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• Calling a standard library function in signal handler.

  - by shadyabhi

  Why is calling a standard library function inside a signal handler discouraged?

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• Data structure for pattern matching.

  - by alvonellos

  Let's say you have an input file with many entries like these: date, ticker, open, high, low, close, <and some other values> And you want to execute a pattern matching routine on the entries(rows) in that file, using a candlestick pattern, for example. (See, Doji) And that pattern can appear on any uniform time interval (let t = 1s, 5s, 10s, 1d, 7d, 2w, 2y, and so on...). Say a pattern matching routine can take an arbitrary number of rows to perform an analysis and contain an arbitrary number of subpatterns. In other words, some patterns may require 4 entries to operate on. Say also that the routine (may) later have to find and classify extrema (local and global maxima and minima as well as inflection points) for the ticker over a closed interval, for example, you could say that a cubic function (x^3) has the extrema on the interval [-1, 1]. (See link) What would be the most natural choice in terms of a data structure? What about an interface that conforms a Ticker object containing one row of data to a collection of Ticker so that an arbitrary pattern can be applied to the data. What's the first thing that comes to mind? I chose a doubly-linked circular linked list that has the following methods: push_front() push_back() pop_front() pop_back() [] //overloaded, can be used with negative parameters But that data structure seems very clumsy, since so much pushing and popping is going on, I have to make a deep copy of the data structure before running an analysis on it. So, I don't know if I made my question very clear -- but the main points are: What kind of data structures should be considered when analyzing sequential data points to conform to a pattern that does NOT require random access? What kind of data structures should be considered when classifying extrema of a set of data points?

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• need explanation on amortization in algorithm

  - by Pradeep

  I am a learning algorithm analysis and came across a analysis tool for understanding the running time of an algorithm with widely varying performance which is called as amortization. The autor quotes " An array with upper bound of n elements, with a fixed bound N, on it size. Operation clear takes O(n) time, since we should dereference all the elements in the array in order to really empty it. " The above statement is clear and valid. Now consider the next content: "Now consider a series of n operations on an initially empty array. if we take the worst case viewpoint, the running time is O(n^2), since the worst case of a sigle clear operation in the series is O(n) and there may be as many as O(n) clear operations in the series." From the above statement how is the time complexity O(n^2)? I did not understand the logic behind it. if 'n' operations are performed how is it O(n ^2)? Please explain what the autor is trying to convey..

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• Common request: export #Tabular model and data to #PowerPivot

  - by Marco Russo (SQLBI)

  I received this request in many courses, messages and also forum discussions: having an Analysis Services Tabular model, it would be nice being able to extract a correspondent PowerPivot data model. In order of priority, here are the specific feature people (including me) would like to see: Create an empty PowerPivot workbook with the same data model of a Tabular model Change the connections of the tables in the PowerPivot workbook extracting data from the Tabular data model Every table should have an EVALUATE ‘TableName’ query in DAX Apply a filter to data extracted from every table For example, you might want to extract all data for a single country or year or customer group Using the same technique of applying filter used for role based security would be nice Expose an API to automate the process of creating a PowerPivot workbook Use case: prepare one workbook for every employee containing only its data, that he can use offline Common request for salespeople who want a mini-BI tool to use in front of the customer/lead/supplier, regardless of a connection available This feature would increase the adoption of PowerPivot and Tabular (and, therefore, Business Intelligence licenses instead of Standard), and would probably raise the sales of Office 2013 / Office 365 driven by ISV, who are the companies who requests this feature more. If Microsoft would do this, it would be acceptable it only works on Office 2013. But if a third-party will do that, it will make sense (for their revenues) to cover both Excel 2010 and Excel 2013. Another important reason for this feature is that the “Offline cube” feature that you have in Excel is not available when your PivotTable is connected to a Tabular model, but it can only be used when you connect to Analysis Services Multidimensional. If you think this is an important features, you can vote this Connect item.

