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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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• 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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• Core Animation performance on iphone

  - by nico

  I'm trying to do some animations using Core Animation on the iphone. I'm using CABasicAnimation on CALayer. It's a straight forward animation from a random place at the top of the screen to the bottom of the screen at random speed, I have 30 elements that doing the same animation continuously until another action happens. But the performance on the iPhone 3G is very sluggish when the animations start. The image is only 8k. Is this the right approach? How should I change so it performs better. // image cached somewhere else. CGImageRef imageRef = [[UIImage imageWithContentsOfFile:[[NSBundle mainBundle] pathForResource:name ofType:@"png"]] CGImage]; - (void)animate:(NSTimer *)timer { int startX = round(radom() % 320); float speed = 1 / round(random() % 100 + 2); CALayer *layer = [CALayer layer]; layer.name = @"layer"; layer.contents = imageRef; // cached image layer.frame = CGRectMake(0, 0, CGImageGetWidth(imageRef), CGImageGetHeight(imageRef)); int width = layer.frame.size.width; int height = layer.frame.size.height; layer.frame = CGRectMake(startX, self.view.frame.origin.y, width, height); [effectLayer addSublayer:layer]; CGPoint start = CGPointMake(startX, 0); CGPoint end = CGPointMake(startX, self.view.frame.size.height); float repeatCount = 1e100; CABasicAnimation *animation = [CABasicAnimation animationWithKeyPath:@"position"]; animation.delegate = self; animation.fromValue = [NSValue valueWithCGPoint:start]; animation.toValue = [NSValue valueWithCGPoint:end]; animation.duration = speed; animation.repeatCount = repeatCount; animation.autoreverses = NO; animation.removedOnCompletion = YES; animation.fillMode = kCAFillModeForwards; [layer addAnimation:animation forKey:@"position"]; } The animations are fired off using a NSTimer. animationTimer = [NSTimer timerWithTimeInterval:0.2 target:self selector:@selector(animate:) userInfo:nil repeats:YES]; [[NSRunLoop currentRunLoop] addTimer:animationTimer forMode:NSDefaultRunLoopMode];

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• How to solve Memory leaks in Lib Xml Parser in objective-C where the list is returned?

  - by Madan Mohan

  Hi Guys, I got leaks in Lib Xml Parser while retrieving the data from the net, Here in the below code, I have allocated the list - (void)getCustomersList { // make an operation so we can push it into the queue SEL method = @selector(parseForData); NSInvocationOperation *op = [[NSInvocationOperation alloc] initWithTarget:self selector:method object:nil]; customersTempList = [[NSMutableArray alloc] initWithCapacity:20];// allocated list [self.retrieverQueue addOperation:op]; [op release]; } // return each recode // in parser .m class one of the condition in endElement where it shows a leak. else if(0 == strncmp((const char *)localname, kCustomerElement, kCustomerElementLength)) { [customersTempList addObject:customer]; printf("\n no of objects in temp list:%d", [customersTempList count]); if ([customersTempList count] == 20) { NSMutableArray* argsList = [customersTempList copy];//////////////////////here it is showing leak. printf("\n Calling reload data with %d new objects", [argsList count]); SEL selector = @selector(parser:addCustomerObject:); NSMethodSignature *sig = [(id)self.delegate methodSignatureForSelector:selector]; if(nil != sig && [self.delegate respondsToSelector:selector]) { NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:sig]; [invocation retainArguments]; [invocation setTarget:self.delegate]; [invocation setSelector:selector]; [invocation setArgument:&self atIndex:2]; [invocation setArgument:&argsList atIndex:3]; [invocation performSelectorOnMainThread:@selector(invoke) withObject:NULL waitUntilDone:NO]; } [customersTempList removeAllObjects]; } } // returned the list after all the records are stored in the list else if(0 == strncmp((const char *)localname, kCustomersElement, kCustomersElementLength)) { printf("\n Calling reload data with %d new objects", [customersTempList count]); NSMutableArray* argsList = [customersTempList copy]; printf("\n Calling reload data with %d new objects", [argsList count]); SEL selector = @selector(parser:addCustomerObject:); NSMethodSignature *sig = [(id)self.delegate methodSignatureForSelector:selector]; if(nil != sig && [self.delegate respondsToSelector:selector]) { NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:sig]; [invocation retainArguments]; [invocation setTarget:self.delegate]; [invocation setSelector:selector]; [invocation setArgument:&self atIndex:2]; [invocation setArgument:&argsList atIndex:3]; [invocation performSelectorOnMainThread:@selector(invoke) withObject:NULL waitUntilDone:NO]; } [customersTempList removeAllObjects]; } } please help me out of this, Thanks, Madan.

