I am developing an application for IPhone and using sqlite to connect to db. I am trying to use the singleton pattern for connecting to the db and retrieving the data.
I would like to know which is the best way to maintain the connection, should I keep the connection open till the application is closed or should I open and close the connection for every call that I make ?
SQLite must re-parse the database schema each time a new connection is made. This can be time consuming. Leaving the connection open also provides opportunities for SQLite to cache data. Since you get ACID transactions even without closing the connection, there is little reason to close it. So, keep the SQLite connection open until the application is closed.
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We recently migrated our EF from 2.0 to 7.0.1. After EF migration, we are facing a challange that sqlite db file not released after calling the DatabaseFacade.Migrate method (we are using the code first apporach). File is open at the EF side due to that unable to access like copy/delete the sqlite db file. Could someone help us on this issue ?
SQlite db has to be release after calling DatabaseFacade.Migrate
The SQLite provider pools connections, improving connection speed significantly but keeping connections open. You can disable pooling by adding Pooling=false to the connection string or calling SqliteConnection.ClearAllPools() at the point where you want them to be closed.
Im setting up an app, a sort of local guide; my idea is to have the app to work even offline, by storing most of its content locally in a SQLite database.
Since i already have the content in a database, i'd like to retrive that database from my server and store it; i already know how to get data from an API and save it in the local database, but i think getting the db file from remote and cloning in the app its lesse labour intensive.
At the moment running the app the first time i can create the empty database, and save the date of the action, i can also GET from http the database, but i dont know where to save it to have my local database use this data (to be honest i don't even know if it is possible), also i would like to periodically check on remote to see if the data was updated and get a fresh db to override the one present.
Anyone know if and where to save the db content from remote?
Thank you
I am working on a project for a while and I am close to finish.
However now some technical questions are coming.
So I am dealing with mongoDB and SpringData layer.
However this is not the DB which matter but more the question behind.
I am building a rest api with jaxrs.
I decided to put all my end point in scope prototype and my services inside scope request (because some services can be used more than one time in the same request).
However comes the question of the database.
- There are some people telling me that a singleton is the best approach to have only one connection but in the other end if the traffic grows all the request will be stuck at database entry
There is as well the solution of the closing connection. I implemented a filter which performs some processes (like renewing token if needed etc) I could plug the close connection here. But some person say that it is really costly to open a connection and close it.
I found some answers but it is more related to the client part (phone for example) and the constraint are not the same.
from the mongodb java driver documentation http://mongodb.github.io/mongo-java-driver/3.4/driver/tutorials/connect-to-mongodb/
The MongoClient() instance represents a pool of connections to the database; you will only need one instance of class MongoClient even with multiple threads.
I might be wrong but I dont think Mongo takes advantage of multiple connections (they run sequentially anyway), making them pointless
I'm developing a project here and everytime I need to send a query to MYSQL I'm opening a new connection.
Is this right or should I only connect once? How should I proceed?
Thank you
Probably you should not open a new connection for every query.
There are exceptions to every general rule, of course, but typically you should connect once, sometime before the first query, and then re-use the same mysqli connection object for multiple queries during the given PHP request.
There is no limit to the number of queries you can run in serial using a given connection. The only limitation is that you can run only one query at a time.
Think of it this way: if you were writing a PHP script to simply read a file, and you knew you were going to read multiple lines from the file, you would keep the file handle open and make multiple read requests from it before you close the file. You would not re-open the file every time you wanted to read from it during a single PHP request.
The overhead of opening new connections to the database is reasonably low (at least for MySQL), but if you have an opportunity to easily reduce that overhead, it's likely worth it to do so.
Re your comment:
You're right, there's no way to keep your $mysqli object across pages. That's what is meant by the term request. Objects and resources are cleaned up at the end of a request.
When you said you were creating a new database connection for every query, I assume you meant that if you execute more than one SQL query during a single request (that is, page view), that you would create a new $mysqli object for each query. That would be unnecessary.
There's one other way you can reuse the database connections from one page view to the next. That is to use persistent connections. This doesn't preserve the $mysqli object -- you still have to run new mysqli on each page load. But internally it is reusing the database connection from a previous PHP request.
All you have to do to open a persistent connection in this way is to add the prefix p: to your hostname.
Servers and databases have a finite number of connections available. If every one of your users keeps an open connection for no reason (like when they are reading a blog post for a page that already loaded) then it will cap the number of people who can connect to your project in production. Unless there is a very specific need to keep a connection open, I recommend not doing so.
Again though, it really depends on the scope of your project. If you are just talking about a single page of a website, typically it's fine to leave the connection open until you are done loading the page.
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.