CODEWITHSUNDEEP
androidsqlite
Julian A.
Julian A.

Reputation: 11470

Does Android SQLite cursor load all records into memory at once?

Does an Android SQLite cursor load all data for a query into memory, or is there some sort of optimization strategy that's part of its implementation?

Upvotes: 13

Views: 4032

Answers (3)

hqt
hqt

Reputation: 30304

Thanks for CommonsWare about Window term so I reversed again Android by navigating those classes SQLiteCursor -> AbstractWindowedCursor -> CursorWindow . Here is CursorWindow constructor:

 public CursorWindow(String name) {
        mStartPos = 0;
        mName = name != null && name.length() != 0 ? name : "<unnamed>";
        if (sCursorWindowSize < 0) {
            /** The cursor window size. resource xml file specifies the value in kB.
             * convert it to bytes here by multiplying with 1024.
             */
            sCursorWindowSize = Resources.getSystem().getInteger(
                com.android.internal.R.integer.config_cursorWindowSize) * 1024;
        }
        mWindowPtr = nativeCreate(mName, sCursorWindowSize);
        if (mWindowPtr == 0) {
            throw new CursorWindowAllocationException("Cursor window allocation of " +
                    (sCursorWindowSize / 1024) + " kb failed. " + printStats());
        }
        mCloseGuard.open("close");
        recordNewWindow(Binder.getCallingPid(), mWindowPtr);
    }

As you can see, sCursorWindowSize is the size that CommonsWare has mentioned:

sCursorWindowSize = Resources.getSystem().getInteger(
                com.android.internal.R.integer.config_cursorWindowSize) * 1024;

As my current version is Android SDK 23.0.1, the value of com.android.internal.R.integer.config_cursorWindowSize is 2048. It means 2MB. I don't have another version SDK for checking.

Upvotes: 13

MarkySmarky
MarkySmarky

Reputation: 1629

Cursor doesn't contain all the results in memory but it does have the total count of the returned query (via getCount). While you iterate over the results it fetches the entries (not one by one I guess but probably in chunks). I'm pretty sure there are optimizations on this level. Once you're done with it you must close it - otherwise why would the system keep it open after the query has been already made.

Upvotes: 4

CommonsWare
CommonsWare

Reputation: 1007658

A SQLiteCursor fills a "window" with data as you navigate through it. My recollection is that the window size is 1MB, but I can't point you to specific code that backs up that recollection. So, for small queries, the net effect is that the SQLiteCursor will hold the entire result set in memory, once you start accessing rows and columns.

Upvotes: 13

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