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• Parallelize incremental processing in Tabular #ssas #tabular

  - by Marco Russo (SQLBI)

  I recently came in a problem trying to improve the parallelism of Tabular processing. As you know, multiple tables can be processed in parallel, whereas the processing of several partitions within the same table cannot be parallelized. When you perform an incremental update by adding only new rows to existing table, what you really do is adding rows to a partition, so adding rows to many tables means adding rows to several partitions. The particular condition you have in this case is that every partition in which you add rows belongs to a different table. Adding rows implies using the ProcessAdd command; its QueryBinding parameter specifies a SQL syntax to read new rows, otherwise the original query specified for the partition will be used, and it could generate duplicated data if you don’t have a dynamic behavior on the SQL side. If you create the required XMLA code manually, you will find that the QueryBinding node that should be part of the ProcessAdd command has to be moved out from ProcessAdd in case you are using a Batch command with more than one Process command (which is the reason why you want to use a single batch: run multiple process operations in parallel!). If you use AMO (Analysis Management Objects) you will find that this combination is not supported, even if you don’t have a syntax error compiling the code, but you might obtain this error at execution time: The syntax for the 'Process' command is incorrect. The 'Bindings' keyword cannot appear under a 'Process' command if the 'Process' command is a part of a 'Batch' command and there are more than one 'Process' commands in the 'Batch' or the 'Batch' command contains any out of line related information. In this case, the 'Bindings' keyword should be a part of the 'Batch' command only. If this is happening to you, the best solution I’ve found is manipulating the XMLA code generated by AMO moving the Binding nodes in the right place. A more detailed description of the issue and the code required to send a correct XMLA batch to Analysis Services is available in my article Parallelize ProcessAdd with AMO. By the way, the same technique (and code) can be used also if you have the same problem in a Multidimensional model.

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• Prob comparing pointers and integer in C

  - by Dimitri

  Hi I have a problem with this code. When i am using this function I have no warnings. : void handler(int sig){ switch(sig) { case SIGINT : { click++; fprintf(stdout,"SIGINT recu\n"); if( click == N){ exit(0); } } case SIGALRM : fprintf(stdout,"SIGALRM received\n"); exit(0); case SIGTERM: fprintf(stdout,"SIGTERM received\n"); exit(0); } } But when i rewrite the function with this new version, I have a " comparison between pointer and integer" warning on the if statement: void handler( int sig){ printf("Signal recu\n"); if( signal == SIGINT){ click++; fprintf(stdout,"SIGINT received; Click = %d\n",click); if(click == N){ fprintf(stdout,"Exiting with SIGINT\n"); exit(0); } } else if(signal == SIGALRM){ fprintf(stdout,"SIGALRM received\n"); exit(0); } else if(signal == SIGTERM){ fprintf(stdout,"SIGTERM received\n"); exit(0); } Can someone tell me where is the prob?

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• handle SIGSEGV in Linux?

  - by user303967

  Hi all, I need handle the SIGSEGV in my Linux app. The reason is some clean up(3-partry lib) must be done before generate core-dump. What is more, the clean up must be performed in the context of calling thread, cannot do in signal handler. So I plan in signal handler to pass the control to the calling thread, after the clean up finished, then use raise(SIGSEGV) to generate the core-dump. The real problem seems the signal_handler cannot pass the control to calling thread, no matter I use post_sem or some others. Any idea to handle this case? Possbile to hijack the SIGSEGV, then in SIGSEGV hander return to another thread to perform some clean up? signal(SIGSEGV, signal_handler); signal_handler() { ... post_sem(); ... } calling thread() { wait_sem(); clean_up(); ... }

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• Measuring "real" phone signal strength on a mobile phone

  - by Serafeim

  I want to programmatically measure the phone signal strength in a mobile phone. I don't actually care about the mobile phone or the programming environment: It can be based on android or windows mobile or even J2ME and can be from any manufacturer (please no iPhone). However, it needs to be a real, commercial mobile phone and not a special measurement device. This problem is not as easy as it seems with a first look. I am aware that there already exist a number of methods that claim to return the phone signal strength. Some of these are: SystemState.PhoneSignalStrength for WM6 RIL_GetCellTowerInfo for WinCe (dwRxLevel member of returned RILCELLTOWERINFO struct) android.telephony.NeighboringCellInfo.getRssi() for android The problem with the above is that they only return a few (under 10) discrete values, meaning that, for instance, the return values of SystemState.PhoneSignalStrength can only be translated to (for instance) -100 dbm, -90 dbm, -80 dbm, -70 dbm and -60 dbm, something that is not useful for my application, since I'd like to have as much precision as possible. It doesn't matter if there is an undocumented solution that only works on only one phone, if you can tell me a way I'd be grateful. Thanks in advance

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• Binding a member signal to a function

