Search Results

Search found 119 results on 5 pages for 'barriers'.

facebook twitter digg google delicious technorati stumbleupon myspace wordpress linkedin gmail igoogle windows live tumblr viadeo yahoo buzz yahoo mail yahoo bookmarks favorites email print

Page 1/5 | 1 2 3 4 5  | Next Page >

  • How do JVM's implicit memory barriers behave when chaining constructors

    - by Joonas Pulakka
    Referring to my earlier question on incompletely constructed objects, I have a second question. As Jon Skeet pointed out, there's an implicit memory barrier in the end of a constructor that makes sure that final fields are visible to all threads. But what if a constructor calls another constructor; is there such a memory barrier in the end of each of them, or only in one being called from outside? That is, when the "wrong" solution is: public class ThisEscape { public ThisEscape(EventSource source) { source.registerListener( new EventListener() { public void onEvent(Event e) { doSomething(e); } }); } } And the correct one would be a factory method version: public class SafeListener { private final EventListener listener; private SafeListener() { listener = new EventListener() { public void onEvent(Event e) { doSomething(e); } } } public static SafeListener newInstance(EventSource source) { SafeListener safe = new SafeListener(); source.registerListener(safe.listener); return safe; } } Would the following work too, or not? public class MyListener { private final EventListener Listener; private MyListener() { listener = new EventListener() { public void onEvent(Event e) { doSomething(e); } } } public MyListener(EventSource source) { this(); source.register(listener); } }

    Read the article

  • Removing Barriers to Create Effective Data Models

    After years of creating and maintaining data models, I have started to notice common barriers that decrease the accuracy and usefulness of models. In my opinion, the main causes of these barriers are the lack of knowledge and communication from within a company. The lack of knowledge in regards to data models or data modeling can take many forms. Company Culture Knowledge Whether documented or undocumented, existing business rules of a company can affect how data is modeled. For example, if a company only allows 1 assigned person per customer to be able to manipulate a customer’s record then then a data model that includes an associated table that joins customers and employee’s would be unneeded because that would allow for the possibility of multiple employees to handle a customer because of the potential for a many to many relationship between Customers and Employees. Technical Knowledge Depending on the data modeler’s proficiency in modeling data they can inadvertently cause issues and/or complications with a design without even noticing. It is important that companies share data modeling responsibilities so that the models are developed from multiple perspectives of a system, company and the original problem.  In addition, the tools that a company selects to create data models can also affect the accuracy of the model if designer are not familiar with the tools or the tools are too complex to use for the designer. Existing System Knowledge In order for a data modeler to model data for an existing system so that new changes can be applied to a system then they need to at least know the basic concepts of a system so that they can work within it. This will promote reusability of data and prevent the chance of duplicating data. Project Knowledge This should be pretty obvious, but it is very hard to create an accurate data model without knowing what data needs to be modeled. I have always found it strange that I have been asked to start modeling data prior to a client formalizing any requirements. Usually when this happens I have to make several iterations to a model, and the client still does not know exactly what they want.  In addition additional issues can arise when certain stakeholders of a project are not consulted prior to the design or after the project is over because it can cause miss understandings and confusion by the end user as well as possibly not solving the original problem for which a project is intended to solve. One common thread between each type of knowledge is that they can all be avoided through the use of good communication. For example, if a modeler is new to a company then they should ask older employees about any business specific rules that may be documented or undocumented that must be applied to projects in general. Furthermore, if a modeler is not really familiar with a specific data modeling software then they need to speak up and ask for help form other employees or their manager. This will not only help the modeler in the project, but also help them in future projects that they do for the company. Additionally, if a project is not clearly defined prior to a data modeler being assigned the modeling project then it is their responsibility to communicate with the other stakeholders to clarify any part of a project that is unclear so that the data model that is created is accurately aligned with a project.

    Read the article

  • Turn off write barriers on ext4 whiche FS is mounted

    - by user462982
    I am doing some IO intensive DB imports that run for several days now and the IO performance has dropped tremendously over times. The DB data files (log files) are on an ext4 formatted logical volume which is mounted with default options (did not specify something special in fstab). Since I just learned that ext4 enables write barriers by default: Q: Is there some way to disable write barriers online (i.e. while the file system is in use), because I cannot interrupt the import and don't want to restart it again. I am aware that write barriers might not be the only thing impeding performance it is a bad idea to have write barriers disabled on journalling file systems if data safty is important (e.g. on a production system)

    Read the article

  • Tackling Security and Compliance Barriers with a Platform Approach to IDM: Featuring SuperValu

    - by Darin Pendergraft
    On October 25, 2012 ISACA and Oracle sponsored a webcast discussing how SUPERVALU has embraced the platform approach to IDM.  Scott Bonnell, Sr. Director of Product Management at Oracle, and Phil Black, Security Director for IAM at SUPERVALU discussed how a platform strategy could be used to formulate an upgrade plan for a large SUN IDM installation. See the webcast replay here: ISACA Webcast Replay (Requires Internet Explorer or Chrome) Some of the main points discussed in the webcast include: Getting support for an upgrade project by aligning with corporate initiatives How to leverage an existing IDM investment while planning for future growth How SUN and Oracle IDM architectures can be used in a coexistance strategy Advantages of a rationalized, modern, IDM Platform architecture ISACA Webcast Featuring SuperValu - Tackling Security and Compliance Barriers with a Platform Approach to Identity Management from OracleIDM  

    Read the article

  • Are memory barriers necessary for atomic reference counting shared immutable data?