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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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• LINQ to SQL - Lightweight O/RM?

  - by CoffeeAddict

  I've heard from some that LINQ to SQL is good for lightweight apps. But then I see LINQ to SQL being used for Stackoverflow, and a bunch of other .coms I know (from interviewing with them). Ok, so is this true? for an e-commerce site that's bringing in millions and you're typically only doing basic CRUDs most the time with the exception of an occasional stored proc for something more complex, is LINQ to SQL complete enough and performance-wise good enough or able to be tweaked enough to run happily on an e-commerce site? I've heard that you just need to tweak performance on the DB side when using LINQ to SQL for a better approach. So there are really 2 questions here: 1) Meaning/scope/definition of a "Lightweight" O/RM solution: What the heck does "lightweight" mean when people say LINQ to SQL is a "lightweight O/RM" and is that true??? If this is so lightweight then why do I see a bunch of huge .coms using it? Is it good enough to run major .coms (obviously it looks like it is) and what determines what the context of "lightweight" is...it's such a generic statement. 2) Performance: I'm working on my own .com and researching different O/RMs. I'm not really looking at the Entity Framework (yet), just want to figure out the LINQ to SQL basics here and determine if it will be efficient enough for me. The problem I think is you can't tweak or control the SQL it generates...

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• Low Throughput on Windows Named Pipe Over WAN

  - by MichaelB76

  I'm having problems with low performance using a Windows named pipe. The throughput drops off rapidly as the network latency increases. There is a roughly linear relationship between messages sent per second and round trip time. It seems that the client must ack each message before the server will send the next one. This leads to very poor performance, I can only send 5 (~100 byte) messages per second over a link with an RTT of 200 ms. The pipe is asynchronous, using multiple overlapped write operations (and multiple overlapped reads at the client end), but this is not improving throughput. Is it possible to send messages in parallel over a named pipe? The pipe is created using PIPE_TYPE_MESSAGE, would PIPE_READMODE_BYTE work better? Is there any other way I can improve performance? This is a deployed solution, so I can't simply replace the pipe with a socket connection (I've read that Windows named pipe aren't recommended for use over a WAN, and I'm wondering if this is why). I'd be grateful for any help with this matter.

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• Limiting object allocation over multiple threads

  - by John

  I have an application which retrieves and caches the results of a clients query. The client then requests different chunks of data and the application sends the relevant results and removes them from the cache. A new requirement for this application is that there needs to be a run-time configurable maximum number of results which may be cached. I've taken the naive approach and implemented this by using a counter under a lock which is incremented every time a result is cached and decremented whenever a result is removed from the cache. Unfortunately, this has drastically reduced the applications performance when processing a large number of concurrent requests. I have tried both a critical section lock and spin-lock; the performance improves a bit with a spin-lock, but is still unacceptably slow. Is there a better way to solve this problem which may improve performance? Right now I have a thread pool that services requests and each request is tied to a Request object which stores that cached results for that particular request. Here is a simplified pseudo code version of my current implementation: void ResultCallback( Result result, Request *request ) { lock totalResultsCached lock cachedLimit if( totalResultsCached + 1 > cachedLimit ) { unlock cachedLimit unlock totalResultsCached //cancel the request return; } ++totalResultsCached; unlock cachedLimit unlock totalResultsCached request.add(result) } void SendResults( int resultsToSend, Request *request ) { while ( resultsToSend > 0 ) { send(request.remove()) lock totalResultsCached --totalResultsCached unlock totalResultsCached --resultsToSend; } }

