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• 'txn-current-lock': Permission denied [500, #13] - Subversion + Apache Configuration Issue

  - by wfoster

  Current Setup Fedora 13 32bit Apache 2.2.16 Subversion repositories setup under /var/www/svn I have two different repositories under this directory so my /etc/httpd/conf.d/subversion.conf setup in this way; LoadModule dav_svn_module modules/mod_dav_svn.so LoadModule authz_svn_module modules/mod_authz_svn.so <Location /svn> DAV svn SVNListParentPath on SVNParentPath /var/www/svn <LimitExcept GET PROPFIND OPTIONS REPORT> AuthType Basic AuthName "Subversion Repository" AuthUserFile /etc/httpd/.htpasswd Require valid-user </LimitExcept> </Location> After copying over my repos and using; chmod 755 -R /var/www/svn chcon -R -t httpd_sys_content_t /var/www/svn chown apache:apache -R /var/www/svn I can browse my repos fine through the browser, and I can update all my working copies, however when I try to check in from anywhere I get the same error Can't open file '/var/www/svn/repo/db/txn-current-lock':Permission denied I have been working on this issue for a while now and cant seem to find a solution to my issues. It might be of some use to know that the repo existed on a different server before this, it has been now moved to this new server. Everything I have read seems to indicate that the permissions for apache are incorrect, however apache is set to run as User apache and Group apache. So as far as I can tell my setup is correct. The behavior is not though. Any Ideas? Solution The only way I was able to get this to work is to disable SELinux, it could also be done by setting the proper booleans with SELinux via setsetbool and getsebool since this is just a home server, I decided to disable SELinux and am reaping the benefits now.

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• I love google Chrome, but some non-static pages like Piwik render it unresponsive

  - by gogowitsch

  The web-stat software Piwik stops reacting on mouse clicks after 1-2 seconds. The same is true for Google Maps and Producteev (but GMail and most other pages work like a charm). These rely heavily on JS, and work without Flash. I can click for a very short time period and then the mouse cursor doesn't feel the UI anymore (it doesn't turn into a I over input fields, though it moves; if the freeze occured while the pointer was over an input field, the cursor keeps being a I) and all clicks on the DOM are being ignored by Chrome. No message appears, neither obvious nor in the Console (F12). There is no obstructing div or the like in the DOM (F12). Since I couldn't find any hints on the source of my problems, I suspected my plugins and extensions. Unfortunately, neither deactivating all plugins nor all extensions solved the problem. for the problematic pages, it always happens no Dropbox running several GB of free RAM the taskmanager doesn't show any high CPU or memory utilization (the offending tab uses 30 MB and uses 0-1 % CPU) all problematic pages work in other browsers (Chrome, Firefox, IE) the rest of the computer is very responsive the computers use different security suites (Kaspersky and Avira) The effect exists between several (synchronized) Chrome instances on different machines, all running Windows 7. Both the OS and Chrome are updated automatically. Other tabs and the Chrome chrome (tabs, menus, toolbar buttons of the browser itself) still work. I really don't like switching between browsers. Any ideas?

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• Repairing inconsistent pages in database

  - by Raj

  We have a SQL 2000 DB. The server crashed due to Raid array failure. Now when we run DBCC CHECKDB, we get an error that there are 27 consistency errors in 9 pages. When we run DBCC PAGE on these pages, we get this: Msg 8939, Level 16, State 106, Line 1 Table error: Object ID 1397580017, index ID 2, page (1:8404521). Test (m_freeCnt == freeCnt) failed. Values are 2 and 19. Msg 8939, Level 16, State 108, Line 1 Table error: Object ID 1397580017, index ID 2, page (1:8404521). Test (emptySlotCnt == 0) failed. Values are 1 and 0. Since the indicated index is non-clustered and is created by a unique constarint that includes 2 columns, we tried dropping and recreating the index. This resulted in the following error: CREATE UNIQUE INDEX terminated because a duplicate key was found for index ID 2. Most significant primary key is '3280'. The statement has been terminated. However running Select var_id,result_on from tests group by var_id,result_on having count(*)>1 returns 0 rows. Here is what we are planning to do: Restore a pre-server crash copy of the DB and run DBCC CHECKDB If that returns clean, then restore again with no recovery Apply all subequent TLOG backups Stop production app, take a tail log backup and apply that too Drop prod DB and rename the freshly restored DB to make it prod Start prod app Could someone please punch holes in this approach? Maybe, suggest a different approach? What we need is minimum downtime. SQL 2000 DB Size 94 GB The table that has corrupt pages has 460 Million+ rows of data Thanks for the help. Raj