    - by Dietrich Epp
    I have some immutable data structures that I would like to manage using reference counts, sharing them across threads on an SMP system. Here's what the release code looks like: void avocado_release(struct avocado *p) { if (atomic_dec(p->refcount) == 0) { free(p->pit); free(p->juicy_innards); free(p); } } Does atomic_dec need a memory barrier in it? If so, what kind of memory barrier? Additional notes: The application must run on PowerPC and x86, so any processor-specific information is welcomed. I already know about the GCC atomic builtins. As for immutability, the refcount is the only field that changes over the duration of the object.

    Read the article

  • Barriers to IPv6 deployment: addressing

    - by sysadmin1138
    There are several things that are keeping IPv6 deployment from being a topic of active discussion here at my work. There are the usual technical issues, but one non-technical one appears to be a major stumbling block on the path to actually getting a deployment project going. Addresses, memorizing of. Specifically, IPv4 addresses are comprehensible, and IPv6 addresses just look like a big long string of hex. The human mind has real trouble memorizing lists of more than 7-8 items, and an IPv4 address (192.168.231.148) has four items in it which makes it easy for us to memorize. A fully populated IPv6 address has not only 8 sections, but each section has 4 hex digits in it. IPv6 addresses were not designed for memorization. To the technician who knows that the DNS server is at 192.168.42.42 (or more likely "42.42", since the company prefix is likely memorized), the idea of memorizing an IPv6 address fills them with dread. Which in turn makes them much less enthusiastic about participating in an IPv6 deployment project. Because of how our network works we're not fully dynamic in terms of v4 addressing. We have several to many subnets that are entirely statically assigned for a variety of reasons, chief among them being that the overhead of static DHCP assignments is perceived as being too great. Also, some devices still aren't smart enough to pull DNS addresses out of DHCP while also having a static assignment, and therefore require manually configured DNS settings. Therefore, some v6 address memorization will have to be done. We're not under any mandate to get v6 out the door, so we don't have pressure from the top. However, it is time to start prepping our infrastructure to handle IPv6 even if we don't convert wholesale. For those of you who have been in IPv6-land for a while, what short-cut methods do you use to discuss or keep track of subnets and specific/critical IP addresses? If I can help reduce some of the dread surrounding IPv6 we might get the project going.

    Read the article

  • We have our standards, and we need them

    - by Tony Davis
    The presenter suddenly broke off. He was midway through his section on how to apply to the relational database the Continuous Delivery techniques that allowed for rapid-fire rounds of development and refactoring, while always retaining a “production-ready” state. He sighed deeply and then launched into an astonishing diatribe against Database Administrators, much of his frustration directed toward Oracle DBAs, in particular. In broad strokes, he painted the picture of a brave new deployment philosophy being frustratingly shackled by the relational database, and by especially by the attitudes of the guardians of these databases. DBAs, he said, shunned change and “still favored tools I’d have been embarrassed to use in the ’80′s“. DBAs, Oracle DBAs especially, were more attached to their vendor than to their employer, since the former was the primary source of their career longevity and spectacular remuneration. He contended that someone could produce the best IDE or tool in the world for Oracle DBAs and yet none of them would give a stuff, unless it happened to come from the “mother ship”. I sat blinking in astonishment at the speaker’s vehemence, and glanced around nervously. Nobody in the audience disagreed, and a few nodded in assent. Although the primary target of the outburst was the Oracle DBA, it made me wonder. Are we who work with SQL Server, database professionals or merely SQL Server fanbois? Do DBAs, in general, have an image problem? Is it a good career-move to be seen to be holding onto a particular product by the whites of our knuckles, to the exclusion of all else? If we seek a broad, open-minded, knowledge of our chosen technology, the database, and are blessed with merely mortal powers of learning, then we like standards. Vendors of RDBMSs generally don’t conform to standards by instinct, but by customer demand. Microsoft has made great strides to adopt the international SQL Standards, where possible, thanks to considerable lobbying by the community. The implementation of Window functions is a great example. There is still work to do, though. SQL Server, for example, has an unusable version of the Information Schema. One cast-iron rule of any RDBMS is that we must be able to query the metadata using the same language that we use to query the data, i.e. SQL, and we do this by running queries against the INFORMATION_SCHEMA views. Developers who’ve attempted to apply a standard query that works on MySQL, or some other database, but doesn’t produce the expected results on SQL Server are advised to shun the Standards-based approach in favor of the vendor-specific one, using the catalog views. The argument behind this is sound and well-documented, and of course we all use those catalog views, out of necessity. And yet, as database professionals, committed to supporting the best databases for the business, whatever they are now and in the future, surely our heart should sink somewhat when we advocate a vendor specific approach, to a developer struggling with something as simple as writing a guard clause. And when we read messages on the Microsoft documentation informing us that we shouldn’t rely on INFORMATION_SCHEMA to identify reliably the schema of an object, in SQL Server!

    Read the article

  • barriers in SMP linux kernel

    - by osgx
    Hello Is there smth like pthread_barrier in SMP Linux kernel? When kernel works simultaneously on 2 and more CPUs with the same structure, the barrier (like pthread_barrier) can be useful. It will stop all CPUs entering to it until last CPU will run the barrier. From this moment all CPUs again works.

