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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 bind a double precision using psycopg2

    - by user337636
    I'm trying to bind a float to a postgresql double precision using psycopg2. ele = 1.0/3.0 dic = {'name': 'test', 'ele': ele} sql = '''insert into waypoints (name, elevation) values (%(name)s, %(ele)s)''' cur = db.cursor() cur.execute(sql, dic) db.commit() sql = """select elevation from waypoints where name = 'test'""" cur.execute(sql_out) ele_out = cur.fetchone()[0] ele_out 0.33333333333300003 ele 0.33333333333333331 Obviously I don't need the precision, but I would like to be able to simply compare the values. I could use the struct module and save it as a string, but thought there should be a better way. Thanks

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  • Committed JDO writes do not apply on local GAE HRD, or possibly reused transaction

    - by eeeeaaii
    I'm using JDO 2.3 on app engine. I was using the Master/Slave datastore for local testing and recently switched over to using the HRD datastore for local testing, and parts of my app are breaking (which is to be expected). One part of the app that's breaking is where it sends a lot of writes quickly - that is because of the 1-second limit thing, it's failing with a concurrent modification exception. Okay, so that's also to be expected, so I have the browser retry the writes again later when they fail (maybe not the best hack but I'm just trying to get it working quickly). But a weird thing is happening. Some of the writes which should be succeeding (the ones that DON'T get the concurrent modification exception) are also failing, even though the commit phase completes and the request returns my success code. I can see from the log that the retried requests are working okay, but these other requests that seem to have committed on the first try are, I guess, never "applied." But from what I read about the Apply phase, writing again to that same entity should force the apply... but it doesn't. Code follows. Some things to note: I am attempting to use automatic JDO caching. So this is where JDO uses memcache under the covers. This doesn't actually work unless you wrap everything in a transaction. all the requests are doing is reading a string out of an entity, modifying part of the string, and saving that string back to the entity. If these requests weren't in transactions, you'd of course have the "dirty read" problem. But with transactions, isolation is supposed to be at the level of "serializable" so I don't see what's happening here. the entity being modified is a root entity (not in a group) I have cross-group transactions enabled Another weird thing is happening. If the concurrent modification thing happens, and I subsequently edit more than 5 more entities (this is the max for cross-group transactions), then nothing happens right away, but when I stop and restart the server I get "IllegalArgumentException: operating on too many entity groups in a single transaction". Could it be possible that the PMF is returning the same PersistenceManager every time, or the PM is reusing the same transaction every time? I don't see how I could possibly get the above error otherwise. The code inside the transaction just edits one root entity. I can't think of any other way that GAE would give me the "too many entity groups" error. The relevant code (this is a simplified version) PersistenceManager pm = PMF.getManager(); Transaction tx = pm.currentTransaction(); String responsetext = ""; try { tx.begin(); // I have extra calls to "makePersistent" because I found that relying // on pm.close didn't always write the objects to cache, maybe that // was only a DataNucleus 1.x issue though Key userkey = obtainUserKeyFromCookie(); User u = pm.getObjectById(User.class, userkey); pm.makePersistent(u); // to make sure it gets cached for next time Key mapkey = obtainMapKeyFromQueryString(); // this is NOT a java.util.Map, just FYI Map currentmap = pm.getObjectById(Map.class, mapkey); Text mapData = currentmap.getMapData(); // mapData is JSON stored in the entity Text newMapData = parseModifyAndReturn(mapData); // transform the map currentmap.setMapData(newMapData); // mutate the Map object pm.makePersistent(currentmap); // make sure to persist so there is a cache hit tx.commit(); responsetext = "OK"; } catch (JDOCanRetryException jdoe) { // log jdoe responsetext = "RETRY"; } catch (Exception e) { // log e responsetext = "ERROR"; } finally { if (tx.isActive()) { tx.rollback(); } pm.close(); } resp.getWriter().println(responsetext); EDIT: so I have verified that it fails after exactly 5 transactions. Here's what I do: I create a Foo (root entity), do a bunch of concurrent operations on that Foo, and some fail and get retried, and some commit but don't apply (as described above). Then, I start creating more Foos, and do a few operations on those new Foos. If I only create four Foos, stopping and restarting app engine does NOT give me the IllegalArgumentException. However if I create five Foos (which is the limit for cross-group transactions), then when I stop and restart app engine, I do get the exception. So it seems that somehow these new Foos I am creating are counting toward the limit of 5 max entities per transaction, even though they are supposed to be handled by separate transactions. It's as if a transaction is still open and is being reused by the servlet when it handles the new requests for the 2nd through 5th Foos. EDIT2: it looks like the IllegalArgument thing is independent of the other bug. In other words, it always happens when I create five Foos, even if I don't get the concurrent modification exception. I don't know if it's a symptom of the same problem or if it's unrelated. EDIT3: I found out what was causing the (unrelated) IllegalArgumentException, it was a dumb mistake on my part. But the other issue is still happening. EDIT4: added pseudocode for the datastore access EDIT5: I am pretty sure I know why this is happening, but I will still award the bounty to anyone who can confirm it. Basically, I think the problem is that transactions are not really implemented in the local version of the datastore. References: https://groups.google.com/forum/?fromgroups=#!topic/google-appengine-java/gVMS1dFSpcU https://groups.google.com/forum/?fromgroups=#!topic/google-appengine-java/deGasFdIO-M https://groups.google.com/forum/?hl=en&fromgroups=#!msg/google-appengine-java/4YuNb6TVD6I/gSttMmHYwo0J Because transactions are not implemented, rollback is essentially a no-op. Therefore, I get a dirty read when two transactions try to modify the record at the same time. In other words, A reads the data and B reads the data at the same time. A attempts to modify the data, and B attempts to modify a different part of the data. A writes to the datastore, then B writes, obliterating A's changes. Then B is "rolled back" by app engine, but since rollbacks are a no-op when running on the local datastore, B's changes stay, and A's do not. Meanwhile, since B is the thread that threw the exception, the client retries B, but does not retry A (since A was supposedly the transaction that succeeded).

