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• Freeing memory twice

  - by benjamin button

  Hi, AFAIK, freeing a NULL pointer will result in nothing. I mean nothing is being done by the compiler/no functionality is performed. Still, I do see some statements where people say that one of the scenarios where memory corruption can occur is "freeing memory twice"? Is this still true?

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• Simulate memory warnings from the code, possible?

  - by krasnyk

  I know i can simulate a memory warning on the simulator by selecting 'Simulate Memory Warning' from the drop down menu of the iPhone Simulator. I can even make a hot key for that. But this is not what I'd like to achieve. I'd like to do that from the code by simply, lets say doing it every 5 seconds. Is that possible?

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• Available memory for iPhone OS app

  - by hgpc

  Is there a function or constant defining the amount of available memory for an app in iPhone OS? I'm looking for a device-independent way (iPod touch, iPhone, iPad) to know how much memory the app has left.

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• No more memory available in Mathematica, Fit the parameters of system of differential equation

  - by user1058051

  I encountered a memory problem in Mathematica, when I tried to process my experimental data. It's a system of two differential equations and I need to find most suitable parameters. Unfortunately I am not a Pro in Mathematica, so the program used a lot of memory, when the parameter epsilon is more than 0.4. When it less than 0.4, the program work properly. The command 'historylength = 0' and attempts to reduce the Accuracy Goal and WorkingPrecision didn`t help. I can't use ' clear Cache ', because there isnt a circle. I'm trying to understand what mistakes I made, and how I may limit the memory usage. I have already bought extra-RAM, now its 4GB, and now I haven't free memory-slots in motherboard Remove["Global`*"]; T=13200; L = 0.085; e = 0.41; v = 0.000557197; q = 0.1618; C0 = 0.0256; R = 0.00075; data = {{L,600,0.141124587},{L,1200,0.254134509},{L,1800,0.342888644}, {L,2400,0.424476295},{L,3600,0.562844542},{L,4800,0.657111356}, {L,6000,0.75137817},{L,7200,0.815876516},{L,8430,0.879823594}, {L,9000,0.900771775},{L,13200,1}}; model[(De_)?NumberQ, (Kf_)?NumberQ, (Y_)?NumberQ] := model[De, Kf, Y] = yeld /.Last[Last[ NDSolve[{ v (Ci^(1,0))[z,t]+(Ci^(0,1))[z,t]== -((3 (1-e) Kf (Ci[z,t]-C0))/ (R e (1-(R Kf (1-R/r[z,t]))/De))), (r^(0,1))[z,t]== (R^2 Kf (Ci[z,t]-C0))/ (q r[z,t]^2 (1-(R Kf (1-R/r[z,t]))/De)), (yeld^(0,1))[z,t]== Y*(v e Ci[z,t])/(L q (1-e)), r[z,0]==R, Ci[z,0]==0, Ci[0,t]==0, yeld[z,0]==0}, {r[z,t],Ci[z,t],yeld},{z,0,L},{t,0,T}]]] fit = FindFit[data, {model[De, Kf, Y][z, t], {Y > 0.97, Y < 1.03, Kf > 10^-6, Kf < 10^-4, De > 10^-13, De < 10^-9}}, {{De,7*10^-13}, {Kf, 10^-5}, {Y, 1}}, {z, t}, Method -> NMinimize] data = {{600,0.141124587},{1200,0.254134509},{1800,0.342888644}, {2400,0.424476295},{3600,0.562844542},{4800,0.657111356}, {6000,0.75137817},{7200,0.815876516},{8430,0.879823594}, {9000,0.900771775},{13200,1}}; YYY = model[ De /. fit[[1]], Kf /. fit[[2]], Y /. fit[[3]]]; Show[Plot[Evaluate[YYY[L,t]],{t,0,T},PlotRange->All], ListPlot[data,PlotStyle->Directive[PointSize[Medium],Red]]] the link on the .nb file http://www.4shared.com/folder/249TSjlz/_online.html

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• querying for memory details in shell

  - by assassin

  Hi, Is there a shell command to know about how much memory is being used at a particular moment and details of how much each process is using, how much virtual memory is left etc?

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• How to guard against memory leaks?

  - by just_wes

  I was recently interviewing for a C++ position, and I was asked how I guard against creating memory leaks. I know I didn't give a satisfactory answer to that question, so I'm throwing it to you guys. What are the best ways to guard against memory leaks? Thanks!