    Read the article

  • Implicit Memory Barriers

    - by foo
    let's say i have variables A, B and C that two threads (T1, T2) share. i have the following code: //T1 //~~ A = 1; B = 1; C = 1; InterlockedExchange(ref Foo, 1); //T2 (executes AFTER T1 calls InterlockedExchange) //~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ InterlockedExchange(ref Bar, 1); WriteLine(A); WriteLine(B); WriteLine(C); Question: does calling InterlockedExchange (implicit full fence) on T1 and T2, gurentess that T2 will "See" the write done by T1 before the fence? (A, B and C variables), even though those variables are not plance on the same cache-line as Foo and Bar?

    Read the article

  • Fastest inline-assembly spinlock

    - by sigvardsen
    I'm writing a multithreaded application in c++, where performance is critical. I need to use a lot of locking while copying small structures between threads, for this I have chosen to use spinlocks. I have done some research and speed testing on this and I found that most implementations are roughly equally fast: Microsofts CRITICAL_SECTION, with SpinCount set to 1000, scores about 140 time units Implementing this algorithm with Microsofts InterlockedCompareExchange scores about 95 time units Ive also tried to use some inline assembly with __asm {} using something like this code and it scores about 70 time units, but I am not sure that a proper memory barrier has been created. Edit: The times given here are the time it takes for 2 threads to lock and unlock the spinlock 1,000,000 times. I know this isn't a lot of difference but as a spinlock is a heavily used object, one would think that programmers would have agreed on the fastest possible way to make a spinlock. Googling it leads to many different approaches however. I would think this aforementioned method would be the fastest if implemented using inline assembly and using the instruction CMPXCHG8B instead of comparing 32bit registers. Furthermore memory barriers must be taken into account, this could be done by LOCK CMPXHG8B (I think?), which guarantees "exclusive rights" to the shared memory between cores. At last [some suggests] that for busy waits should be accompanied by NOP:REP that would enable Hyper-threading processors to switch to another thread, but I am not sure whether this is true or not? From my performance-test of different spinlocks, it is seen that there is not much difference, but for purely academic purpose I would like to know which one is fastest. However as I have extremely limited experience in the assembly-language and with memory barriers, I would be happy if someone could write the assembly code for the last example I provided with LOCK CMPXCHG8B and proper memory barriers in the following template: __asm { spin_lock: ;locking code. spin_unlock: ;unlocking code. }

    Read the article

  • What are the biggest barriers to walking the MOTU/developer path?

    - by maco
    For those who are not MOTU (people who maintain the Universe and Multiverse software repositories) and do not have plans of the "I will apply to MOTU by $date" variety: What keeps you and others like you from trying to become MOTU? What makes you think you couldn't become one? I'm referring to both social and technological barriers. EDIT: I'm only saying MOTU because it's a pretty generic group, but "why aren't you packaging / patching and intending to eventually try for upload rights?" is an even more general version.

    Read the article

  • Thread Synchronisation 101

    - by taspeotis
    Previously I've written some very simple multithreaded code, and I've always been aware that at any time there could be a context switch right in the middle of what I'm doing, so I've always guarded access the shared variables through a CCriticalSection class that enters the critical section on construction and leaves it on destruction. I know this is fairly aggressive and I enter and leave critical sections quite frequently and sometimes egregiously (e.g. at the start of a function when I could put the CCriticalSection inside a tighter code block) but my code doesn't crash and it runs fast enough. At work my multithreaded code needs to be a tighter, only locking/synchronising at the lowest level needed. At work I was trying to debug some multithreaded code, and I came across this: EnterCriticalSection(&m_Crit4); m_bSomeVariable = true; LeaveCriticalSection(&m_Crit4); Now, m_bSomeVariable is a Win32 BOOL (not volatile), which as far as I know is defined to be an int, and on x86 reading and writing these values is a single instruction, and since context switches occur on an instruction boundary then there's no need for synchronising this operation with a critical section. I did some more research online to see whether this operation did not need synchronisation, and I came up with two scenarios it did: The CPU implements out of order execution or the second thread is running on a different core and the updated value is not written into RAM for the other core to see; and The int is not 4-byte aligned. I believe number 1 can be solved using the "volatile" keyword. In VS2005 and later the C++ compiler surrounds access to this variable using memory barriers, ensuring that the variable is always completely written/read to the main system memory before using it. Number 2 I cannot verify, I don't know why the byte alignment would make a difference. I don't know the x86 instruction set, but does mov need to be given a 4-byte aligned address? If not do you need to use a combination of instructions? That would introduce the problem. So... QUESTION 1: Does using the "volatile" keyword (implicity using memory barriers and hinting to the compiler not to optimise this code) absolve a programmer from the need to synchronise a 4-byte/8-byte on x86/x64 variable between read/write operations? QUESTION 2: Is there the explicit requirement that the variable be 4-byte/8-byte aligned? I did some more digging into our code and the variables defined in the class: class CExample { private: CRITICAL_SECTION m_Crit1; // Protects variable a CRITICAL_SECTION m_Crit2; // Protects variable b CRITICAL_SECTION m_Crit3; // Protects variable c CRITICAL_SECTION m_Crit4; // Protects variable d // ... }; Now, to me this seems excessive. I thought critical sections synchronised threads between a process, so if you've got one you can enter it and no other thread in that process can execute. There is no need for a critical section for each variable you want to protect, if you're in a critical section then nothing else can interrupt you. I think the only thing that can change the variables from outside a critical section is if the process shares a memory page with another process (can you do that?) and the other process starts to change the values. Mutexes would also help here, named mutexes are shared across processes, or only processes of the same name? QUESTION 3: Is my analysis of critical sections correct, and should this code be rewritten to use mutexes? I have had a look at other synchronisation objects (semaphores and spinlocks), are they better suited here? QUESTION 4: Where are critical sections/mutexes/semaphores/spinlocks best suited? That is, which synchronisation problem should they be applied to. Is there a vast performance penalty for choosing one over the other? And while we're on it, I read that spinlocks should not be used in a single-core multithreaded environment, only a multi-core multithreaded environment. So, QUESTION 5: Is this wrong, or if not, why is it right? Thanks in advance for any responses :)

