Overview The default method by which SQLite implements atomic commit and rollback is a rollback journal. Beginning with version 3. There are advantages and disadvantages to using WAL instead of a rollback journal.
WAL mode can only be changed when there are no transactions in progress. Remarks This method enables parallel execution of queries from multiple threads on the same database.
It does this by opening multiple connections to the database and using a different database connection for each query. The database journal mode is also changed to enable writes to proceed concurrently with reads.
When write-ahead logging is not enabled the defaultit 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.
In contrast, when write-ahead logging is enabled by calling this methodwrite 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.
When the write completes, readers on other threads will then perceive the new state of the database. 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.
After calling this method, execution of queries in parallel is enabled as long as the database remains open. To disable execution of queries in parallel, either call SQLiteDatabase. DisableWriteAheadLogging or close the database and reopen it.
The maximum number of connections used to execute queries in parallel is dependent upon the device memory and possibly other properties. If a query is part of a transaction, then it is executed on the same database handle the transaction was begun. Writers should use SQLiteDatabase.
Non-exclusive mode allows database file to be in readable by other threads executing queries. If the database has any attached databases, then execution of queries in parallel is NOT possible. Likewise, write-ahead logging is not supported for read-only databases or memory databases.
In such cases, SQLiteDatabase. The best way to enable write-ahead logging is to pass the SQLiteDatabase. This is more efficient than calling SQLiteDatabase.
EnableWriteAheadLogging after opening the database.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.
Jun 06, · plombier-nemours.comOpenHelper Called when the database connection is being configured, to enable features such as write-ahead logging or foreign key support. From class plombier-nemours.com Object: clone() Creates and returns a copy of this object. On Fri, Mar 14, at PM, Nick Parker wrote: Hello Rod, SQLCipher for Android does support the WAL journal mode, however as you noted below, the Java API is based on an older version of the.
Write-Ahead Logging The default method by which SQLite implements atomic commit and rollback is a rollback journal. Beginning with version (), a new "Write-Ahead Log" option (hereafter referred to as "WAL") is available. So I am doing some experiments with the Android SQLite implementation and I am totally stuck on using WAL (write-ahead-logging) with parallel transactions.
It's definitely enabled and should work - . You need to execute a Sqlite specific command (just like you'd execute other SQL queries): pragma journal_mode=wal For the specifics of using this pragma, please read plombier-nemours.com#pragma_journal_mode.
Here are some highlights: Your Sqlite library must be >=