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• Memory not being freed, causing giant memory leak

  - by Delan Azabani

  In my Unicode library for C++, the ustring class has operator= functions set for char* values and other ustring values. When doing the simple memory leak test: #include <cstdio> #include "ucpp" main() { ustring a; for(;;)a="MEMORY"; } the memory used by the program grows uncontrollably (characteristic of a program with a big memory leak) even though I've added free() calls to both of the functions. I am unsure why this is ineffective (am I missing free() calls in other places?) This is the current library code: #include <cstdlib> #include <cstring> class ustring { int * values; long len; public: long length() { return len; } ustring() { len = 0; values = (int *) malloc(0); } ustring(const ustring &input) { len = input.len; values = (int *) malloc(sizeof(int) * len); for (long i = 0; i < len; i++) values[i] = input.values[i]; } ustring operator=(ustring input) { ustring result(input); free(values); len = input.len; values = input.values; return * this; } ustring(const char * input) { values = (int *) malloc(0); long s = 0; // s = number of parsed chars int a, b, c, d, contNeed = 0, cont = 0; for (long i = 0; input[i]; i++) if (input[i] < 0x80) { // ASCII, direct copy (00-7f) values = (int *) realloc(values, sizeof(int) * ++s); values[s - 1] = input[i]; } else if (input[i] < 0xc0) { // this is a continuation (80-bf) if (cont == contNeed) { // no need for continuation, use U+fffd values = (int *) realloc(values, sizeof(int) * ++s); values[s - 1] = 0xfffd; } cont = cont + 1; values[s - 1] = values[s - 1] | ((input[i] & 0x3f) << ((contNeed - cont) * 6)); if (cont == contNeed) cont = contNeed = 0; } else if (input[i] < 0xc2) { // invalid byte, use U+fffd (c0-c1) values = (int *) realloc(values, sizeof(int) * ++s); values[s - 1] = 0xfffd; } else if (input[i] < 0xe0) { // start of 2-byte sequence (c2-df) contNeed = 1; values = (int *) realloc(values, sizeof(int) * ++s); values[s - 1] = (input[i] & 0x1f) << 6; } else if (input[i] < 0xf0) { // start of 3-byte sequence (e0-ef) contNeed = 2; values = (int *) realloc(values, sizeof(int) * ++s); values[s - 1] = (input[i] & 0x0f) << 12; } else if (input[i] < 0xf5) { // start of 4-byte sequence (f0-f4) contNeed = 3; values = (int *) realloc(values, sizeof(int) * ++s); values[s - 1] = (input[i] & 0x07) << 18; } else { // restricted or invalid (f5-ff) values = (int *) realloc(values, sizeof(int) * ++s); values[s - 1] = 0xfffd; } len = s; } ustring operator=(const char * input) { ustring result(input); free(values); len = result.len; values = result.values; return * this; } ustring operator+(ustring input) { ustring result; result.len = len + input.len; result.values = (int *) malloc(sizeof(int) * result.len); for (long i = 0; i < len; i++) result.values[i] = values[i]; for (long i = 0; i < input.len; i++) result.values[i + len] = input.values[i]; return result; } ustring operator[](long index) { ustring result; result.len = 1; result.values = (int *) malloc(sizeof(int)); result.values[0] = values[index]; return result; } operator char * () { return this -> encode(); } char * encode() { char * r = (char *) malloc(0); long s = 0; for (long i = 0; i < len; i++) { if (values[i] < 0x80) r = (char *) realloc(r, s + 1), r[s + 0] = char(values[i]), s += 1; else if (values[i] < 0x800) r = (char *) realloc(r, s + 2), r[s + 0] = char(values[i] >> 6 | 0x60), r[s + 1] = char(values[i] & 0x3f | 0x80), s += 2; else if (values[i] < 0x10000) r = (char *) realloc(r, s + 3), r[s + 0] = char(values[i] >> 12 | 0xe0), r[s + 1] = char(values[i] >> 6 & 0x3f | 0x80), r[s + 2] = char(values[i] & 0x3f | 0x80), s += 3; else r = (char *) realloc(r, s + 4), r[s + 0] = char(values[i] >> 18 | 0xf0), r[s + 1] = char(values[i] >> 12 & 0x3f | 0x80), r[s + 2] = char(values[i] >> 6 & 0x3f | 0x80), r[s + 3] = char(values[i] & 0x3f | 0x80), s += 4; } return r; } };

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• How to prevent latex memory overflow