    Read the article

  • Java LockSupport Memory Consistency

    - by Lachlan
    Java 6 API question. Does calling LockSupport.unpark(thread) have a happens-before relationship to the return from LockSupport.park in the just-unparked thread? I strongly suspect the answer is yes, but the Javadoc doesn't seem to mention it explicitly.

    Read the article

  • Compiler reordering around mutex boundaries?

    - by shojtsy
    Suppose I have my own non-inline functions LockMutex and UnlockMutex, which are using some proper mutex - such as boost - inside. How will the compiler know not to reorder other operations with regard to calls to the LockMutex and UnlockMutex? It can not possibly know how will I implement these functions in some other compilation unit. void SomeClass::store(int i) { LockMutex(_m); _field = i; // could the compiler move this around? UnlockMutex(_m); } ps: One is supposed to use instances of classes for holding locks to guarantee unlocking. I have left this out to simplify the example.

    Read the article

  • Implementing Barrier system solution in C or C++

    - by hardikpatel172
    Actually I have been assigned to implement Barrier system solution in either C or C++ programming language... But I have zero knowledge about it ... I know the problem as well as solution theoritically.. But I have no idea how to implement it.... How can it be possible in C++ to stop or run or wait any process.... Plz yaar... Anyone help me... It's urgent...

    Read the article

  • What are the barriers to understanding pointers and what can be done to overcome them?

    - by David McGraw
    Why are pointers such a leading factor of confusion for many new, and even old, college level students in the C/C++ language? Are there any tools or thought processes that helped you understand how pointers work at the variable, function, and beyond level? What are some good practice things that can be done to bring somebody to the level of, "Ah-hah, I got it," without getting them bogged down in the overall concept? Basically, drill like scenarios.

    Read the article

  • ???Flashback Log???????Redo Log?