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  • What is the best practice to segment c#.net projects based on a single base project

    - by Anthony
    Honestly, I can't word my question any better without describing it. I have a base project (with all its glory, dlls, resources etc) which is a CMS. I need to use this project as a base for othe custom bake projects. This base project is to be maintained and updated among all custom bake projects. I use subversion (Collabnet and Tortise SVN) I have two questions: 1 - Can I use subversion to share the base project among other projects What I mean here is can I "Checkout" the base project into another "Checked Out" project and have both update and commit seperatley. So, to paint a picture, let's say I am working on a custom project and I modify the core/base prject in some way (which I know will suit the others) can I then commit those changes and upon doing so when I update the base project in the other "Checked out" resources will it pull the changes? In short, I would like not to have to manually deploy updated core files whenever I make changes into each seperate project. 2 - If I create a custom file (let's say an webcontrol or aspx page etc) can I have it compile seperatley from the base project Another tricky one to explain. When I publish my web application it creates DLLs based on the namespaces of projects attached to it. So I may have a number of DLLs including the "Website's" namespace DLL, which could simply be website. I want to be able to make a seperate, custom, control which does not compile into those DLLs as the custom files should not rely on those DLLS to run. Is it as simple to set a seperate namespace for those files like CustomFiles.ProjectName for example? Think of the whole idea as adding modules to the .NET project, I don't want the module's code in any of the core DLLs but I do need for module to be able to access the core dlls. (There is no need for the core project to access the module code as it should be one way only in theory, though I reckon it woould not be possible anyway without using JSON/SOAP or something like that, maybe I am wrong.) I want to create a pluggable environment much like that of Joomla/Wordpress as since PHP generally doesn't have to be compiled first I see this is the reason why all this is possible/easy. The idea is to allow pluggable themes, modules etc etc. (I haven't tried simply adding .NET themes after compile/publish but I am assuming this is possible anyway? OR does the compiler need to reference items in the files?)

