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  • How to perform fresh linux install while preserving software raid and user accounts

    - by slayton
    I have a system with two software raid arrays. The OS is Ubuntu 9.04 and is no longer receiving updates. I'd like to update the system to 12.04 rather than trying to do the automatic update from 9.04-> 9.10-> ... -> 12.04. My main drive has 2 partitions that are mounted at / and /home. Is it possible to do a fresh install of linux to the partition where / is mounted while preserving user accounts and preferences (such as passwords, home dir locations, etc...)? Additionally what do I need to do to keep my software raid array intact following the OS re-install?

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  • How do I log file system read/writes by filename in Linux?

    - by Casey
    I'm looking for a simple method that will log file system operations. It should display the name of the file being accessed or modified. I'm familiar with powertop, and it appears this works to an extent, in so much that it show the user files that were written to. Is there any other utilities that support this feature. Some of my findings: powertop: best for write access logging, but more focused on CPU activity iotop: shows real time disk access by process, but not file name lsof: shows the open files per process, but not real time file access iostat: shows the real time I/O performance of disk/arrays but does not indicate file or process

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  • Terrible Performance with SATA Drives on Dell PowerEdge, steps to troubleshoot?

    - by Tom
    I had asked this question earlier and the question went missing so here it is again. Bought a DELL Poweredge 2950 to use as in-house QA Server. Disk performance is beyond terrible, 1000-4000 ms response time on the drive with our SQL Server database .mdf. Sql Server disk queue upwards of 300 at times. I'm a software guy, can anyone help me with steps to determine the issue? I don't know what RAID controller it has, how can I determine that? I'm speculating it could be BIOS issue. Perhaps the server used to have another kind of drive in it and when I added SATA the ??? buffer size is wrong??? Perhaps I chose wrong options (chose defaults) when setting up the RAID 1 arrays? I thought RAID 1 was a performance array?

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  • Any experience with SATA SAS Interposer Cards?

    - by korkman
    Driven by the current price difference between SATA and SAS disks on one side and the potentially bad behaviour of SATA disks in bigger storage arrays on the other side, I have found so-called SATA-to-SAS interposer cards. Advertised as "seamlessly adding SAS capabilities to existing SATA disk drives", I wonder if anyone here has had some experience with these or similar products. The major benefits I can identify are the increased cable voltage (if all drives are SAS connected), the ability to power-cycle the drive and multipath (if desired). Obviously the SATA drive will still have to be RAID edition. The question is: Do these cards indeed increase the overall reliability of a storage system, or will failing SATA disks cause trouble nevertheless? Edit: I'm not asking for hypothetical answers, only actual experience please. I'm well aware that the typical 10k SAS drive is more reliable (and better performing) than 7200 SATA drives. But how does a nearline SAS, which is phyiscally the same disk as its SATA counterpart, compare to the SATA version with interposer?

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  • FreeNAS/ZFS/Raid-Z slightly different disks

    - by muskratt
    I'm considering using FreeNAS and "recycling" some of my older 1TB disks. Two are the exact same model Western Digital while another is Seagate and the fourth is Samsung. Typically, since all disks are not equal, I'll create my arrays on a Windows-based server 1GB undersized to prevent a replacement disk not being large enough. Dell is notorious for sending replacement SATA disks of different brand---knock on wood, no problems yet. Since not all drives are created equally and they can vary a few MBs, is there a way to make the the FreeNas/ZFS/Raid-Z function in the same way I do for my Windows-based servers above? Thanks

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  • My SSD stopped working as it ends up in blue death right after windows 7 launches, how can I reset it for new windows install?

    - by HattoriHanzo
    As I mentioned in the title my SSD suddenly started to fail as after launching Windows 7 it goes straight to completely idle and after a few minutes it goes to blue death and restarts. I have an another HD with a windows xp on it and it works fine and I can also see the SSD and can access everything on it. Windows 7 on the SSD does work in safe mode though yet I didn't manage to find out what causes the problem. Since I can sill access the files and save them to another HD I'm looking for the best way to wipe and reinstall Windows 7. I have yet failed to find an easy to follow (or even understand) guide, different sources on the internet recommend different ways of doing this. And some guides are just simply full of terms I have no clue about. It's an OCZ Vertex 2 120GB. I"d very much appreciate if someone could give me an advice on what I should do, preferably in a way so I could regain the best possible performance as well. it doesn't matter if I don't understand the science behind it as long as I can follow the steps. Thanks!