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• Protocol to mount fat32 network filesystem on Linux with ability to lock files ( not advisory locks

  - by nagul

  I have a fat32 filesystem sitting on a NAS storage device (nslu2) that I need to mount on my Ubuntu system. I've tried Samba and NFS mounts, but both don't seem to support proper locking. More specifically, I am unable to save files to the mounted drive through GNUcash, KeepassX etc, which makes the share fairly useless. Is there a protocol that allows me to achieve this ? Note that the NAS storage device is running a linux OS so I can run pretty much any protocol that has a linux implementation. The only option I'm not looking for is to reformat the partition to ext3, which I'm not able to do due to other constraints. Alternatively, has anyone managed proper locking of a fat32 system over the network using Samba ? Or, is advisory locking the best you get with a network-mounted fat32 file system ? I've thought of trying sshfs but I've not found any indication that this will solve my problem. Edit: Okay, maybe I can reformat the drive, but to any file system except ext3. The "unslung" nslu2 doesn't like more than one ext3 drive, and I already have one attached. So any solution that involves reformatting the drive to ntfs, hfs etc is fine, as long as I can mount it on linux and lock files.

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• Timeout settings for Remote Desktop Sessions to lock

  - by atroon

  Our office uses a Windows 2003 server to provide access to an accounting application. Recently I was asked to increase the amount of time it takes for the session to lock itself and require the entry of the user's password to resume. That seems to be about ten minutes, at present. I am familiar with group policy and have tweaked those settings to scavenge sessions (and thereby licenses) from sessions that have been disconnected (by the user closing the mstsc.exe client or by a network issue). That's simple and straightforward. But I can't find anything in GP to allow a longer time period before the RDP client window goes black and then, when clicked upon, requires a username and password to resume the session. I must admit this would be nice personally as well, since most of my time is spent documenting the application and/or monitoring its database, so I usually have a window open to the terminal server along with the rest of the staff in the accounting center, but I interact with it very little. I usually enter my password 10-15 times per workday, but I'm pretty good at it by now. ;) So, can this timeout period be adjusted, or are we out of luck?

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• SQLDeveloper using over 100MB of PGA

  - by Leigh Riffel

  Perhaps this is normal, but in my Oracle 11g database I am seeing programmers using Oracle's SQL Developer regularly consume more than 100MB of combined UGA and PGA memory. I'd like to know if this is normal and what can be done about it. Our database is on the 32 bit version of Windows 2008, so memory limitations are becoming an increasing concern. I am using the following query to show the memory usage: SELECT e.SID, e.username, e.status, b.PGA_MEMORY FROM v$session e LEFT JOIN (select y.SID, y.value pga, TO_CHAR(ROUND(y.value/1024/1024),99999999) || ' MB' PGA_MEMORY from v$sesstat y, v$statname z where y.STATISTIC# = z.STATISTIC# and NAME = 'session pga memory') b ON e.sid=b.sid WHERE (PGA)/1024/1024 > 20 ORDER BY 4 DESC; It seems that the resource usage goes up any time a table is opened in SQLDeveloper, but even when it is closed the memory does not go away. The problem is worse if the table is sorted while it was open as that seems to use even more memory. I understand how this would use memory while it is sorting, and perhaps even while it is still open, but to use memory after it is closed seems wrong to me. Can anyone confirm this? Update: I discovered that my numbers were off due to not understanding that the UGA is stored in the PGA under dedicated server mode. This makes the numbers lower than they were, but the problem still remains that SQL Developer seems to use excessive PGA.

