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  • Producer / Consumer - I/O Disk

    - by Pedro Magalhaes
    Hi, I have a compressed file in the disk, that a partitioned in blocks. I read a block from disk decompress it to memory and the read the data. It is possible to create a producer/consumer, one thread that recovers compacted blocks from disk and put in a queue and another thread that decompress and read the data? Will the performance be better? Thanks!

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  • Basic concepts in file system implementation

    - by darkie15
    I am a unclear about file system implementation. Specifically (Operating Systems - Tannenbaum (Edition 3), Page 275) states "The first word of each block is used as a pointer to the next one. The rest of block is data". Can anyone please explain to me the hierarchy of the division here? Like, each disk partition contains blocks, blocks contain words, and so on...

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  • smart page resizing

    - by Anton
    Suppose I have an HTML page with three blocks of fixed width (their height can vary if that's important), like shown on picture: I would like to make it behave as shown on next picture: when browser screen width is reduced so it can't fit all three blocks in one line, first block goes down. Is it possible to achieve such behavior? Preferably with CSS only but any working solution would be great.

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  • What is Get-Command -CommandType Script?

    - by Roman Kuzmin
    What is Get-Command -CommandType Script? What kind of commands does it cover? Help about Script tells “-- Script: Script blocks in the current session.” but I am not sure what kind of script blocks it means. Are there cases when Get-Command -CommandType Script actually returns anything?

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  • jquery, manipulate content inserted by ajax, without using the callback

    - by Cody
    I am using ajax to insert a series of informational blocks via a loop. The blocks each have a title, and long description in them that is hidden by default. They function like an accordion, only showing one description at a time amongst all of the blocks. The problem is opening the description on the first block. I would REALLY like to do it with javascript right after the loop that is creating them is done. Is it possible to manipulate elements created ofter an ajax call without using the callback? <!-- example code--> <style> .placeholder, .long_description{ display:none;} </style> </head><body> <script> /* yes, this script is in the body, dont know if it matters */ $(document).ready(function() { $(".placeholder").each(function(){ // Use the divs to get the blocks var blockname = $(this).html(); // the contents if the div is the ID for the ajax POST $.post("/service_app/dyn_block",'form='+blockname, function(data){ var divname = '#div_' + blockname; $(divname).after(data); $(this).setupAccrdFnctly(); //not the actual code }); }); /* THIS LINE IS THE PROBLEM LINE, is it possible to reference the code ajax inserted */ /* Display the long description in the first dyn_block */ $(".dyn_block").first().find(".long_description").addClass('active').slideDown('fast'); }); </script> <!-- These lines are generated by PHP --> <!-- It is POSSIBLE to display the dyn_blocks --> <!-- here but I would really rather not --> <div id="div_servicetype" class="placeholder">servicetype</div> <div id="div_custtype" class="placeholder">custtype</div> <div id="div_custinfo" class="placeholder">custinfo</div> <div id="div_businfo" class="placeholder">businfo</div> </body>

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  • .NET and C# Exceptions. What is it reasonable to catch.

    - by djna
    Disclaimer, I'm from a Java background. I don't do much C#. There's a great deal of transfer between the two worlds, but of course there are differences and one is in the way Exceptions tend to be thought about. I recently answered a C# question suggesting that under some circstances it's reasonable to do this: try { some work } catch (Exeption e) { commonExceptionHandler(); } (The reasons why are immaterial). I got a response that I don't quite understand: until .NET 4.0, it's very bad to catch Exception. It means you catch various low-level fatal errors and so disguise bugs. It also means that in the event of some kind of corruption that triggers such an exception, any open finally blocks on the stack will be executed, so even if the callExceptionReporter fuunction tries to log and quit, it may not even get to that point (the finally blocks may throw again, or cause more corruption, or delete something important from the disk or database). May I'm more confused than I realise, but I don't agree with some of that. Please would other folks comment. I understand that there are many low level Exceptions we don't want to swallow. My commonExceptionHandler() function could reasonably rethrow those. This seems consistent with this answer to a related question. Which does say "Depending on your context it can be acceptable to use catch(...), providing the exception is re-thrown." So I conclude using catch (Exception ) is not always evil, silently swallowing certain exceptions is. The phrase "Until .NET 4 it is very bad to Catch Exception" What changes in .NET 4? IS this a reference to AggregateException, which may give us some new things to do with exceptions we catch, but I don't think changes the fundamental "don't swallow" rule. The next phrase really bothers be. Can this be right? It also means that in the event of some kind of corruption that triggers such an exception, any open finally blocks on the stack will be executed (the finally blocks may throw again, or cause more corruption, or delete something important from the disk or database) My understanding is that if some low level code had lowLevelMethod() { try { lowestLevelMethod(); } finally { some really important stuff } } and in my code I call lowLevel(); try { lowLevel() } catch (Exception e) { exception handling and maybe rethrowing } Whether or not I catch Exception this has no effect whatever on the excution of the finally block. By the time we leave lowLevelMethod() the finally has already run. If the finally is going to do any of the bad things, such as corrupt my disk, then it will do so. My catching the Exception made no difference. If It reaches my Exception block I need to do the right thing, but I can't be the cause of dmis-executing finallys

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  • manipulate content inserted by ajax, without using the callback

    - by Cody
    I am using ajax to insert a series of informational blocks via a loop. The blocks each have a title, and long description in them that is hidden by default. They function like an accordion, only showing one description at a time amongst all of the blocks. The problem is opening the description on the first block. I would REALLY like to do it with javascript right after the loop that is creating them is done. Is it possible to manipulate elements created ofter an ajax call without using the callback? <!-- example code--> <style> .placeholder, .long_description{ display:none;} </style> </head><body> <script> /* yes, this script is in the body, dont know if it matters */ $(document).ready(function() { $(".placeholder").each(function(){ // Use the divs to get the blocks var blockname = $(this).html(); // the contents if the div is the ID for the ajax POST $.post("/service_app/dyn_block",'form='+blockname, function(data){ var divname = '#div_' + blockname; $(divname).after(data); $(this).setupAccrdFnctly(); //not the actual code }); }); /* THIS LINE IS THE PROBLEM LINE, is it possible to reference the code ajax inserted */ /* Display the long description in the first dyn_block */ $(".dyn_block").first().find(".long_description").addClass('active').slideDown('fast'); }); </script> <!-- These lines are generated by PHP --> <!-- It is POSSIBLE to display the dyn_blocks --> <!-- here but I would really rather not --> <div id="div_servicetype" class="placeholder">servicetype</div> <div id="div_custtype" class="placeholder">custtype</div> <div id="div_custinfo" class="placeholder">custinfo</div> <div id="div_businfo" class="placeholder">businfo</div> </body>

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  • CakePHP requestAction and eval code

    - by Naveed
    Hi, I am using cakephp for my site. I have stored multiple blocks in database and trying to access the code with following syntax. foreach($blocks as $block){ if($block['Block']['position'] == 'left'){ $str = $block['Block']['value']; eval("\"echo $str\";"); } } And i m getting this error; : Undefined property: View::$requestAction [APP\views\layouts\home.ctp(60) : eval()'d code Your Help will be highly appreciated. Thanks,

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  • it takes 2 seconds to compile a hello world C++ project in netbeans (windows)

    - by Ethan
    I used code:blocks as the C++ IDE on Windows. I switched to netbeans 6.8 (with C/C++ plugin, MinGW, MSYS) recently, because netbeas have the nice feature of "checking syntax errors when typing" (same as working on Java or PHP projects). But the painful thing is that, it takes 2 seconds to compile a simple hello world project in netbeans. Any trick to make it as fast as code:blocks, or at least make the compiling time no more than 0.5 second?