  - by drasto

  I've got a latex macro that makes small pictures. In that picture I need to draw area. Borders of that area are quadratic bezier curves and that area is to be filled. I did not know how to do it so currently I'm "filling" the area by drawing a plenty of bezier curves inside it... This slows down typeseting and when a macro is used multiple times (so tex is drawing really a lot of quadratic bezier curves) it produces following error: ! TeX capacity exceeded, sorry [main memory size=3000000]. How can I prevent this error ? (by freeing memory after macro or such...) Or even better how do I fill the area determined by two quadratic bezier curves? Code that produces error: \usepackage{forloop} \usepackage{picture} \usepackage{eepic} ... \linethickness{\lineThickness\unitlength}% \forloop[\lineThickness]{cy}{\cymin}{\value{cy} < \cymax}{% \qbezier(\ax, \ay)(\cx, \value{cy})(\bx, \by)% }% Here are some example values for variables: \setlength{\unitlength}{0.01pt} \lineThickness=20 %cy is just a counter - inital value is not important \cymin=450 \cymax=900 %from following only the difference between \ax and \bx is important \ax=0 \ay=0 \bx=550 \by=0 Note: To reproduce the error this code have to execute approximately 150 times (could be more depending on your latex memory settings). Thanks a lot for any help

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• C++ Memory Leak, Can't find where

  - by Nicholas

  I'm using Visual Studio 2008, Developing an OpenGL window. I've created several classes for creating a skeleton, one for joints, one for skin, one for a Body(which is a holder for several joints and skin) and one for reading a skel/skin file. Within each of my classes, I'm using pointers for most of my data, most of which are declared using = new int[XX]. I have a destructor for each Class that deletes the pointers, using delete[XX]. Within my GLUT display function I have it declaring a body, opening the files and drawing them, then deleting the body at the end of the display. But there's still a memory leak somewhere in the program. As Time goes on, it's memory usage just keep increasing, at a consistent rate, which I'm interpreting as something that's not getting deleted. I'm not sure if it's something in the glut display function that's just not deleting the Body class, or something else. I've followed the steps for memory leak detection in Visual Studio 2008 and it doesn't report any leak, but I'm not 100% sure if it's working right for me. I'm not fluent in C++, so there maybe something I'm overlooking, can anyone see it?

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• Can this code cause a memory leak (Arduino)

  - by tbraun89

  I have a arduino project and I created this struct: struct Project { boolean status; String name; struct Project* nextProject; }; In my application I parse some data and create Project objects. To have them in a list there is a pointer to the nextProject in each Project object expect the last. This is the code where I add new projects: void RssParser::addProject(boolean tempProjectStatus, String tempData) { if (!startProject) { startProject = true; firstProject.status = tempProjectStatus; firstProject.name = tempData; firstProject.nextProject = NULL; ptrToLastProject = &firstProject; } else { ptrToLastProject->nextProject = new Project(); ptrToLastProject->nextProject->status = tempProjectStatus; ptrToLastProject->nextProject->name = tempData; ptrToLastProject->nextProject->nextProject = NULL; ptrToLastProject = ptrToLastProject->nextProject; } } firstProject is an private instance variable and defined in the header file like this: Project firstProject; So if there actually no project was added, I use firstProject, to add a new one, if firstProject is set I use the nextProject pointer. Also I have a reset() method that deletes the pointer to the projects: void RssParser::reset() { delete ptrToLastProject; delete firstProject.nextProject; startProject = false; } After each parsing run I call reset() the problem is that the memory used is not released. If I comment out the addProject method there are no issues with my memory. Someone can tell me what could cause the memory leak?

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• Android - Memory leak when dynamically building UI with image resource backgrounds

  - by Rich

  I have an Activity that I swear is leaking memory. The app I'm working on does a lot with images, so I've had to be pretty stingy with memory when working directly with Bitmaps. I added an Activity, and now if you use this new Activity it basically puts me over the edge with mem usage and I end up throwing the "Bitmap exceeds VM budget" exception. If you never launch this Activity, everything is smooth as it was previously. I started reading about memory leaks, and I think that I have a similar situation to what is described in the article in the Android docs. I'm dynamically creating a bunch of image views and adding a BackgroundDrawable from the resources and adding an OnClickListener as well. I imagine I have to do some cleanup when the Activity hits onPause in its life cycle, but I'd like to know specifically what is the correct way. Here is the code that should demonstrate the objects I'm working with... LinearLayout templateContainer; . . . ImageView imgTemplatePreview = (ImageView) item.findViewById(R.id.imgTemplatePreview); . . . imgTemplatePreview.setBackgroundDrawable(getResources().getDrawable(previewId)); imgTemplatePreview.setOnClickListener(imgClick); templateContainer.addView(item);