  - by the_drow

  This line of code compiles correctly without a problem: boost::bind(boost::ref(connected_), boost::dynamic_pointer_cast<session<version> >(shared_from_this()), boost::asio::placeholders::error); However when assigning it to a boost::function or as a callback like this: socket_->async_connect(connection_->remote_endpoint(), boost::bind(boost::ref(connected_), boost::dynamic_pointer_cast<session<version> >(shared_from_this()), boost::asio::placeholders::error)); I'm getting a whole bunch of incomprehensible errors (linked since it's too long to fit here). On the other hand I have succeeded binding a free signal to a boost::function like this: void print(const boost::system::error_code& error) { cout << "session connected"; } int main() { boost::signal<void(const boost::system::error_code &)> connected_; connected_.connect(boost::bind(&print, boost::asio::placeholders::error)); client<>::connection_t::socket_ptr socket_(new client<>::connection_t::socket_t(conn->service())); // shared_ptr of a tcp socket socket_->async_connect(conn->remote_endpoint(), boost::bind(boost::ref(connected_), boost::asio::placeholders::error)); conn->service().run(); // io_service.run() return 0; } This works and prints session connected correctly. What am I doing wrong here?

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• Django's post_save signal behaves weirdly with models using multi-table inheritance

  - by hekevintran

  Django's post_save signal behaves weirdly with models using multi-table inheritance I am noticing an odd behavior in the way Django's post_save signal works when using a model that has multi-table inheritance. I have these two models: class Animal(models.Model): category = models.CharField(max_length=20) class Dog(Animal): color = models.CharField(max_length=10) I have a post save callback called echo_category: def echo_category(sender, **kwargs): print "category: '%s'" % kwargs['instance'].category post_save.connect(echo_category, sender=Dog) I have this fixture: [ { "pk": 1, "model": "animal.animal", "fields": { "category": "omnivore" } }, { "pk": 1, "model": "animal.dog", "fields": { "color": "brown" } } ] In every part of the program except for in the post_save callback the following is true: from animal.models import Dog Dog.objects.get(pk=1).category == u'omnivore' # True When I run syncdb and the fixture is installed, the echo_category function is run. The output from syncdb is: $ python manage.py syncdb --noinput Installing json fixture 'initial_data' from '~/my_proj/animal/fixtures'. category: '' Installed 2 object(s) from 1 fixture(s) The weird thing here is that the dog object's category attribute is an empty string. Why is it not 'omnivore' like it is everywhere else? As a temporary (hopefully) workaround I reload the object from the database in the post_save callback: def echo_category(sender, **kwargs): instance = kwargs['instance'] instance = sender.objects.get(pk=instance.pk) print "category: '%s'" % instance.category post_save.connect(echo_category, sender=Dog) This works but it is not something I like because I must remember to do it when the model inherits from another model and it must hit the database again. The other weird thing is that I must do instance.pk to get the primary key. The normal 'id' attribute does not work (I cannot use instance.id). I do not know why this is. Maybe this is related to the reason why the category attribute is not doing the right thing?

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• Statistical analysis on large data set to be published on the web

  - by dassouki

  I have a non-computer related data logger, that collects data from the field. This data is stored as text files, and I manually lump the files together and organize them. The current format is through a csv file per year per logger. Each file is around 4,000,000 lines x 7 loggers x 5 years = a lot of data. some of the data is organized as bins item_type, item_class, item_dimension_class, and other data is more unique, such as item_weight, item_color, date_collected, and so on ... Currently, I do statistical analysis on the data using a python/numpy/matplotlib program I wrote. It works fine, but the problem is, I'm the only one who can use it, since it and the data live on my computer. I'd like to publish the data on the web using a postgres db; however, I need to find or implement a statistical tool that'll take a large postgres table, and return statistical results within an adequate time frame. I'm not familiar with python for the web; however, I'm proficient with PHP on the web side, and python on the offline side. users should be allowed to create their own histograms, data analysis. For example, a user can search for all items that are blue shipped between week x and week y, while another user can search for sort the weight distribution of all items by hour for all year long. I was thinking of creating and indexing my own statistical tools, or automate the process somehow to emulate most queries. This seemed inefficient. I'm looking forward to hearing your ideas Thanks

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• Android Signal 11 (SIGSEGV)