    - by Liu Maclean(???)
    ????????????????????redo log?   RVWR( Recovery Writer)?3s??flashback generate buffer??block before image?????????? ?????block change???RVWR??block before image ?flashback log? ?????????,Oracle???????????before image????????,????????flashback database logs?????   ???????????,????? ??????????????????,???????????before image?????shared pool??flashback log buffer?,RVWR??????flashback log buffer??????????? ?DBWR???????????????,DBWR?????buffer header??FBA(Flashback Byte Address)?flashback log buffer?????????? ???? ?????? ??? ????????????? , RVWR???????????(flashback markers)?flashback database logs?? ????(flashback markers)?????????????Oracle??flashback ??????????  ??????????, Oracle ??????(flashback markers)????????????flashback database log???????????block image; ??Oracle ???????(forward recovery)?????????????????SCN?????? flashback markers for example: **** Record at fba: (lno 1 thr 1 seq 1 bno 4 bof 8184) **** RECORD HEADER: Type: 3 (Skip) Size: 8132 RECORD DATA (Skip): **** Record at fba: (lno 1 thr 1 seq 1 bno 4 bof 52) **** RECORD HEADER: Type: 7 (Begin Crash Recovery Record) Size: 36 RECORD DATA (Begin Crash Recovery Record): Previous logical record fba: (lno 1 thr 1 seq 1 bno 3 bof 316) Record scn: 0x0000.00000000 [0.0] **** Record at fba: (lno 1 thr 1 seq 1 bno 3 bof 8184) **** RECORD HEADER: Type: 3 (Skip) Size: 7868 RECORD DATA (Skip): **** Record at fba: (lno 1 thr 1 seq 1 bno 3 bof 316) **** RECORD HEADER: Type: 2 (Marker) Size: 300 RECORD DATA (Marker): Previous logical record fba: (lno 0 thr 0 seq 0 bno 0 bof 0) Record scn: 0x0000.00000000 [0.0] Marker scn: 0x0000.0060e024 [0.6348836] 06/13/2012 15:56:35 Flag 0x0 Flashback threads: 1, Enabled redo threads 1 Recovery Start Checkpoint: scn: 0x0000.0060e024 [0.6348836] 06/13/2012 15:56:12 thread:1 rba:(0x80.180.10) Flashback thread Markers: Thread:1 status:0 fba: (lno 1 thr 1 seq 1 bno 2 bof 8184) Redo Thread Checkpoint Info: Thread:1 rba:(0x80.180.10) **** Record at fba: (lno 1 thr 1 seq 1 bno 2 bof 8184) **** RECORD HEADER: Type: 3 (Skip) Size: 8168 RECORD DATA (Skip): End-Of-Thread reached ????????????????block change ????before image????????flashback log?? ?????block change???flashback log record ????????? redo log???!????flashback log ???????before image ? redo log??? change vector ?  Oracle?????????????????????????????????????,??????I/O??????????????: ??hot block??,Oracle???????????block image?????; Oracle ?????????(flashback barriers)???????????????,flashback barriers???????(???15??),??????????(flashback barriers)????(flashback markers)????????? ????, ??????change?????, ???????????????????????????, ?15????????????????????flashback log????????before image?????????????,?????????????????????,?????????????? ????????,??????????????(flashback barriers), flashback barriers???????,?????15????? ?????flashback barriers????????(flashback markers)???????????????,???????????????????(????barriers?????)??????block image ,????????????????????????????????? ??????????flashback log????redo log????! ????,????????????????, ?????????? SQL> select * from v$version; BANNER -------------------------------------------------------------------------------- Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - 64bit Production PL/SQL Release 11.2.0.3.0 - Production CORE 11.2.0.3.0 Production TNS for Linux: Version 11.2.0.3.0 - Production NLSRTL Version 11.2.0.3.0 - Production SQL> select * from global_name; GLOBAL_NAME -------------------------------------------------------------------------------- www.oracledatabase12g.com SQL> create table flash_maclean (t1 varchar2(200)) tablespace users; Table created. SQL> insert into flash_maclean values('MACLEAN LOVE HANNA'); 1 row created. SQL> commit; Commit complete. SQL> startup force; ORACLE instance started. Total System Global Area 939495424 bytes Fixed Size 2233960 bytes Variable Size 713034136 bytes Database Buffers 218103808 bytes Redo Buffers 6123520 bytes Database mounted. Database opened. SQL> update flash_maclean set t1='HANNA LOVE MACLEAN'; 1 row updated. commit; Commit complete. SQL> alter system checkpoint; System altered. SQL> select dbms_rowid.rowid_block_number(rowid),dbms_rowid.rowid_relative_fno(rowid) from flash_maclean; DBMS_ROWID.ROWID_BLOCK_NUMBER(ROWID) DBMS_ROWID.ROWID_RELATIVE_FNO(ROWID) ------------------------------------ ------------------------------------ 140431 4 datafile 4 block 140431 ??RDBA rdba: 0x0102248f (4/140431) SQL> ! ps -ef|grep rvwr|grep -v grep oracle 26695 1 0 15:56 ? 00:00:00 ora_rvwr_G11R23 SQL> oradebug setospid 26695 Oracle pid: 20, Unix process pid: 26695, image: [email protected] (RVWR) SQL> ORADEBUG DUMP FBTAIL 1; Statement processed. To dump the last 2000 flashback records , ??ORADEBUG DUMP FBTAIL 1????????2000?????? SQL> oradebug tracefile_name /s01/orabase/diag/rdbms/g11r23/G11R23/trace/G11R23_rvwr_26695.trc ? TRACE?????????block? before image **** Record at fba: (lno 1 thr 1 seq 1 bno 55 bof 2564) **** RECORD HEADER: Type: 1 (Block Image) Size: 28 RECORD DATA (Block Image): file#: 4 rdba: 0x0102248f Next scn: 0x0000.00000000 [0.0] Flag: 0x0 Block Size: 8192 BLOCK IMAGE: buffer rdba: 0x0102248f scn: 0x0000.00609044 seq: 0x01 flg: 0x06 tail: 0x90440601 frmt: 0x02 chkval: 0xc626 type: 0x06=trans data Hex dump of block: st=0, typ_found=1 Dump of memory from 0x00002B1D94183C00 to 0x00002B1D94185C00 2B1D94183C00 0000A206 0102248F 00609044 06010000 [.....$..D.`.....] 2B1D94183C10 0000C626 00000001 00014AD4 0060903A [&........J..:.`.] 2B1D94183C20 00000000 00320002 01022488 00090006 [......2..$......] 2B1D94183C30 00000CC8 00C00340 000D0542 00008000 [[email protected].......] 2B1D94183C40 006040BC 000F000A 00000920 00C002E4 [.@`..... .......] 2B1D94183C50 0017048F 00002001 00609044 00000000 [..... ..D.`.....] 2B1D94183C60 00000000 00010100 0014FFFF 1F6E1F77 [............w.n.] 2B1D94183C70 00001F6E 1F770001 00000000 00000000 [n.....w.........] 2B1D94183C80 00000000 00000000 00000000 00000000 [................] Repeat 500 times 2B1D94185BD0 00000000 00000000 2C000000 4D120102 [...........,...M] 2B1D94185BE0 454C4341 4C204E41 2045564F 4E4E4148 [ACLEAN LOVE HANN] 2B1D94185BF0 01002C41 43414D07 4E41454C 90440601 [A,...MACLEAN..D.] Block header dump: 0x0102248f Object id on Block? Y seg/obj: 0x14ad4 csc: 0x00.60903a itc: 2 flg: E typ: 1 - DATA brn: 0 bdba: 0x1022488 ver: 0x01 opc: 0 inc: 0 exflg: 0 Itl Xid Uba Flag Lck Scn/Fsc 0x01 0x0006.009.00000cc8 0x00c00340.0542.0d C--- 0 scn 0x0000.006040bc 0x02 0x000a.00f.00000920 0x00c002e4.048f.17 --U- 1 fsc 0x0000.00609044 bdba: 0x0102248f data_block_dump,data header at 0x2b1d94183c64 =============== tsiz: 0x1f98 hsiz: 0x14 pbl: 0x2b1d94183c64 76543210 flag=-------- ntab=1 nrow=1 frre=-1 fsbo=0x14 fseo=0x1f77 avsp=0x1f6e tosp=0x1f6e 0xe:pti[0] nrow=1 offs=0 0x12:pri[0] offs=0x1f77 block_row_dump: tab 0, row 0, @0x1f77 tl: 22 fb: --H-FL-- lb: 0x2 cc: 1 col 0: [18] 4d 41 43 4c 45 41 4e 20 4c 4f 56 45 20 48 41 4e 4e 41 end_of_block_dump SQL> select dump('MACLEAN LOVE HANNA',16) from dual; DUMP('MACLEANLOVEHANNA',16) -------------------------------------------------------------------- Typ=96 Len=18: 4d,41,43,4c,45,41,4e,20,4c,4f,56,45,20,48,41,4e,4e,41 ???????????????????????,??flashback log??before image????????? create table flash_maclean1 (t1 int) tablespace users; SQL> select vs.name, ms.value 2 from v$mystat ms, v$sysstat vs 3 where vs.statistic# = ms.statistic# 4 and vs.name in ('redo size','db block changes'); NAME VALUE ---------------------------------------------------------------- ---------- db block changes 0 redo size 0 SQL> select name,value from v$sysstat where name like 'flashback log%'; NAME VALUE ---------------------------------------------------------------- ---------- flashback log writes 49 flashback log write bytes 9306112 SQL> begin 2 for i in 1..5000 loop 3 update flash_maclean1 set t1=t1+1; 4 commit; 5 end loop; 6 end; 7 / PL/SQL procedure successfully completed. SQL> select vs.name, ms.value 2 from v$mystat ms, v$sysstat vs 3 where vs.statistic# = ms.statistic# 4 and vs.name in ('redo size','db block changes'); NAME VALUE ---------------------------------------------------------------- ---------- db block changes 20006 redo size 3071288 SQL> select name,value from v$sysstat where name like 'flashback log%'; NAME VALUE ---------------------------------------------------------------- ---------- flashback log writes 52 flashback log write bytes 10338304 ??????????? ??hot block,???20006 ?block changes???? ??? 3000k ?redo log ? ??1000k? flashback log ?

