Logo Questions Linux Laravel Mysql Ubuntu Git Menu
 

How can I avoid concurrency problems when using SQLite on Android?

What would be considered the best practices when executing queries on an SQLite database within an Android app?

Is it safe to run inserts, deletes and select queries from an AsyncTask's doInBackground? Or should I use the UI Thread? I suppose that database queries can be "heavy" and should not use the UI thread as it can lock up the app - resulting in an Application Not Responding (ANR).

If I have several AsyncTasks, should they share a connection or should they open a connection each?

Are there any best practices for these scenarios?

like image 259
Vidar Vestnes Avatar asked Mar 22 '10 15:03

Vidar Vestnes


People also ask

Can SQLite handle concurrency?

SQLite does support multiple concurrent connections, and therefore it can be used with a multi-threaded or multi-process application. The catch is that when SQLite opens a write transaction, it will lock all the tables.

Is SQLite good for Android?

SQLite Database is an open-source database provided in Android which is used to store data inside the user's device in the form of a Text file. We can perform so many operations on this data such as adding new data, updating, reading, and deleting this data.

What are the several important methods that can be used in SQLite database for Android?

Methods of SQLiteDatabase classexecutes the sql query not select query. inserts a record on the database. The table specifies the table name, nullColumnHack doesn't allow completely null values. If second argument is null, android will store null values if values are empty.

What is the alternative of SQLite in Android?

But if you want to replace SQLite completely, there are also quite a few alternative databases: Couchbase Lite, Interbase, LevelDB, Oracle Berkeley DB (formerly Oracle's mobile database was "Oracle Database Lite"), Realm, SnappyDB, Sparksee Mobile (graph database, brand-new at the time of this article), SQL Anywhere, ...


1 Answers

Inserts, updates, deletes and reads are generally OK from multiple threads, but Brad's answer is not correct. You have to be careful with how you create your connections and use them. There are situations where your update calls will fail, even if your database doesn't get corrupted.

The basic answer.

The SqliteOpenHelper object holds on to one database connection. It appears to offer you a read and write connection, but it really doesn't. Call the read-only, and you'll get the write database connection regardless.

So, one helper instance, one db connection. Even if you use it from multiple threads, one connection at a time. The SqliteDatabase object uses java locks to keep access serialized. So, if 100 threads have one db instance, calls to the actual on-disk database are serialized.

So, one helper, one db connection, which is serialized in java code. One thread, 1000 threads, if you use one helper instance shared between them, all of your db access code is serial. And life is good (ish).

If you try to write to the database from actual distinct connections at the same time, one will fail. It will not wait till the first is done and then write. It will simply not write your change. Worse, if you don’t call the right version of insert/update on the SQLiteDatabase, you won’t get an exception. You’ll just get a message in your LogCat, and that will be it.

So, multiple threads? Use one helper. Period. If you KNOW only one thread will be writing, you MAY be able to use multiple connections, and your reads will be faster, but buyer beware. I haven't tested that much.

Here's a blog post with far more detail and an example app.

  • Android Sqlite Locking (Updated link 6/18/2012)
  • Android-Database-Locking-Collisions-Example by touchlab on GitHub

Gray and I are actually wrapping up an ORM tool, based off of his Ormlite, that works natively with Android database implementations, and follows the safe creation/calling structure I describe in the blog post. That should be out very soon. Take a look.


In the meantime, there is a follow up blog post:

  • Single SQLite connection

Also checkout the fork by 2point0 of the previously mentioned locking example:

  • Android-Database-Locking-Collisions-Example by 2point0 on GitHub
like image 82
Kevin Galligan Avatar answered Sep 30 '22 13:09

Kevin Galligan