使用Android时，blob的最大大小是什么?这是在哪里记录的？开发者社区

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E/CursorWindow: The size of (0, 2) is too big (4194304), so replace the value to NULL

    java.lang.NullPointerException: Parameter specified as non-null is null: method kotlin.jvm.internal.Intrinsics.checkNotNullParameter, parameter bytes

    fun checkCursorWindowSize() {
        val context = this
        val TEST_TABLE_NAME = "tcw"
        val TEST_DATABASE_NAME = "tcw"
        val TEST_COLUMN_NAME = "testblob"
        val reducer = 1024 * 1024 / 16 /* size to reduce BLOB by per iteration */
        val allowance =
            1 /* size to reduce BLOB by for all extractions (reason for use probably best to not be on a power of 2 boundary????) */
        val ba = ByteArray(1024 * 1024 * 4) /* initial size of BLOB  when storing*/
        var csr: Cursor
        val tcwDbPath: String = context.getDatabasePath(TEST_DATABASE_NAME).getPath()
        val dbFile: File = context.getDatabasePath(TEST_DATABASE_NAME)
        val dbDirectory: File = dbFile.getParentFile()
        /* If the database exists then delete it = should never exist */if (dbFile.exists()) {
            dbFile.delete()
        /* Ensure that the databases directory exists - otherwise openOrCreate fails */if (!dbDirectory.exists()) {
            Log.d(
                "DEBUGINFO",
                "Database directory " + dbDirectory.getPath()
                    .toString() + " does not exist - Creating"
            dbDirectory.mkdirs()
        /* Finally create the database */
        val db = SQLiteDatabase.openOrCreateDatabase(tcwDbPath, null, null)
        /* Do everything inside a transaction to reduce writes */db.beginTransaction()
        /* Create the table into which the BLOB will be loaded */db.execSQL("CREATE TABLE IF NOT EXISTS $TEST_TABLE_NAME ($TEST_COLUMN_NAME BLOB)")
        /* Insert the over-sized BLOB */
        val cv = ContentValues()
        cv.put(TEST_COLUMN_NAME, ba)
        db.insert(TEST_TABLE_NAME, null, cv)
        /* Prepare to repeatedly extract an eve decreasing part of the blob */
        var retrieveSize = ba.size /* first try to retrieve entire BLOB */
        var caught = 0 /* the number of caught exceptions */
        /* Try 1024 attempts at getting smaller BLOB */
        for (i in 0..1024) {
            Log.d("DEBUG", "Iteration is " + (i + 1) + ". Retrieve Size is " + retrieveSize)
            try {
                /* Build the query to extract part of the blob (using the SQLite substr function) according to
                    the current retrieve size less the allowance
                    only getting 1 row (should only be 1 row)
                    NOTE!! retrieving an oversize BLOB does not fail here, rather the failure is when attempting to read the data (getBlob method)
                csr = db.query(
                    TEST_TABLE_NAME,
                    arrayOf("substr(" + TEST_COLUMN_NAME + ",1," + (retrieveSize - allowance) + ") AS " + TEST_COLUMN_NAME),
                    null,
                    null,
                    null,
                    null,
                    null,
                var test: ByteArray?=null
                while (csr.moveToNext()) {
                    test = csr.getBlob(0) /* get the Blob from the  1st (only) column */
                    Log.d("DEBUG", "Received value: ${test?.size}")
                if (test != null) {
                    break
            } catch (e: SQLException) {
                caught++
                //e.printStackTrace();
            } finally {
                retrieveSize =
                    retrieveSize - reducer /* reduce the retrieveSize ready for the next iteration (if one )*/
                if (retrieveSize < 0) break
        Log.d("DEBUGINFO", "Caught $caught SQlite Exceptions")
        /* Done with the database so clean up */db.endTransaction()
        db.close()
        File(tcwDbPath).delete()
        /* adjust the retrieve size as it has been adjusted in preparation for the next iteration */
        Log.d("DEBUGINFO","MaxCursorSize = " + (retrieveSize + reducer).toLong())
    }