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• Storing C++ templated objects as same type

  - by JaredC

  I have a class that is a core component of a performance sensitive code path, so I am trying to optimize it as much as possible. The class used to be: class Widget { Widget(int n) : N(n) {} .... member functions that use the constant value N .... const int N; // just initialized, will never change } The arguments to the constructor are known at compile time, so I have changed this class to a template, so that N can be compiled into the functions: template<int N> class Widget { .... member functions that use N .... } I have another class with a method: Widget & GetWidget(int index); However, after templating Widget, each widget has a different type so I cannot define the function like this anymore. I considered different inheritance options, but I'm not sure that the performance gain from the template would outweigh the cost of inherited function invocations. SO, my question is this: I am pretty sure I want the best of both worlds (compile-time / run-time), and it may not be possible. But, is there a way to gain the performance of knowing N at compile time, but still being able to return Widgets as the same type? Thanks!

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• Windows web server and SQL Server on same dedicated server

  - by asinc

  I'm currently trying to decide on the best approach to handle hosting a few moderate traffic websites for production e-commerce and online applications. We'd like to move to a dedicated server and are looking at this as the most likely machine: Quad Core Intel Core2Quad Q9550 Processor, 2.83 Ghz X 4, 4 GB Kingston Ram This would run Windows Web Server 2008 R2 x64 and potentially also Sql Server Web 2008 and SmarterMail server. Given that we already pay for a high-end VPS for development, testing, shared version control we'd like to avoid going with two servers for production. We'd like to avoid using shared sql server hosting and have thought of using the development server as the database server as an option too - but potentially a security risk due to use for development by internal and contract users. The questions are: - Do you feel there would be performance degradation by running this on the same machine? - Are there significant issues to be concerned about if we do this? We understand that best practice would be to run separate db and app servers but the volume of traffic is currently not that high and adding another server just for database is currently too costly. - What are others doing out there? Alternatively, would you recommend instead going with two separate VPS servers with 2GB RAM each on Hyper-v which would be about the same cost as the single dedicated server above? Thanks!

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• How to compare old laptop to new laptop?

  - by Lasse V. Karlsen

  I hope this question doesn't get closed at once :) I have an old laptop, a Compaq NC4200, which is going its final laps around the track these days. Battery is dead, and everything kinda runs slow. It also has only 1GB of memory, and even though I don't know if it can take more, I probably wouldn't be able to get hold of any that matches without having to special order it. The size, however, has been ideal for my usage pattern, so I'm looking to replace it with a similarly sized laptop, at least in the same size category. However, it's been a while since I tried keeping track of CPUs, so I have a question. The old laptop has a Intel Pentium M 760 1.86GHz processor. One laptop I found online has a Intel Pentium SU4100 1.3GHz dual-core. This type of processor seems to be quite common in the price and size-range I've been looking. What kind of relative performance boost could I expect from the old one to the new one? I am not expecting a "about 7.45x speed", but some indication would be nice. For instance, dual-core tells me it might be akin to 2.6GHz, but I assume I can't simply compare 1.86GHz to 2.6GHz and expect the new one to run about 1.4x as fast, I expect more these days. Or is that unrealistic for this kind of processor? Do I need to up my price range and go for a 2+ GHz processor?