  - by Naturjoghurt

  I read many posts here and on other sites, but can not find the problem creating my Error: I use an AsyncTask because I want to easily manipulate the UI Thread before and after Execution. In doInBackground I create a ThreadPoolExecutor and execute Runnables. If I only execute 1 Runnable with the Executor, there is no Problem, but if I execute another Runnable I get following Error: 06-26 18:00:42.288: A/libc(25073): Fatal signal 11 (SIGSEGV) at 0x7f486162 (code=1), thread 25106 (pool-1-thread-2) 06-26 18:00:42.304: D/dalvikvm(25073): GC_CONCURRENT freed 119K, 2% free 8908K/9056K, paused 4ms+4ms, total 45ms 06-26 18:00:42.327: I/System.out(25073): In Check All with Prefix: a and Length: 4 06-26 18:00:42.390: I/DEBUG(126): *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** 06-26 18:00:42.390: I/DEBUG(126): Build fingerprint: 'google/yakju/maguro:4.2.2/JDQ39/573038:user/release-keys' 06-26 18:00:42.390: I/DEBUG(126): Revision: '9' 06-26 18:00:42.390: I/DEBUG(126): pid: 25073, tid: 25106, name: pool-1-thread-2 >>> de.uni_duesseldorf.cn.distributed_computing2 <<< 06-26 18:00:42.390: I/DEBUG(126): signal 11 (SIGSEGV), code 1 (SEGV_MAPERR), fault addr 7f486162 ... 06-26 18:00:42.538: I/DEBUG(126): memory map around fault addr 7f486162: 06-26 18:00:42.538: I/DEBUG(126): 60292000-60391000 06-26 18:00:42.538: I/DEBUG(126): (no map for address) 06-26 18:00:42.538: I/DEBUG(126): bed14000-bed35000 [stack] I set up the ThreadPoolExecutor like this: // numberOfPackages: Number of Runnables to be executed public void initializeThreadPoolExecutor (int numberOfPackages) { int corePoolSize = Runtime.getRuntime().availableProcessors(); int maxPoolSize = numberOfPackages; long keepAliveTime = 60; final BlockingQueue workingQueue = new LinkedBlockingQueue(); executor = new ThreadPoolExecutor(corePoolSize, maxPoolSize, keepAliveTime, TimeUnit.SECONDS, workingQueue); } I have no clue, why it fails when starting the second Thread. Maybe Memory Leaks? Any Help appreciated. Thanks in Advance

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• pthread_join from a signal handler

  - by liv2hak

  I have a capture program which in addition do capturing data and writing it into a file also prints some statistics.The function that prints the statistics static void* report(void) { /*Print statistics*/ } is called roughly every second using an ALARM that expires every second.So The program is like void capture_program() { pthread_t report_thread while(!exit_now) { if(pthread_create(&report_thread,NULL,report,NULL)){ fprintf(stderr,"Error creating reporting thread! \n"); } /* Capturing code -------------- -------------- */ if(doreport) usleep(5); } } void *report(void *param) { while(true) { if(doreport) { doreport = 0 //access some register from hardware usleep(5) } } } The expiry of the timer sets the doreport flag.If this flag is set report() is called which clears the flag.I am using usleep to alternate between two threads in the program.This seems to work fine. I also have a signal handler to handle SIGINT (i.e CTRL+C) static void anysig(int sig) { if (sig != SIGINT) dagutil_set_signal_handler(SIG_DFL); /* Tell the main loop to exit */ exit_now = 1; return; } My question: 1) Is it safe to call pthread_join from inside the signal handler? 2) Should I use exit_now flag for the report thread as well?

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• Why my linux signal handler run only once

  - by Henry Fané

  #include <iostream> #include <signal.h> #include <fenv.h> #include <string.h> void signal_handler(int sig, siginfo_t *siginfo, void* context) { std::cout << " signal_handler " << fetestexcept(FE_ALL_EXCEPT) << std::endl; throw "exception"; } void divide() { float a = 1000., b = 0., c, f = 1e-300; c = a / b; std::cout << c << " and f = " << f << std::endl; } void init_sig_hanlder() { feenableexcept(FE_ALL_EXCEPT); struct sigaction sa, initial_sa; sa.sa_sigaction = &signal_handler ; sigemptyset( &sa.sa_mask ) ; sa.sa_flags = SA_SIGINFO; // man sigaction(3) // allows for void(*)(int,siginfo_t*,void*) handler sigaction(SIGFPE, &sa, &initial_sa); } int main(int argc, char** argv) { init_sig_hanlder(); while(true) { try { sleep(1); divide(); } catch(const char * a) { std::cout << "Exception in catch: " << a << std::endl; } catch(...) { std::cout << "Exception in ..." << std::endl; } } return 0; } Produce the following results on Linux/g++4.2: signal_handler 0 Exception in catch: exception inf and f = 0 inf and f = 0 inf and f = 0 inf and f = 0 So, signal handler is executed the first time but the next fp exception does not trigger the handler again. Where am I wrong ?

