Android: Why is Room so slow? - sqlite

Question

I am working on a simple database procedure in Kotlin using Room, and I can't explain why the process is so slow, mostly on the Android Studio emulator.
The table I am working on is this:
#Entity(tableName = "folders_items_table", indices = arrayOf(Index(value = ["folder_name"]), Index(value = ["item_id"])))
data class FoldersItems(
#PrimaryKey(autoGenerate = true)
var uid: Long = 0L,
#ColumnInfo(name = "folder_name")
var folder_name: String = "",
#ColumnInfo(name = "item_id")
var item_id: String = ""
)
And what I am just trying to do is this: checking if a combination folder/item is already present, insert a new record. If not, ignore it. on the emulator, it takes up to 7-8 seconds to insert 100 records. On a real device, it is much faster, but still, it takes around 3-4 seconds which is not acceptable for just 100 records. It looks like the "insert" query is particularly slow.
Here is the procedure that makes what I have just described (inside a coroutine):
val vsmFoldersItems = FoldersItems()
items.forEach{
val itmCk = database.checkFolderItem(item.folder_name, it)
if (itmCk == 0L) {
val newFolderItemHere = vsmFoldersItems.copy(
folder_name = item.folder_name,
item_id = it
)
database.insertFolderItems(newFolderItemHere)
}
}
the variable "items" is an array of Strings.
Here is the DAO definitions of the above-called functions:
#Query("SELECT uid FROM folders_items_table WHERE folder_name = :folder AND item_id = :item")
fun checkFolderItem(folder: String, item: String): Long
#Insert
suspend fun insertFolderItems(item: FoldersItems)

Answer 1

Placing the loop inside a single transaction should significantly reduce the time taken.
The reason is that each transaction (by default each SQL statement that makes a change to the database) will result in a disk write. So that's 100 disk writes for your loop.
If you begin a transaction before the loop and then set the transaction successful when the loop is completed and then end the transaction a single disk write is required.
What I am unsure of is exactly how to do this when using a suspended function (not that familiar with Kotlin).
As such I'd suggest either dropping the suspend or having another Dao for use within loops.
Then have something like :-
val vsmFoldersItems = FoldersItems()
your_RoomDatabase.beginTransaction()
items.forEach{
val itmCk = database.checkFolderItem(item.folder_name, it)
if (itmCk == 0L) {
val newFolderItemHere = vsmFoldersItems.copy(
folder_name = item.folder_name,
item_id = it
)
database.insertFolderItems(newFolderItemHere)
}
}
your_RoomDatabase.setTransactionSuccessful() //<<<<<<< IF NOT set then ALL updates will be rolled back
your_RoomDatabase.endTransaction()
You may wish to refer to:-
https://developer.android.com/reference/androidx/room/RoomDatabase
You may wish to especially refer to runInTransaction