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  • Library to parse C/C++ source code

    - by John
    Which library should I use to parse C/C++ source code file? I need to parse source file, calculate how much useful strings inside, how much 'for' blocks, 'if' blocks, how much comments inside. I also may need to insert a comment or small piece of code after each 'for' block. Is there any libraries? May be any library included in Microsoft Visual Studio?

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  • Sample MS application for Enterprise library?

    - by DotnetDude
    Does MS have a sample enterprise application that demonstrates the use of different Enterprise library blocks (Logging, Dataaccess, Exception, Validation etc)? I am looking for something that uses best practices in using and integrating all these blocks in a single application.

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  • Methods in Ruby: objects or not?

    - by Mladen Jablanovic
    Inspired by this discussion, after some googling I wasn't able to find an answer to a pretty simple question regarding methods in Ruby: are they objects or not? There are different opinions here and there, and I would really like to hear, let's say, an in-depth explanation. I'm aware of Object#method method, which takes a method name and returns a Method instance, but, on the other hand, there's a similar thing you can do with blocks to make them into Proc instances, and blocks aren't objects, so what makes methods any different?

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  • How do I read and write to a file using threads in java?

    - by WarmWaffles
    I'm writing an application where I need to read blocks in from a single file, each block is roughly 512 bytes. I am also needing to write blocks simultaneously. One of the ideas I had was BlockReader implements Runnable and BlockWriter implements Runnable and BlockManager manages both the reader and writer. The problem that I am seeing with most examples that I have found was locking problems and potential deadlock situations. Any ideas how to implement this?

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  • CUDA threads for inner loop

    - by Manolete
    I've got this kernel __global__ void kernel1(int keep, int include, int width, int* d_Xco, int* d_Xnum, bool* d_Xvalid, float* d_Xblas) { int i, k; i = threadIdx.x + blockIdx.x * blockDim.x; if(i < keep){ for(k = 0; k < include ; k++){ int val = (d_Xblas[i*include + k] >= 1e5); int aux = d_Xnum[i]; d_Xblas[i*include + k] *= (!val); d_Xco[i*width + aux] = k; d_Xnum[i] +=val; d_Xvalid[i*include + k] = (!val); } } } launched with int keep = 9000; int include = 23000; int width = 0.2*include; int threads = 192; int blocks = keep+threads-1/threads; kernel1 <<< blocks,threads >>>( keep, include, width, d_Xco, d_Xnum, d_Xvalid, d_Xblas ); This kernel1 works fine but it is obviously not totally optimized. I thought it would be straight forward to eliminate the inner loop k but for some reason it doesn't work fine. My first idea was: __global__ void kernel2(int keep, int include, int width, int* d_Xco, int* d_Xnum, bool* d_Xvalid, float* d_Xblas) { int i, k; i = threadIdx.x + blockIdx.x * blockDim.x; k = threadIdx.y + blockIdx.y * blockDim.y; if((i < keep) && (k < include) ) { int val = (d_Xblas[i*include + k] >= 1e5); int aux = d_Xnum[i]; d_Xblas[i*include + k] *= (float)(!val); d_Xco[i*width + aux] = k; atomicAdd(&d_Xnum[i], val); d_Xvalid[i*include + k] = (!val); } } launched with a 2D grid: int keep = 9000; int include = 23000; int width = 0.2*include; int th = 32; dim3 threads(th,th); dim3 blocks (keep+threads.x-1/threads.x, include+threads.y-1/threads.y); kernel2 <<< blocks,threads >>>( keep, include, width, d_Xco, d_Xnum, d_Xvalid, d_Xblas ); Although I believe the idea is fine, it does not work and I am running out of ideas here. Could you please help me out here? I also think the problem could be in d_Xco which stores the position k in a smaller array , so the order matters, but I can't think of any other way of doing it...

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  • Degraded RAID5 and no md superblock on one of remaining drive