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• SQL SERVER – Plan Cache and Data Cache in Memory

  - by pinaldave

  I get following question almost all the time when I go for consultations or training. I often end up providing the scripts to my clients and attendees. Instead of writing new blog post, today in this single blog post, I am going to cover both the script and going to link to original blog posts where I have mentioned about this blog post. Plan Cache in Memory USE AdventureWorks GO SELECT [text], cp.size_in_bytes, plan_handle FROM sys.dm_exec_cached_plans AS cp CROSS APPLY sys.dm_exec_sql_text(plan_handle) WHERE cp.cacheobjtype = N'Compiled Plan' ORDER BY cp.size_in_bytes DESC GO Further explanation of this script is over here: SQL SERVER – Plan Cache – Retrieve and Remove – A Simple Script Data Cache in Memory USE AdventureWorks GO SELECT COUNT(*) AS cached_pages_count, name AS BaseTableName, IndexName, IndexTypeDesc FROM sys.dm_os_buffer_descriptors AS bd INNER JOIN ( SELECT s_obj.name, s_obj.index_id, s_obj.allocation_unit_id, s_obj.OBJECT_ID, i.name IndexName, i.type_desc IndexTypeDesc FROM ( SELECT OBJECT_NAME(OBJECT_ID) AS name, index_id ,allocation_unit_id, OBJECT_ID FROM sys.allocation_units AS au INNER JOIN sys.partitions AS p ON au.container_id = p.hobt_id AND (au.TYPE = 1 OR au.TYPE = 3) UNION ALL SELECT OBJECT_NAME(OBJECT_ID) AS name, index_id, allocation_unit_id, OBJECT_ID FROM sys.allocation_units AS au INNER JOIN sys.partitions AS p ON au.container_id = p.partition_id AND au.TYPE = 2 ) AS s_obj LEFT JOIN sys.indexes i ON i.index_id = s_obj.index_id AND i.OBJECT_ID = s_obj.OBJECT_ID ) AS obj ON bd.allocation_unit_id = obj.allocation_unit_id WHERE database_id = DB_ID() GROUP BY name, index_id, IndexName, IndexTypeDesc ORDER BY cached_pages_count DESC; GO Further explanation of this script is over here: SQL SERVER – Get Query Plan Along with Query Text and Execution Count Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, SQL, SQL Authority, SQL Optimization, SQL Performance, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, T SQL Tagged: SQL Memory

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• Why isn't DSM for unstructured memory done today?

  - by sinned

  Ages ago, Djikstra invented IPC through mutexes which then somehow led to shared memory (SHM) in multics (which afaik had the necessary mmap first). Then computer networks came up and DSM (distributed SHM) was invented for IPC between computers. So DSM is basically a not prestructured memory region (like a SHM) that magically get's synchronized between computers without the applications programmer taking action. Implementations include Treadmarks (inofficially dead now) and CRL. But then someone thought this is not the right way to do it and invented Linda & tuplespaces. Current implementations include JavaSpaces and GigaSpaces. Here, you have to structure your data into tuples. Other ways to achieve similar effects may be the use of a relational database or a key-value-store like RIAK. Although someone might argue, I don't consider them as DSM since there is no coherent memory region where you can put data structures in as you like but have to structure your data which can be hard if it is continuous and administration like locking can not be done for hard coded parts (=tuples, ...). Why is there no DSM implementation today or am I just unable to find one?

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• How much of slow and fast flash memory a "flash memory" have?

  - by gsc-frank

  Trying to know what is the best of my flash memories to use ReadyBoost I realize that I don't know how much of fast flash memory each of my flash drives have. One can read: In some situations, you might not be able to use all of the memory on your device to speed up your computer. For example, some flash memory devices contain both slow and fast flash memory, but ReadyBoost can only use fast flash memory to speed up your computer. From http://windows.microsoft.com/is-IS/windows7/Using-memory-in-your-storage-device-to-speed-up-your-computer

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• How much of slow and fast flash memory a "flash memory" have? [migrated]

  - by gsc-frank

  Trying to know what is the best of my flash memories to use ReadyBoost I realize that I don't know how much of fast flash memory each of my flash drives have. One can read: In some situations, you might not be able to use all of the memory on your device to speed up your computer. For example, some flash memory devices contain both slow and fast flash memory, but ReadyBoost can only use fast flash memory to speed up your computer. From http://windows.microsoft.com/is-IS/windows7/Using-memory-in-your-storage-device-to-speed-up-your-computer

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• Windows 7 memory usage

  - by lydonchandra

  Physical memory(MB) for Windows 7 Total 4021 Cached 1113 Available 768 Free 174 Memory used 3.25GB At this point, windows7 asks me to close some programs because "system memory is low". From my understanding reading articles, I still have 768 MB free memory, why does windows7 complain? Also what does Cached memory refer to? Is this part of memory that Windows7 reserved for itself meaning it's free to use by Windows7 (and means I have about 768 + 1113 MB of free mem?)?