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  • When using RAID10 + BBWC why is it better to separate PostgreSQL data files from OS and transaction logs than to keep them all on the same array?

    - by Vlad
    I've seen the advice everywhere (including here and here): keep your OS partition, DB data files and DB transaction logs on separate discs/arrays. The general recommendation is to use RAID1 for OS, RAID10 for data (or RAID5 if load is very read-biased) and RAID1 for transaction logs. However, considering that you will need at least 6 or 8 drives to build this setup, wouldn't a RAID10 over 6-8 drives with BBWC perform better? What if the drives are SSDs? I'm talking here about internal server drives, not SAN.

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  • Is it a good Idea to switch to a SSD to use less battery?

    - by Walter Maier-Murdnelch
    I am thinking of buying a SSD for my laptop, mainly for the purpose of extended operating time when running on battery. At the moment I use a Hitachi HTS545032B9A300 (320GB) (Datasheet) as main drive and a Seagate Momentus 5400.3 120GB as secondary drive. I dualboot Windows and Linux but I don't need the windows partition any longer, a 120GB SDD would be more than sufficient space-wise. Speed is not an issue for me, I make heavy use of tmpfs (ramdrive) within Linux and transfers of bigger files are mainly through some network filesystem anyways, thus a cheaper SSD should do. For the purpose of comparison I chose the OCZ Vertex Plus 120GB. Power consumption always is a big promotional thing the industry uses to make me want to buy their SSDs, some sheet on the OCZ page provides an astonishing comparison of desktop HDDS and SSDs. The numbers I got comparing my laptop HDD and their SSD were not really astonishing any longer. Hitachi 320GB HDD: Startup (W, peak, max.) 4.5 Seek (W, avg.) 1.7 Read / Write (W, avg.) 1.4 Performance idle (W, avg.) 1.3 Active idle (W, avg.) 0.8 Low power idle (W, avg.) 0.5 Standby (W, avg.) 0.2 Sleep 0.1 OCZ 120GB SSD: 1.5W active 0.3W standby I see that there are differences, but actually they don't seem that high as I though they were. And compared to the power consuption of the rest of my system I wonder if it makes a difference at all. Have I just taken the wrong look at the whole thing or may I be better off to buy another battery for my laptop?

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  • Remove values from array on foreach PHP

    - by user104531
    I have an array like this: Array ( [0] => Array ( [id] => 68 [type] => onetype [type_id] => 131 [name] => name1 ) [1] => Array ( [id] => 32 [type] => anothertype [type_id] => 101 [name] => name2 ) ) I need to remove some arrays from it if the users has permissions or not to see that kind of type. I am thinking on doing it with a for each, and do the needed ifs inside it to remove or let it as it. My question is: What's the most efficent way to do this? The array will have no more than 100 records. But several users will request it and do the filtering over and over.

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  • 5 x 3GB drives and 4 x 1500GB drive best raid setup?

    - by Zen_Silence
    Hello, I am building a file server my plan is the have the Operating system on one raid partition and the data storage on another partition. I currently have 5 x 3GB IDE drives that i would like to put the operating system on theses drives are old but that doesnt matter to me at the moment i have a ton of them so for this raid partition i would probably want to be able to pull out dead a drive and rebuild the array. My file partition is going to consist of 4 x 1.5TB SATA drives I would like the maximum storage with some redundancy. Any suggestions to which Raid level i should use would be greatly appreciated and if you could also suggest a PCI or PCI-e raid controller to handle theses arrays. Thanks in Advance, Zen_Silence

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  • Does having TRIM enabled affect other hard drives on a computer (and how do you know when Windows is using it)?

