoots off the scale: My Firefox profile is on an Intel X25-M G2 SSD. The problem doesn't seem to occur if I create a new profile on a hard disk drive. However, I'd like to know why the problem exists on the SSD in the first place (because it's an annoying problem which contradicts the reason I bought an SSD, and it might happen with other applications too), and how to prevent it. It still occurs if Firefox is started in safe mode, and with the recent beta versions. Updates: VACUUMing the Firefox profile databases does not help with this problem. The SSD Optimizer in the Intel SSD Toolbox does not help either.

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• Server specification recommendation

  - by foo

  To cut the story short, I can't buy an item (server/cpu/motherboard/ram) that costs more than USD 330. However, I can combine them, meaning, I can buy a CPU that costs USD 330 and motherboard that costs USD 330. With this limitation, I can't buy a powerful 1U server which will definitely costs me more USD 330. With that in mind, I was hoping to build a powerful desktop PC which will be used as a database server. However, through my experience, desktop PC doesn't last very long, usually the motherboard will just die by itself after 1 or 2 years. So, what would you guys recommend me to buy with this kind of budget? Every item must be <= USD 330. Will be used as a MySQL server. RAID would be nice. 1TB is pretty big for my data. I do not need external graphic card (onboard would do just fine), mouse, keyboard, monitor. Linux friendly. One ethernet port is good enough. It's important that those hardware is made of components that will last long (at least 3 years or something). The server will be placed in an air conditioned room, but a good ventilation for the server is always preferred. I won't overclock it. Intel processor is preferred. Thanks in advance.

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• My system is always disk-bound (the disk light is always on). Why is this?

  - by Scoobie

  I have been given a laptop by the good folks at my company on which to do my work (Java development). I usually use eclipse as my primary development platform. The laptop is a Dell D830 and runs Windows 7 - 32 bit. Although the processor supports a 64 bit instruction-set, licensing limits me to running the 32 bit OS. The HDD is a WD1600BEVT (Western Digital). I have noticed that my disk is always very slow. Windows start up is usually pretty quick, however as soon as I log on, my disk light stays on and usually, the laptop takes about 4 minutes (after logging in -- immediately upon getting the prompt to press Ctrl + Alt + Del to log in) before it's usable. Questions: Is this expected behavior? What can I do to examine the disk and determine the cause of the problem? What can I do to improve my disk's performance? Any optimizations you may be able to suggest? Other Questions: Some have suggested running Process Monitor (from sysinternals), but how would i get the log since start up? Instead of trying to fix this myself, should I simply push this onto the system administrator? Thanks all.

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• How to force GNOME panels et. al. to display on a different monitor without mirroring?

  - by GrueKun

  So, I recently purchased a new 23" monitor for my PC. However, I can't use it with the PC currently as I am waiting on a replacement heatsink. In the mean time, I wanted to use it with my Dell laptop. I hooked it up to the VGA port, and it seems to be working properly. However, I wanted to know if there was a way I could move all of the main display elements over to the attached monitor? I wanted to shut the LCD panel off on the laptop and hook it up like a desktop. Relevant specs: Ubuntu 10.10 x64 Intel graphics chipset The attached monitor is currently set as the default monitor. Any suggestions are welcome. :)

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• Windows system monitoring and profiling

  - by Aris

  I have several dozen 64-bit Windows 2003 servers in a high performance environment with very bursty system utilization. I am looking for a tool (or tools) to monitor and analyze system performance (eg, CPU utilization, bandwidth, etc). This tool can either query servers from a central location (SNMP) or require installation of a component on each server. It should poll on a 1-second interval. It should be able to generate pretty graphs which show trends over time. As a nice-to-have, it should be able to send out emails or IMs when certain thresholds are exceeded. The tools I have investigated so far, including Solarwinds and PRTG, are not designed to poll this frequently. They seem to be designed for a ~30-second interval. Solarwinds wouldn't go lower than 3-sec, and PRTG chokes at 1-sec. They both default to 1-min. All three tools seem more focused on outage monitoring and reporting than metric collection. Given the bursty nature of our applications, such infrequent polling would result in a very inaccurate picture of performance. I am considering rolling my own solution using perfmon. This would be a lot of work, and seems like reinventing the wheel. Are there any tools out there that meet my needs?

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• How to modernize an enormous legacy database?

  - by smayers81

  I have a question, just looking for suggestions here. So, my application is 'modernizing' a desktop application by converting it to the web, with an ICEFaces UI and server side written in Java. However, they are keeping around the same Oracle database, which at current count has about 700-900 tables and probably a billion total records in the tables. Some individual tables have 250 million rows, many have over 25 million. Needless to say, the database is not scaling well. As a result, the performance of the application is looking to be abysmal. The architects / decision makers-that-be have all either refused or are unwilling to restructure the persistence. So, basically we are putting a fresh coat of paint on a functional desktop application that currently serves most user needs and does so with relative ease and quick performance. I am having trouble sleeping at night thinking of how poorly this application is going to perform and how difficult it is going to be for everyday users to do their job. So, my question is, what options do I have to mitigate this impending disaster? Is there some type of intermediate layer I can put in between the database and the Java code to speed up performance while at the same time keeping the database structure intact? Caching is obviously an option, but I don't see that as being a cure-all. Is it possible to layer a NoSQL DB in between or something?