    - by ark1214
    This is actually on a QNAP TS-509 NAS. The RAID is basically a Linux RAID. The NAS was configured with RAID 5 with 5 drives (/md0 with /dev/sd[abcde]3). At some point, /dev/sde failed and drive was replaced. While rebuilding (and not completed), the NAS rebooted itself and /dev/sdc dropped out of the array. Now the array can't start because essentially 2 drives have dropped out. I disconnected /dev/sde and hoped that /md0 can resume in degraded mode, but no luck.. Further investigation shows that /dev/sdc3 has no md superblock. The data should be good since the array was unable to assemble after /dev/sdc dropped off. All the searches I done showed how to reassemble the array assuming 1 bad drive. But I think I just need to restore the superblock on /dev/sdc3 and that should bring the array up to a degraded mode which will allow me to backup data and then proceed with rebuilding with adding /dev/sde. Any help would be greatly appreciated. mdstat does not show /dev/md0 # cat /proc/mdstat Personalities : [linear] [raid0] [raid1] [raid10] [raid6] [raid5] [raid4] [multipath] md5 : active raid1 sdd2[2](S) sdc2[3](S) sdb2[1] sda2[0] 530048 blocks [2/2] [UU] md13 : active raid1 sdd4[3] sdc4[2] sdb4[1] sda4[0] 458880 blocks [5/4] [UUUU_] bitmap: 40/57 pages [160KB], 4KB chunk md9 : active raid1 sdd1[3] sdc1[2] sdb1[1] sda1[0] 530048 blocks [5/4] [UUUU_] bitmap: 33/65 pages [132KB], 4KB chunk mdadm show /dev/md0 is still there # mdadm --examine --scan ARRAY /dev/md9 level=raid1 num-devices=5 UUID=271bf0f7:faf1f2c2:967631a4:3c0fa888 ARRAY /dev/md5 level=raid1 num-devices=2 UUID=0d75de26:0759d153:5524b8ea:86a3ee0d spares=2 ARRAY /dev/md0 level=raid5 num-devices=5 UUID=ce3e369b:4ff9ddd2:3639798a:e3889841 ARRAY /dev/md13 level=raid1 num-devices=5 UUID=7384c159:ea48a152:a1cdc8f2:c8d79a9c With /dev/sde removed, here is the mdadm examine output showing sdc3 has no md superblock # mdadm --examine /dev/sda3 /dev/sda3: Magic : a92b4efc Version : 00.90.00 UUID : ce3e369b:4ff9ddd2:3639798a:e3889841 Creation Time : Sat Dec 8 15:01:19 2012 Raid Level : raid5 Used Dev Size : 1463569600 (1395.77 GiB 1498.70 GB) Array Size : 5854278400 (5583.08 GiB 5994.78 GB) Raid Devices : 5 Total Devices : 4 Preferred Minor : 0 Update Time : Sat Dec 8 15:06:17 2012 State : active Active Devices : 4 Working Devices : 4 Failed Devices : 1 Spare Devices : 0 Checksum : d9e9ff0e - correct Events : 0.394 Layout : left-symmetric Chunk Size : 64K Number Major Minor RaidDevice State this 0 8 3 0 active sync /dev/sda3 0 0 8 3 0 active sync /dev/sda3 1 1 8 19 1 active sync /dev/sdb3 2 2 8 35 2 active sync /dev/sdc3 3 3 8 51 3 active sync /dev/sdd3 4 4 0 0 4 faulty removed [~] # mdadm --examine /dev/sdb3 /dev/sdb3: Magic : a92b4efc Version : 00.90.00 UUID : ce3e369b:4ff9ddd2:3639798a:e3889841 Creation Time : Sat Dec 8 15:01:19 2012 Raid Level : raid5 Used Dev Size : 1463569600 (1395.77 GiB 1498.70 GB) Array Size : 5854278400 (5583.08 GiB 5994.78 GB) Raid Devices : 5 Total Devices : 4 Preferred Minor : 0 Update Time : Sat Dec 8 15:06:17 2012 State : active Active Devices : 4 Working Devices : 4 Failed Devices : 1 Spare Devices : 0 Checksum : d9e9ff20 - correct Events : 0.394 Layout : left-symmetric Chunk Size : 64K Number Major Minor RaidDevice State this 1 8 19 1 active sync /dev/sdb3 0 0 8 3 0 active sync /dev/sda3 1 1 8 19 1 active sync /dev/sdb3 2 2 8 35 2 active sync /dev/sdc3 3 3 8 51 3 active sync /dev/sdd3 4 4 0 0 4 faulty removed [~] # mdadm --examine /dev/sdc3 mdadm: No md superblock detected on /dev/sdc3. [~] # mdadm --examine /dev/sdd3 /dev/sdd3: Magic : a92b4efc Version : 00.90.00 UUID : ce3e369b:4ff9ddd2:3639798a:e3889841 Creation Time : Sat Dec 8 15:01:19 2012 Raid Level : raid5 Used Dev Size : 1463569600 (1395.77 GiB 1498.70 GB) Array Size : 5854278400 (5583.08 GiB 5994.78 GB) Raid Devices : 5 Total Devices : 4 Preferred Minor : 0 Update Time : Sat Dec 8 15:06:17 2012 State : active Active Devices : 4 Working Devices : 4 Failed Devices : 1 Spare Devices : 0 Checksum : d9e9ff44 - correct Events : 0.394 Layout : left-symmetric Chunk Size : 64K Number Major Minor RaidDevice State this 3 8 51 3 active sync /dev/sdd3 0 0 8 3 0 active sync /dev/sda3 1 1 8 19 1 active sync /dev/sdb3 2 2 8 35 2 active sync /dev/sdc3 3 3 8 51 3 active sync /dev/sdd3 4 4 0 0 4 faulty removed fdisk output shows /dev/sdc3 partition is still there. [~] # fdisk -l Disk /dev/sdx: 128 MB, 128057344 bytes 8 heads, 32 sectors/track, 977 cylinders Units = cylinders of 256 * 512 = 131072 bytes Device Boot Start End Blocks Id System /dev/sdx1 1 8 1008 83 Linux /dev/sdx2 9 440 55296 83 Linux /dev/sdx3 441 872 55296 83 Linux /dev/sdx4 873 977 13440 5 Extended /dev/sdx5 873 913 5232 83 Linux /dev/sdx6 914 977 8176 83 Linux Disk /dev/sda: 1500.3 GB, 1500301910016 bytes 255 heads, 63 sectors/track, 182401 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Device Boot Start End Blocks Id System /dev/sda1 * 1 66 530113+ 83 Linux /dev/sda2 67 132 530145 82 Linux swap / Solaris /dev/sda3 133 182338 1463569695 83 Linux /dev/sda4 182339 182400 498015 83 Linux Disk /dev/sda4: 469 MB, 469893120 bytes 2 heads, 4 sectors/track, 114720 cylinders Units = cylinders of 8 * 512 = 4096 bytes Disk /dev/sda4 doesn't contain a valid partition table Disk /dev/sdb: 1500.3 GB, 1500301910016 bytes 255 heads, 63 sectors/track, 182401 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Device Boot Start End Blocks Id System /dev/sdb1 * 1 66 530113+ 83 Linux /dev/sdb2 67 132 530145 82 Linux swap / Solaris /dev/sdb3 133 182338 1463569695 83 Linux /dev/sdb4 182339 182400 498015 83 Linux Disk /dev/sdc: 1500.3 GB, 1500301910016 bytes 255 heads, 63 sectors/track, 182401 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Device Boot Start End Blocks Id System /dev/sdc1 1 66 530125 83 Linux /dev/sdc2 67 132 530142 83 Linux /dev/sdc3 133 182338 1463569693 83 Linux /dev/sdc4 182339 182400 498012 83 Linux Disk /dev/sdd: 2000.3 GB, 2000398934016 bytes 255 heads, 63 sectors/track, 243201 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Device Boot Start End Blocks Id System /dev/sdd1 1 66 530125 83 Linux /dev/sdd2 67 132 530142 83 Linux /dev/sdd3 133 243138 1951945693 83 Linux /dev/sdd4 243139 243200 498012 83 Linux Disk /dev/md9: 542 MB, 542769152 bytes 2 heads, 4 sectors/track, 132512 cylinders Units = cylinders of 8 * 512 = 4096 bytes Disk /dev/md9 doesn't contain a valid partition table Disk /dev/md5: 542 MB, 542769152 bytes 2 heads, 4 sectors/track, 132512 cylinders Units = cylinders of 8 * 512 = 4096 bytes Disk /dev/md5 doesn't contain a valid partition table

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  • Reconstructing the disk order in RAID 6 with 7 disks