    - by Breakthrough
    I recently purchased a solid state drive (an OCZ Vertex 2 (80 GB)) to use as my primary operating system partition. I also have three other SATA hard drives of assorted sizes. I successfully installed Windows 7 Professional onto the SSD (works awesome, great response time and transfer rate), and used the other three HDDs for data storage. I was browsing through the Bible of OCZ SSDs, and noticed the following in Section 60-76 - Tweaks and TRIM: Q. How do I know if TRIM is enabled on my OCZ SSD? A. In Windows 7, go to start/run/cmd), type the following: fsutil.exe behaviour query DisableDeleteNotify It should respond back with: DisableDeleteNotify=0 if TRIM support is ready and active. If it's not, then type: fsutil.exe behavior set DisableDeleteNotify 0 After a bit of searching on Google, I found similar results elsewhere (set DisableDeleteNotify to 0, which makes sense since for TRIM to work, the solid-state drive needs to be notified when deletes occur (for the garbage collector) unlike a normal hard drive). When I run the query on fsutil, I get the following result: DisableDeleteNotify = 48 Following the instructions I found, I set this to 0 instead of 48. However, I am beginning to wonder. Is this all the proof I really need that the OS is using TRIM? Also, since this applies globally for the computer, is TRIM data being sent to the other hard drives connected to the computer? And if so, would this cause any degradation in disk performance?

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  • RAID 10, how layout works ?

    - by Bastien974
    I'm trying to figure out how exactly works the RAID 10 in linux with mdadm. I want to create a RAID 10 out of 4 partitions, let's say a, b, c and d. a and b are on the array 1, c and d array 2. So what I want is to have the couple a and b, c and d in RAID 0. Then on top of that, a RAID 1. The option in the mdadm command to configure the layout is -p, --layout with option : near, far, offset see here I want to keep my data safe if the array 1 fails for example, that would mean that every chunk of data are always copied on both arrays. How do I have to set my RAID 10, near or far ?

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  • How to prevent an SSD from disappearing from BIOS

    - by Midimatt
    I've only recently upgraded my old machine to a new one with a brand new 60gb SSD as my boot drive and a 1TB main drive. Paranoid about completely breaking my SSD, I read up on a lot of issues that I needed to watch out for, including making sure AHCI was turned on and trim enabled. PC has been working fine for a few weeks now, until today. My wife was watching some TV on the machine when it started to act strange and eventually blue screened. She rebooted and the boot mgr was missing. When I got home from work I checked the BIOS and the drive had disappeared. I panicked and looked up some possible fixes, and I discovered a large amount of people having problems with the drive firmware, especially on OCZ Vertex and Agility drives, and my drive is an Agility 3 drive. The problems included blue screens followed by missing drives, and a solution was to reset the CMOS and try again. This worked, and now everything seems to be working fine. My question is, is there any way to prevent this from happening? Am I missing a setting for my SSD? All of the posts I found were from early to mid-2011 nothing for the end of 2011 to 2012. So I am wondering if I've missed anything. EDIT: Checked my drives firmware and it is 2.15, which has had issues reported by users.

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  • How do I log file system read/writes by filename in Linux?

    - by Casey
    I'm looking for a simple method that will log file system operations. It should display the name of the file being accessed or modified. I'm familiar with powertop, and it appears this works to an extent, in so much that it show the user files that were written to. Is there any other utilities that support this feature. Some of my findings: powertop: best for write access logging, but more focused on CPU activity iotop: shows real time disk access by process, but not file name lsof: shows the open files per process, but not real time file access iostat: shows the real time I/O performance of disk/arrays but does not indicate file or process

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  • How to remove a drive from a 2-drive RAID 5 array?

    - by DrSAR
    There is some information available on shape changes in RAID arrays but I'm a little nervous and would like confirmation: Problem: I have 2 500GB drive as software raid 5 (mdadm). I would like to free one of the two drives since RAID-redundancy is for wimps... Can I just mdadm --grow --array-size=1 followed by a mdadm --grow --raid-disks 1? This seems too simple. How would I specify which drive gets freed? Part of the reason for this maneuver is that I don't have additional space to run a backup.

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  • HP DL380 Losing Drive Array

    - by jidl
    I have an HP Proliant DG380 G7 dropping one of it's arrays every hour, on the hour, for 2-5 minutes. The OS is SBS 2011 Standard, the servers runs Exchange, DC, files & Trend WFBS 8. I can watch the D Drive disappear for the duration of the problem - then it just comes back up and all is well again. There is no loss of network connectivity, although the mapped drives also disappear. We thought it might be to do with Sharepoint / VSS writers failing but it looks as though this is a symptom rather than cause. It survives a reboot. Any ideas as to what could be running on a regular schedule like this?