    Read the article

  • Cache consistency & spawning a thread

    - by Dave Keck
    Background I've been reading through various books and articles to learn about processor caches, cache consistency, and memory barriers in the context of concurrent execution. So far though, I have been unable to determine whether a common coding practice of mine is safe in the strictest sense. Assumptions The following pseudo-code is executed on a two-processor machine: int sharedVar = 0; myThread() { print(sharedVar); } main() { sharedVar = 1; spawnThread(myThread); sleep(-1); } main() executes on processor 1 (P1), while myThread() executes on P2. Initially, sharedVar exists in the caches of both P1 and P2 with the initial value of 0 (due to some "warm-up code" that isn't shown above.) Question Strictly speaking – preferably without assuming any particular CPU – is myThread() guaranteed to print 1? With my newfound knowledge of processor caches, it seems entirely possible that at the time of the print() statement, P2 may not have received the invalidation request for sharedVar caused by P1's assignment in main(). Therefore, it seems possible that myThread() could print 0. References These are the related articles and books I've been reading. (It wouldn't allow me to format these as links because I'm a new user - sorry.) Shared Memory Consistency Models: A Tutorial hpl.hp.com/techreports/Compaq-DEC/WRL-95-7.pdf Memory Barriers: a Hardware View for Software Hackers rdrop.com/users/paulmck/scalability/paper/whymb.2009.04.05a.pdf Linux Kernel Memory Barriers kernel.org/doc/Documentation/memory-barriers.txt Computer Architecture: A Quantitative Approach amazon.com/Computer-Architecture-Quantitative-Approach-4th/dp/0123704901/ref=dp_ob_title_bk

    Read the article

  • BPM Industry papers Financial Services & Insurance & Retail and BPM additional material

    - by JuergenKress
    Whitepaper: BPM for Financial Services Oracle BPM for Insurance Oracle BPM for Retail BPM 11g Patterns and Practices in Industry BPM Without Barriers Assessment: BPM Maturity - Online Self Assessment - Link New Book: "Oracle BPM Suite 11g: Advanced BPMN Topics" by Mark Nelson and Tanya Williams - Packt Publishing SOA & BPM Partner Community For regular information on Oracle SOA Suite become a member in the SOA & BPM Partner Community for registration please visit  www.oracle.com/goto/emea/soa (OPN account required) If you need support with your account please contact the Oracle Partner Business Center. Blog Twitter LinkedIn Mix Forum Technorati Tags: BPM,BPM FSI,BPM Insurance,BPM retail,BPM industries,BPM without barriers,Oracle SOA,Oracle BPM,Community,OPN,Jürgen Kress