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  • How to create an entity with a composite primary key containing a generated value.

    - by David
    Using Hibernate + annotations, I'm trying to do the following: Two entities, Entity1 and Entity2. Entity1 contains a simple generated value primary key. Entity2 primary key is composed by a simple generated value + the id of entity one (with a many to one relationship) Unfortunately, I can't make it work. Here is an excerpt of the code: @Entity public class Entity1 { @Id @GeneratedValue private Long id; private String name; ... } @Entity public class Entity2 { @EmbeddedId private Entity2PK pk = new Entity2PK(); private String miscData; ... } @Embeddable public class Entity2PK implements Serializable { @GeneratedValue private Long id; @ManyToOne private Entity1 entity; } void test() { Entity1 e1 = new Entity1(); e1.setName("nameE1"); Entity2 e2 = new Entity2(); e2.setEntity1(e1); e2.setMiscData("test"); Transaction transaction = session.getTransaction(); try { transaction.begin(); session.save(e1); session.save(e2); transaction.commit(); } catch (Exception e) { transaction.rollback(); } finally { session.close(); } } When I run the test method I get the following errors: Hibernate: insert into Entity1 (id, name) values (null, ?) Hibernate: call identity() Hibernate: insert into Entity2 (miscData, entity_id, id) values (?, ?, ?) 07-Jun-2010 10:51:11 org.hibernate.util.JDBCExceptionReporter logExceptions WARNING: SQL Error: 0, SQLState: null 07-Jun-2010 10:51:11 org.hibernate.util.JDBCExceptionReporter logExceptions SEVERE: failed batch 07-Jun-2010 10:51:11 org.hibernate.event.def.AbstractFlushingEventListener performExecutions SEVERE: Could not synchronize database state with session org.hibernate.exception.GenericJDBCException: Could not execute JDBC batch update at org.hibernate.exception.SQLStateConverter.handledNonSpecificException(SQLStateConverter.java:103) at org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:91) at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:43) at org.hibernate.jdbc.AbstractBatcher.executeBatch(AbstractBatcher.java:254) at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:266) at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:167) at org.hibernate.event.def.AbstractFlushingEventListener.performExecutions(AbstractFlushingEventListener.java:298) at org.hibernate.event.def.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:27) at org.hibernate.impl.SessionImpl.flush(SessionImpl.java:1001) at org.hibernate.impl.SessionImpl.managedFlush(SessionImpl.java:339) at org.hibernate.transaction.JDBCTransaction.commit(JDBCTransaction.java:106) at test.App.main(App.java:32) Caused by: java.sql.BatchUpdateException: failed batch at org.hsqldb.jdbc.jdbcStatement.executeBatch(Unknown Source) at org.hsqldb.jdbc.jdbcPreparedStatement.executeBatch(Unknown Source) at org.hibernate.jdbc.BatchingBatcher.doExecuteBatch(BatchingBatcher.java:48) at org.hibernate.jdbc.AbstractBatcher.executeBatch(AbstractBatcher.java:247) ... 8 more Note that I use HSQLDB. Any ideas about what is wrong ?

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  • Have I to count transactions before rollback one in catch block in T-SQL?

    - by abatishchev
    I have next block in the end of each my stored procedure for SQL Server 2008 BEGIN TRY BEGIN TRAN -- my code COMMIT END TRY BEGIN CATCH IF (@@trancount > 0) BEGIN ROLLBACK DECLARE @message NVARCHAR(MAX) DECLARE @state INT SELECT @message = ERROR_MESSAGE(), @state = ERROR_STATE() RAISERROR (@message, 11, @state) END END CATCH Is it possible to switch CATCH-block to BEGIN CATCH ROLLBACK DECLARE @message NVARCHAR(MAX) DECLARE @state INT SELECT @message = ERROR_MESSAGE(), @state = ERROR_STATE() RAISERROR (@message, 11, @state) END CATCH or just BEGIN CATCH ROLLBACK END CATCH ?

