Disabling sqlite Write-Ahead logging in Android Pie

问题

In Android Pie sqlite Write-Ahead logging (WAL) has been enabled by default. This is causing errors for my existing code only in Pie devices. I have been unable to turn off WAL successfully using SQLiteDatabase.disableWriteAheadLogging() or PRAGMA journal_mode due to the way I access the database. I would like to disable WAL completely with an Android setting called db_compatibility_wal_supported :

Compatibility WAL (Write-Ahead Logging) for Apps

Does anyone know how to configure this? I don't know if this file can be altered programmatically at startup or if it is changed manually.

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Further Details about the problem

I have a sqlite database (20mb+ / 250k records) in my app. This db is generated using plain java on my server. It contains a food database and the user of the app can add to the database (and the server is updated). This is stored in the assets folder in android. During first installation the database is copied from assets to the app folder so that it can be written to, using effectively this method :

Copy SQLite database from assets folder

Unfortunately, once I start writing to the database using SqlDroid wal is enabled and the tables which were in the original db have vanished and only any newly created tables remain. The size of the database however is still 20mb+. All the database errors are due to the missing tables. The table copying and writing method works perfectly in versions of Android prior to Pie.

回答1:

The best and simplest way to disable WAL mode in your Database is as follows:

public class MyDbHelper extends SQLiteOpenHelper {

    //...

    @Override
    public void onOpen(SQLiteDatabase db) {
        db.disableWriteAheadLogging();  // Here the solution
        super.onOpen(db);
    }

    //...
}

This way, all access to your database will be with WAL mode disabled. As much as you open and close multiple connections throughout the implementation of your App

回答2:

@Rockvole please share error that you are facing, that help us to find appropriate solution.

Mean while, i understand that you want to close that WAL in android pie and you are using "SQLDroid" lib to create Sqlite DB.

This lib internally using "SQLiteDatabase" to store data locally, I think you need to call "SQLiteDatabase.disableWriteAheadLogging()" in "SQLiteDatabase" class where DB instance created the package name is "package org.sqldroid;"

or Get internal SQLiteDatabase instance and call disableWriteAheadLogging().

Second solution is create "config.xml" inside values folder and wirte "<bool name="db_compatibility_wal_supported">false</bool>" and run and check its work.

回答3:

I finally found the answer. It seems that the database errors I was receiving is not directly related to WAL. It is because the widely used code to copy a database from assets has a bug in it where the database is left open during the copy operation. This only started causing a problem in Android P. The solution is to close the database after you get the database file name.

SQLiteDatabase destinationDatabase = sqLiteOpenHelper.getWritableDatabase();
String dbFileName=destinationDatabase.getPath();
destinationDatabase.close();
// Now write the destinationDatabase using the dbFileName

This is detailed more here : Android P - 'SQLite: No Such Table Error' after copying database from assets

回答4:

one cannot use SQLDroidDriver.ADDITONAL_DATABASE_FLAGS, simply because there is no constant available, which would negate flag ENABLE_WRITE_AHEAD_LOGGING.

WAL can still be disabled by creating either of these scenarios:

a) set flag OPEN_READONLY (applies to situations where R/O access does suffice).

b) run PRAGMA journal_mode=DELETE as the first query, in order to override PRAGMA journal_mode=WAL.

c) file an issue against SQLDroidConnection.java, in order to have .enableWriteAheadLogging() and .disableWriteAheadLogging() supported on the driver-level.

回答5:

If you are using Room, you won't have direct access to the database but you can instead set the journal mode when you are building/opening the database:

db = Room.databaseBuilder(context, Database.class, "Database")
         .setJournalMode(JournalMode.TRUNCATE)
         .build();

来源：https://stackoverflow.com/questions/53659206/disabling-sqlite-write-ahead-logging-in-android-pie