A checkpoint can only complete when no other transactions are running, which means the WAL file cannot be reset in the middle of a write transaction.
There are advantages and disadvantages to using WAL instead of a rollback journal. The wal-index helps find content in the WAL file much faster, but performance still falls off with increasing WAL file size.
Likewise, write-ahead logging is not supported for read-only databases or memory databases.
Writers merely append new content to the end of the WAL file. Checkpoint also requires more seeking. The opening process must have write privileges for "-shm" wal-index shared memory file associated with the database, if that file exists, or else write access on the directory containing the database file if the "-shm" file does not exist.
When the write completes, readers on other threads will then perceive the new state of the database. Or they can turn off the automatic checkpoints and run checkpoints during idle moments or in a separate thread or process. This helps to prevent "latch-up" in applications running on a busy disk drive.
Before modifying the database, the writer implicitly acquires an exclusive lock on the database which prevents readers from accessing the database until the write is completed.
Thus, if an older version of SQLite attempts to connect to an SQLite database that is operating in WAL mode, it will report an error along the lines of "file is encrypted or is not a database".
However, compile-time and run-time options exist that can disable or defer this automatic checkpoint. Applications using WAL do not have to do anything in order to for these checkpoints to occur. This mechanism prevents a WAL file from growing without bound.
The decision of how often to run checkpoints may therefore vary from one application to another depending on the relative read and write performance requirements of the application. If a database file is separated from its WAL file, then transactions that were previously committed to the database might be lost, or the database file might become corrupted.
How WAL Works The traditional rollback journal works by writing a copy of the original unchanged database content into a separate rollback journal file and then writing changes directly into the database file.
As for the log about frame recovery, that's caused by the fact that SQLite checkpoints and deletes the WAL files when all the connections are closed. There are advantages and disadvantages to using WAL instead of a rollback journal.
Because writers do nothing that would interfere with the actions of readers, writers and readers can run at the same time. Thus a COMMIT can happen without ever writing to the original database, which allows readers to continue operating from the original unaltered database while changes are simultaneously being committed into the WAL.
WAL mode can only be changed when there are no transactions in progress. This means that the underlying VFS must support the "version 2" shared-memory. To prevent older versions of SQLite prior to version 3.
When write-ahead logging is not enabled (the default), it is not possible for reads and writes to occur on the database at the same time. Before modifying the database, the writer implicitly acquires an exclusive lock on the database which prevents readers from accessing the database until the write is completed.
Alphabetical List Of SQLite Documents; An Asynchronous I/O Module For SQLite; An Introduction To The SQLite C/C++ Interface; Android Bindings; Appropriate Uses For SQLite; Architecture of SQLite; Atomic Commit In SQLite; Automatic Undo/Redo With SQLite; Write-Ahead Logging.
Android Studio Google Play Android Jetpack Docs News An interface to map the behavior of thesanfranista.comOpenHelper. Write-ahead logging cannot be used with read-only databases so the value of this flag is ignored if the database is opened read-only.
Jun 06, · Android Studio Google Play Android Jetpack Docs News thesanfranista.comOpenHelper Called when the database connection is being configured, to enable features such as write-ahead logging or foreign key support. Nov 16, · Learn about these advanced features of SQLite: WAL - Write-Ahead Logging, In-Memory DB, Triggers, Pragma statement, Foreign Keys, Full Text.
Oct 09, · Likewise, write-ahead logging is not supported for read-only databases or memory databases.
In such cases, enableWriteAheadLogging() returns false. The best way to enable write-ahead logging is to pass the ENABLE_WRITE_AHEAD_LOGGING flag to openDatabase(File, thesanfranista.comrams).Write ahead logging sqlite android studio