在Android上备份sqlite数据库以使数据保留在用户的Google云端硬盘中的最佳方法是什么？我想理想地进行增量备份，而不是一直备份整个数据。
当前，我使用的策略是每天将所有三个数据库文件{db_name}.db，{db_name}-wal.db和{db_name}-shm.db备份到用户的google驱动器，然后为用户还原所有这些文件当用户登录到新设备时。这是我用于备份的WorkManager代码的一部分：-
File databaseFile = new File(context.getDatabasePath("db1").getAbsolutePath());
File databaseWalFile = new File(context.getDatabasePath("db1-wal").getAbsolutePath());
File databaseShmFile = new File(context.getDatabasePath("db1-shm").getAbsolutePath());
if (!databaseFile.exists() || !databaseWalFile.exists() || !databaseShmFile.exists()) {
return Result.SUCCESS;
}
long totalBackupSize = databaseFile.length() + databaseWalFile.length() + databaseShmFile.length();
GoogleSignInAccount account = GoogleSignIn.getLastSignedInAccount(getApplicationContext());
DriveResourceClient driveResourceClient = Drive.getDriveResourceClient(getApplicationContext(), account);
final Task<DriveFolder> appFolderTask = driveResourceClient.getAppFolder();
final Task<DriveContents> createContentsDbTask = driveResourceClient.createContents();
final Task<DriveContents> createContentsDbWalTask = driveResourceClient.createContents();
final Task<DriveContents> createContentsDbShmTask = driveResourceClient.createContents();
Tasks.whenAll(appFolderTask, createContentsDbTask, createContentsDbWalTask, createContentsDbShmTask)
.continueWithTask(task -> {
DriveFolder parent = appFolderTask.getResult();
DriveContents dbContents = createContentsDbTask.getResult();
DriveContents dbWalContents = createContentsDbWalTask.getResult();
DriveContents dbShmContents = createContentsDbShmTask.getResult();
if (dbContents != null && dbWalContents != null && dbShmContents != null) {
Utility.copy(new FileInputStream(databaseFile), dbContents.getOutputStream());
Utility.copy(new FileInputStream(databaseWalFile), dbWalContents.getOutputStream());
Utility.copy(new FileInputStream(databaseShmFile), dbShmContents.getOutputStream());
MetadataChangeSet changeSet = new MetadataChangeSet.Builder()
.setTitle(AppConstants.GoogleDriveBackupDbFileName)
.setMimeType(AppConstants.DatabaseMimeType)
.build();
MetadataChangeSet changeWalSet = new MetadataChangeSet.Builder()
.setTitle(AppConstants.GoogleDriveBackupDbWalFileName)
.setMimeType(AppConstants.DatabaseMimeType)
.build();
MetadataChangeSet changeShmSet = new MetadataChangeSet.Builder()
.setTitle(AppConstants.GoogleDriveBackupDbShmFileName)
.setMimeType(AppConstants.DatabaseMimeType)
.build();
return Tasks.whenAll(driveResourceClient.createFile(parent, changeSet, dbContents),
driveResourceClient.createFile(parent, changeWalSet, dbWalContents),
driveResourceClient.createFile(parent, changeShmSet, dbShmContents));
}
TaskCompletionSource<DriveFile> tcs = new TaskCompletionSource<>();
tcs.setException(new Exception("Failed to copy database file"));
return Tasks.whenAll(tcs.getTask());
}).addOnSuccessListener(driveFile -> {
SharedPreferences.Editor editor = context.getSharedPreferences(PreferenceConstants.INSTANCE.getPreferenceName(), Context.MODE_PRIVATE).edit();
editor.putLong(PreferenceConstants.INSTANCE.getLastGoogleDriveBackupTime(), new Date().getTime());