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• SQLDeveloper using over 100MB of PGA+UGA

  - by Leigh Riffel

  Perhaps this is normal, but in my Oracle 11g database I am seeing programmers using Oracle's SQL Developer regularly consume more than 100MB of combined UGA and PGA memory. I'd like to know if this is normal and what can be done about it. Our database is on the 32 bit version of Windows 2008, so memory limitations are becoming an increasing concern. I am using the following query to show the memory usage: SELECT e.SID, e.username, e.status, b.PGA_MEMORY FROM v$session e LEFT JOIN (select y.SID, y.value pga, TO_CHAR(ROUND(y.value/1024/1024),99999999) || ' MB' PGA_MEMORY from v$sesstat y, v$statname z where y.STATISTIC# = z.STATISTIC# and NAME = 'session pga memory') b ON e.sid=b.sid WHERE (PGA)/1024/1024 > 20 ORDER BY 4 DESC; It seems that the resource usage goes up any time a table is opened in SQLDeveloper, but even when it is closed the memory does not go away. The problem is worse if the table is sorted while it was open as that seems to use even more memory. I understand how this would use memory while it is sorting, and perhaps even while it is still open, but to use memory after it is closed seems wrong to me. Can anyone confirm this? Update: I discovered that my numbers were off due to not understanding that the UGA is stored in the PGA under dedicated server mode. This makes the numbers lower than they were, but the problem still remains that SQL Developer seems to use excessive PGA.

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• JDBC Lock a row using SELECT FOR UPDATE, doesn't work

  - by Rachid

  I am having issues with MySQL's SELECT .. FOR UPDATE, here is the query I am trying to run: SELECT * FROM tableName WHERE HostName='UnknownHost' ORDER BY UpdateTimestamp asc limit 1 FOR UPDATE After this, the concerned thread will do an UPDATE and change the HostName, which is then it should unlock the row. I am running a multi-threaded java application, so 3 threads are running this SQL statement, but when thread 1 runs this, it doesn't lock its results from thread 2 & 3. Therefore threads 2 & 3 are getting the same results and they could update the same row. Also each thread is on its own mysql connection. I'm using Innodb, with transaction-isolation = READ-COMMITTED, and the Autocommit is off before executing the select for update may I miss something? OR perhaps there is a better solution? Thanks a lot. Code : public BasicJDBCDemo() { Le_Thread newThread1=new Le_Thread(); Le_Thread newThread2=new Le_Thread(); newThread1.start(); newThread2.start(); } Thread : class Le_Thread extends Thread { public void run() { tring name = Thread.currentThread().getName(); System.out.println( name+": Debut."); long oid=Util.doSelectLockTest(name); Util.doUpdateTest(oid,name); } } Select : public static long doSelectLockTest(String threadName) { System.out.println("[OUTPUT FROM SELECT Lock ]...threadName="+threadName); PreparedStatement pst = null; ResultSet rs=null; Connection conn=null; long oid=0; try { String query = "SELECT * FROM table WHERE Host=? ORDER BY Timestamp asc limit 1 FOR UPDATE"; conn=getNewConnection(); pst = conn.prepareStatement(query); pst.setString(1, DbProperties.UnknownHost); System.out.println("pst="+threadName+"__"+pst); rs = pst.executeQuery(); if (rs.first()) { String s = rs.getString("HostName"); oid = rs.getLong("OID"); System.out.println("oid_oldest/host/threadName=="+oid+"/"+s+"/"+threadName); } } catch (SQLException ex) { ex.printStackTrace(); } finally { DBUtil.close(pst); DBUtil.close(rs); DBUtil.close(conn); } return oid; } Please help.... : Result : Thread-1: Debut. Thread-2: Debut. [OUTPUT FROM SELECT Lock ]...threadName=Thread-1 New connection.. [OUTPUT FROM SELECT Lock ]...threadName=Thread-2 New connection.. pst=Thread-2: SELECT * FROM b2biCheckPoint WHERE HostName='UnknownHost' ORDER BY UpdateTimestamp asc limit 1 FOR UPDATE pst=Thread-1: SELECT * FROM b2biCheckPoint WHERE HostName='UnknownHost' ORDER BY UpdateTimestamp asc limit 1 FOR UPDATE oid_oldest/host/threadName==1/UnknownHost/Thread-2 oid_oldest/host/threadName==1/UnknownHost/Thread-1 [Performing UPDATE] ... oid = 1, thread=Thread-2 New connection.. [Performing UPDATE] ... oid = 1, thread=Thread-1 pst_threadname=Thread-2: UPDATE b2bicheckpoint SET HostName='1_host_Thread-2',UpdateTimestamp=1294940161838 where OID = 1 New connection.. pst_threadname=Thread-1: UPDATE b2bicheckpoint SET HostName='1_host_Thread-1',UpdateTimestamp=1294940161853 where OID = 1

