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  • Persistent (purely functional) Red-Black trees on disk performance

    - by Waneck
    I'm studying the best data structures to implement a simple open-source object temporal database, and currently I'm very fond of using Persistent Red-Black trees to do it. My main reasons for using persistent data structures is first of all to minimize the use of locks, so the database can be as parallel as possible. Also it will be easier to implement ACID transactions and even being able to abstract the database to work in parallel on a cluster of some kind. The great thing of this approach is that it makes possible implementing temporal databases almost for free. And this is something quite nice to have, specially for web and for data analysis (e.g. trends). All of this is very cool, but I'm a little suspicious about the overall performance of using a persistent data structure on disk. Even though there are some very fast disks available today, and all writes can be done asynchronously, so a response is always immediate, I don't want to build all application under a false premise, only to realize it isn't really a good way to do it. Here's my line of thought: - Since all writes are done asynchronously, and using a persistent data structure will enable not to invalidate the previous - and currently valid - structure, the write time isn't really a bottleneck. - There are some literature on structures like this that are exactly for disk usage. But it seems to me that these techniques will add more read overhead to achieve faster writes. But I think that exactly the opposite is preferable. Also many of these techniques really do end up with a multi-versioned trees, but they aren't strictly immutable, which is something very crucial to justify the persistent overhead. - I know there still will have to be some kind of locking when appending values to the database, and I also know there should be a good garbage collecting logic if not all versions are to be maintained (otherwise the file size will surely rise dramatically). Also a delta compression system could be thought about. - Of all search trees structures, I really think Red-Blacks are the most close to what I need, since they offer the least number of rotations. But there are some possible pitfalls along the way: - Asynchronous writes -could- affect applications that need the data in real time. But I don't think that is the case with web applications, most of the time. Also when real-time data is needed, another solutions could be devised, like a check-in/check-out system of specific data that will need to be worked on a more real-time manner. - Also they could lead to some commit conflicts, though I fail to think of a good example of when it could happen. Also commit conflicts can occur in normal RDBMS, if two threads are working with the same data, right? - The overhead of having an immutable interface like this will grow exponentially and everything is doomed to fail soon, so this all is a bad idea. Any thoughts? Thanks! edit: There seems to be a misunderstanding of what a persistent data structure is: http://en.wikipedia.org/wiki/Persistent_data_structure

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  • How to search through all commits in the repository?

    - by Josip
    I have a git repository with few branches and dangling commits. I would like to search all such commits in repository for a specific string. I know how to get a log of all commits in history, but these don't include branches or dangling blobs, just HEAD's history. I want to get them all, to find a specific commit that got misplaced. I would also like to know how to do this in mercurial, as I'm considering the switch.

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  • Issue in Adding data into database using hibernate

    - by sarah
    Hi , I am getting the following exception "org.hibernate.HibernateException: The database returned no natively generated identity value "while adding data into database i am using the following code.Please let me know what is wrong Sesion session=HibernateUtil.getSession(); Transaction tx = session.beginTransaction(); session.save(user); logger.info("Successfully data insert in database"); tx.commit(); isSaved=true; Thankx

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  • Hessian on Windows Phone 7/ Silverlight ??

    - by Michal
    Hi, I'm using hessian protocol for communication betwee server (java) and various client applications. Now I started to develop Windows Phone 7 client. I downloaded hessian C# implementation but it does not compile for windows phone 7/silverlight. Does anyone managed to make it work on WP7/Silverlight? It's looks like there is many thing to be done/changed to make it work, which I'd like to avoid if it has been done by someone already. Thanks.

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  • Similar to SSL Local Forwarding

    - by whoi
    Hi; As you know SSL protocol supports up to some max value of local forwarding and it is a really good feature. My question is: is there any similar project just making this local forwarding thing? I do not need all this bunch of features coming with SSL.. Thanks

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  • Git dirctet acyclic graph - children know their parents but not the other way around

    - by dayscott
    Git is implemented as a directed acyclic graph. Children know their parents but not the other way round. This makes sense because i can reach every commit only through a branch or a tag ( generally speaking through a reference). That's how i traverse the tree. What other reasons had the developers of Git to make "the children know their parents but not the other way around"?/ What are the key benefits of this?

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  • What does really happen when we do a BEGIN TRAN in SQL Server 2005?

    - by Misnomer
    Hi all, I came across this issue or maybe something I didn't realize but I did a Begin Tran and had some code inside it and never ran a commit or rollback as I forgot about it. That caused all many of the database queries or even just a simple select top 1000 command were just sitting on loading..? Now it probably has put some locks on the tables I guess since it did not let me query them..but I just wanted to know what exactly happened and what are the practices to be followed here ?

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  • How to detect a pending JDO transaction?

    - by Stevko
    I believe I am getting JDO commit Exceptions due to the transactions nesting although I'm not sure. Will this detect the situation where I am starting a transaction when another is pending? PersistenceManager pm = PersistenceManagerFactory.get().getPersistenceManager(); assert pm.currentTransaction().isActive() == false : "arrrgh"; pm.currentTransaction().begin(); Is there a better or more reliable way?