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• Willy Rotstein on Analytics and Social Media in Retail

  - by sarah.taylor(at)oracle.com

  Recently I came across a presentation from Dan Zarrella on "The Science of Retweets. (http://www.slideshare.net/HubSpot/the-science-of-retweets-with-dan-zarrella). It is an insightful, fact-based analysis of how tweets propagate and what makes them successful. The analysis is of course very interesting for those of us interested Tweeting. However, what really caught my attention is how well it illustrates, form a very different angle, some of the issues I am discussing with retailers these days. In particular the opportunities that e-commerce and social media open to those retailers with the appetite and vision to tackle the associated analytical challenges. And these challenges are of course not straightforward.   In his presentation Dan introduces the concept of Observability, I haven't had the opportunity to discuss with Dan his specific definition for the term. However, in practical retail terms, I would say that it means that through social media (and other web channels such as search) we can analyze and track processes by measuring Indicators that were not measurable before. The focus is in identifying patterns across a large number of consumers rather than what a particular individual "Likes".   The potential impact for retailers is huge. It opens the opportunity to monitor changes in consumer preference  and plan the business accordingly. And you can do this almost "real time" rather than through infrequent surveys that provide a "rear view" picture of your consumer behaviour. For instance, you could envision identifying when a particular set of fashion styles are breaking out from the pack, and commit a re-buy. Or you could monitor when the preference for a specific mobile device has declined and hence markdowns should be considered; or how demand for a specific ready-made food typically flows across regions and manage the inventory accordingly. Search, blogging, website and store data may need to be considered in identifying these trends. The data volumes involved are huge (check Andrea Morgan's recent post on "Big Data" in retail) but so are the benefits. As Andrea says, for the first time we can start getting insight into "Why" the business is performing in a certain way rather than just reporting on what is happening. And it is not just about the data volumes. Tackling the challenge also calls for integrated planning systems that can bring data and insight into the context of the Decision Making process Buyers, Merchandisers and Supply Chain managers are following. I strongly believe that only when data and process come together you can move from the anecdotal to systematically improving business performance.   I would love to hear your opinions on these trends and where you think Retail is heading to exploit these topics - please email me: [email protected]

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• #SSAS #Tabular Workshop and Community Events in Netherlands and Denmark

  - by Marco Russo (SQLBI)

  Next week I will finally start the roadshow of the SSAS Tabular Workshop, a 2-day seminar about the new BISM Tabular model for Analysis Services that has been introduced in SQL Server 2012. During these roadshows, we always try to arrange some speeches at local community events in the evening - we already defined for Copenhagen, we have some logistic issue in Amsterdam that we're trying to solve. Here is the timetable: Netherlands SSAS Workshop in Amsterdam, NL – April 16-17, 2012 2-day seminar, I and Alberto will be the trainers for this event, register here We're trying to manage a Community event but we still don't have a confirmation, stay tuned        Denmark SSAS Workshop in Copenhagen, DK – April 26-27, 2012 2-day seminar, I and Alberto will be the trainers for this event, register here Community event on April 26, 2012 This event will run in Hellerup, at Microsoft venue All details available here: http://msbip.dk/events/26/msbip-mode-nr-5/ People from Sweden are welcome! Just register to this private group on LinkedIn in order to announce your presence, so we’ll know how many people will attend In community events we’ll deliver two speeches – here are the descriptions: Inside xVelocity (VertiPaq) PowerPivot and BISM Tabular models in Analysis Services share a great columnar-based database engine called xVelocity in-memory analytics engine (VertiPaq). If you want to improve performance and optimize memory used, you have to understand some basic principles about how this engine works, how data is compressed, and how you can design a data model for better optimization. Prepare yourself to change your mind. xVelocity optimization techniques might seem counterintuitive and are absolutely different than OLAP and SQL ones! Choosing between Tabular and Multidimensional You have a new project and you have to make an important decision upfront. Should you use Tabular or Multidimensional? It is not easy to answer, because sometime there is a clear choice, but most of the times both decisions might be correct, at least at the beginning. In this session we’ll help you making an informed decision, correctly evaluating pros and cons of each one according to common scenarios, considering both short-term and long-term consequences of your choice. I hope to meet many people in this first dates. We have many other events coming in May and June, including an online event (for US time zones), and you can also attend our PreCon Day at TechEd US in Orland (PRC06) or TechEd Europe in Amsterdam. I’ll be a good customer for airline companies in the next three months! I’m just sorry that I hadn’t time to write other articles in the last month, but I’m accumulating material that I will need to write down during some flight – stay tuned…

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• RoboCopy Log File Analysis

  - by BobJim

  Is it possible to analyse the log text file outputted from RoboCopy and extract the lines which are defined as "New Dir" and "Extra Dir"? I would like the line from the log contain all the details returned regarding this "New Dir" or "Extra Dir" The reason for completing this task is to understand how two folder structures have change over time. One version has been kept internally at the parent company, the second has been used by a consultancy. For your information I am using Windows 7.