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• raid md device is not remove from memory, how to overcome this problem

  - by santhosha

  i create raid 10 , i removed two arrays form md11 one by one , after that i going to editing the contents those are mounted ( it will be not responding stage), after i try for remove arrays those are left it is shows device or resource busy ( is not removed from memory). i try to terminate process this is also not work, i absorve from 4 days resync will be 8.0% it can not modifying. cat /proc/mdstat Personalities : [raid1] [raid0] [raid6] [raid5] [raid4] [linear] [raid10] md11 : active raid10 sde1[3] sdj14 286743936 blocks 64K chunks 2 near-copies [4/1] [___U] [1:2:3:0] [=...................] resync = 8.0% (23210368/286743936) finish=289392.6min speed=15K/sec mdadm -D /dev/md11 /dev/md11: Version : 00.90.03 Creation Time : Sun Jan 16 16:20:01 2011 Raid Level : raid10 Array Size : 286743936 (273.46 GiB 293.63 GB) Device Size : 143371968 (136.73 GiB 146.81 GB) Raid Devices : 4 Total Devices : 2 Preferred Minor : 11 Persistence : Superblock is persistent Update Time : Sun Jan 16 16:56:07 2011 State : active, degraded, resyncing Active Devices : 1 Working Devices : 1 Failed Devices : 1 Spare Devices : 0 Layout : near=2, far=1 Chunk Size : 64K Rebuild Status : 8% complete UUID : 5e124ea4:79a01181:dc4110d3:a48576ea Events : 0.23 Number Major Minor RaidDevice State 0 0 0 0 removed 1 0 0 1 removed 4 8 145 2 faulty spare rebuilding /dev/sdj1 3 8 65 3 active sync /dev/sde1 umount /dev/md11 umount: /dev/md11: not mounted mdadm -S /dev/md11 mdadm: fail to stop array /dev/md11: Device or resource busy lsof /dev/md11 COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME mount 2128 root 3r BLK 9,11 4058 /dev/md11 mount 5018 root 3r BLK 9,11 4058 /dev/md11 mdadm 27605 root 3r BLK 9,11 4058 /dev/md11 mount 30562 root 3r BLK 9,11 4058 /dev/md11 badblocks 30591 root 3r BLK 9,11 4058 /dev/md11 kill -9 2128 kill -9 5018 kill -9 27605 kill -9 30562 kill -3 30591 mdadm -S /dev/md11 mdadm: fail to stop array /dev/md11: Device or resource busy lsof /dev/md11 COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME mount 2128 root 3r BLK 9,11 4058 /dev/md11 mount 5018 root 3r BLK 9,11 4058 /dev/md11 mdadm 27605 root 3r BLK 9,11 4058 /dev/md11 mount 30562 root 3r BLK 9,11 4058 /dev/md11 badblocks 30591 root 3r BLK 9,11 4058 /dev/md11 cat /proc/mdstat Personalities : [raid1] [raid0] [raid6] [raid5] [raid4] [linear] [raid10] md11 : active raid10 sde1[3] sdj14 286743936 blocks 64K chunks 2 near-copies [4/1] [___U] [1:2:3:0] [=...................] resync = 8.0% (23210368/286743936) finish=289392.6min speed=15K/sec

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• Optimizing hash lookup & memory performance in Go

  - by Moishe

  As an exercise, I'm implementing HashLife in Go. In brief, HashLife works by memoizing nodes in a quadtree so that once a given node's value in the future has been calculated, it can just be looked up instead of being re-calculated. So eg. if you have a node at the 8x8 level, you remember it by its four children (each at the 2x2 level). So next time you see an 8x8 node, when you calculate the next generation, you first check if you've already seen a node with those same four children. This is extended up through all levels of the quadtree, which gives you some pretty amazing optimizations if eg. you're 10 levels above the leaves. Unsurprisingly, it looks like the perfmance crux of this is the lookup of nodes by child-node values. Currently I have a hashmap of {&upper_left_node,&upper_right_node,&lower_left_node,&lower_right_node} -> node So my lookup function is this: func FindNode(ul, ur, ll, lr *Node) *Node { var node *Node var ok bool nc := NodeChildren{ul, ur, ll, lr} node, ok = NodeMap[nc] if ok { return node } node = &Node{ul, ur, ll, lr, 0, ul.Level + 1, nil} NodeMap[nc] = node return node } What I'm trying to figure out is if the "nc := NodeChildren..." line causes a memory allocation each time the function is called. If it does, can I/should I move the declaration to the global scope and just modify the values each time this function is called? Or is there a more efficient way to do this? Any advice/feedback would be welcome. (even coding style nits; this is literally the first thing I've written in Go so I'd love any feedback)