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• sysbench memory test on ec2 small instance

  - by caribio

  I'm seeing a problem with sysbench memory test (the default version that's compiled in). This is on Ubuntu Maverick, sysbench installed via apt-get install sysbench. Running the same thing on Ubuntu @ Rackspace worked just as expected. While the CPU and I/O tests worked fine on EC2 servers, the memory test just runs without doing anything (notice the 0M in the test results). The instance used was the publicly available 'stock' Ubuntu image with no changes to it: ./ec2-run-instances ami-ccf405a5 --instance-type m1.small --region us-east-1 --key mykey Supplying more arguments (such as: --memory-block-size=1K --memory-total-size=102400M) didn't help. What am I doing wrong? Thanks. sysbench --num-threads=4 --test=memory run sysbench 0.4.12: multi-threaded system evaluation benchmark Running the test with following options: Number of threads: 4 Doing memory operations speed test Memory block size: 1K Memory transfer size: 0M Memory operations type: write Memory scope type: global Threads started! Done. Operations performed: 0 ( 0.00 ops/sec) 0.00 MB transferred (0.00 MB/sec) Test execution summary: total time: 0.0003s total number of events: 0 total time taken by event execution: 0.0000 per-request statistics: min: 18446744073709.55ms avg: 0.00ms max: 0.00ms Threads fairness: events (avg/stddev): 0.0000/0.00 execution time (avg/stddev): 0.0000/0.00

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• Linux released memory

  - by user59088

  If My process allocates some big memory and then deallocates, would top or gnome-system-monitor show that my memory usage of that process decreased ? or kernel will still reserve that memory for that process ? What I see is I am deallocating memory. But I still see gnome-system-monitor displaying growing memory for my program. I don't find memory leak in my end. I want to know whether its not displaying released memory ? or there is really a memory leak at my end ?

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• What are the advantages of registered memory?

  - by odd parity

  I'm browsing for a few low-end servers for a startup and I'm a bit confused about the different memory types. The advantage of ECC is clear - single-bit error correction. When it comes to registered memory it seems more vague, especially in systems that support both registered and unbuffered memory. A Google search mostly finds copies of the Wikipedia article, which states that registered memory chips "...place less electrical load on the memory controller and allow single systems to remain stable with more memory modules than they would have otherwise". However I can't find any quantification of this. What I'm wondering about is: Is registered memory an improvement over unbuffered when it comes to soft error rate, or is it purely about the maximum number of modules supported? If yes, at what point (amount of modules or GB of memory) do these improvements start to become noticeable? For a specific example, the HP ProLiant DL 120 G6 server manual states that maximum supported memory configuration is 16 GB unbuffered (4x4GB) or 12 GB registered (6x2GB). In this case I'd rather have the extra 4GB of memory if the reliability difference is negligible.

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• Calculating memory footprints using /proc/sysvipc/shm

  - by MarkTeehan

  This is for a SLES 10 database server. One of my servers runs three databases and three app servers; I am analyzing how their shared memory segments grow and shrink to avoid intermittent out-of-memory scenarios. "Top" is hot helpful for this since its calculations for RES and VIRT are inconsistent. I am doing this by matching up the contents of /proc/sysvipc/shm with memory usage reported by the database admin console. I do this by totaling up saving the contents of /proc/sysvipc/shm and then total up "bytes" for all of the segments for the offending userid. This is a large server with hundreds of segments and tens (or hundreds) of GB of allocated memory per userid. However it doesn't match up - the database management software claims to be using around 25% more memory than the total I calculate. Negligible swap space is in use, so I am ignoring that. I am running it as root so I am sure I see all shared memory segments. My question is : is all (significant) allocated memory recorded in /proc/sysvipc/shm, or is this only shared memory (*and not "un-shared" memory?). If this is incorrect, what is the correct way to calculate out the total allocated memory for each userid? Also: I believe doing a 'cat' on this file locks server IPC. I check it every 5 seconds - is it likely that this frequency could be problematic? Thanks! Mark Teehan Singapore

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• Memory Usage in LINUX

  - by Incredible

  I have a debian system. It has 8GB memory. When I do top it shows 7.9 GB memory used and rest free. I add up the memory usage of all the programs running from top and they hardly sum up to around 50 MB. So, where is rest of the memory being used? Can I have a better detailed info of the memory usage? What is a better way to check the memory usage?