    - by rkotulla
    a little background to this question first: I am running a RAID-6 within a QNAP TS869L external RAID/NAS system. I started with 5 disks of 3 TB each back in the day, and later added another 2 disks of 3TB to the RAID. The QNAP internals handled the growing and re-syncing etc, and everything seemd to be perfectly fine. About 2 weeks ago, I had one of the disks (disk #5, disk #2 has gone bad in the mean time) fail, and somehow (I have no idea why), also disks 1 and 2 got kicked out of the array. I replaced disk #5, but the RAID didn't start working again. After some calls to QNAP technical support, they re-created the array (using mdadm --create --force --assume-clean ...), but the resulting array couldn't find a filesystem, and I was kindly referred to contact a data recovery company that I can't afford. After some digging through old log files, resetting the disk to factory default, etc, I found a few errors that were made during this re-create - I wish I still had some of the original metadata, but unfortunately i don't (I definitely learned that lesson). I'm currently at the point where I know the correct chunk-size (64K), metadata-version (1.0; factory default was 0.9, but from what I read 0.9 doesn't handle disks over 2 TB, mine are 3 TB), and I now find the ext4 filesystem that should be on the disks. Only variable left to determine is the right disk order! I started using the description found in answer #4 of "Recover RAID 5 data after created new array instead of re-using" but am a little confused on what the order should be for a proper RAID-6. RAID-5 is pretty well documented in a number of places, but RAID-6 much less so. Also, does the layout, i.e. distribution of parity and data chunks across the disks, change after the growing of the array from 5 to 7 disks, or does the re-sync re-organize them in such a way a native 7-disk RAID-6 would have been? Thanks some more mdadm output that might be helpful: mdadm version: [~] # mdadm --version mdadm - v2.6.3 - 20th August 2007 mdadm details from one of the disks in the array: [~] # mdadm --examine /dev/sda3 /dev/sda3: Magic : a92b4efc Version : 1.0 Feature Map : 0x0 Array UUID : 1c1614a5:e3be2fbb:4af01271:947fe3aa Name : 0 Creation Time : Tue Jun 10 10:27:58 2014 Raid Level : raid6 Raid Devices : 7 Used Dev Size : 5857395112 (2793.02 GiB 2998.99 GB) Array Size : 29286975360 (13965.12 GiB 14994.93 GB) Used Size : 5857395072 (2793.02 GiB 2998.99 GB) Super Offset : 5857395368 sectors State : clean Device UUID : 7c572d8f:20c12727:7e88c888:c2c357af Update Time : Tue Jun 10 13:01:06 2014 Checksum : d275c82d - correct Events : 7036 Chunk Size : 64K Array Slot : 0 (0, 1, failed, 3, failed, 5, 6) Array State : Uu_u_uu 2 failed mdadm details for the array in the current disk-order (based on my best guess reconstructed from old log-files) [~] # mdadm --detail /dev/md0 /dev/md0: Version : 01.00.03 Creation Time : Tue Jun 10 10:27:58 2014 Raid Level : raid6 Array Size : 14643487680 (13965.12 GiB 14994.93 GB) Used Dev Size : 2928697536 (2793.02 GiB 2998.99 GB) Raid Devices : 7 Total Devices : 5 Preferred Minor : 0 Persistence : Superblock is persistent Update Time : Tue Jun 10 13:01:06 2014 State : clean, degraded Active Devices : 5 Working Devices : 5 Failed Devices : 0 Spare Devices : 0 Chunk Size : 64K Name : 0 UUID : 1c1614a5:e3be2fbb:4af01271:947fe3aa Events : 7036 Number Major Minor RaidDevice State 0 8 3 0 active sync /dev/sda3 1 8 19 1 active sync /dev/sdb3 2 0 0 2 removed 3 8 51 3 active sync /dev/sdd3 4 0 0 4 removed 5 8 99 5 active sync /dev/sdg3 6 8 83 6 active sync /dev/sdf3 output from /proc/mdstat (md8, md9, and md13 are internally used RAIDs holding swap, etc; the one I'm after is md0) [~] # more /proc/mdstat Personalities : [linear] [raid0] [raid1] [raid10] [raid6] [raid5] [raid4] [multipath] md0 : active raid6 sdf3[6] sdg3[5] sdd3[3] sdb3[1] sda3[0] 14643487680 blocks super 1.0 level 6, 64k chunk, algorithm 2 [7/5] [UU_U_UU] md8 : active raid1 sdg2[2](S) sdf2[3](S) sdd2[4](S) sdc2[5](S) sdb2[6](S) sda2[1] sde2[0] 530048 blocks [2/2] [UU] md13 : active raid1 sdg4[3] sdf4[4] sde4[5] sdd4[6] sdc4[2] sdb4[1] sda4[0] 458880 blocks [8/7] [UUUUUUU_] bitmap: 21/57 pages [84KB], 4KB chunk md9 : active raid1 sdg1[6] sdf1[5] sde1[4] sdd1[3] sdc1[2] sda1[0] sdb1[1] 530048 blocks [8/7] [UUUUUUU_] bitmap: 37/65 pages [148KB], 4KB chunk unused devices: <none>

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  • linux raid 1: right after replacing and syncing one drive, the other disk fails - understanding what is going on with mdstat/mdadm

    - by devicerandom
    We have an old RAID 1 Linux server (Ubuntu Lucid 10.04), with four partitions. A few days ago /dev/sdb failed, and today we noticed /dev/sda had pre-failure ominous SMART signs (~4000 reallocated sector count). We replaced /dev/sdb this morning and rebuilt the RAID on the new drive, following this guide: http://www.howtoforge.com/replacing_hard_disks_in_a_raid1_array Everything went smooth until the very end. When it looked like it was finishing to synchronize the last partition, the other old one failed. At this point I am very unsure of the state of the system. Everything seems working and the files seem to be all accessible, just as if it synchronized everything, but I'm new to RAID and I'm worried about what is going on. The /proc/mdstat output is: Personalities : [raid1] [linear] [multipath] [raid0] [raid6] [raid5] [raid4] [raid10] md3 : active raid1 sdb4[2](S) sda4[0] 478713792 blocks [2/1] [U_] md2 : active raid1 sdb3[1] sda3[2](F) 244140992 blocks [2/1] [_U] md1 : active raid1 sdb2[1] sda2[2](F) 244140992 blocks [2/1] [_U] md0 : active raid1 sdb1[1] sda1[2](F) 9764800 blocks [2/1] [_U] unused devices: <none> The order of [_U] vs [U_]. Why aren't they consistent along all the array? Is the first U /dev/sda or /dev/sdb? (I tried looking on the web for this trivial information but I found no explicit indication) If I read correctly for md0, [_U] should be /dev/sda1 (down) and /dev/sdb1 (up). But if /dev/sda has failed, how can it be the opposite for md3 ? I understand /dev/sdb4 is now spare because probably it failed to synchronize it 100%, but why does it show /dev/sda4 as up? Shouldn't it be [__]? Or [_U] anyway? The /dev/sda drive now cannot even be accessed by SMART anymore apparently, so I wouldn't expect it to be up. What is wrong with my interpretation of the output? I attach also the outputs of mdadm --detail for the four partitions: /dev/md0: Version : 00.90 Creation Time : Fri Jan 21 18:43:07 2011 Raid Level : raid1 Array Size : 9764800 (9.31 GiB 10.00 GB) Used Dev Size : 9764800 (9.31 GiB 10.00 GB) Raid Devices : 2 Total Devices : 2 Preferred Minor : 0 Persistence : Superblock is persistent Update Time : Tue Nov 5 17:27:33 2013 State : clean, degraded Active Devices : 1 Working Devices : 1 Failed Devices : 1 Spare Devices : 0 UUID : a3b4dbbd:859bf7f2:bde36644:fcef85e2 Events : 0.7704 Number Major Minor RaidDevice State 0 0 0 0 removed 1 8 17 1 active sync /dev/sdb1 2 8 1 - faulty spare /dev/sda1 /dev/md1: Version : 00.90 Creation Time : Fri Jan 21 18:43:15 2011 Raid Level : raid1 Array Size : 244140992 (232.83 GiB 250.00 GB) Used Dev Size : 244140992 (232.83 GiB 250.00 GB) Raid Devices : 2 Total Devices : 2 Preferred Minor : 1 Persistence : Superblock is persistent Update Time : Tue Nov 5 17:39:06 2013 State : clean, degraded Active Devices : 1 Working Devices : 1 Failed Devices : 1 Spare Devices : 0 UUID : 8bcd5765:90dc93d5:cc70849c:224ced45 Events : 0.1508280 Number Major Minor RaidDevice State 0 0 0 0 removed 1 8 18 1 active sync /dev/sdb2 2 8 2 - faulty spare /dev/sda2 /dev/md2: Version : 00.90 Creation Time : Fri Jan 21 18:43:19 2011 Raid Level : raid1 Array Size : 244140992 (232.83 GiB 250.00 GB) Used Dev Size : 244140992 (232.83 GiB 250.00 GB) Raid Devices : 2 Total Devices : 2 Preferred Minor : 2 Persistence : Superblock is persistent Update Time : Tue Nov 5 17:46:44 2013 State : clean, degraded Active Devices : 1 Working Devices : 1 Failed Devices : 1 Spare Devices : 0 UUID : 2885668b:881cafed:b8275ae8:16bc7171 Events : 0.2289636 Number Major Minor RaidDevice State 0 0 0 0 removed 1 8 19 1 active sync /dev/sdb3 2 8 3 - faulty spare /dev/sda3 /dev/md3: Version : 00.90 Creation Time : Fri Jan 21 18:43:22 2011 Raid Level : raid1 Array Size : 478713792 (456.54 GiB 490.20 GB) Used Dev Size : 478713792 (456.54 GiB 490.20 GB) Raid Devices : 2 Total Devices : 2 Preferred Minor : 3 Persistence : Superblock is persistent Update Time : Tue Nov 5 17:19:20 2013 State : clean, degraded Active Devices : 1 Working Devices : 2 Failed Devices : 0 Spare Devices : 1 Number Major Minor RaidDevice State 0 8 4 0 active sync /dev/sda4 1 0 0 1 removed 2 8 20 - spare /dev/sdb4 The active sync on /dev/sda4 baffles me. I am worried because if tomorrow morning I have to replace /dev/sda, I want to be sure what should I sync with what and what is going on. I am also quite baffled by the fact /dev/sda decided to fail exactly when the raid finished resyncing. I'd like to understand what is really happening. Thanks a lot for your patience and help. Massimo