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  • SAN for Medium Business - Where to start? [closed]

    - by Henson
    I've always run Linux on my home computers, and done PC repair for years, but this is my first experience with needing to buy a SAN. I thought I was knowledgeable, but I feel a bit lost. I need to be able to support 25 VMs, which are currently managed through vSphere. The company I'm at is growing quickly though, so I'd like to plan for the future. Ideally, I want a solution that I can just tack arrays onto and manage as one large, iSCSI drive. Suggestions? Good resources? If I can find something that appears to software as one large drive, am I better off going with a solution like FreeNAS or Starwind, or an all-in-one proprietary solution like NetApp? Cost, is (of course, and always I'm sure) an issue.

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  • 5x5 matrix multiplication in C

    - by Rick
    I am stuck on this problem in my homework. I've made it this far and am sure the problem is in my three for loops. The question directly says to use 3 for loops so I know this is probably just a logic error. #include<stdio.h> void matMult(int A[][5],int B[][5],int C[][5]); int printMat_5x5(int A[5][5]); int main() { int A[5][5] = {{1,2,3,4,6}, {6,1,5,3,8}, {2,6,4,9,9}, {1,3,8,3,4}, {5,7,8,2,5}}; int B[5][5] = {{3,5,0,8,7}, {2,2,4,8,3}, {0,2,5,1,2}, {1,4,0,5,1}, {3,4,8,2,3}}; int C[5][5] = {0}; matMult(A,B,C); printMat_5x5(A); printf("\n"); printMat_5x5(B); printf("\n"); printMat_5x5(C); return 0; } void matMult(int A[][5], int B[][5], int C[][5]) { int i; int j; int k; for(i = 0; i <= 2; i++) { for(j = 0; j <= 4; j++) { for(k = 0; k <= 3; k++) { C[i][j] += A[i][k] * B[k][j]; } } } } int printMat_5x5(int A[5][5]){ int i; int j; for (i = 0;i < 5;i++) { for(j = 0;j < 5;j++) { printf("%2d",A[i][j]); } printf("\n"); } } EDIT: Here is the question, sorry for not posting it the first time. (2) Write a C function to multiply two five by five matrices. The prototype should read void matMult(int a[][5],int b[][5],int c[][5]); The resulting matrix product (a times b) is returned in the two dimensional array c (the third parameter of the function). Program your solution using three nested for loops (each generating the counter values 0, 1, 2, 3, 4) That is, DO NOT code specific formulas for the 5 by 5 case in the problem, but make your code general so it can be easily changed to compute the product of larger square matrices. Write a main program to test your function using the arrays a: 1 2 3 4 6 6 1 5 3 8 2 6 4 9 9 1 3 8 3 4 5 7 8 2 5 b: 3 5 0 8 7 2 2 4 8 3 0 2 5 1 2 1 4 0 5 1 3 4 8 2 3 Print your matrices in a neat format using a C function created for printing five by five matrices. Print all three matrices. Generate your test arrays in your main program using the C array initialization feature. enter code here

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  • Visual C++ 2010 Winform Errors C2238, C2059, C1075.