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• SQL SERVER – Weekly Series – Memory Lane – #052

  - by Pinal Dave

  Let us continue with the final episode of the Memory Lane Series. Here is the list of selected articles of SQLAuthority.com across all these years. Instead of just listing all the articles I have selected a few of my most favorite articles and have listed them here with additional notes below it. Let me know which one of the following is your favorite article from memory lane. 2007 Set Server Level FILLFACTOR Using T-SQL Script Specifies a percentage that indicates how full the Database Engine should make the leaf level of each index page during index creation or alteration. fillfactor must be an integer value from 1 to 100. The default is 0. Limitation of Online Index Rebuld Operation Online operation means when online operations are happening in the database are in normal operational condition, the processes which are participating in online operations does not require exclusive access to the database. Get Permissions of My Username / Userlogin on Server / Database A few days ago, I was invited to one of the largest database company. I was asked to review database schema and propose changes to it. There was special username or user logic was created for me, so I can review their database. I was very much interested to know what kind of permissions I was assigned per server level and database level. I did not feel like asking Sr. DBA the question about permissions. Simple Example of WHILE Loop With CONTINUE and BREAK Keywords This question is one of those questions which is very simple and most of the users get it correct, however few users find it confusing for the first time. I have tried to explain the usage of simple WHILE loop in the first example. BREAK keyword will exit the stop the while loop and control is moved to the next statement after the while loop. CONTINUE keyword skips all the statement after its execution and control is sent to the first statement of while loop. Forced Parameterization and Simple Parameterization – T-SQL and SSMS When the PARAMETERIZATION option is set to FORCED, any literal value that appears in a SELECT, INSERT, UPDATE or DELETE statement is converted to a parameter during query compilation. When the PARAMETERIZATION database option is SET to SIMPLE, the SQL Server query optimizer may choose to parameterize the queries. 2008 Transaction and Local Variables – Swap Variables – Update All At Once Concept Summary : Transaction have no effect over memory variables. When UPDATE statement is applied over any table (physical or memory) all the updates are applied at one time together when the statement is committed. First of all I suggest that you read the article listed above about the effect of transaction on local variant. As seen there local variables are independent of any transaction effect. Simulate INNER JOIN using LEFT JOIN statement – Performance Analysis Just a day ago, while I was working with JOINs I find one interesting observation, which has prompted me to create following example. Before we continue further let me make very clear that INNER JOIN should be used where it cannot be used and simulating INNER JOIN using any other JOINs will degrade the performance. If there are scopes to convert any OUTER JOIN to INNER JOIN it should be done with priority. 2009 Introduction to Business Intelligence – Important Terms & Definitions Business intelligence (BI) is a broad category of application programs and technologies for gathering, storing, analyzing, and providing access to data from various data sources, thus providing enterprise users with reliable and timely information and analysis for improved decision making. Difference Between Candidate Keys and Primary Key Candidate Key – A Candidate Key can be any column or a combination of columns that can qualify as unique key in database. There can be multiple Candidate Keys in one table. Each Candidate Key can qualify as Primary Key. Primary Key – A Primary Key is a column or a combination of columns that uniquely identify a record. Only one Candidate Key can be Primary Key. 2010 Taking Multiple Backup of Database in Single Command – Mirrored Database Backup I recently had a very interesting experience. In one of my recent consultancy works, I was told by our client that they are going to take the backup of the database and will also a copy of it at the same time. I expressed that it was surely possible if they were going to use a mirror command. In addition, they told me that whenever they take two copies of the database, the size of the database, is always reduced. Now this was something not clear to me, I said it was not possible and so I asked them to show me the script. Corrupted Backup File and Unsuccessful Restore The CTO, who was also present at the location, got very upset with this situation. He then asked when the last successful restore test was done. As expected, the answer was NEVER.There were no successful restore tests done before. During that time, I was present and I could clearly see the stress, confusion, carelessness and anger around me. I did not appreciate the feeling and I was pretty sure that no one in there wanted the atmosphere like me. 2011 TRACEWRITE – Wait Type – Wait Related to Buffer and Resolution SQL Trace is a SQL Server database engine technology which monitors specific events generated when various actions occur in the database engine. When any event is fired it goes through various stages as well various routes. One of the routes is Trace I/O Provider, which sends data to its final destination either as a file or rowset. DATEDIFF – Accuracy of Various Dateparts If you want to have accuracy in seconds, you need to use a different approach. In the first example, the accurate method is to find the number of seconds first and then divide it by 60 to convert it in minutes. Dedicated Access Control for SQL Server Express Edition http://www.youtube.com/watch?v=1k00z82u4OI Book Signing at SQLPASS 2012 Who I Am And How I Got Here – True Story as Blog Post If there was a shortcut to success – I want to know. I learnt SQL Server hard way and I am still learning. There are so many things, I have to learn. There is not enough time to learn everything which we want to learn. I am constantly working on it every day. I welcome you to join my journey as well. Please join me in my journey to learn SQL Server – more the merrier. Vacation, Travel and Study – A New Concept Even those who have advanced degrees and went to college for years, or even decades, find studying hard.  There is a difference between studying for a career and studying for a certification.  At least to get a degree there is a variety of subjects, with labs, exams, and practice problems to make things more interesting. Order By Numeric Values Formatted as String We have a table which has a column containing alphanumeric data. The data always has first as an integer and later part as a string. The business need is to order the data based on the first part of the alphanumeric data which is an integer. Now the problem is that no matter how we use ORDER BY the result is not produced as expected. Let us understand this with an example. Resolving SQL Server Connection Errors – SQL in Sixty Seconds #030 – Video One of the most famous errors related to SQL Server is about connecting to SQL Server itself. Here is how it goes, most of the time developers have worked with SQL Server and knows pretty much every error which they face during development language. However, hardly they install fresh SQL Server. As the installation of the SQL Server is a rare occasion unless you are a DBA who is responsible for such an instance – the error faced during installations are pretty rare as well. http://www.youtube.com/watch?v=1k00z82u4OI Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: Memory Lane, PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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• SQL SERVER – Weekly Series – Memory Lane – #034