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  • Fast block placement algorithm, advice needed?

    - by James Morris
    I need to emulate the window placement strategy of the Fluxbox window manager. As a rough guide, visualize randomly sized windows filling up the screen one at a time, where the rough size of each results in an average of 80 windows on screen without any window overlapping another. It is important to note that windows will close and the space that closed windows previously occupied becomes available once more for the placement of new windows. The window placement strategy has three binary options: Windows build horizontal rows or vertical columns (potentially) Windows are placed from left to right or right to left Windows are placed from top to bottom or bottom to top Why is the algorithm a problem? It needs to operate to the deadlines of a real time thread in an audio application. At this moment I am only concerned with getting a fast algorithm, don't concern yourself over the implications of real time threads and all the hurdles in programming that that brings. So far I have two choices which I have built loose prototypes for: 1) A port of the Fluxbox placement algorithm into my code. The problem with this is, the client (my program) gets kicked out of the audio server (JACK) when I try placing the worst case scenario of 256 blocks using the algorithm. This algorithm performs over 14000 full (linear) scans of the list of blocks already placed when placing the 256th window. 2) My alternative approach. Only partially implemented, this approach uses a data structure for each area of rectangular free unused space (the list of windows can be entirely separate, and is not required for testing of this algorithm). The data structure acts as a node in a doubly linked list (with sorted insertion), as well as containing the coordinates of the top-left corner, and the width and height. Furthermore, each block data structure also contains four links which connect to each immediately adjacent (touching) block on each of the four sides. IMPORTANT RULE: Each block may only touch with one block per side. The problem with this approach is, it's very complex. I have implemented the straightforward cases where 1) space is removed from one corner of a block, 2) splitting neighbouring blocks so that the IMPORTANT RULE is adhered to. The less straightforward case, where the space to be removed can only be found within a column or row of boxes, is only partially implemented - if one of the blocks to be removed is an exact fit for width (ie column) or height (ie row) then problems occur. And don't even mention the fact this only checks columns one box wide, and rows one box tall. I've implemented this algorithm in C - the language I am using for this project (I've not used C++ for a few years and am uncomfortable using it after having focused all my attention to C development, it's a hobby). The implementation is 700+ lines of code (including plenty of blank lines, brace lines, comments etc). The implementation only works for the horizontal-rows + left-right + top-bottom placement strategy. So I've either got to add some way of making this +700 lines of code work for the other 7 placement strategy options, or I'm going to have to duplicate those +700 lines of code for the other seven options. Neither of these is attractive, the first, because the existing code is complex enough, the second, because of bloat. The algorithm is not even at a stage where I can use it in the real time worst case scenario, because of missing functionality, so I still don't know if it actually performs better or worse than the first approach. What else is there? I've skimmed over and discounted: Bin Packing algorithms: their emphasis on optimal fit does not match the requirements of this algorithm. Recursive Bisection Placement algorithms: sounds promising, but these are for circuit design. Their emphasis is optimal wire length. Both of these, especially the latter, all elements to be placed/packs are known before the algorithm begins. I need an algorithm which works accumulatively with what it is given to do when it is told to do it. What are your thoughts on this? How would you approach it? What other algorithms should I look at? Or even what concepts should I research seeing as I've not studied computer science/software engineering? Please ask questions in comments if further information is needed. [edit] If it makes any difference, the units for the coordinates will not be pixels. The units are unimportant, but the grid where windows/blocks/whatever can be placed will be 127 x 127 units.

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  • Keypress detection wont work after seemingly unrelated code change

    - by LukeZaz
    I'm trying to have the Enter key cause a new 'map' to generate for my game, but for whatever reason after implementing full-screen in it the input check won't work anymore. I tried removing the new code and only pressing one key at a time, but it still won't work. Here's the check code and the method it uses, along with the newMap method: public class Game1 : Microsoft.Xna.Framework.Game { // ... protected override void Update(GameTime gameTime) { // ... // Check if Enter was pressed - if so, generate a new map if (CheckInput(Keys.Enter, 1)) { blocks = newMap(map, blocks, console); } // ... } // Method: Checks if a key is/was pressed public bool CheckInput(Keys key, int checkType) { // Get current keyboard state KeyboardState newState = Keyboard.GetState(); bool retType = false; // Return type if (checkType == 0) { // Check Type: Is key currently down? if (newState.IsKeyDown(key)) { retType = true; } else { retType = false; } } else if (checkType == 1) { // Check Type: Was the key pressed? if (newState.IsKeyDown(key)) { if (!oldState.IsKeyDown(key)) { // Key was just pressed retType = true; } else { // Key was already pressed, return false retType = false; } } } // Save keyboard state oldState = newState; // Return result if (retType == true) { return true; } else { return false; } } // Method: Generate a new map public List<Block> newMap(Map map, List<Block> blockList, Console console) { // Create new map block coordinates List<Vector2> positions = new List<Vector2>(); positions = map.generateMap(console); // Clear list and reallocate memory previously used up by it blockList.Clear(); blockList.TrimExcess(); // Add new blocks to the list using positions created by generateMap() foreach (Vector2 pos in positions) { blockList.Add(new Block() { Position = pos, Texture = dirtTex }); } // Return modified list return blockList; } // ... } and the generateMap code: // Generate a list of Vector2 positions for blocks public List<Vector2> generateMap(Console console, int method = 0) { ScreenTileWidth = gDevice.Viewport.Width / 16; ScreenTileHeight = gDevice.Viewport.Height / 16; maxHeight = gDevice.Viewport.Height; List<Vector2> blockLocations = new List<Vector2>(); if (useScreenSize == true) { Width = ScreenTileWidth; Height = ScreenTileHeight; } else { maxHeight = Height; } int startHeight = -500; // For debugging purposes, the startHeight is set to an // hopefully-unreachable value - if it returns this, something is wrong // Methods of land generation /// <summary> /// Third version land generation /// Generates a base land height as the second version does /// but also generates a 'max change' value which determines how much /// the land can raise or lower by which it now does by a random amount /// during generation /// </summary> if (method == 0) { // Get the land height startHeight = rnd.Next(1, maxHeight); int maxChange = rnd.Next(1, 5); // Amount ground will raise/lower by int curHeight = startHeight; for (int w = 0; w < Width; w++) { // Run a chance to lower/raise ground level int changeBy = rnd.Next(1, maxChange); int doChange = rnd.Next(0, 3); if (doChange == 1 && !(curHeight <= (1 + maxChange))) { curHeight = curHeight - changeBy; } else if (doChange == 2 && !(curHeight >= (29 - maxChange))) { curHeight = curHeight + changeBy; } for (int h = curHeight; h < Height; h++) { // Location variables float x = w * 16; float y = h * 16; blockLocations.Add(new Vector2(x, y)); } } console.newMsg("[INFO] Cur, height change maximum: " + maxChange.ToString()); } /// <summary> /// Second version land generator /// Generates a solid mass of land starting at a random height /// derived from either screen height or provided height value /// </summary> else if (method == 1) { // Get the land height startHeight = rnd.Next(0, 30); for (int w = 0; w < Width; w++) { for (int h = startHeight; h < ScreenTileHeight; h++) { // Location variables float x = w * 16; float y = h * 16; // Add a tile at set location blockLocations.Add(new Vector2(x, y)); } } } /// <summary> /// First version land generator /// Generates land completely randomly either across screen or /// in a box set by Width and Height values /// </summary> else { // For each tile in the map... for (int w = 0; w < Width; w++) { for (int h = 0; h < Height; h++) { // Location variables float x = w * 16; float y = h * 16; // ...decide whether or not to place a tile... if (rnd.Next(0, 2) == 1) { // ...and if so, add a tile at that location. blockLocations.Add(new Vector2(x, y)); } } } } console.newMsg("[INFO] Cur, base height: " + startHeight.ToString()); return blockLocations; } I never touched any of the above code for this when it broke - changing keys won't seem to fix it. Despite this, I have camera movement set inside another Game1 method that uses WASD and works perfectly. All I did was add a few lines of code here: private int BackBufferWidth = 1280; // Added these variables private int BackBufferHeight = 800; public Game1() { graphics = new GraphicsDeviceManager(this); graphics.PreferredBackBufferWidth = BackBufferWidth; // and this graphics.PreferredBackBufferHeight = BackBufferHeight; // this Content.RootDirectory = "Content"; this.graphics.IsFullScreen = true; // and this } When I try adding a console line to be printed in the event the key is pressed, it seems that the If is never even triggered despite the correct key being pressed.