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• Excel techniques for perfmon csv log file analysis

  - by Aszurom

  I have perfmon running against several servers, where I'm outputting to a .csv file data like CPU %time, memory bytes free, hard disk I/O metrics like s/write and writes/s. The ones graphing the SQL servers are also collecting SQL stats. The web servers are collecting .Net relevant stuff. I am aware of PAL, and used it as a template of what data to capture based on server type actually. I just don't think the output it generates is detailed or flexible enough - but it does a pretty remarkable job of parsing logs and making graphs. I'm borderline incompetent with Excel, so I'm hoping to be directed to some knowledge of how to take a perfmon output .csv and mine it in Excel to produce some numbers that are meaningful to me as a sysadmin. I could of course just pick a range of data and assemble a graph out of that and look for spikes and trends, but I'm convinced there is some technique to this that makes it more manageable than looking at a monsterous spreadsheet of numbers and trying to make graphs of it. Plus, it's pretty time consuming and not something I can do as a "take a glance at the servers" sort of routine. I'm graphing CPU, disk use, network b/sec, etc. in Cacti as well, which is nice for seeing big trends. The problem is that it is 5 minute averages, so a server could have a problem but it's intermittent and washes out in a 5 min average. What do you do with perfmon data that I could learn from?

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• Linux installation analysis

  - by blunders

  "Ending company IT Admin relationship" has a good checklist for taking over an existing IT system, but I'm wondering as it relates to Linux: What is the most effective way to assess the scope of existing custom configurations, installs, scripts, etc done? Is there any software that will check if the kernel, system files, etc mirror the default files for the version installed? At this point I don't know what distro of Linux the server (though using Netcraft I do know the server appears to be Linux) -- so it's possible without knowing that information that this would be a hard question to answer.

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• Computer speakers receive radio station signal

  - by squircle

  I have a set of Logitech 5.1 speakers where each speaker and the source plug into the subwoofer. I'm using a Griffin Firewave with output from my MacBook Pro, and output from my custom-built desktop with a switch in the middle (built it myself out of an old Belkin A/B parallel switch). Recently, I've noticed that I can hear a local Punjabi radio station being picked up by my speakers, and the volume of this interference increases as I increase the volume of the speakers. I'm fairly sure that this radio station is at the low-end of the FM spectrum, below 90MHz (or it may be at the high end, above 105MHz, my memory isn't infallible). It gets quite annoying as I can't put my audio very loud without the interference. I've tried to put a ferrite core on the input cable just before the 3.5mm jacks plug into the subwoofer. I don't know if putting the same core around all three of the cables (green, black, orange) would negate the effects, but I'm assuming not. There has been no change. Is there any reason why this would be happening? I'm assuming the interference is coming somewhere between the FireWave and the subwoofer, because the noise gets amplified with volume increases. If anybody has any suggestions, I'd be grateful!

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• MySql Data Loss - post mortem analysis - RackSpace Cloud Server

  - by marfarma

  After a recent 'emergency migration' of a RS cloud server, the mysql databases on our server snapshot image proved to be days out of date from the backup date. And yet files that were uploaded through the impacted webapp had been written to the file system. Related metadata that was written to the database was lost, but the files themselves were backed-up. Once I was able to manually access the mysql data files before the mysql server started (server was configured to start mysql on boot), I was able to see that the update time for ib_logfile1, ib_logfile0 and ibdata1 was days old. As with this poster, mysql data loss after server crash, it's as if some caching controller had told the OS / mysql server that it had committed data that was still in cache, and it was lost instead of flushed. I can't quite wrap my head around how the uploaded files got written but the database data did not. I would have thought that any cache would have flushed system wide, rather than process by process. Any suggestions as to how this might have happened?