  - by Pinal Dave

  Here is the list of selected articles of SQLAuthority.com across all these years. Instead of just listing all the articles I have selected a few of my most favorite articles and have listed them here with additional notes below it. Let me know which one of the following is your favorite article from memory lane. 2007 UDF – User Defined Function to Strip HTML – Parse HTML – No Regular Expression The UDF used in the blog does fantastic task – it scans entire HTML text and removes all the HTML tags. It keeps only valid text data without HTML task. This is one of the quite commonly requested tasks many developers have to face everyday. De-fragmentation of Database at Operating System to Improve Performance Operating system skips MDF file while defragging the entire filesystem of the operating system. It is absolutely fine and there is no impact of the same on performance. Read the entire blog post for my conversation with our network engineers. Delay Function – WAITFOR clause – Delay Execution of Commands How do you delay execution of the commands in SQL Server – ofcourse by using WAITFOR keyword. In this blog post, I explain the same with the help of T-SQL script. Find Length of Text Field To measure the length of TEXT fields the function is DATALENGTH(textfield). Len will not work for text field. As of SQL Server 2005, developers should migrate all the text fields to VARCHAR(MAX) as that is the way forward. Retrieve Current Date Time in SQL Server CURRENT_TIMESTAMP, GETDATE(), {fn NOW()} There are three ways to retrieve the current datetime in SQL SERVER. CURRENT_TIMESTAMP, GETDATE(), {fn NOW()} Explanation and Comparison of NULLIF and ISNULL An interesting observation is NULLIF returns null if it comparison is successful, whereas ISNULL returns not null if its comparison is successful. In one way they are opposite to each other. Here is my question to you - How to create infinite loop using NULLIF and ISNULL? If this is even possible? 2008 Introduction to SERVERPROPERTY and example SERVERPROPERTY is a very interesting system function. It returns many of the system values. I use it very frequently to get different server values like Server Collation, Server Name etc. SQL Server Start Time We can use DMV to find out what is the start time of SQL Server in 2008 and later version. In this blog you can see how you can do the same. Find Current Identity of Table Many times we need to know what is the current identity of the column. I have found one of my developers using aggregated function MAX () to find the current identity. However, I prefer following DBCC command to figure out current identity. Create Check Constraint on Column Some time we just need to create a simple constraint over the table but I have noticed that developers do many different things to make table column follow rules than just creating constraint. I suggest constraint is a very useful concept and every SQL Developer should pay good attention to this subject. 2009 List Schema Name and Table Name for Database This is one of the blog post where I straight forward display script. One of the kind of blog posts, which I still love to read and write. Clustered Index on Separate Drive From Table Location A table devoid of primary key index is called heap, and here data is not arranged in a particular order, which gives rise to issues that adversely affect performance. Data must be stored in some kind of order. If we put clustered index on it then the order will be forced by that index and the data will be stored in that particular order. Understanding Table Hints with Examples Hints are options and strong suggestions specified for enforcement by the SQL Server query processor on DML statements. The hints override any execution plan the query optimizer might select for a query. 2010 Data Pages in Buffer Pool – Data Stored in Memory Cache One of my earlier year article, which I still read it many times and point developers to read it again. It is clear from the Resultset that when more than one index is used, datapages related to both or all of the indexes are stored in Memory Cache separately. TRANSACTION, DML and Schema Locks Can you create a situation where you can see Schema Lock? Well, this is a very simple question, however during the interview I notice over 50 candidates failed to come up with the scenario. In this blog post, I have demonstrated the situation where we can see the schema lock in database. 