    - by tracelez
    It errors when I try compile. I cut the code out of the program and the program works and complies correctly. Not sure why it doesn't like this. This part of the code does single digit math with numeric strings that are converted into a char arrays. ** Error 2 error C2238: unexpected token(s) preceding ';' C:\Users\Alpha\documents\visual studio 2010\Projects\Win32 Form c++\Win32 Form c++\Win32 Form c++.cpp 10 1 Win32 Form c++ ** Error 1 error C2059: syntax error : 'namespace' C:\Users\Alpha\documents\visual studio 2010\Projects\Win32 Form c++\Win32 Form c++\Win32 Form c++.cpp 10 1 Win32 Form c++ ** Error 3 error C1075: end of file found before the left brace '{' at 'c:\users\alpha\documents\visual studio 2010\projects\win32 form c++\win32 form c++\Form1.h(40)' was matched C:\Users\Alpha\documents\visual studio 2010\Projects\Win32 Form c++\Win32 Form c++\Win32 Form c++.cpp 23 1 Win32 Form c++ ////// ////// // chX[] and chY[] are char arrays from functional part of program std::reverse( chX, &chX[ strlen( chX ) ] ); std::reverse( chY, &chY[ strlen( chY ) ] ); // makes sure x is larger or equal to y...makes looping logic easier if (strlen(chX) < strlen(chY)) { char *chZ = chX; chX = chY; chY = chZ; } //Variables for this part of the program char chX2; char chY2; std::string strSum; int sum = 0; bool carryth1 = false; int x=0; int y=0; for (int i = 0; i <= (strlen(chX)-1); i++) { if (i <= strlen(chY)-1) { chX2= chX[i]; chY2= chY[i]; x = atoi(chX2); y = atoi(chY2); //x = atoi(chX[i]); sum = x+y+(int)carryth1; carryth1 = false; if (sum > 9) { if(i == 0) { sum -=10; strSum = itoa(sum); carryth1 = true; } else { sum -=10; strSum += itoa(sum); carryth1 = true; } } else { if(i == 0) { strSum = itoa(sum); } else { strSum += itoa(sum); } } else { y = 0; chX2= chX[i]; x = atoi(chX2); sum = x+y+(int)carryth1; if((i == strlen(chX)-1)&& (carryth1 == true) && (x == 9)) { strSum += "10"; } else { strSum = itoa(sum); } } std::reverse( strSum, &strSum[ strlen( strSum ) ] ); //Creates new string for txtDisplay this simplifies conversions String^ strDisplay = "X is " + gcnew String((strX1.c_str())) + " Y is " +gcnew String((strY1.c_str())) + " \r\n " ; strDisplay += "The sum of the X + Y = "; txtDisplay->Text = gcnew String((strSum.c_str())) ;

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  • Save blob to DB using hibernate

    - by Link123
    Hey! I tried save file to MySQL using blob with hibernate3. But I always have java.lang.UnsupportedOperationException: Blob may not be manipulated from creating session org.hibernate.lob.BlobImpl.excep(BlobImpl.java:127) Here some code. package com.uni.domain; public class File extends Identifier { private byte[] data; private String contentType; public byte[] getData() { return data; } public File() {} public void setData(byte[] photo) { this.data = photo; } public boolean isNew() { return true; } public String getContentType() { return contentType; } public void setContentType(String contentType) { this.contentType = contentType; } } package com.uni.domain; import org.hibernate.Hibernate; import org.hibernate.HibernateException; import org.hibernate.usertype.UserType; import java.io.InputStream; import java.io.OutputStream; import java.io.Serializable; import java.sql.*; import java.util.Arrays; public class PhotoType implements UserType { public int[] sqlTypes() { return new int[]{Types.BLOB}; } public Class returnedClass() { return byte[].class; } public boolean equals(Object o, Object o1) throws HibernateException { return Arrays.equals((byte[]) o, (byte[]) o1); } public int hashCode(Object o) throws HibernateException { return o.hashCode(); } public Object nullSafeGet(ResultSet resultSet, String[] strings, Object o) throws HibernateException, SQLException { Blob blob = resultSet.getBlob(strings[0]); return blob.getBytes(1, (int) blob.length()); } public void nullSafeSet(PreparedStatement st, Object value, int index) throws HibernateException, SQLException { st.setBlob(index, Hibernate.createBlob((byte[]) value)); } public Object deepCopy(Object value) { if (value == null) return null; byte[] bytes = (byte[]) value; byte[] result = new byte[bytes.length]; System.arraycopy(bytes, 0, result, 0, bytes.length); return result; } public boolean isMutable() { return true; } public Serializable disassemble(Object o) throws HibernateException { return null; . } public Object assemble(Serializable serializable, Object o) throws HibernateException { return null; . } public Object replace(Object o, Object o1, Object o2) throws HibernateException { return null; . } <?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> <hibernate-mapping package="com.uni.domain"> <class name="com.uni.domain.File"> <id name="id"> <generator class="native"/> </id> <property name="data" type="com.uni.domain.FleType"/> <property name="contentType"/> </class> </hibernate-mapping> Help me please. Where I’m wrong?