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• FAT filesystem analysis tool

  - by Andy

  I have a dump a FAT file system. Is there a windows tool I can use to analyse it, including: Provide basic information (sector size etc.) Validate the file system, basic corruption checking Allow the files and directory structure to be viewed and possibly edited (i.e mounting as a windows partition) Thanks, Andy

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• Windows File System Analysis

  - by bouvierr

  I am looking for a FREE tool to perform analyses on the NTFS file system of my Windows 7 PC. I want to easily see the amount of data distributed throught out the entire file system. The following applications seem very good, but they are not free and probably overkill for my requirements: FolderSizes 5 MailMeter Windows File System Reporting Tool I am aware that some applications (like Folder Size 2.5) can add a column in Windows Explorer to show the size of each folder, but I am looking for something more like a reporting tool. Thank you for your suggestions.

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• Server hang - data loss on reboot, post mortem analysis

  - by rovangju

  A development server I'm responsible for (ext3 on raid 5 w/Debian Squeeze) froze up over the weekend and I was forced to reset it, as in unresponsive from KVM/physical keyboard access, no eth devices responding, etc. Not even the backup process ran (Figures, the one time I don't check for confirmation) So after the reset, it turns out that every trace of disk IO activity that should have happened for a period of ~24H is completely gone. The log files have a big gap in the dates and times. As if the writes were never committed to disk, no processes seemed to have run. Luckily it was a weekend and nothing of value would have been lost and I don't suspect a hack. What can I do in post mortem to this event - to prevent it from ever happening again? I've seen this happen before on a completely different machine running FreeBSD. I am rounding up the disk checking tools right now - but there must be more going on! Mount options: /dev/sda1 on / type ext3 (rw,errors=remount-ro) Kernel: Linux dev 2.6.32-5-686-bigmem Disk/Inodes: 13%/3%

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• Forensic Analysis of the OOM-Killer