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  • vim is not obeying command aliases

    - by Nadal
    I use bash on mac and one of the aliases is like this alias gitlog='git --no-pager log -n 20 --pretty=format:%h%x09%an%x09%ad%x09%s --date=short --no-merges' However when I do :! gitlog I get /bin/bash: gitlog: command not found I know I can add aliases like this in my .gitconfig [alias] co = checkout st = status ci = commit br = branch df = diff However I don't want to add all my bash aliases to .gitconfig. That is not DRY. Is there a better solution?

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  • How to inject "history" into a subversion repository?

    - by Ran Biron
    We're migrating from StarTeam (aka "the horrible") to SubVersion (aka "the alleged great"). We've already migrated the files by doing a "dumb" commit to all files and started working on the SubVersion repository. However, we're still forced to use StarTeam because we lack the per-file history of check-ins. Is it possible to inject that history into SubVersion after the first check-in has been done? If yes - how?

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  • Version Control software (client server model)

    - by Amira Elsayed
    Hi All, I'm using windows 7 , and all what i want is to install Version Control server on one machine and let other developers to connect to it using the machine IP address and chekout, update and commit files I have tried VisualSVN and it works well for me , I also have tried to install Apache Server and try to configure it to run with subversion but I failed to do so , so if any one can help me I will appreciated Thanks in Advance Edit what I want if any one can suggest an alternative like VisualSVN that let me compare and choose from different options Thanks in Advance

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  • globalize2 with xml/json support

    - by Philipp Bolliger
    I'm implementing a distributed application, server with rails and mobile clients in objective c (iPhone). To enable internationalization, I use the rails plugin 'globalize2' by joshmh. However, it turned out that this plugin does not translate attributes when calling to_xml or to_json on an ActiveRecord. Does anyone know of a workaround / patch? Do you have any ideas how to fix this, where to alter globalize2? Using: Rails 2.3.5 globalize2: commit from 2010-01-11

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  • SQLAlchemy autocommiting?

    - by muckabout
    I have an issue with SQLAlchemy apparently committing. A rough sketch of my code: trans = self.conn.begin() try: assert not self.conn.execute(my_obj.__table__.select(my_obj.id == id)).first() self.conn.execute(my_obj.__table__.insert().values(id=id)) assert not self.conn.execute(my_obj.__table__.select(my_obj.id == id)).first() except: trans.rollback() raise I don't commit, and the second assert always fails! In other words, it seems the data is getting inserted into the database even though the code is within a transaction! Is this assessment accurate?

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  • Mercurial permament delete?

    - by Arnis L.
    I commit some 3rd party tools that i decided not to use afterwards and removed them from hg again. Thing that i dislike - they are still kept in history. Normally this is a good thing of course, but for this particular case - that's just a waste of space. What are options to intentionally mess around with hg repository history and weed it out?

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  • Git log: fatal object [sha1] is corrupted

    - by Keyo
    Is there any way I can repair my repository with commit history in tact. # git log fatal: object 01aeb2bf2e93b238f0e0422816b3e55518321ae7 is corrupted From reading the link below it looks like I'll have zap it and start over. http://www.miek.nl/s/7e76eadefe/

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  • Git Reverting the Repository to Previous State

    - by azamsharp
    I have a .gitignore file in my project directory and I placed the following entry in the file to not to commit the files in the following folder: EStudyMongoDb.Integration.Test\ For some reason Git pushed the files to repository anyway! Anyway! now I want to remove those files that have been pushed to the repository but I don't want to loose my local changes to the files inside the folder. How can I do that?