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  • Why your Netapp is so slow...

    - by Darius Zanganeh
    Have you ever wondered why your Netapp FAS box is slow and doesn't perform well at large block workloads?  In this blog entry I will give you a little bit of information that will probably help you understand why it’s so slow, why you shouldn't use it for applications that read and write in large blocks like 64k, 128k, 256k ++ etc..  Of course since I work for Oracle at this time, I will show you why the ZS3 storage boxes are excellent choices for these types of workloads. Netapp’s Fundamental Problem The fundamental problem you have running these workloads on Netapp is the backend block size of their WAFL file system.  Every application block on a Netapp FAS ends up in a 4k chunk on a disk. Reference:  Netapp TR-3001 Whitepaper Netapp has proven this lacking large block performance fact in at least two different ways. They have NEVER posted an SPC-2 Benchmark yet they have posted SPC-1 and SPECSFS, both recently. In 2011 they purchased Engenio to try and fill this GAP in their portfolio. Block Size Matters So why does block size matter anyways?  Many applications use large block chunks of data especially in the Big Data movement.  Some examples are SAS Business Analytics, Microsoft SQL, Hadoop HDFS is even 64MB! Now let me boil this down for you.  If an application such MS SQL is writing data in a 64k chunk then before Netapp actually writes it on disk it will have to split it into 16 different 4k writes and 16 different disk IOPS.  When the application later goes to read that 64k chunk the Netapp will have to again do 16 different disk IOPS.  In comparison the ZS3 Storage Appliance can write in variable block sizes ranging from 512b to 1MB.  So if you put the same MSSQL database on a ZS3 you can set the specific LUNs for this database to 64k and then when you do an application read/write it requires only a single disk IO.  That is 16x faster!  But, back to the problem with your Netapp, you will VERY quickly run out of disk IO and hit a wall.  Now all arrays will have some fancy pre fetch algorithm and some nice cache and maybe even flash based cache such as a PAM card in your Netapp but with large block workloads you will usually blow through the cache and still need significant disk IO.  Also because these datasets are usually very large and usually not dedupable they are usually not good candidates for an all flash system.  You can do some simple math in excel and very quickly you will see why it matters.  Here are a couple of READ examples using SAS and MSSQL.  Assume these are the READ IOPS the application needs even after all the fancy cache and algorithms.   Here is an example with 128k blocks.  Notice the numbers of drives on the Netapp! Here is an example with 64k blocks You can easily see that the Oracle ZS3 can do dramatically more work with dramatically less drives.  This doesn't even take into account that the ONTAP system will likely run out of CPU way before you get to these drive numbers so you be buying many more controllers.  So with all that said, lets look at the ZS3 and why you should consider it for any workload your running on Netapp today.  ZS3 World Record Price/Performance in the SPC-2 benchmark ZS3-2 is #1 in Price Performance $12.08ZS3-2 is #3 in Overall Performance 16,212 MBPS Note: The number one overall spot in the world is held by an AFA 33,477 MBPS but at a Price Performance of $29.79.  A customer could purchase 2 x ZS3-2 systems in the benchmark with relatively the same performance and walk away with $600,000 in their pocket.

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  • Big Data – Basics of Big Data Architecture – Day 4 of 21

    - by Pinal Dave
    In yesterday’s blog post we understood how Big Data evolution happened. Today we will understand basics of the Big Data Architecture. Big Data Cycle Just like every other database related applications, bit data project have its development cycle. Though three Vs (link) for sure plays an important role in deciding the architecture of the Big Data projects. Just like every other project Big Data project also goes to similar phases of the data capturing, transforming, integrating, analyzing and building actionable reporting on the top of  the data. While the process looks almost same but due to the nature of the data the architecture is often totally different. Here are few of the question which everyone should ask before going ahead with Big Data architecture. Questions to Ask How big is your total database? What is your requirement of the reporting in terms of time – real time, semi real time or at frequent interval? How important is the data availability and what is the plan for disaster recovery? What are the plans for network and physical security of the data? What platform will be the driving force behind data and what are different service level agreements for the infrastructure? This are just basic questions but based on your application and business need you should come up with the custom list of the question to ask. As I mentioned earlier this question may look quite simple but the answer will not be simple. When we are talking about Big Data implementation there are many other important aspects which we have to consider when we decide to go for the architecture. Building Blocks of Big Data Architecture It is absolutely impossible to discuss and nail down the most optimal architecture for any Big Data Solution in a single blog post, however, we can discuss the basic building blocks of big data architecture. Here is the image which I have built to explain how the building blocks of the Big Data architecture works. Above image gives good overview of how in Big Data Architecture various components are associated with each other. In Big Data various different data sources are part of the architecture hence extract, transform and integration are one of the most essential layers of the architecture. Most of the data is stored in relational as well as non relational data marts and data warehousing solutions. As per the business need various data are processed as well converted to proper reports and visualizations for end users. Just like software the hardware is almost the most important part of the Big Data Architecture. In the big data architecture hardware infrastructure is extremely important and failure over instances as well as redundant physical infrastructure is usually implemented. NoSQL in Data Management NoSQL is a very famous buzz word and it really means Not Relational SQL or Not Only SQL. This is because in Big Data Architecture the data is in any format. It can be unstructured, relational or in any other format or from any other data source. To bring all the data together relational technology is not enough, hence new tools, architecture and other algorithms are invented which takes care of all the kind of data. This is collectively called NoSQL. Tomorrow Next four days we will answer the Buzz Words – Hadoop. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: Big Data, PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL