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  • Using UUIDs for cheap equals() and hashCode()

    - by Tom McIntyre
    I have an immutable class, TokenList, which consists of a list of Token objects, which are also immutable: @Immutable public final class TokenList { private final List<Token> tokens; public TokenList(List<Token> tokens) { this.tokens = Collections.unmodifiableList(new ArrayList(tokens)); } public List<Token> getTokens() { return tokens; } } I do several operations on these TokenLists that take multiple TokenLists as inputs and return a single TokenList as the output. There can be arbitrarily many TokenLists going in, and each can have arbitrarily many Tokens. These operations are expensive, and there is a good chance that the same operation (ie the same inputs) will be performed multiple times, so I would like to cache the outputs. However, performance is critical, and I am worried about the expense of performing hashCode() and equals() on these objects that may contain arbitrarily many elements (as they are immutable then hashCode could be cached, but equals will still be expensive). This led me to wondering whether I could use a UUID to provide equals() and hashCode() simply and cheaply by making the following updates to TokenList: @Immutable public final class TokenList { private final List<Token> tokens; private final UUID uuid; public TokenList(List<Token> tokens) { this.tokens = Collections.unmodifiableList(new ArrayList(tokens)); this.uuid = UUID.randomUUID(); } public List<Token> getTokens() { return tokens; } public UUID getUuid() { return uuid; } } And something like this to act as a cache key: @Immutable public final class TopicListCacheKey { private final UUID[] uuids; public TopicListCacheKey(TopicList... topicLists) { uuids = new UUID[topicLists.length]; for (int i = 0; i < uuids.length; i++) { uuids[i] = topicLists[i].getUuid(); } } @Override public int hashCode() { return Arrays.hashCode(uuids); } @Override public boolean equals(Object other) { if (other == this) return true; if (other instanceof TopicListCacheKey) return Arrays.equals(uuids, ((TopicListCacheKey) other).uuids); return false; } } I figure that there are 2^128 different UUIDs and I will probably have at most around 1,000,000 TokenList objects active in the application at any time. Given this, and the fact that the UUIDs are used combinatorially in cache keys, it seems that the chances of this producing the wrong result are vanishingly small. Nevertheless, I feel uneasy about going ahead with it as it just feels 'dirty'. Are there any reasons I should not use this system? Will the performance costs of the SecureRandom used by UUID.randomUUID() outweigh the gains (especially since I expect multiple threads to be doing this at the same time)? Are collisions going to be more likely than I think? Basically, is there anything wrong with doing it this way?? Thanks.

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  • python: what are efficient techniques to deal with deeply nested data in a flexible manner?

    - by AlexandreS
    My question is not about a specific code snippet but more general, so please bear with me: How should I organize the data I'm analyzing, and which tools should I use to manage it? I'm using python and numpy to analyse data. Because the python documentation indicates that dictionaries are very optimized in python, and also due to the fact that the data itself is very structured, I stored it in a deeply nested dictionary. Here is a skeleton of the dictionary: the position in the hierarchy defines the nature of the element, and each new line defines the contents of a key in the precedent level: [AS091209M02] [AS091209M01] [AS090901M06] ... [100113] [100211] [100128] [100121] [R16] [R17] [R03] [R15] [R05] [R04] [R07] ... [1263399103] ... [ImageSize] [FilePath] [Trials] [Depth] [Frames] [Responses] ... [N01] [N04] ... [Sequential] [Randomized] [Ch1] [Ch2] Edit: To explain a bit better my data set: [individual] ex: [AS091209M02] [imaging session (date string)] ex: [100113] [Region imaged] ex: [R16] [timestamp of file] ex [1263399103] [properties of file] ex: [Responses] [regions of interest in image ] ex [N01] [format of data] ex [Sequential] [channel of acquisition: this key indexes an array of values] ex [Ch1] The type of operations I perform is for instance to compute properties of the arrays (listed under Ch1, Ch2), pick up arrays to make a new collection, for instance analyze responses of N01 from region 16 (R16) of a given individual at different time points, etc. This structure works well for me and is very fast, as promised. I can analyze the full data set pretty quickly (and the dictionary is far too small to fill up my computer's ram : half a gig). My problem comes from the cumbersome manner in which I need to program the operations of the dictionary. I often have stretches of code that go like this: for mk in dic.keys(): for rgk in dic[mk].keys(): for nk in dic[mk][rgk].keys(): for ik in dic[mk][rgk][nk].keys(): for ek in dic[mk][rgk][nk][ik].keys(): #do something which is ugly, cumbersome, non reusable, and brittle (need to recode it for any variant of the dictionary). I tried using recursive functions, but apart from the simplest applications, I ran into some very nasty bugs and bizarre behaviors that caused a big waste of time (it does not help that I don't manage to debug with pdb in ipython when I'm dealing with deeply nested recursive functions). In the end the only recursive function I use regularly is the following: def dicExplorer(dic, depth = -1, stp = 0): '''prints the hierarchy of a dictionary. if depth not specified, will explore all the dictionary ''' if depth - stp == 0: return try : list_keys = dic.keys() except AttributeError: return stp += 1 for key in list_keys: else: print '+%s> [\'%s\']' %(stp * '---', key) dicExplorer(dic[key], depth, stp) I know I'm doing this wrong, because my code is long, noodly and non-reusable. I need to either use better techniques to flexibly manipulate the dictionaries, or to put the data in some database format (sqlite?). My problem is that since I'm (badly) self-taught in regards to programming, I lack practical experience and background knowledge to appreciate the options available. I'm ready to learn new tools (SQL, object oriented programming), whatever it takes to get the job done, but I am reluctant to invest my time and efforts into something that will be a dead end for my needs. So what are your suggestions to tackle this issue, and be able to code my tools in a more brief, flexible and re-usable manner?