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• improve Collision detection memory usage (blocks with bullets)

  - by Eddy

  i am making a action platform 2D game, something like Megaman. I am using XNA to make it. already made player phisics,collisions, bullets, enemies and AIs, map editor, scorolling X Y camera (about 75% of game is finished ). as i progressed i noticed that my game would be more interesting to play if bullets would be destroyed on collision with regular(stationary ) map blocks, only problem is that if i use my collision detection (each bullet with each block) sometimes it begins to lag(btw if my bullet exits the screen player can see it is removed from bullet list) So how to improve my collision detection so that memory usage would be so high? :) ( on a map 300x300 blocks for example don't think that bigger map should be made); int block = 0; int bulet= 0; bool destroy_bullet = false; while (bulet < bullets.Count) { while (block < blocks.Count) { if (bullets[bulet].P_Bul_rec.Intersects( blocks[block].rect)) {//bullets and block are Lists that holds objects of bullet and block classes //P_Bul_rec just bullet rectangle destroy_bullet = true; } block++; } if (destroy_bullet) { bullets.RemoveAt(bulet); destroy_bullet = false; } else { bulet++; } block = 0; }

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• Entry level engineer question regarding memory mangement

  - by Ealianis

  It has been a few months since I started my position as an entry level software developer. Now that I am past some learning curves (e.g. the language, jargon, syntax of VB and C#) I'm starting to focus on more esoteric topics, as to write better software. A simple question I presented to a fellow coworker was responded with "I'm focusing on the wrong things." While I respect this coworker I do disagree that this is a "wrong thing" to focus upon. Here was the code (in VB) and followed by the question. Note: The Function GenerateAlert() returns an integer. Dim alertID as Integer = GenerateAlert() _errorDictionary.Add(argErrorID, NewErrorInfo(Now(), alertID)) vs... _errorDictionary.Add(argErrorID, New ErrorInfo(Now(), GenerateAlert())) I originally wrote the ladder and rewrote it with the "Dim alertID" so that someone else might find it easier to read. But here was my concern and question. "Should one write this with the Dim AlertID, it would in fact take up more memory; finite but more, and should this method be called many times could it lead to an issue? How will .NET handle this object AlertID. Outside of .NET should one manually dispose of the object after use (near the end of the sub)." I want to ensure I become a knowledgeable programmer that does not just rely upon garbage collection. Am I over thinking this? Am I focusing on the wrong things?

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• Am I running out of memory or do I have two logical drives instead of one

  - by user30904

  I did a complete reinstall of Ubuntu 13.04 a couple of months ago. Since then, I have switched out my motherboard with another. I kept the same hard drive. I just did an upgrade to 13.10. Recently, after this install, I keep getting the message that I'm running out of memory. I just checked my system usage and was surprised by what I found. I believed that I installed Ubuntu as a fresh install but when I check the system usage, it seems like there are two logical drives. I just did the basic install, so I was only expecting to see one partition but instead I see two. One is a small 300mb partition, the other is a 300gb partition I was expecting. Can anyone tell me if I have two partitions and/or logical drives and if so how I can fix this? I seem to have been running on the smaller drive and now I'm obviously out of space. I want to be able to use the bigger one at least.

