I am creating an application with sqlite. I am performing all kind of task on the database Insert, Update, Delete, Select.
For that I open the database every time, Then execute my query using sqlite3_step() and after the result I use sqlite3_finalize() and sqlite3_close() methods. It is working well in most cases. I am not getting when its happening but some times my database gets locked with the same process I follow and some time it works.
I need to unlock database so even in any case my database get locked then I can unlock it or Plz guide me if I can check by code that my database is locked so I can replace my database with the resource database.
I am using webservice too so I don't have issue about data loss.
Is it make sense if I replace my database if it get locked or if there is any way to unlock the database.
Open database once in the beginning. And close it in the end in AppWillterminate function. You are only consuming time by opening and closing it in every database function.
As far as database lock is concerned, it gets locked when some application is still using it and other application is trying to get its access.
This could be your app, or possibly the sqlite manager add-on of your firefox.
I faced same problem once and what i did was
Disabled the option in sqlite add-on where it remembers the previously opened database.
Restart xcode, simulator.
Make a copy of the sqlite file (desktop), delete it from the project and then add in project again from desktop.
The last solution sounds weird, but i was mad that time.
I hope this could help you.
Related
I have transaction log file that goes back 6 months. I need to roll back everything that happened after 5/20/2013 from a database. Can anyone please enlighten me on how to do this?
First of all, copy the database MDF and LDF files. Better safe than sorry
The database can be restored to a point in time in SQL Server 2008R2, also. There's no need to create a transaction log backup first, it'll be done automatically by SQL Server. You can find more about the log-tail backup here: Tail-Log Backups
Select to restore the database in the database context menu
Leave Database as Source. Click Timeline
Select Specific date and time. If you drag the time pointer, you'll able to see how long back your transaction log goes. Note that bright green shows that the transactions have never been backed up
After all is done, schedule transaction log backups. There's no point to have a database in Full recovery model and never backup the online transaction log
I am using sqlite database for my application. When i create tables in it dynamically the app works fine for the first time but when I re start the app i can only read the earlier values that i inserted but no new values get inserted.
there is nothing wrong with the code all finalize and all related statements are in place.
Any suggestion why it is happening, the sqlite is giving the error that the database is locked.
As many time mentioned:
"Open the database once at the start of your app, then close it in applicationWillTerminate of the AppDelegate. After every exec you will want to do a reset to clear the connection state."
so did you close your database at app quit?
try sqlite3_reset(stmt) befor finalize
I have an app with a very large Core Data database. I have versioned it many times over the past year.
The last time I versioned the database I made one simple change to an entity: I added a new optional attribute. For some reason it would not migrate using Light-weight Migration. I found out much later that this was due to a bug in Apple's Light-weight Migration code resulting from the 'renaming identifiers' that I had needed back in another versioning.
Anyway, I digress...
Because of the bug that kept me from using Light-weight migration, I created a mapping file to help with the migration, not understanding that this would was a much heavier process and would force my users to wait while the app loaded the entire database into memory while doing the migration. It turns out that this is not really an option at all with very large databases and many of my users were unable to migrate the database at all due to memory problems, etc.
So now I want to re-release my app and clear up this problem. The trouble is, some of my users have a database that is somehow marked as being 'in the middle of migrating'. Even with my new code, which gets rid of the mapping file and supports Light-weight migration, users that are in this state, 'in the middle of a migration', don't seem to get reset.
What are my options for backing out a migration?
- I can detect that I am in this state because there is a '.myDB.sqlite.migrationdestination_41b5a6b5c6e848c462a8480cd24caef3' file in the Documents directory. Deleting this file does not clear up the migration. My guess is that the database is somehow flagged as being in this state, or is already partially migrated.
- I can detect this state and then delete the database altogether. But this forces my users to re-download their data.
Any Thoughts?
Thanks for you help.
The only thing that occurs to me would be crack open the SQL store of an affected file and look for flags or something else that might signal the db being in a transitory state. You might be able to write directly to the file and alter something.
That's really ugly problem.
Short version
If my process is terminated in the middle of a transaction, or while SQLite is committing a transaction, what are the chances that the database file will be corrupted?