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  • Why is processing a sorted array faster than an unsorted array?

    - by GManNickG
    Here is a piece of code that shows some very peculiar performance. For some strange reason, sorting the data miraculously speeds up the code by almost 6x: #include <algorithm> #include <ctime> #include <iostream> int main() { // generate data const unsigned arraySize = 32768; int data[arraySize]; for (unsigned c = 0; c < arraySize; ++c) data[c] = std::rand() % 256; // !!! with this, the next loop runs faster std::sort(data, data + arraySize); // test clock_t start = clock(); long long sum = 0; for (unsigned i = 0; i < 100000; ++i) { // primary loop for (unsigned c = 0; c < arraySize; ++c) { if (data[c] >= 128) sum += data[c]; } } double elapsedTime = static_cast<double>(clock() - start) / CLOCKS_PER_SEC; std::cout << elapsedTime << std::endl; std::cout << "sum = " << sum << std::endl; } Without std::sort(data, data + arraySize);, the code runs in 11.54 seconds. With the sorted data, the code runs in 1.93 seconds. Initially I thought this might be just a language or compiler anomaly. So I tried it Java... import java.util.Arrays; import java.util.Random; public class Main { public static void main(String[] args) { // generate data int arraySize = 32768; int data[] = new int[arraySize]; Random rnd = new Random(0); for (int c = 0; c < arraySize; ++c) data[c] = rnd.nextInt() % 256; // !!! with this, the next loop runs faster Arrays.sort(data); // test long start = System.nanoTime(); long sum = 0; for (int i = 0; i < 100000; ++i) { // primary loop for (int c = 0; c < arraySize; ++c) { if (data[c] >= 128) sum += data[c]; } } System.out.println((System.nanoTime() - start) / 1000000000.0); System.out.println("sum = " + sum); } } with a similar but less extreme result. My first thought was that sorting brings the data into cache, but my next thought was how silly that is because the array was just generated. What is going on? Why is a sorted array faster than an unsorted array? The code is summing up some independent terms, the order should not matter.

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  • Parallel processing via multithreading in Java