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• Entry level engineer question regarding memory management

  - by Ealianis

  It has been a few months since I started my position as an entry level software developer. Now that I am past some learning curves (e.g. the language, jargon, syntax of VB and C#) I'm starting to focus on more esoteric topics, as to write better software. A simple question I presented to a fellow coworker was responded with "I'm focusing on the wrong things." While I respect this coworker I do disagree that this is a "wrong thing" to focus upon. Here was the code (in VB) and followed by the question. Note: The Function GenerateAlert() returns an integer. Dim alertID as Integer = GenerateAlert() _errorDictionary.Add(argErrorID, NewErrorInfo(Now(), alertID)) vs... _errorDictionary.Add(argErrorID, New ErrorInfo(Now(), GenerateAlert())) I originally wrote the latter and rewrote it with the "Dim alertID" so that someone else might find it easier to read. But here was my concern and question: Should one write this with the Dim AlertID, it would in fact take up more memory; finite but more, and should this method be called many times could it lead to an issue? How will .NET handle this object AlertID. Outside of .NET should one manually dispose of the object after use (near the end of the sub). I want to ensure I become a knowledgeable programmer that does not just rely upon garbage collection. Am I over thinking this? Am I focusing on the wrong things?

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• "Could not register destruction callback" warn message leads to memory leaks?

  - by Séb

  Hello all, I'm in the exact same situation as this old question: http://stackoverflow.com/questions/2077558/warn-could-not-register-destruction-callback In short: I see a warning saying that a destruction callback could not be registered for some beans. My question is: since the beans whose destruction callback cannot be registered are two persistance beans, could this be the source of a memory leak? I am experiencing a leak in my app. Although the session timeout is set (to 30 minutes), my profiler shows me more instances of the hibernate SessionImpl each time I run a thread dump. The number of instances of SessionImpl is exactly the number of times I tried to login between two thread dumps. Thanks for your help...

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• What is the complexity of the below code with respect to memory ?

  - by Cshah

  Hi, I read about Big-O Notation from here and had few questions on calculating the complexity.So for the below code i have calculated the complexity. need your inputs for the same. private void reverse(String strToRevers) { if(strToRevers.length() == 0) { return ; } else { reverse(strToRevers.substring(1)); System.out.print(strToRevers.charAt(0)); } } If the memory factor is considered then the complexity of above code for a string of n characters is O(n^2). The explanation is for a string that consists of n characters, the below function would be called recursively n-1 times and each function call creates a string of single character(stringToReverse.charAT(0)). Hence it is n*(n-1)*2 which translates to o(n^2). Let me know if this is right ?

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• Getting Out Of Memory: Java heap space, but while viewing heap space it max uses 50 MB

  - by ikky

  Hi! I'm using ASANT to run a xml file which points to a NARS.jar file. (i do not have the project file of the NARS.jar) I'm getting "java.lang.OutOfMemoryError: Java heap space. I used VisualVM to look at the heap while running the NARS.jar, and it says that it max uses 50 MB of the heapspace. I've set the initial and max size of heapspace to 512 MB. Does anyone have an ide of what could be wrong? I got 1 GB physical Memory and created a 5 GB pagefile (for test purpose). Thanks in advance.

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• zlib memory usage / performance. With 500kb of data.

  - by unixman83

  Is zLib Worth it? Are there other better suited compressors? I am using an embedded system. Frequently, I have only 3MB of RAM or less available to my application. So I am considering using zlib to compress my buffers. I am concerned about overhead however. The buffer's average size will be 30kb. This probably won't get compressed by zlib. Anyone know of a good compressor for extremely limited memory environments? However, I will experience occasional maximum buffer sizes of 700kb, with 500kb much more common. Is zlib worth it in this case? Or is the overhead too much to justify? My sole considerations for compression are RAM overhead of algorithm and performance at least as good as zlib.

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• How do I load the Oracle schema into memory instead of the hard drive?

  - by Andrew

  I have a certain web application that makes upwards of ~100 updates to an Oracle database in succession. This can take anywhere from 3-5 minutes, which sometimes causes the webpage to time out. A re-design of the application is scheduled soon but someone told me that there is a way to configure a "loader file" which loads the schema into memory and runs the transactions there instead of on the hard drive, supposedly improving speed by several orders of magnitude. I have tried to research this "loader file" but all I can find is information about the SQL* bulk data loader. Does anyone know what he's talking about? Is this really possible and is it a feasible quick fix or should I just wait until the application is re-designed?

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• Of these 3 methods for reading linked lists from shared memory, why is the 3rd fastest?

