Forensic analysis of SQLite databases is often concluded by simply opening a database file in one or another database viewer. One common drawback of using a free or commercially available database viewer for examining SQLite databases is the inherent inability of such viewers to access and display recently deleted erased as well as recently added but not yet committed records. Belkasoft Evidence Center is an all-in-one digital forensic tool to help investigators reliably carve the disk or disk image for SQLite databases, extract and analyze information from all available sources including freelists, rollback journals and write ahead logs. Belkasoft Evidence Center is perfectly equipped to handle existing, emptied, deleted or corrupted SQLite databases The powerful carving algorithms can identify and extract known types of data such as browser history or mobile app data among many others from existing, deleted and unreferenced database records.
This task can potentially take a few minutes. To prevent the rest of the application seeing incomplete data you will execute everything in one transaction and then commit it after the work is done.
Everything sounds good… Except, this is wrong and can lead to various hidden problems. By default — changes that are being done in a transaction on a single SQLite database connection can be visible to other transactions on that connection immediately — even before calling SQLiteDatabase.
This is a fatal issue. Let me quote https: But a transaction can have several writes to the database spanned over a longer time e. You would block other queries in the rest of the application.
Or you need to start using WAL mode mentioned in this article. This will prevent cases where several threads write on a same connection — potentially leading to inconsistent data. Simple thread synchronisation can solve this. Execute whole database statements whole transactions synchronised on one common object.
This version is present on Android 3. In WAL mode, changes are not written to the original database file. This has to be called right after opening a database connection. It is a good idea to enable write-ahead logging whenever a database will be concurrently accessed and modified by multiple threads at the same time.
However, write-ahead logging uses significantly more memory than ordinary journaling because there are multiple connections to the same database. So if a database will only be used by a single thread, or if optimizing concurrency is not very important, then write-ahead logging should be disabled.
Using WAL mode allows transaction separation without the need to manually open new connections. This is a good way to solve problems where you have several threads accessing the database and you want to ensure that the changes are not visible until committed.
In WAL — While a write is in progress, other readers can access the database and perceive the state of the database as it was before the write began. You can only have one! You are only able to execute read queries while the transaction is in progress.
Cannot perform this operation because the connection pool has been closed. The close method itself is synchronised, but this will not prevent a case where one thread closes the DB and a second thread has a reference to that database you just closed in the mean time. Difference between getReadableDatabase and getWritableDatabase I think not many people are aware that there usually is no difference between these two methods.
This will be the same object returned by getWritableDatabase unless some problem, such as a full disk, requires the database to be opened read-only. In that case, a read-only database object will be returned. The database connection is cached so repeated calls to getWritableDatabase or getReadableDatabase will return the same DB connection instance.
Unless you close the connection explicitly between the calls.In my database-heavy Android application, we enabled write-ahead logging on capable devices (honeycomb+) hoping to see reads occur in parallel and our .
In contrast, when write-ahead logging is enabled (by calling this method), write operations occur in a separate log file which allows reads to proceed concurrently.
While a write is in progress, readers on other threads will perceive the state of the database as it was before the write began.
Solving transaction isolation issues with WAL — Write Ahead Logging SQLite version (–07–21) introduced WAL mode. This version is present on Android and newer. In this article, we’ll examine the forensic implications of three features of the SQLite database engine: Free Lists, Write Ahead Log and Unallocated Space.
SQLite Recovery and Analysis Tool For the purpose of this article, we’ll be using Belkasoft Evidence Center to illustrate the low-level approach to handle SQLite databases.
I want to use the Write-Ahead Logging feature of SQLite in a j2se program. Please help me with a java implemention example. Stack Overflow. Log In Sign Up; current community. Stack Overflow help chat. Meta Stack Overflow Implementing WAL in Android.
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My sqlite database is running into locks even though I have WAL enabled and I'm using a singleton instance of my DbHelper across the entire app, which is as follows: public class DbHelper extends.