    Read the article

  • Xen DomU on DRBD device: barrier errors

    - by Halfgaar
    I'm testing setting up a Xen DomU with a DRBD storage for easy failover. Most of the time, immediatly after booting the DomU, I get an IO error: [ 3.153370] EXT3-fs (xvda2): using internal journal [ 3.277115] ip_tables: (C) 2000-2006 Netfilter Core Team [ 3.336014] nf_conntrack version 0.5.0 (3899 buckets, 15596 max) [ 3.515604] init: failsafe main process (397) killed by TERM signal [ 3.801589] blkfront: barrier: write xvda2 op failed [ 3.801597] blkfront: xvda2: barrier or flush: disabled [ 3.801611] end_request: I/O error, dev xvda2, sector 52171168 [ 3.801630] end_request: I/O error, dev xvda2, sector 52171168 [ 3.801642] Buffer I/O error on device xvda2, logical block 6521396 [ 3.801652] lost page write due to I/O error on xvda2 [ 3.801755] Aborting journal on device xvda2. [ 3.804415] EXT3-fs (xvda2): error: ext3_journal_start_sb: Detected aborted journal [ 3.804434] EXT3-fs (xvda2): error: remounting filesystem read-only [ 3.814754] journal commit I/O error [ 6.973831] init: udev-fallback-graphics main process (538) terminated with status 1 [ 6.992267] init: plymouth-splash main process (546) terminated with status 1 The manpage of drbdsetup says that LVM (which I use) doesn't support barriers (better known as tagged command queuing or native command queing), so I configured the drbd device not to use barriers. This can be seen in /proc/drbd (by "wo:f, meaning flush, the next method drbd chooses after barrier): 3: cs:Connected ro:Primary/Secondary ds:UpToDate/UpToDate C r---- ns:2160152 nr:520204 dw:2680344 dr:2678107 al:3549 bm:9183 lo:0 pe:0 ua:0 ap:0 ep:1 wo:f oos:0 And on the other host: 3: cs:Connected ro:Secondary/Primary ds:UpToDate/UpToDate C r---- ns:0 nr:2160152 dw:2160152 dr:0 al:0 bm:8052 lo:0 pe:0 ua:0 ap:0 ep:1 wo:f oos:0 I also enabled the option disable_sendpage, as per the drbd docs: cat /sys/module/drbd/parameters/disable_sendpage Y I also tried adding barriers=0 to fstab as mount option. Still it sometimes says: [ 58.603896] blkfront: barrier: write xvda2 op failed [ 58.603903] blkfront: xvda2: barrier or flush: disabled I don't even know if ext3 has a nobarrier option. And, because only one of my storage systems is battery backed, it would not be smart anyway. Why does it still compain about barriers when I disabled that? Both host are: Debian: 6.0.4 uname -a: Linux 2.6.32-5-xen-amd64 drbd: 8.3.7 Xen: 4.0.1 Guest: Ubuntu 12.04 LTS uname -a: Linux 3.2.0-24-generic pvops drbd resource: resource drbdvm { meta-disk internal; device /dev/drbd3; startup { # The timeout value when the last known state of the other side was available. 0 means infinite. wfc-timeout 0; # Timeout value when the last known state was disconnected. 0 means infinite. degr-wfc-timeout 180; } syncer { # This is recommended only for low-bandwidth lines, to only send those # blocks which really have changed. #csums-alg md5; # Set to about half your net speed rate 60M; # It seems that this option moved to the 'net' section in drbd 8.4. (later release than Debian has currently) verify-alg md5; } net { # The manpage says this is recommended only in pre-production (because of its performance), to determine # if your LAN card has a TCP checksum offloading bug. #data-integrity-alg md5; } disk { # Detach causes the device to work over-the-network-only after the # underlying disk fails. Detach is not default for historical reasons, but is # recommended by the docs. # However, the Debian defaults in drbd.conf suggest the machine will reboot in that event... on-io-error detach; # LVM doesn't support barriers, so disabling it. It will revert to flush. Check wo: in /proc/drbd. If you don't disable it, you get IO errors. no-disk-barrier; } on host1 { # universe is a VG disk /dev/universe/drbdvm-disk; address 10.0.0.1:7792; } on host2 { # universe is a VG disk /dev/universe/drbdvm-disk; address 10.0.0.2:7792; } } DomU cfg: bootloader = '/usr/lib/xen-default/bin/pygrub' vcpus = '2' memory = '512' # # Disk device(s). # root = '/dev/xvda2 ro' disk = [ 'phy:/dev/drbd3,xvda2,w', 'phy:/dev/universe/drbdvm-swap,xvda1,w', ] # # Hostname # name = 'drbdvm' # # Networking # # fake IP for posting vif = [ 'ip=1.2.3.4,mac=00:16:3E:22:A8:A7' ] # # Behaviour # on_poweroff = 'destroy' on_reboot = 'restart' on_crash = 'restart' In my test setup: the primary host's storage is 9650SE SATA-II RAID PCIe with battery. The secondary is software RAID1. Isn't DRBD+Xen widely used? With these problems, it's not going to work.

    Read the article

  • What Color is your Jetpack ?