Long version
My application uses an SQLite database for storage (directly, not via Core Data). I'm working on a new version of the application which will require an update to the database schema. On launch, the app will check the database and, if it needs updating, execute a series of SQL statements to do so.
Depending on the amount of data in the database, the update may be long running (on the order of seconds), so I need to consider the possibility that the process may be terminated before the update is completed. (For context, this on an iPhone, where the processor is slow and the app may be terminated by an incoming phone call.) I will, of course, wrap the upgrade SQL statements in a transaction. Will that be enough to guarantee that the database will not be corrupted?
I'm assuming that transactions work as advertised, and that if the process is terminated in the middle of the transaction, the file will be OK. But I'm also assuming there is a window of time during the COMMIT where something can go wrong.
To play it safe, I could create a backup copy of the database file before starting the update, but if the transactions are safe then that would be overkill. It would also make the update process take longer, which increases the chance it would be interrupted, and then I'd have to consider that the file copy operation might be interrupted... I'd like to keep the code as simple as possible (but no simpler).
In the course of researching this question I've started reading "Atomic Commit In SQLite", which is more detail than I probably need to know, but is giving me faith that I don't need to second-guess SQLite's ability to protect the database file. But I'd still like to hear from Stack Overflow: is a transaction good enough, or should I be more cautious?
I have read the Atomic Commit in SQLite document. It may not be overkill if you really want to understand what's going on, but in a nutshell, a transaction goes like this:
Lock the database file
Create the rollback journal
Determine what portions of the database file are going to be changing
Write copies of those pages to the journal file
Write the journal file header
Write your intended changes to the database file
Delete the rollback journal (THIS IS THE COMMIT)
When the user is done talking to mom and re-starts your app, when it tries to open the database file, if there is a rollback journal present, it will write the original data back to the datafile using a similarly safe process. Even if you lose your transaction, and lose a rollback, it will eventually be taken care of once mom's nervous breakdown is properly thwarted and he can run the app for more than a couple seconds at a time.
If it were me, I would trust the transactions. With so many users of SQLite, even in embedded apps, I think transaction commit failures would be a very hot topic all over the net if they weren't working properly.
Are you using CoreData with a SQLite backend? If so, I actually find that the best way to handle this problem is to create two separate NSManagedObjectContexts (a read-only and an editing). When the process completes, just save the "editing" context and then the two contexts will be in sync. If something happens during your operation, the editing context won't get saved, so you'll be fine.
i know this is an often asked question on these boards. And usually the question has been about how to manage the changes being made to the database before you even get around to deploy them.Mostly the answer has been to script the database and save it under sourcecontrol and then any additional updates are saved as scripts under version control too.(ex. Tool to upgrade SQL Express database after deployment)
my question is when is it best to apply the database updates , in the installer or when the new version first runs and connects to the database? note this is a WinApp that is deployed to customers each have their own databases.
One thing to add to the script: Back up the database (or at least the tables you're changing!) before applying the changes.
As a user I think I'd prefer it happens during the install, and going a little further that the installer can roll itself back in the event of a failure. My thinking here is that if I am installing an update, I'd like to know when the update is done that it actually is done and has succeeded. I don't want a message coming up the next time I run it informing me that something failed and I've potentially lost all my data. I would assume that a system admin would probably also appreciate install time feedback (of course, that doesn't matter if your web app isn't something that will be installed on a network). Also, as ראובן said, backing up the database would be a nice convenience.
You haven't said much about the architecture of the application, but since an installer is involved I assume it's a client/server application.
If you have a server installer, that's where you want to put it, since the database structure is only going to change once. Since the client installers are going to need to know about the change, it would be nice to have a way to detect the database version change, and for the old client to be able to download the client update from the server automatically and apply it.
If you only have a client installer, I still think it's better to put it there (maybe as a custom action that fires off the executable for updating the database). But it really isn't going to matter, because conceptually one installer or first-time user of the new version is going to have to fire off the changes to the database anyway. The database changes are going to put structural locks on the database so, in practical terms, everyone is going to have to be kicked off the system at that time for the database update to be applied.
Of course, this is all BS if it's not client-server.