SQLite Android Database Cursor window allocation o

问题:

I have a routine that runs different queries against an SQLite database many times per second. After a while I would get the error

"android.database.CursorWindowAllocationException: - Cursor window allocation of 2048 kb failed. # Open Cursors = " appear in LogCat.

I had the app log memory usage, and indeed when usage reaches a certain limit the I get this error, implying it runs out. My intuition tells me that the database engine is creating a NEW buffer (CursorWindow) every time I run a query, and even though I mark the .close() the cursors, neither the garbage collector nor SQLiteDatabase.releaseMemory() are quick enough at freeing memory. I think the solution may lie in "forcing" the database to always write into the same buffer, and not create new ones, but I have been unable to find a way to do this. I have tried instantiating my own CursorWindow, and tried setting it to and SQLiteCursor to no avail.

¿Any ideas?

EDIT: re example code request from @GrahamBorland:

public static CursorWindow cursorWindow = new CursorWindow("cursorWindow"); 
public static SQLiteCursor sqlCursor;
public static void getItemsVisibleArea(GeoPoint mapCenter, int latSpan, int lonSpan) {
query = "SELECT * FROM Items"; //would be more complex in real code
sqlCursor = (SQLiteCursor)db.rawQuery(query, null);
sqlCursor.setWindow(cursorWindow);
}

Ideally I would like to be able to .setWindow() before giving a new query, and have the data put into the same CursorWindow everytime I get new data.

回答1:

Most often the cause for this error are non closed cursors. Make sure you close all cursors after using them (even in the case of an error).

Cursor cursor = null;
try {
    cursor = db.query(...
    // do some work with the cursor here.
} finally {
    // this gets called even if there is an exception somewhere above
    if(cursor != null)
        cursor.close();
}

回答2:

If you're having to dig through a significant amount of SQL code you may be able to speed up your debugging by putting the following code snippet in your MainActivity to enable StrictMode. If leaked database objects are detected then your app will now crash with log info highlighting exactly where your leak is. This helped me locate a rogue cursor in a matter of minutes.

@Override
protected void onCreate(Bundle savedInstanceState) {
   if (BuildConfig.DEBUG) {     
         StrictMode.setVmPolicy(new StrictMode.VmPolicy.Builder()
         .detectLeakedSqlLiteObjects()
         .detectLeakedClosableObjects()
         .penaltyLog()
         .penaltyDeath()
         .build());
    }
    super.onCreate(savedInstanceState);
    ...
    ...

回答3:

I have just experienced this issue - and the the suggested answer of not closing the cursor while valid, was not how I fixed it. My issue was closing the database when SQLite was trying to repopulate it's cursor. I would open the database, query the database to get a cursor to a data set, close the database and iterate over the cursor. I noticed whenever I hit a certain record in that cursor, my app would crash with this same error in OP.

I assume that for the cursor to access certain records, it needs to re-query the database and if it is closed, it will throw this error. I fixed it by not closing the database until I had completed all the work I needed.

回答4:

There is indeed a maximum size Android SQLite cursor windows can take and that is 2MB, anything more than this size would result into the above error. Mostly, this error is either caused by a large image byte array stored as blob in sql database or too long strings. Here is how i fixed it.

Create a java class eg. FixCursorWindow and put below code in it.

    public static void fix() {
        try {
            Field field = CursorWindow.class.getDeclaredField("sCursorWindowSize");
            field.setAccessible(true);
            field.set(null, 102400 * 1024); //the 102400 is the new size added
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

Now go to your application class (create one if you don't have already) and make a call to the FixCursorWindow like this

public class App extends Application {

public void onCreate()
{
    super.onCreate();
    CursorWindowFixer.fix();

}

}

Finally, ensure you include your application class in your manifest on the application tag like this

    android:name=".App">

That's all, it should work perfectly now.

回答5:

This is a Normal Exception while we are using External SQLite especially. You can resolve it by closing the Cursor Object just like as follow:

if(myCursor != null)
        myCursor.close();

What it means is, IF the cursor has memory and it's opened then close it so the Application will be faster, all the Methods will take less space, and the functionalities related to the Database will also be improved.

回答6:

public class CursorWindowFixer {

  public static void fix() {
    try {
      Field field = CursorWindow.class.getDeclaredField("sCursorWindowSize");
      field.setAccessible(true);
      field.set(null, 102400 * 1024);
    } catch (Exception e) {
      e.printStackTrace();
    }
  }
}