  - by Joseph Garvin

  I have a 'server' program that updates many linked lists in shared memory in response to external events. I want client programs to notice an update on any of the lists as quickly as possible (lowest latency). The server marks a linked list's node's state_ as FILLED once its data is filled in and its next pointer has been set to a valid location. Until then, its state_ is NOT_FILLED_YET. I am using memory barriers to make sure that clients don't see the state_ as FILLED before the data within is actually ready (and it seems to work, I never see corrupt data). Also, state_ is volatile to be sure the compiler doesn't lift the client's checking of it out of loops. Keeping the server code exactly the same, I've come up with 3 different methods for the client to scan the linked lists for changes. The question is: Why is the 3rd method fastest? Method 1: Round robin over all the linked lists (called 'channels') continuously, looking to see if any nodes have changed to 'FILLED': void method_one() { std::vector<Data*> channel_cursors; for(ChannelList::iterator i = channel_list.begin(); i != channel_list.end(); ++i) { Data* current_item = static_cast<Data*>(i->get(segment)->tail_.get(segment)); channel_cursors.push_back(current_item); } while(true) { for(std::size_t i = 0; i < channel_list.size(); ++i) { Data* current_item = channel_cursors[i]; ACQUIRE_MEMORY_BARRIER; if(current_item->state_ == NOT_FILLED_YET) { continue; } log_latency(current_item->tv_sec_, current_item->tv_usec_); channel_cursors[i] = static_cast<Data*>(current_item->next_.get(segment)); } } } Method 1 gave very low latency when then number of channels was small. But when the number of channels grew (250K+) it became very slow because of looping over all the channels. So I tried... Method 2: Give each linked list an ID. Keep a separate 'update list' to the side. Every time one of the linked lists is updated, push its ID on to the update list. Now we just need to monitor the single update list, and check the IDs we get from it. void method_two() { std::vector<Data*> channel_cursors; for(ChannelList::iterator i = channel_list.begin(); i != channel_list.end(); ++i) { Data* current_item = static_cast<Data*>(i->get(segment)->tail_.get(segment)); channel_cursors.push_back(current_item); } UpdateID* update_cursor = static_cast<UpdateID*>(update_channel.tail_.get(segment)); while(true) { if(update_cursor->state_ == NOT_FILLED_YET) { continue; } ::uint32_t update_id = update_cursor->list_id_; Data* current_item = channel_cursors[update_id]; if(current_item->state_ == NOT_FILLED_YET) { std::cerr << "This should never print." << std::endl; // it doesn't continue; } log_latency(current_item->tv_sec_, current_item->tv_usec_); channel_cursors[update_id] = static_cast<Data*>(current_item->next_.get(segment)); update_cursor = static_cast<UpdateID*>(update_cursor->next_.get(segment)); } } Method 2 gave TERRIBLE latency. Whereas Method 1 might give under 10us latency, Method 2 would inexplicably often given 8ms latency! Using gettimeofday it appears that the change in update_cursor-state_ was very slow to propogate from the server's view to the client's (I'm on a multicore box, so I assume the delay is due to cache). So I tried a hybrid approach... Method 3: Keep the update list. But loop over all the channels continuously, and within each iteration check if the update list has updated. If it has, go with the number pushed onto it. If it hasn't, check the channel we've currently iterated to. void method_three() { std::vector<Data*> channel_cursors; for(ChannelList::iterator i = channel_list.begin(); i != channel_list.end(); ++i) { Data* current_item = static_cast<Data*>(i->get(segment)->tail_.get(segment)); channel_cursors.push_back(current_item); } UpdateID* update_cursor = static_cast<UpdateID*>(update_channel.tail_.get(segment)); while(true) { for(std::size_t i = 0; i < channel_list.size(); ++i) { std::size_t idx = i; ACQUIRE_MEMORY_BARRIER; if(update_cursor->state_ != NOT_FILLED_YET) { //std::cerr << "Found via update" << std::endl; i--; idx = update_cursor->list_id_; update_cursor = static_cast<UpdateID*>(update_cursor->next_.get(segment)); } Data* current_item = channel_cursors[idx]; ACQUIRE_MEMORY_BARRIER; if(current_item->state_ == NOT_FILLED_YET) { continue; } found_an_update = true; log_latency(current_item->tv_sec_, current_item->tv_usec_); channel_cursors[idx] = static_cast<Data*>(current_item->next_.get(segment)); } } } The latency of this method was as good as Method 1, but scaled to large numbers of channels. The problem is, I have no clue why. Just to throw a wrench in things: if I uncomment the 'found via update' part, it prints between EVERY LATENCY LOG MESSAGE. Which means things are only ever found on the update list! So I don't understand how this method can be faster than method 2. The full, compilable code (requires GCC and boost-1.41) that generates random strings as test data is at: http://pastebin.com/e3HuL0nr

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• How to get accuracy memory usage on iphone device.