    - by Robz
    There are certain algorithms whose running time can decrease significantly when one divides up a task and gets each part done in parallel. One of these algorithms is merge sort, where a list is divided into infinitesimally smaller parts and then recombined in a sorted order. I decided to do an experiment to test whether or not I could I increase the speed of this sort by using multiple threads. I am running the following functions in Java on a Quad-Core Dell with Windows Vista. One function (the control case) is simply recursive: // x is an array of N elements in random order public int[] mergeSort(int[] x) { if (x.length == 1) return x; // Dividing the array in half int[] a = new int[x.length/2]; int[] b = new int[x.length/2+((x.length%2 == 1)?1:0)]; for(int i = 0; i < x.length/2; i++) a[i] = x[i]; for(int i = 0; i < x.length/2+((x.length%2 == 1)?1:0); i++) b[i] = x[i+x.length/2]; // Sending them off to continue being divided mergeSort(a); mergeSort(b); // Recombining the two arrays int ia = 0, ib = 0, i = 0; while(ia != a.length || ib != b.length) { if (ia == a.length) { x[i] = b[ib]; ib++; } else if (ib == b.length) { x[i] = a[ia]; ia++; } else if (a[ia] < b[ib]) { x[i] = a[ia]; ia++; } else { x[i] = b[ib]; ib++; } i++; } return x; } The other is in the 'run' function of a class that extends thread, and recursively creates two new threads each time it is called: public class Merger extends Thread { int[] x; boolean finished; public Merger(int[] x) { this.x = x; } public void run() { if (x.length == 1) { finished = true; return; } // Divide the array in half int[] a = new int[x.length/2]; int[] b = new int[x.length/2+((x.length%2 == 1)?1:0)]; for(int i = 0; i < x.length/2; i++) a[i] = x[i]; for(int i = 0; i < x.length/2+((x.length%2 == 1)?1:0); i++) b[i] = x[i+x.length/2]; // Begin two threads to continue to divide the array Merger ma = new Merger(a); ma.run(); Merger mb = new Merger(b); mb.run(); // Wait for the two other threads to finish while(!ma.finished || !mb.finished) ; // Recombine the two arrays int ia = 0, ib = 0, i = 0; while(ia != a.length || ib != b.length) { if (ia == a.length) { x[i] = b[ib]; ib++; } else if (ib == b.length) { x[i] = a[ia]; ia++; } else if (a[ia] < b[ib]) { x[i] = a[ia]; ia++; } else { x[i] = b[ib]; ib++; } i++; } finished = true; } } It turns out that function that does not use multithreading actually runs faster. Why? Does the operating system and the java virtual machine not "communicate" effectively enough to place the different threads on different cores? Or am I missing something obvious?

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  • Android: Having trouble creating a subclass of application to share data with multiple Activities

    - by Mike
    Hello, I just finished a couple of activities in my game and now I was going to start to wire them both up to use real game data, instead of the test data I was using just to make sure each piece worked. Since multiple Activities will need access to this game data, I started researching the best way to pass this data to my Activities. I know about using putExtra with intents, but my GameData class has quite a bit of data and not just simple key value pairs. Besides quite a few basic data types, it also has large arrays. I didn't really want to try and pass all that, unless I can pass the entire object, instead of just key/data pairs. I read the following post and thought it would be the way to go, but so far, I haven't got it to work. Android: How to declare global variables? I created a simple test app to try this method out, but it keeps crashing and my code seems to look the same as in the post above - except I changed the names. Here is the error I am getting. Can someone help me understand what I am doing wrong? 12-23 00:50:49.762: ERROR/AndroidRuntime(608): Caused by: java.lang.ClassCastException: android.app.Application It crashes on the following statement: GameData newGameData = ((GameData)getApplicationContext()); Here is my code: package mrk.examples.StaticGameData; import android.app.Application; public class GameData extends Application { private int intTest; GameData () { intTest = 0; } public int getIntTest(){ return intTest; } public void setIntTest(int value){ intTest = value; } } // My main activity package mrk.examples.StaticGameData; import android.app.Activity; import android.content.Intent; import android.os.Bundle; import android.util.Log; public class StaticGameData extends Activity { int intStaticTest; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); GameData newGameData = ((GameData)getApplicationContext()); newGameData.setIntTest(0); intStaticTest = newGameData.getIntTest(); Log.d("StaticGameData", "Well: IntStaticTest = " + intStaticTest); newGameData.setIntTest(1); Log.d("StaticGameData", "Well: IntStaticTest = " + intStaticTest + " newGameData: " + newGameData.getIntTest()); Intent intentNew = new Intent(this, PassData2Activity.class); startActivity (intentNew); } } // My test Activity to see if it can access the data and its previous state from the last activity package mrk.examples.StaticGameData; import android.app.Activity; import android.os.Bundle; import android.util.Log; public class PassData2Activity extends Activity { @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); GameData gamedataPass = ((GameData)getApplicationContext()); Log.d("PassData2Activity", "IntTest = " + gamedataPass.getIntTest()); } } Below is the relevant portion of my manifest: <application android:icon="@drawable/icon" android:label="@string/app_name"> <activity android:name=".StaticGameData" android:label="@string/app_name"> <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity> <activity android:name=".PassData2Activity"></activity> </application> <application android:name=".GameData" android:icon="@drawable/icon" android:label="@string/app_name"> </application> Thanks in advance for helping me understand why this code is crashing. Also, if you think this is just the wrong approach to let multiple activities have access to the same data, please give your suggestion. Please keep in mind that I am talking about quite a few variables and some large arrays.

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