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  • Parallel Dev: Should developers work within the same branch?

    - by Zombies
    Should multiple developers work within the same branch, and update - modify - commit ? Or should each developer have his/her own each branch exclusively? And how would sharing branches impact an environment where you are doing routine maintenance as opposed to unmaintained code streams? Also, how would this work if you deploy each developers work as soon as it is done and passes testing (rapidly, as opposed to putting all of their work into a single release).

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  • Problem with SharedPreferences

    - by user547995
    Code for restore: final SharedPreferences settings = getSharedPreferences("pref", 0); settings.getString("user", ""); settings.getString("pw", ""); Code for store: SharedPreferences.Editor editor = settings.edit(); editor.putString("user", etuser.getText().toString()); editor.putString("pw", etpw.getText().toString()); editor.commit(); This code don't work, and no error occur

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  • Build server polling vs. event-driven builds

    - by Daniel T.
    Why do build servers poll for changes instead of SVN firing off an event (or a post-commit step) that tells the build server to start a build? It seems terribly inefficient to poll for changes, especially when the number of projects increases and the polling period is set to a very low value (for example, 30 seconds).

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  • Accidentally committed dev database to Git

    - by Euwyn
    I accidentally committed my development.sqlite3 file to Git, and it seems to be slowing down my commits. I know about .gitignore, but does this take the file out of my repository once I've done so? My concern is is with reducing the commit and push times.

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  • How does your team work together in a remote setup?

    - by Carl Rosenberger
    Hi, we are a distributed team working on the object database db4o. The way we work: We try to program in pairs only. We use Skype and VNC or SharedView to connect and work together. In our online Tuesday meeting every week (usually about 1 hour) we talk about the tasks done last week we create new pairs for the next week with a random generator so knowledge and friendship distribute evenly we set the priority for any new tasks or bugs that have come in each team picks the tasks it likes to do from the highest prioritized ones. From Tuesday to Wednesday we estimate tasks. We have a unit of work we call "Ideal Developer Session" (IDS), maybe 2 or 3 hours of working together as a pair. It's not perfectly well defined (because we know estimation always is inaccurate) but from our past shared experience we have a common sense of what an IDS is. If we can't estimate a task because it feels too long for a week we break it down into estimatable smaller tasks. During a short meeting on Wednesday we commit to a workload we feel is well doable in a week. We commit to complete. If a team runs out of committed tasks during the week, it can pick new ones from the prioritized queue we have in Jira. When we started working this way, some of us found that remote pair programming takes a lot of energy because you are so focussed. If you pair program for more than 5 or 6 hours per day, you get drained. On the other hand working like this has turned out to be very efficient. The knowledge about our codebase is evenly distributed and we have really learnt lots from eachother. I would be very interested to hear about the experiences from other teams working in a similar way. Things like: How often do you meet? Have you tried different sprint lengths (one week, two week, longer) ? Which tools do you use? Which issue tracker do you use? What do you do about time zone differences? How does it work for you to integrate new people into the team? How many hours do you usually work per week? How does your management interact with the way you are working? Do you get put on a waterfall with hard deadlines? What's your unit of work? What is your normal velocity? (units of work done per week) Programming work should be fun and for us it usually is great fun. I would be happy about any new ideas how to make it even more fun and/or more efficient.

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  • Good book for learning Bash shell?

    - by John Isaacks
    I want to learn how to write shell scripts. Particularly I want to write a svn post-commit script to upload files from a test server to a production server. I am sure I will want to write more as I get more into it. I have very little linux/unix knowledge. Can anyone recommend a good book?

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  • Mercurial stuck "waiting for lock"

    - by jm
    Got a bluescreen in windows while cloning a mercurial repository. After reboot, I now get this message for almost all hg commands: c:\srchg commit waiting for lock on repository c:\src\McVrsServer held by '\x00\x00\x00\x00\x00\ x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00' interrupted! Google is no help. Any tips?

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