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  • Old School Wizardry Tip: Batch File Comments

    - by jkauffman
    Johnny, the Endangered Keyboard-Driven Windows User Some of my proudest, obscure Windows tricks are losing their relevance. I know I’m not alone. Keyboard shortcuts are going the way of the dodo. I used to induce fearful awe by slapping Ctrl+Shift+Esc in front of the lowly, pedestrian Windows users. No windows key on the keyboard? No problem: Ctrl+Esc. No menu key on the keyboard: Shift+F10. I am also firmly planted in the habit of closing windows with the Alt+Space menu (Alt+Space, C); and I harbor a brooding, slow=growing list of programs that fail to support this correctly (that means you, Paint.NET). Every time a new version of windows comes out, the support for some of these minor time-saving habits get pared out. Will I complain publicly? Nope, I know my old ways should be axed to conserve precious design energy. In fact, I disapprove of fierce un-intuitiveness for the sake of alleged productivity. Like vim, for example. If you approach a program after being away for 5 years, having to recall encyclopedic knowledge is a flaw. The RTFM disciples have lost. Anyway, some of the items in my arsenal of goofy time-saving tricks are still relevant today. I wanted to draw attention to one that’s stood the test of time. Remember Batch Files? Yes, it’s true, batch files are fading faster than the world of print. But they're not dead yet. I still run into some situations where I opt to use batch files. They are still relevant for build processes, or just various development workflow tools. Sure, there’s powershell, but there’s that stupid Set-ExecutionPolicy speed bump standing in your way; can you really spare the time to A) hunt down that setting on all machines affected and/or B) make futile efforts to convince your coworkers/boss that the hassle was worth it? When possible, I prefer the batch file wild card. And whenever I return to batch files, I end up researching some of the unintuitive aspects such as parameters, quote handling, and ERRORLEVEL. But I never have to remember to use “REM” for comment lines, because there’s a cleaner way to do them! Double Colon For Eye-Friendly Comments Here is a very simple batch file, with pretty much minimal content: @ECHO OFF SETLOCAL REM This is a comment ECHO This batch file doesn’t do much If you code on a daily basis, this may be more suitable to your eyes: @ECHO OFF SETLOCAL :: This is a comment ECHO This batch file doesn’t do much Works great! I imagine I find it preferable due to the similarity to comments in other situations: // or ;  or # I’ve often make visual pseudo-line breaks in my code, and this colon-based syntax works wonders: @ECHO OFF SETLOCAL :: Do stuff ECHO Doing Stuff :::::::::::::::::::::::::::: :: Do more stuff ECHO This batch file doesn’t do much Not only is it more readable, but there’s a slight performance benefit. The batch file engine sees this as an invalid line label and immediately reads the following line. Use that fact to your advantage if this trick leads you into heated nerd debate. Two Pitfalls to Avoid Be aware of that there are a couple situations where this hack will fail you. It most likely won’t be a problem unless you’re getting really sophisticated with your batch files. Pitfall #1: Inline comments @ECHO OFF SETLOCAL IF EXIST C:\SomeFile.txt GOTO END ::This will fail :END Unfortunately, this fails. You can only have whitespace to the left of your comments. Pitfall #2: Code Blocks @ECHO OFF SETLOCAL IF EXIST C:\SomeFile.txt (         :: This will fail         ECHO HELLO ) Code blocks, such as if statements and for loops, cannot contain these comments. This is ultimately due to the fact that entire code blocks are processed as a single line. I originally learned this from Rob van der Woude’s site. He goes into more depth about the behavior of the pitfalls as well, if you are interested in further details. I hope this trick earns you serious geek rep!

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  • Thoughts on my new template language/HTML generator?

    - by Ralph
    I guess I should have pre-faced this with: Yes, I know there is no need for a new templating language, but I want to make a new one anyway, because I'm a fool. That aside, how can I improve my language: Let's start with an example: using "html5" using "extratags" html { head { title "Ordering Notice" jsinclude "jquery.js" } body { h1 "Ordering Notice" p "Dear @name," p "Thanks for placing your order with @company. It's scheduled to ship on {@ship_date|dateformat}." p "Here are the items you've ordered:" table { tr { th "name" th "price" } for(@item in @item_list) { tr { td @item.name td @item.price } } } if(@ordered_warranty) p "Your warranty information will be included in the packaging." p(class="footer") { "Sincerely," br @company } } } The "using" keyword indicates which tags to use. "html5" might include all the html5 standard tags, but your tags names wouldn't have to be based on their HTML counter-parts at all if you didn't want to. The "extratags" library for example might add an extra tag, called "jsinclude" which gets replaced with something like <script type="text/javascript" src="@content"></script> Tags can be optionally be followed by an opening brace. They will automatically be closed at the closing brace. If no brace is used, they will be closed after taking one element. Variables are prefixed with the @ symbol. They may be used inside double-quoted strings. I think I'll use single-quotes to indicate "no variable substitution" like PHP does. Filter functions can be applied to variables like @variable|filter. Arguments can be passed to the filter @variable|filter:@arg1,arg2="y" Attributes can be passed to tags by including them in (), like p(class="classname"). You will also be able to include partial templates like: for(@item in @item_list) include("item_partial", item=@item) Something like that I'm thinking. The first argument will be the name of the template file, and subsequent ones will be named arguments where @item gets the variable name "item" inside that template. I also want to have a collection version like RoR has, so you don't even have to write the loop. Thoughts on this and exact syntax would be helpful :) Some questions: Which symbol should I use to prefix variables? @ (like Razor), $ (like PHP), or something else? Should the @ symbol be necessary in "for" and "if" statements? It's kind of implied that those are variables. Tags and controls (like if,for) presently have the exact same syntax. Should I do something to differentiate the two? If so, what? This would make it more clear that the "tag" isn't behaving like just a normal tag that will get replaced with content, but controls the flow. Also, it would allow name-reuse. Do you like the attribute syntax? (round brackets) How should I do template inheritance/layouts? In Django, the first line of the file has to include the layout file, and then you delimit blocks of code which get stuffed into that layout. In CakePHP, it's kind of backwards, you specify the layout in the controller.view function, the layout gets a special $content_for_layout variable, and then the entire template gets stuffed into that, and you don't need to delimit any blocks of code. I guess Django's is a little more powerful because you can have multiple code blocks, but it makes your templates more verbose... trying to decide what approach to take Filtered variables inside quotes: "xxx {@var|filter} yyy" "xxx @{var|filter} yyy" "xxx @var|filter yyy" i.e, @ inside, @ outside, or no braces at all. I think no-braces might cause problems, especially when you try adding arguments, like @var|filter:arg="x", then the quotes would get confused. But perhaps a braceless version could work for when there are no quotes...? Still, which option for braces, first or second? I think the first one might be better because then we're consistent... the @ is always nudged up against the variable. I'll add more questions in a few minutes, once I get some feedback.