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• How to set shmall, shmmax, shmni, etc ... in general and for postgresql

  - by jpic

  I've used the documentation from PostgreSQL to set it for example this config: >>> cat /proc/meminfo MemTotal: 16345480 kB MemFree: 1770128 kB Buffers: 382184 kB Cached: 10432632 kB SwapCached: 0 kB Active: 9228324 kB Inactive: 4621264 kB Active(anon): 7019996 kB Inactive(anon): 548528 kB Active(file): 2208328 kB Inactive(file): 4072736 kB Unevictable: 0 kB Mlocked: 0 kB SwapTotal: 0 kB SwapFree: 0 kB Dirty: 3432 kB Writeback: 0 kB AnonPages: 3034588 kB Mapped: 4243720 kB Shmem: 4533752 kB Slab: 481728 kB SReclaimable: 440712 kB SUnreclaim: 41016 kB KernelStack: 1776 kB PageTables: 39208 kB NFS_Unstable: 0 kB Bounce: 0 kB WritebackTmp: 0 kB CommitLimit: 8172740 kB Committed_AS: 14935216 kB VmallocTotal: 34359738367 kB VmallocUsed: 399340 kB VmallocChunk: 34359334908 kB HardwareCorrupted: 0 kB AnonHugePages: 456704 kB HugePages_Total: 0 HugePages_Free: 0 HugePages_Rsvd: 0 HugePages_Surp: 0 Hugepagesize: 2048 kB DirectMap4k: 12288 kB DirectMap2M: 16680960 kB >>> ipcs -l ------ Shared Memory Limits -------- max number of segments = 4096 max seg size (kbytes) = 4316816 max total shared memory (kbytes) = 4316816 min seg size (bytes) = 1 ------ Semaphore Limits -------- max number of arrays = 128 max semaphores per array = 250 max semaphores system wide = 32000 max ops per semop call = 32 semaphore max value = 32767 ------ Messages Limits -------- max queues system wide = 31918 max size of message (bytes) = 8192 default max size of queue (bytes) = 16384 sysctl.conf extract: kernel.shmall = 1079204 kernel.shmmax = 4420419584 postgresql.conf non defaults: max_connections = 60 # (change requires restart) shared_buffers = 4GB # min 128kB work_mem = 4MB # min 64kB wal_sync_method = open_sync # the default is the first option checkpoint_segments = 16 # in logfile segments, min 1, 16MB each checkpoint_completion_target = 0.9 # checkpoint target duration, 0.0 - 1.0 effective_cache_size = 6GB Is this appropriate ? If not (or not necessarily), in which case would it be appropriate ? We did note nice performance improvements with this config, how would you improve it ? How should kernel memory management parameters be set ? Can anybody explain how to really set them from the ground up ?

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• big speed difference on a network link with and without VPN tunnel

  - by xirtyllo

  Scenario: We have a network link between two offices. The link is provided by a third party company through a VLAN on their network, but to us it is totally transparent -as if we had a simple ethernet cable going from one location to the other-. We have one router at each side of the link, with 3 VPN tunnels in between the two. The test: When I test the speed of the network link with the routers in place, with one laptop directly connected to the router on each side, I consistently get ~30/35Mbps. But if I take out the routers and I test the link connecting the laptops directly to the ethernet cable at each side, I consistently get ~85/88Mbps. It's quite a big performance hit, and I would tend to think that the VPN tunnels are responsible for the slow down. Is it normal that this configuration (two routers with three VPN tunnels between them) takes away so much bandwidth? More info: The encryption algorithm used for the VPN tunnels is AES128. The routers model is Zyxel USG200 and Zyxel USG1000, and their CPU, memory, and storage use is well within normal limits. The nominal bandwidth of the network link is 100Mbps. The network link in question is supplied by a third party company (the building in between our two offices). Basically it passes through their network as a VLAN, but the VLAN is completely transparent to us (e.g. no configuration required on our side, just like one single cable from end to end). Unfortunately (or maybe fortunately) I cannot directly test different routers configurations as I'm not the person in charge of it.