  - by Favo Yang

  I want to output accuracy memory usage on iphone device, the method I used was taking from, http://landonf.bikemonkey.org/code/iphone/Determining%5FAvailable%5FMemory.20081203.html natural_t mem_used = (vm_stat.active_count + vm_stat.inactive_count + vm_stat.wire_count) * pagesize; natural_t mem_free = vm_stat.free_count * pagesize; natural_t mem_total = mem_used + mem_free; The issue is that the total value is always changed after testing on device! used: 60200.0KB free: 2740.0KB total: 62940.0KB used: 53156.0KB free: 2524.0KB total: 55680.0KB used: 52500.0KB free: 2544.0KB total: 55044.0KB Have a look for the function implementation, it already sum active, inactive, wire and free pages, is there anything I missing here?

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• Why is memory management so visible in Java VM?

  - by Emil

  I'm playing around with writing some simple Spring-based web apps and deploying them to Tomcat. Almost immediately, I run into the need to customize the Tomcat's JVM settings with -XX:MaxPermSize (and -Xmx and -Xms); without this, the server easily runs out of PermGen space. Why is this such an issue for Java VMs compared to other garbage collected languages? Comparing counts of "tune X memory usage" for X in Java, Ruby, Perl and Python, shows that Java has easily an order of magnitude more hits in Google than the other languages combined. I'd also be interested in references to technical papers/blog-posts/etc explaining design choices behind JVM GC implementations, across different JVMs or compared to other interpreted language VMs (e.g. comparing Sun or IBM JVM to Parrot). Are there technical reasons why JVM users still have to deal with non-auto-tuning heap/permgen sizes?

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• memory of drawables, is it better to have resources inside APK, outside APK or is it the same for me

  - by Daniel Benedykt

  Hi I have an application that draws a lot of graphics and change them. Since I have many graphics, I thought of having the images outside the APK, downloaded from the internet as needed, and saved on the files application folder. But I started to get outOfMemory exceptions. The question is: Does android handle memory different if I load a graphic from APK than if I load it from 'disk'? code using APK: topView.setBackgroundResource(R.drawable.bg); code if image is outside APK: Drawable d = Drawable.createFromPath(pathName); topView.setBackgroundDrawable(d); Thanks Daniel

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• Local variable assign versus direct assign; properties and memory.

  - by Typeoneerror

  In objective-c I see a lot of sample code where the author assigns a local variable, assigns it to a property, then releases the local variable. Is there a practical reason for doing this? I've been just assigning directly to the property for the most part. Would that cause a memory leak in any way? I guess I'd like to know if there's any difference between this: HomeScreenBtns *localHomeScreenBtns = [[HomeScreenBtns alloc] init]; self.homeScreenBtns = localHomeScreenBtns; [localHomeScreenBtns release]; and this: self.homeScreenBtns = [[HomeScreenBtns alloc] init]; Assuming that homeScreenBtns is a property like so: @property (nonatomic, retain) HomeScreenBtns *homeScreenBtns; I'm getting ready to submit my application to the app store so I'm in full optimize/QA mode.

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• UIScrollView: Is 806k Image too much too handle? (Crash, out of memory)?

  - by Jordan

  I'm loading a 2400x1845 png image into a scroll view. The program crashes out of memory, is there a better way to handle this? mapScrollView is an UIScrollView in IB, along with a couple of UIButtons. -(void)loadMapWithName:(NSString *)mapName { NSString* bundlePath = [[NSBundle mainBundle] bundlePath]; UIImage *image = [UIImage imageWithContentsOfFile:[NSString stringWithFormat:@"%@/path/%@", bundlePath, [maps objectForKey:mapName]]]; UIImageView *imageView = [[UIImageView alloc] initWithImage:image]; CGSize imgSize = image.size; mapScrollView.contentSize = imgSize; [mapScrollView addSubview:imageView]; [imageView release]; [self.view addSubview:mapScrollView]; }

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