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  • Subterranean IL: Compiling C# exception handlers

    - by Simon Cooper
    An exception handler in C# combines the IL catch and finally exception handling clauses into a single try statement: try { Console.WriteLine("Try block") // ... } catch (IOException) { Console.WriteLine("IOException catch") // ... } catch (Exception e) { Console.WriteLine("Exception catch") // ... } finally { Console.WriteLine("Finally block") // ... } How does this get compiled into IL? Initial implementation If you remember from my earlier post, finally clauses must be specified with their own .try clause. So, for the initial implementation, we take the try/catch/finally, and simply split it up into two .try clauses (I have to use label syntax for this): StartTry: ldstr "Try block" call void [mscorlib]System.Console::WriteLine(string) // ... leave.s End EndTry: StartIOECatch: ldstr "IOException catch" call void [mscorlib]System.Console::WriteLine(string) // ... leave.s End EndIOECatch: StartECatch: ldstr "Exception catch" call void [mscorlib]System.Console::WriteLine(string) // ... leave.s End EndECatch: StartFinally: ldstr "Finally block" call void [mscorlib]System.Console::WriteLine(string) // ... endfinally EndFinally: End: // ... .try StartTry to EndTry catch [mscorlib]System.IO.IOException handler StartIOECatch to EndIOECatch catch [mscorlib]System.Exception handler StartECatch to EndECatch .try StartTry to EndTry finally handler StartFinally to EndFinally However, the resulting program isn't verifiable, and doesn't run: [IL]: Error: Shared try has finally or fault handler. Nested try blocks What's with the verification error? Well, it's a condition of IL verification that all exception handling regions (try, catch, filter, finally, fault) of a single .try clause have to be completely contained within any outer exception region, and they can't overlap with any other exception handling clause. In other words, IL exception handling clauses must to be representable in the scoped syntax, and in this example, we're overlapping catch and finally clauses. Not only is this example not verifiable, it isn't semantically correct. The finally handler is specified round the .try. What happens if you were able to run this code, and an exception was thrown? Program execution enters top of try block, and exception is thrown within it CLR searches for an exception handler, finds catch Because control flow is leaving .try, finally block is run The catch block is run leave.s End inside the catch handler branches to End label. We're actually running the finally before the catch! What we do about it What we actually need to do is put the catch clauses inside the finally clause, as this will ensure the finally gets executed at the correct time (this time using scoped syntax): .try { .try { ldstr "Try block" call void [mscorlib]System.Console::WriteLine(string) // ... leave.s End } catch [mscorlib]System.IO.IOException { ldstr "IOException catch" call void [mscorlib]System.Console::WriteLine(string) // ... leave.s End } catch [mscorlib]System.Exception { ldstr "Exception catch" call void [mscorlib]System.Console::WriteLine(string) // ... leave.s End } } finally { ldstr "Finally block" call void [mscorlib]System.Console::WriteLine(string) // ... endfinally } End: ret Returning from methods There is a further semantic mismatch that the C# compiler has to deal with; in C#, you are allowed to return from within an exception handling block: public int HandleMethod() { try { // ... return 0; } catch (Exception) { // ... return -1; } } However, you can't ret inside an exception handling block in IL. So the C# compiler does a leave.s to a ret outside the exception handling area, loading/storing any return value to a local variable along the way (as leave.s clears the stack): .method public instance int32 HandleMethod() { .locals init ( int32 retVal ) .try { // ... ldc.i4.0 stloc.0 leave.s End } catch [mscorlib]System.Exception { // ... ldc.i4.m1 stloc.0 leave.s End } End: ldloc.0 ret } Conclusion As you can see, the C# compiler has quite a few hoops to jump through to translate C# code into semantically-correct IL, and hides the numerous conditions on IL exception handling blocks from the C# programmer. Next up: catch-all blocks, and how the runtime deals with non-Exception exceptions.

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  • How to resize / enlarge / grow a non-LVM ext4 partition

    - by Mischa
    I have already searched the forums, but couldnt find a good suitable answer: I have an Ubuntu Server 10.04 as KVM Host and a guest system, that also runs 10.04. The host system uses LVM and there are three logical volumes, which are provided to the guest as virtual block devices - one for /, one for /home and one for swap. The guest had been partitioned without LVM. I have already enlarged the logical volume in the host system - the guest successfully sees the bigger virtual disk. However, this virtual disk contains one "good old" partition, which still has the old small size. The output of fdisk -l is me@produktion:/$ LC_ALL=en_US sudo fdisk -l Disk /dev/vda: 32.2 GB, 32212254720 bytes 255 heads, 63 sectors/track, 3916 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x000c8ce7 Device Boot Start End Blocks Id System /dev/vda1 * 1 3917 31455232 83 Linux Disk /dev/vdb: 2147 MB, 2147483648 bytes 244 heads, 47 sectors/track, 365 cylinders Units = cylinders of 11468 * 512 = 5871616 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x000f2bf7 Device Boot Start End Blocks Id System /dev/vdb1 1 366 2095104 82 Linux swap / Solaris Partition 1 has different physical/logical beginnings (non-Linux?): phys=(0, 32, 33) logical=(0, 43, 28) Partition 1 has different physical/logical endings: phys=(260, 243, 47) logical=(365, 136, 44) Disk /dev/vdc: 225.5 GB, 225485783040 bytes 255 heads, 63 sectors/track, 27413 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x00027f25 Device Boot Start End Blocks Id System /dev/vdc1 1 9138 73398272 83 Linux The output of parted print all is Model: Virtio Block Device (virtblk) Disk /dev/vda: 32.2GB Sector size (logical/physical): 512B/512B Partition Table: msdos Number Start End Size Type File system Flags 1 1049kB 32.2GB 32.2GB primary ext4 boot Model: Virtio Block Device (virtblk) Disk /dev/vdb: 2147MB Sector size (logical/physical): 512B/512B Partition Table: msdos Number Start End Size Type File system Flags 1 1049kB 2146MB 2145MB primary linux-swap(v1) Model: Virtio Block Device (virtblk) Disk /dev/vdc: 225GB Sector size (logical/physical): 512B/512B Partition Table: msdos Number Start End Size Type File system Flags 1 1049kB 75.2GB 75.2GB primary ext4 What I want to achieve is to simply grow or resize the partition /dev/vdc1 so that it uses the whole space provided by the virtual block device /dev/vdc. The problem is, that when I try to do that with parted, it complains: (parted) select /dev/vdc Using /dev/vdc (parted) print Model: Virtio Block Device (virtblk) Disk /dev/vdc: 225GB Sector size (logical/physical): 512B/512B Partition Table: msdos Number Start End Size Type File system Flags 1 1049kB 75.2GB 75.2GB primary ext4 (parted) resize 1 WARNING: you are attempting to use parted to operate on (resize) a file system. parted's file system manipulation code is not as robust as what you'll find in dedicated, file-system-specific packages like e2fsprogs. We recommend you use parted only to manipulate partition tables, whenever possible. Support for performing most operations on most types of file systems will be removed in an upcoming release. Start? [1049kB]? End? [75.2GB]? 224GB Error: File system has an incompatible feature enabled. Compatible features are has_journal, dir_index, filetype, sparse_super and large_file. Use tune2fs or debugfs to remove features. So what can I do? This is a headless production system. What is a safe way to grow this partition? I CAN unmount it, though - so this is not the problem.

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