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• SQL Server slow in production environment

  - by Lieven Cardoen

  I have a weird problem in a customer's production environment. I can't give any details on the infrastructure, except that SQL server runs on a virtual server. The data, log and filestream file are on another storage server (data and filestream together and log on a separate server). In our local Test environment, there's one particular query that executes with these durations: first we clear the cache 300ms (First time it takes longer, but from then on it's cached.) 20ms 15ms 17ms In the customer's production environment, the SQL Server is more powerful, these are the durations (I didn't have the rights to clear the cache. Will try this tomorrow). 2500ms 2600ms 2400ms The servers in the customer's production environment are more powerful but they do have virtual servers (we don't). What could be the cause... Not enough memory? Fragmentation? Physical storage? How would you tackle this performance problem? EDIT: Some people have asked me if the data set is equal and it is. I restored their database on our environment. It's true that this was the first thing I looked at. (@Everyone: I added the edit because it will be the first thing that many will think off).

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• Win 7 running slowly with low CPU usage and memory

  - by guywhoneedsahand

  I have a relatively new (under 2 yrs old) windows 7 machine. It has 9GB of RAM, and an i7 core CPU (930 @ 2.8GHz w/ 8 CPUs). After about 8 months since a clean install, I noticed my computer was running slowly. I figure it was fragmentation etc, and I did a complete wipe & clean reinstall. However, my problems are somehow persisting. The computer is running painfully slowly (but in leaps and bounds - sometimes it will work fine for 3 hrs, then suddenly freeze up just from clicking the start button). The 'freezes' happen randomly - not during any especially intensive computing. I initially thought something might be eating through my CPU and/or Memory, but Task Manager indicates that neither the CPU or Memory spike. In fact, even during serious lag, CPU usage remains at less than 5% and Memory at ~ 1.5GB. It's beyond me why a fresh install on a powerful machine is performing so poorly... and it certainly is frustrating! What could be causing the poor performance, and what can I do to fix it?

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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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• What is optimal hardware configuration for heavy load LAMP application

  - by Piotr K.

  I need to run Linux-Apache-PHP-MySQL application (Moodle e-learning platform) for a large number of concurrent users - I am aiming 5000 users. By concurrent I mean that 5000 people should be able to work with the application at the same time. "Work" means not only do database reads but writes as well. The application is not very typical, since it is doing a lot of inserts/updates on the database, so caching techniques are not helping to much. We are using InnoDB storage engine. In addition application is not written with performance in mind. For instance one Apache thread usually occupies about 30-50 MB of RAM. I would be greatful for information what hardware is needed to build scalable configuration that is able to handle this kind of load. We are using right now two HP DLG 380 with two 4 core processors which are able to handle much lower load (typically 300-500 concurrent users). Is it reasonable to invest in this kind of boxes and build cluster using them or is it better to go with some more high-end hardware? I am particularly curious how many and how powerful servers are needed (number of processors/cores, size of RAM) what network equipment should be used (what kind of switches, network cards) any other hardware, like particular disc storage solutions, etc, that are needed Another thing is how to put together everything, that is what is the most optimal architecture. Clustering with MySQL is rather hard (people are complaining about MySQL Cluster, even here on Stackoverflow).

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• How to compare old CPU to new CPU?

  - by Lasse V. Karlsen

  I hope this question doesn't get closed at once :) I have an old laptop, a Compaq NC4200, which is going its final laps around the track these days. Battery is dead, and everything kinda runs slow. It also has only 1GB of memory, and even though I don't know if it can take more, I probably wouldn't be able to get hold of any that matches without having to special order it. The size, however, has been ideal for my usage pattern, so I'm looking to replace it with a similarly sized laptop, at least in the same size category. However, it's been a while since I tried keeping track of CPUs, so I have a question. The old laptop has a Intel Pentium M 760 1.86GHz processor. One laptop I found online has a Intel Pentium SU4100 1.3GHz dual-core. This type of processor seems to be quite common in the price and size-range I've been looking. What kind of relative performance boost could I expect from the old one to the new one? I am not expecting a "about 7.45x speed", but some indication would be nice. For instance, dual-core tells me it might be akin to 2.6GHz, but I assume I can't simply compare 1.86GHz to 2.6GHz and expect the new one to run about 1.4x as fast, I expect more these days. Or is that unrealistic for this kind of processor? Do I need to up my price range and go for a 2+ GHz processor?

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