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• Preloading Winforms

  - by msarchet

  I am currently working on a project where we have a couple very control heavy user controls that are being used inside a MDI Controller. This is a Line of Business app and it is very data driven. The problem that we were facing was the aforementioned controls would load very very slowly, we dipped our toes into the waters of multi-threading for the control loading but that was not a solution for a plethora of reasons. Our solution to increasing the performance of the controls ended up being to 'pre-load' the forms onto a hidden window, create a stack of the existing forms, and pop off of the stack as the user requested a form. Now the current issue that I'm seeing that will arise as we push this 'fix' out to our testers, and the ultimately our users is this: Currently the 'hidden' window that contains the preloaded forms is visible in task manager, and can be shut down thus causing all of the controls to be lost. Then you have to create them on the fly losing the performance increase. Secondly, when the user uses up the stack we lose the performance increase (current solution to this is discussed below). For the first problem, is there a way to hide this window from task manager, perhaps by creating a parent form that encapsulates both the main form for the program and the hidden form? Our current solution to the second problem is to have an inactivity timer that when it fires checks the stacks for the forms, and loads a new form onto the stack if it isn't full. However this still has the potential of causing a hang in the UI while it creates the forms. A possible solutions for this would be to put 'used' forms back onto the stack, but I feel like there may be a better way.

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• SQL Server Multi-statement UDF - way to store data temporarily required

  - by Kharlos Dominguez

  Hello, I have a relatively complex query, with several self joins, which works on a rather large table. For that query to perform faster, I thus need to only work with a subset of the data. Said subset of data can range between 12 000 and 120 000 rows depending on the parameters passed. More details can be found here: http://stackoverflow.com/questions/3054843/sql-server-cte-referred-in-self-joins-slow As you can see, I was using a CTE to return the data subset before, which caused some performance problems as SQL Server was re-running the Select statement in the CTE for every join instead of simply being run once and reusing its data set. The alternative, using temporary tables worked much faster (while testing the query in a separate window outside the UDF body). However, when I tried to implement this in a multi-statement UDF, I was harshly reminded by SQL Server that multi-statement UDFs do not support temporary tables for some reason... UDFs do allow table variables however, so I tried that, but the performance is absolutely horrible as it takes 1m40 for my query to complete whereas the the CTE version only took 40minutes. I believe the table variables is slow for reasons listed in this thread: http://stackoverflow.com/questions/1643687/table-variable-poor-performance-on-insert-in-sql-server-stored-procedure Temporary table version takes around 1 seconds, but I can't make it into a function due to the SQL Server restrictions, and I have to return a table back to the caller. Considering that CTE and table variables are both too slow, and that temporary tables are rejected in UDFs, What are my options in order for my UDF to perform quickly? Thanks a lot in advance.

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• How can I apply a PSSM efficiently?

  - by flies

  I am fitting for position specific scoring matrices (PSSM aka Position Specific Weight Matrices). The fit I'm using is like simulated annealing, where I the perturb the PSSM, compare the prediction to experiment and accept the change if it improves agreement. This means I apply the PSSM millions of times per fit; performance is critical. In my particular problem, I'm applying a PSSM for an object of length L (~8 bp) at every position of a DNA sequence of length M (~30 bp) (so there are M-L+1 valid positions). I need an efficient algorithm to apply a PSSM. Can anyone help improve performance? My best idea is to convert the DNA into some kind of a matrix so that applying the PSSM is matrix multiplication. There are efficient linear algebra libraries out there (e.g. BLAS), but I'm not sure how best to turn an M-length DNA sequence into a matrix M x 4 matrix and then apply the PSSM at each position. The solution needs to work for higher order/dinucleotide terms in the PSSM - presumably this means representing the sequence-matrix for mono-nucleotides and separately for dinucleotides. My current solution iterates over each position m, then over each letter in word from m to m+L-1, adding the corresponding term in the matrix. I'm storing the matrix as a multi-dimensional STL vector, and profiling has revealed that a lot of the computation time is just accessing the elements of the PSSM (with similar performance bottlenecks accessing the DNA sequence). If someone has an idea besides matrix multiplication, I'm all ears.

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• What do you use to play sound in iPhone games?

  - by zoul

  Hello! I have a performance-intensive iPhone game I would like to add sounds to. There seem to be about three main choices: (1) AVAudioPlayer, (2) Audio Queues and (3) OpenAL. I’d hate to write pages of low-level code just to play a sample, so that I would like to use AVAudioPlayer. The problem is that it seems to kill the performace – I’ve done a simple measuring using CFAbsoluteTimeGetCurrent and the play message seems to take somewhere from 9 to 30 ms to finish. That’s quite miserable, considering that 25 ms == 40 fps. Of course there is the prepareToPlay method that should speed things up. That’s why I wrote a simple class that keeps several AVAudioPlayers at its disposal, prepares them beforehand and then plays the sample using the prepared player. No cigar, still it takes the ~20 ms I mentioned above. Such performance is unusable for games, so what do you use to play sounds with a decent performance on iPhone? Am I doing something wrong with the AVAudioPlayer? Do you play sounds with Audio Queues? (I’ve written something akin to AVAudioPlayer before 2.2 came out and I would love to spare that experience.) Do you use OpenAL? If yes, is there a simple way to play sounds with OpenAL, or do you have to write pages of code? Update: Yes, playing sounds with OpenAL is fairly simple.

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