  - by Oddthinking

  Ubuntu's Out-Of-Memory Killer wreaked havoc on my server, quietly assassinating my applications, sendmail, apache and others. I've managed to learn what the OOM Killer is, and about its "badness" rules. While my machine is small, my applications are even smaller, and typically only half of my physical memory is in use, let alone swap-space, so I was surprised. I am trying to work out the culprit, but I don't know how to read the OOM-Killer logs. Can anyone please point me to a tutorial on how to read the data in the logs (what are ve, free and gen?), or help me parse these logs? Apr 20 20:03:27 EL135 kernel: kill_signal(13516.0): selecting to kill, queued 0, seq 1, exc 2326 0 goal 2326 0... Apr 20 20:03:27 EL135 kernel: kill_signal(13516.0): task ebb0c6f0, thg d33a1b00, sig 1 Apr 20 20:03:27 EL135 kernel: kill_signal(13516.0): selected 1, signalled 1, queued 1, seq 1, exc 2326 0 red 61795 745 Apr 20 20:03:27 EL135 kernel: kill_signal(13516.0): selecting to kill, queued 0, seq 2, exc 122 0 goal 383 0... Apr 20 20:03:27 EL135 kernel: kill_signal(13516.0): task ebb0c6f0, thg d33a1b00, sig 1 Apr 20 20:03:27 EL135 kernel: kill_signal(13516.0): selected 1, signalled 1, queued 1, seq 2, exc 383 0 red 61795 745 Apr 20 20:03:27 EL135 kernel: kill_signal(13516.0): task ebb0c6f0, thg d33a1b00, sig 2 Apr 20 20:03:27 EL135 kernel: OOM killed process watchdog (pid=14490, ve=13516) exited, free=43104 gen=24501. Apr 20 20:03:27 EL135 kernel: OOM killed process tail (pid=4457, ve=13516) exited, free=43104 gen=24502. Apr 20 20:03:27 EL135 kernel: OOM killed process ntpd (pid=10816, ve=13516) exited, free=43104 gen=24503. Apr 20 20:03:27 EL135 kernel: OOM killed process tail (pid=27401, ve=13516) exited, free=43104 gen=24504. Apr 20 20:03:27 EL135 kernel: OOM killed process tail (pid=29009, ve=13516) exited, free=43104 gen=24505. Apr 20 20:03:27 EL135 kernel: OOM killed process apache2 (pid=10557, ve=13516) exited, free=49552 gen=24506. Apr 20 20:03:27 EL135 kernel: OOM killed process apache2 (pid=24983, ve=13516) exited, free=53117 gen=24507. Apr 20 20:03:27 EL135 kernel: OOM killed process apache2 (pid=29129, ve=13516) exited, free=68493 gen=24508. Apr 20 20:03:27 EL135 kernel: OOM killed process sendmail-mta (pid=941, ve=13516) exited, free=68803 gen=24509. Apr 20 20:03:27 EL135 kernel: OOM killed process tail (pid=12418, ve=13516) exited, free=69330 gen=24510. Apr 20 20:03:27 EL135 kernel: OOM killed process python (pid=22953, ve=13516) exited, free=72275 gen=24511. Apr 20 20:03:27 EL135 kernel: OOM killed process apache2 (pid=6624, ve=13516) exited, free=76398 gen=24512. Apr 20 20:03:27 EL135 kernel: OOM killed process python (pid=23317, ve=13516) exited, free=94285 gen=24513. Apr 20 20:03:27 EL135 kernel: OOM killed process tail (pid=29030, ve=13516) exited, free=95339 gen=24514. Apr 20 20:03:28 EL135 kernel: OOM killed process apache2 (pid=20583, ve=13516) exited, free=101663 gen=24515. Apr 20 20:03:28 EL135 kernel: OOM killed process logger (pid=12894, ve=13516) exited, free=101694 gen=24516. Apr 20 20:03:28 EL135 kernel: OOM killed process bash (pid=21119, ve=13516) exited, free=101849 gen=24517. Apr 20 20:03:28 EL135 kernel: OOM killed process atd (pid=991, ve=13516) exited, free=101880 gen=24518. Apr 20 20:03:28 EL135 kernel: OOM killed process apache2 (pid=14649, ve=13516) exited, free=102748 gen=24519. Apr 20 20:03:28 EL135 kernel: OOM killed process grep (pid=21375, ve=13516) exited, free=132167 gen=24520. Apr 20 20:03:57 EL135 kernel: kill_signal(13516.0): selecting to kill, queued 0, seq 4, exc 4215 0 goal 4826 0... Apr 20 20:03:57 EL135 kernel: kill_signal(13516.0): task ede29370, thg df98b880, sig 1 Apr 20 20:03:57 EL135 kernel: kill_signal(13516.0): selected 1, signalled 1, queued 1, seq 4, exc 4826 0 red 189481 331 Apr 20 20:03:57 EL135 kernel: kill_signal(13516.0): task ede29370, thg df98b880, sig 2 Apr 20 20:04:53 EL135 kernel: kill_signal(13516.0): selecting to kill, queued 0, seq 5, exc 3564 0 goal 3564 0... Apr 20 20:04:53 EL135 kernel: kill_signal(13516.0): task c6c90110, thg cdb1a100, sig 1 Apr 20 20:04:53 EL135 kernel: kill_signal(13516.0): selected 1, signalled 1, queued 1, seq 5, exc 3564 0 red 189481 331 Apr 20 20:04:53 EL135 kernel: kill_signal(13516.0): task c6c90110, thg cdb1a100, sig 2 Apr 20 20:07:14 EL135 kernel: kill_signal(13516.0): selecting to kill, queued 0, seq 6, exc 8071 0 goal 8071 0... Apr 20 20:07:14 EL135 kernel: kill_signal(13516.0): task d7294050, thg c03f42c0, sig 1 Apr 20 20:07:14 EL135 kernel: kill_signal(13516.0): selected 1, signalled 1, queued 1, seq 6, exc 8071 0 red 189481 331 Apr 20 20:07:14 EL135 kernel: kill_signal(13516.0): task d7294050, thg c03f42c0, sig 2 Watchdog is a watchdog task, that was idle; nothing in the logs to suggest it had done anything for days. Its job is to restart one of the applications if it dies, so a bit ironic that it is the first to get killed. Tail was monitoring a few logs files. Unlikely to be consuming memory madly. The apache web-server only serves pages to a little old lady who only uses it to get to church on Sundays a couple of developers who were in bed asleep, and hadn't visited a page on the site for a few weeks. The only traffic it might have had is from the port-scanners; all the content is password-protected and not linked from anywhere, so no spiders are interested. Python is running two separate custom applications. Nothing in the logs to suggest they weren't humming along as normal. One of them was a relatively recent implementation, which makes suspect #1. It doesn't have any data-structures of any significance, and normally uses only about 8% of the total physical RAW. It hasn't misbehaved since. The grep is suspect #2, and the one I want to be guilty, because it was a once-off command. The command (which piped the output of a grep -r to another grep) had been started at least 30 minutes earlier, and the fact it was still running is suspicious. However, I wouldn't have thought grep would ever use a significant amount of memory. It took a while for the OOM killer to get to it, which suggests it wasn't going mad, but the OOM killer stopped once it was killed, suggesting it may have been a memory-hog that finally satisfied the OOM killer's blood-lust.

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