    - by JoshReuben
    I’m a programmer, Im approaching 40, and I’m fairly decent at my job – I’ll keep doing what I’m doing for as long as they let me!   So what are your career options if you know how to code? A Programmer could be ..   An Algorithm developer Pros Interesting High barriers of entry, potential for startup competitive factor Cons Do you have the skill, qualifications? What are working conditions n this mystery niche ? micro-focus An Academic Pros Low pressure Job security – or is this an illusion ? Cons Low Pay Need a PhD A Software Architect Pros: strategic, rather than tactical Setting technology platform and high level vision You say how it should work, others have to figure out why its not working the way its supposed to ! broad view – you are paid to learn (how do you con people into paying for you to learn ??) Cons: Glorified developer – more often than not! competitive – everyone wants to do it ! loose touch with underlying tech in tough times, first guy to get the axe ! A Software Engineer Pros: interesting, always more to learn fun I can do it Fallback Cons: Nothing new under the sun – been there, done that Dealing with poor requirements, deadlines, other peoples code, overtime C#, XAML, Web - Low barriers of entry –> à race to the bottom A Team leader Pros: Setting code standards and proposing technology choices Cons: Glorified developer – more often than not! Inspecting other peoples code and debugging the problems they cannot fix Dealing with mugbies and prima donas Responsible for QA of others A Project Manager Pros No need for debugging other peoples code Cons Low barrier of entry High pressure Responsible for QA of others Loosing touch with technology A lot of bullshit meetings Have to be an asshole A Product Manager Pros No need for debugging other peoples code Learning new skillset of sales and marketing Cons Travel (I'm a family man) May need to know the bs details of an uninteresting product things I want to work with: AI, algorithms, Numerical Computing, Mathematica, C++ AMP – unfortunately, the work here is few & far between. VS & TFS Extensibility, DSLs (Workflow , Lightswitch), Code Generation – one day, code will write code ! Unity3D, WebGL – fun, fun, fun ! Modern Web – Knockout, SignalR, MVC, Node.Js ??? (tentative – I'll wait until things stabilize as this area is undergoing a pre-Cambrian explosion) Things I don’t want to work with: (but will if I'm asked to !) C# – same old, same old – not learning anything new here Old code – blech ! Environment with code & fix mentality , ad hoc requirements, excessive overtime Pc support, System administration – even after 20 years, people still ask you to do this sometimes ! debugging – my skills are just not there yet Oracle Old tech: VB 6, XSLT, WinForms, Net 3.51 or less Old style Web dev Information Systems: ASP.NET webforms, Reporting services / crystal reports, SQL Server CRUD with manual data layer, XAML MVVM – variations of the same concept, ad nauseaum. Low barriers of entry –> race to the bottom.  Metro – an elegant API coupled to a horrendous UX – I'll wait for market penetration viability before investing further in this.   Conclusion So if you are in a slump, take heart: Programming is a great career choice compared to every other job !

    Read the article

  • Is SQL Azure a newbies springboard?

    - by jamiet
    Earlier today I was considering the various SQL Server platforms that are available today and I wondered aloud, wonder how long until the majority of #sqlserver newcomers use @sqlazure instead of installing locally Let me explain. My first experience of development was way back in the early 90s when I would crank open VBA in Access or Excel and start hammering out some code, usually by recording macros and looking at the code that they produced (sound familiar?). The reason was simple, Office was becoming ubiquitous so the barrier to entry was incredibly low and, save for a short hiatus at university, I’ve been developing on the Microsoft platform ever since. These days spend most of my time using SQL Server. I take a look at SQL Azure today I see a lot of similarities with those early experiences, the barrier to entry is low and getting lower. I don’t have to download some software or actually install anything other than a web browser in order to get myself a fully functioning SQL Server  database against which I can ostensibly start hammering out some code and I believe that to be incredibly empowering. Having said that there are still a few pretty high barriers, namely: I need to get out my credit card Its pretty useless without some development tools such as SQL Server Management Studio, which I do have to install. The second of those barriers will disappear pretty soon when Project Houston delivers a web-based admin and presentation tool for SQL Azure so that just leaves the matter of my having to use a credit card. If Microsoft have any sense at all then they will realise the huge potential of opening up a free, throttled version of SQL Azure for newbies to party on; they get to developers early (just like they did with me all those years ago) and it gives potential customers an opportunity to try-before-they-buy. Perhaps in 20 years time people will be talking about SQL Azure as being their first foray into the world of coding! @Jamiet Share this post: email it! | bookmark it! | digg it! | reddit! | kick it! | live it!

    Read the article

  • Does learning to develop for iOS create a lock-in?

    - by Jungle Hunter
    If I begin my career (first job) with developing on the iOS platform, does that lock me in into iOS and Mac OS X development only? By locking me in I mean will that create barriers for me to switch technologies as I would be mainly working with Objective-C. If yes, does that make my career choices limited? I'm interested in comparing this with Android development, which if pursued will leave me with Java skills (correct me if I'm wrong) which I can use elsewhere.

    Read the article

  • dd oflag=direct 5x fast

    - by César
    I have Centos 6.2 in server with this specs: 2xCPU 16 Core AMD Opteron 6282 SE 64GB RAM Raid controller H700 1GB cache NV - 2HD 74GB SAS 15Krpm RAID1 stripe 16k (OS Centos 6.2) sda - 4HD 146GB SAS 15Krpm RAID10 stripe 16k (ext4 bs 4096, no barriers) sdb -> /vol01 Raid controller H800 1GB cache nv - MD1200 12HD 300GB SAS 15Krpm RAID10 stripe 256k (For DB Postgres 8.3.18) (ext4 bs 4096, stride 64, stripe-width 384, no barriers) sdc -> /vol02 I'm benchmarking IO speed with dd, and view thah if in RAID10 12 disk exec: dd if=/dev/zero of=DD bs=8M count=10000 oflag=direct 10000+0 records in 10000+0 records out 83886080000 bytes (84 GB) copied, 126,03 s, 666 MB/s but if I remove "oflag=direct" option obtain about 80 MB/s. In read benchmark, results are similar: dd of=/dev/null if=DD bs=8M count=10000 iflag=direct 10000+0 records in 10000+0 records out 83886080000 bytes (84 GB) copied, 79,5918 s, 1,1 GB/s If remove iflag=direct obtain 150MB/s... I don't understand this huge differences, on other machines y don't have this behavior. Can I have some kernel parameter misconfigured? Thanks!

    Read the article

facebook twitter digg google delicious technorati stumbleupon myspace wordpress linkedin gmail igoogle windows live tumblr viadeo yahoo buzz yahoo mail yahoo bookmarks favorites email print

1 2 3 4 5  | Next Page >