editor.putLong(PreferenceConstants.INSTANCE.getFileSize(), totalBackupSize);
editor.apply();
Log.v("BackupWorker", "Backup successful");
result[0] = Result.SUCCESS;
countDownLatch.countDown();
}).addOnFailureListener(e -> {
Log.e("BackupWorker", "Unable to create file", e);
result[0] = Result.FAILURE;
countDownLatch.countDown();
});
使用上述策略备份和还原，但我担心的是：-
我考虑过将备份存储在CSV文件中，然后将其存储在Google云端硬盘中。然后，我可以将所有后续备份的更改都写入CSV文件。但是我觉得这会大大增加开发人员的工作量。有更好的解决方案吗？
答案 0 :(得分：1)
仅对主数据库文件进行备份不起作用 我。
如果在执行备份之前使用TRUNCATE选项正确地检查了数据库，则应该无需备份-wal和-shm文件（因为它们为空）。
此外，如果您关闭所有连接，则还应该完成检查点。例如，考虑以下内容（logDBSizeInfo输出文件大小，addsomeData和deleteSomeData照其说做）
mDBHlpr = new DBHelper(this);
logDBSizeInfo(this,DBHelper.DBNAME);
if (DatabaseUtils.queryNumEntries(mDBHlpr.getWritableDatabase(),"table1") < 1) {
addSomeData(100000);
deleteSomeData(1000);
} else {
addSomeData(1000);
deleteSomeData(100);
}
logDBSizeInfo(this,DBHelper.DBNAME);
mDBHlpr.close();
//checkpointIfWALEnabled(this,DBHelper.DBNAME);
logDBSizeInfo(this,DBHelper.DBNAME);
结果：-
05-24 20:25:47.195 D/DBSIZEINFO: Database Size is 34312192 05-24 20:25:47.195 D/DBSIZEINFO: Database -wal file Size is 0 path is /data/user/0/aso.so56286308backupwal/databases/mydb-wal 05-24 20:25:47.196 D/DBSIZEINFO: Database -shm file Size is 32768 path is /data/user/0/aso.so56286308backupwal/databases/mydb-shm 05-24 20:25:47.199 D/ADDSOMEDATA: Adding about 1000 rows 05-24 20:25:47.365 D/ADDSOMEDATA: Deleting about 100 rows 05-24 20:25:47.397 D/DBSIZEINFO: Database Size is 34656256 05-24 20:25:47.397 D/DBSIZEINFO: Database -wal file Size is 420272 path is /data/user/0/aso.so56286308backupwal/databases/mydb-wal 05-24 20:25:47.397 D/DBSIZEINFO: Database -shm file Size is 32768 path is /data/user/0/aso.so56286308backupwal/databases/mydb-shm <<<<<<<<<<After Close>>>>>>>>>> 05-24 20:25:47.400 D/DBSIZEINFO: Database Size is 34656256 05-24 20:25:47.400 D/DBSIZEINFO: Database -wal file does not exist 05-24 20:25:47.400 D/DBSIZEINFO: Database file -shm does not exist
我使用以下方法来确保在备份之前对文件进行检查（仅是数据库文件）：-
private void checkpointIfWALEnabled(Context context, String databaseName) {
Cursor csr;
int wal_busy = -99, wal_log = -99, wal_checkpointed = -99;
SQLiteDatabase db = SQLiteDatabase.openDatabase(context.getDatabasePath(databaseName).getPath(),null,SQLiteDatabase.OPEN_READWRITE);
csr = db.rawQuery("PRAGMA journal_mode",null);
if (csr.moveToFirst()) {
String mode = csr.getString(0);
if (mode.toLowerCase().equals("wal")) {
csr = db.rawQuery("PRAGMA wal_checkpoint",null);
if (csr.moveToFirst()) {
wal_busy = csr.getInt(0);
wal_log = csr.getInt(1);
wal_checkpointed = csr.getInt(2);
}
csr = db.rawQuery("PRAGMA wal_checkpoint(TRUNCATE)",null);
csr.getCount();
csr = db.rawQuery("PRAGMA wal_checkpoint",null);
if (csr.moveToFirst()) {
wal_busy = csr.getInt(0);
wal_log = csr.getInt(1);
wal_checkpointed = csr.getInt(2);
}
}
}
csr.close();
db.close();
}
另一个可以减小备份大小的选项是使用VACUUM INTO。我没有尝试过这种方法。但是，由于使用了日志记录，因此以后进行检查点也是明智的选择（然后您不仅可以将文件用作备份，还可以替换原始文件）。
增量备份数据库可能被证明是不切实际且耗时的，除非您基本上已经建立了已记录的事务，因此可能不会问这个问题。通常，增量备份系统由相对容易检测到的更改驱动。