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  • Disctinct from the table

    - by bharat
    ICriteria crit = session.CreateCriteria(); foreach (ICriteriaItem<object> param in filters) { crit.Add(Expression.Eq(param.PropertyName, param.FilterValue)); } crit.SetProjection(Projections.Distinct(Projections.ProjectionList())); -- disctinct not working can you please help me crit.AddOrder(new Order(sortField, sortOrderAscending)); crit.SetFirstResult(pageNumber * pageSize); crit.SetMaxResults(pageSize); transaction.Commit(); return crit.List<IHCOSpendTable>();

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  • Delete Drag and Drop Behavior of IKImageBrowserView

    - by PF1
    Hi Everyone: By default (it seems), IKImageBrowserView enables drag and drop to locations in the Finder. I would like to turn off this behavior but am unsure of how to do so. I was thinking that perhaps implementing the NSDraggingDestination protocol and overriding it could solve this, but so far it hasn't worked for me. Thanks for any help!

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  • iPhone: Core Data save Class object

    - by Nic Hubbard
    I have an entity in core data called Location. Inside this I have a few fields, such as date. But, I would also like to save a class object in it that I created called Annotation. What type of attribute would I use for this, since it is a custom class object that I created? Location (object) |__ Date |__ Annotation (MKAnnotation protocol)

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  • Ruby: How can I have a Hash take multiple keys?

    - by zxcvbnm
    I'm taking 5 strings (protocol, source IP and port, destination IP and port) and using them to store some values in a hash. The problem is that if the IPs or ports are switched between source and destination, the key is supposed to be the same. If I was doing this in C#/Java/whatever I'd have to create a new class and overwrite the hashcode()/equals() methods, but that seems error prone from the little I've read about it and I was wondering if there would be a better alternative here.

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  • JBoss warning - "Unable to fill pool"

    - by Marcus
    We're getting this random warning from JBoss.. any idea why? It happens at random times when there are no active threads. Everything works when any processing resumes. 13:49:31,764 WARN [JBossManagedConnectionPool] [ ] Unable to fill pool org.jboss.resource.JBossResourceException: Could not create connection; - nested throwable: (java.sql.SQLException: Listener ref used the connection with the following error: ORA-12516, TNS:listener could not find available handler with matching protocol stack The Connection descriptor used by the client was: //localhost:1521/orcl

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  • Frustrations about which language to use [closed]

    - by Joshua
    I am way too indecisive. I have an idea for a (admittedly craptastic) GUI program, so I start writing it in C# .NET WinForms. Then like halfway through I'm like, damn I should have written this in Qt. So I start writing it in Qt and remember why I hate C++ STL iterators so much. So in my head I go LINQ C++ STL So I'm like, maybe I'll do it in WPF, I like markup to make UIs hey this is kinda like web development (read: ez pz) BUT ITS LIKE WHY GOD WHY CANT I JUST PICK ONE AND COMMIT

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  • does the concept of flow apply to tcp as well as udp?

    - by liv2hak
    I have a very large network trace file which contains both tcp and udp packets.I want to find out the flows in the trace file.For that I have a hash function which takes in source ip address,destination ip address,source port,destination port and protocol.In case of TCP I can understand that the flow means all the packets which have the same 5 parameters same.But what does it mean in case of UDP.how does the concept of flow apply in case of UDP.? I am a novice in packet processing.

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  • WCF hosting in .NET compact framework

    - by jauwaad
    I would like to host a service on a WinCE device. The WinCE device is the host which can be accessed(control and data acquisition) by multiple clients (PC or WinCE) over serial port, TCP, USB etc. I was considering using Protocol Buffers for serialization on the wire. It would be ideal to use WCF or remoting but as far as I see they are not implement on the Compact Framework. Anyone have any ideas how this can be achieved.

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  • Transaction Isolation on select, insert, delete

    - by Bradford
    What could possibly go wrong with the following transaction if executed by concurrent users in the default isolation level of READ COMMITTED? BEGIN TRANSACTION SELECT * FROM t WHERE pid = 10 and r between 40 and 60 -- ... this returns tid = 1, 3, 5 -- ... process returned data ... DELETE FROM t WHERE tid in (1, 3, 5) INSERT INTO t (tid, pid, r) VALUES (77, 10, 35) INSERT INTO t (tid, pid, r) VALUES (78, 10, 37) INSERT INTO t (tid, pid, r) VALUES (79, 11, 39) COMMIT

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  • Fatal IO error 0 (Success) on X server

    - by Ori Pessach
    What does the error "Fatal IO error 0 (Success) on X server" mean? The error is produced when an X client tries to call XvCreateImage(), and it results in the client terminating. X.0.log shows the following version information: X.Org X Server 1.6.4 Release Date: 2009-9-27 X Protocol Version 11, Revision 0 Build Operating System: Linux 2.6.24-23-server i686 Ubuntu Current Operating System: Linux ori-laptop 2.6.31-17-generic #54-Ubuntu SMP Thu Dec 10 16:20:31 UTC 2009 i686 Kernel command line: BOOT_IMAGE=/boot/vmlinuz-2.6.31-17-generic root=UUID=df637de9-47ed-4453-9393-67e2e2ffaa2f ro quiet splas

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