2011 Solution – Puzzle – Statistics are not updated but are Created Once In this example I have created following situation: Create Table Insert 1000 Records Check the Statistics Now insert 10 times more 10,000 indexes Check the Statistics – it will be NOT updated Auto Update Statistics and Auto Create Statistics for database is TRUE Now I have requested two things in the example 1) Why this is happening? 2) How to fix this issue? Selecting Domain from Email Address This is a straight to script blog post where I explain how to select only domain name from entire email address. Solution – Generating Zero Without using Any Numbers in T-SQL How to get zero digit without using any digit? This is indeed a very interesting question and the answer is even interesting. Try to come up with answer in next 10 minutes and if you can’t come up with the answer the blog post read this post for solution. 2012 Simple Explanation and Puzzle with SOUNDEX Function and DIFFERENCE Function In simple words - SOUNDEX converts an alphanumeric string to a four-character code to find similar-sounding words or names. DIFFERENCE function returns an integer value. The  integer returned is the number of characters in the SOUNDEX values that are the same. Read Only Files and SQL Server Management Studio (SSMS) I have come across a very interesting feature in SSMS related to “Read Only” files. I believe it is a little unknown feature as well so decided to write a blog about the same. Identifying Column Data Type of uniqueidentifier without Querying System Tables How do I know if any table has a uniqueidentifier column and what is its value without using any DMV or System Catalogues? Only information you know is the table name and you are allowed to return any kind of error if the table does not have uniqueidentifier column. Read the blog post to find the answer. Solution – User Not Able to See Any User Created Object in Tables – Security and Permissions Issue Interesting question – “When I try to connect to SQL Server, it lets me connect just fine as well let me open and explore the database. I noticed that I do not see any user created instances but when my colleague attempts to connect to the server, he is able to explore the database as well see all the user created tables and other objects. Can you help me fix it?” Importing CSV File Into Database – SQL in Sixty Seconds #018 – Video Here is interesting small 60 second video on how to import CSV file into Database. ColumnStore Index – Batch Mode vs Row Mode Here is the logic behind when Columnstore Index uses Batch Mode and when it uses Row Mode. A batch typically represents about 1000 rows of data. Batch mode processing also uses algorithms that are optimized for the multicore CPUs and increased memory throughput. Follow up – Usage of $rowguid and $IDENTITY This is an excellent follow up blog post of my earlier blog post where I explain where to use $rowguid and $identity.  If you do not know the difference between them, this is a blog with a script example. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: Memory Lane, PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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• Appserver runs out of memory

  - by sarego

  We have been facing Out of Memory errors in our App server for sometime. We see the used heap size increasing gradually until finally it reaches the available heap in size. This happens every 3 weeks after which a server restart is needed to fix this. Upon analysis of the heap dumps we find the problem to be objects used in JSPs. Can JSP objects be the real cause of Appserver memory issues? How do we free up JSP objects (Objects which are being instantiated using usebean or other tags)? We have a clustered Websphere appserver with 2 nodes and an IHS.

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• How to free up memory?

  - by sarego

  We have been facing Out of Memory errors in our App server for sometime. We see the used heap size increasing gradually until finally it reaches the available heap in size. This happens every 3 weeks after which a server restart is needed to fix this. Upon analysis of the heap dumps we find the problem to be objects used in JSPs. Can JSP objects be the real cause of Appserver memory issues? How do we free up JSP objects (Objects which are being instantiated using usebean or other tags)? We have a clustered Websphere appserver with 2 nodes and an IHS.

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