long checkCursorWindowSize(Context context) {
        final String TEST_TABLE_NAME = "tcw";
        final String TEST_DATABASE_NAME = "tcw";
        final String TEST_COLUMN_NAME = "testblob";
        final int reducer = 1024 * 1024 / 16; /* size to reduce BLOB by per iteration */
        final int allowance = 1; /* size to reduce BLOB by for all extractions (reason for use probably best to not be on a power of 2 boundary????) */
        byte[] ba = new byte[1024 * 1024 * 4]; /* initial size of BLOB  when storing*/
        Cursor csr;
        String tcwDbPath = context.getDatabasePath(TEST_DATABASE_NAME).getPath();
        File dbFile = context.getDatabasePath(TEST_DATABASE_NAME);
        File dbDirectory = dbFile.getParentFile();
        /* If the database exists then delete it = should never exist */
        if (dbFile.exists()) {
            dbFile.delete();
        /* Ensure that the databases directory exists - otherwise openOrCreate fails */
        if (!dbDirectory.exists()) {
            Log.d("DEBUGINFO", "Database directory " + dbDirectory.getPath() + " does not exist - Creating");
            dbDirectory.mkdirs();
        /* Finally create the database */
        SQLiteDatabase db = SQLiteDatabase.openOrCreateDatabase(tcwDbPath,null,null);
        /* Do everything inside a transaction to reduce writes */
        db.beginTransaction();
        /* Create the table into which the BLOB will be loaded */
        db.execSQL("CREATE TABLE IF NOT EXISTS " + TEST_TABLE_NAME + " (" + TEST_COLUMN_NAME + " BLOB)");
        /* Insert the over-sized BLOB */
        ContentValues cv = new ContentValues();
        cv.put(TEST_COLUMN_NAME,ba);
        db.insert(TEST_TABLE_NAME,null,cv);
         /* Prepare to repeatedly extract an eve decreasing part of the blob */
        int retrieveSize = ba.length; /* first try to retrieve entire BLOB */
        int caught = 0; /* the number of caught exceptions */
        /* Try 1024 attempts at getting smaller BLOB */
        for (int i=0; i <= 1024; i++  ) {
            Log.d("DEBUG","Iteration is " + (i + 1) + ". Retrieve Size is " + retrieveSize);
            try {
                /* Build the query to extract part of the blob (using the SQLite substr function) according to
                    the current retrieve size less the allowance
                    only getting 1 row (should only be 1 row)
                    NOTE!! retrieving an oversize BLOB does not fail here, rather the failure is when attempting to read the data (getBlob method)
                csr = db.query(TEST_TABLE_NAME, new String[]{"substr(" + TEST_COLUMN_NAME + ",1," + (retrieveSize - allowance) + ") AS " + TEST_COLUMN_NAME},null,null,null,null,null,"1");
                while (csr.moveToNext()) {
                    byte[] test = csr.getBlob(0); /* get the Blob from the  1st (only) column */
                break; /* if no Exception  then all done */
            } catch (SQLException e) {
                retrieveSize = retrieveSize - reducer; /* reduce the retrieveSize ready for the next iteration (if one )*/
                caught++;
                //e.printStackTrace();
        Log.d("DEBUGINFO","Caught " + caught + " SQlite Exceptions");
        /* Done with the database so clean up */
        db.endTransaction();
        db.close();
        new File(tcwDbPath).delete();
        /* adjust the retrieve size as it has been adjusted in preparation for the next iteration */
            return retrieveSize + reducer;
    }

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Log.d("DEBUGINFO","MaxCursorSize = " + checkCursorWindowSize(this));
}

2022-08-29 10:58:06.798 D/DEBUG: Iteration is 16. Retrieve Size is 3211264
2022-08-29 10:58:06.802 W/CursorWindow: Window is full: requested allocation 3211263 bytes, free space 2096720 bytes, window size 2097152 bytes
2022-08-29 10:58:06.802 E/SQLiteQuery: exception: Row too big to fit into CursorWindow requiredPos=0, totalRows=1; query: SELECT substr(testblob,1,3211263) AS testblob FROM tcw LIMIT 1
2022-08-29 10:58:06.802 D/DEBUG: Iteration is 17. Retrieve Size is 3145728
2022-08-29 10:58:06.806 W/CursorWindow: Window is full: requested allocation 3145727 bytes, free space 2096720 bytes, window size 2097152 bytes
2022-08-29 10:58:06.807 E/SQLiteQuery: exception: Row too big to fit into CursorWindow requiredPos=0, totalRows=1; query: SELECT substr(testblob,1,3145727) AS testblob FROM tcw LIMIT 1
2022-08-29 10:58:06.807 D/DEBUG: Iteration is 18. Retrieve Size is 3080192
2022-08-29 10:58:06.810 W/CursorWindow: Window is full: requested allocation 3080191 bytes, free space 2096720 bytes, window size 2097152 bytes
2022-08-29 10:58:06.810 E/SQLiteQuery: exception: Row too big to fit into CursorWindow requiredPos=0, totalRows=1; query: SELECT substr(testblob,1,3080191) AS testblob FROM tcw LIMIT 1
2022-08-29 10:58:06.810 D/DEBUG: Iteration is 19. Retrieve Size is 3014656
2022-08-29 10:58:06.813 W/CursorWindow: Window is full: requested allocation 3014655 bytes, free space 2096720 bytes, window size 2097152 bytes
2022-08-29 10:58:06.813 E/SQLiteQuery: exception: Row too big to fit into CursorWindow requiredPos=0, totalRows=1; query: SELECT substr(testblob,1,3014655) AS testblob FROM tcw LIMIT 1
2022-08-29 10:58:06.813 D/DEBUG: Iteration is 20. Retrieve Size is 2949120
2022-08-29 10:58:06.818 W/CursorWindow: Window is full: requested allocation 2949119 bytes, free space 2096720 bytes, window size 2097152 bytes
2022-08-29 10:58:06.819 E/SQLiteQuery: exception: Row too big to fit into CursorWindow requiredPos=0, totalRows=1; query: SELECT substr(testblob,1,2949119) AS testblob FROM tcw LIMIT 1
2022-08-29 10:58:06.819 D/DEBUG: Iteration is 21. Retrieve Size is 2883584
2022-08-29 10:58:06.824 W/CursorWindow: Window is full: requested allocation 2883583 bytes, free space 2096720 bytes, window size 2097152 bytes
2022-08-29 10:58:06.824 E/SQLiteQuery: exception: Row too big to fit into CursorWindow requiredPos=0, totalRows=1; query: SELECT substr(testblob,1,2883583) AS testblob FROM tcw LIMIT 1
2022-08-29 10:58:06.825 D/DEBUG: Iteration is 22. Retrieve Size is 2818048
2022-08-29 10:58:06.829 W/CursorWindow: Window is full: requested allocation 2818047 bytes, free space 2096720 bytes, window size 2097152 bytes
2022-08-29 10:58:06.829 E/SQLiteQuery: exception: Row too big to fit into CursorWindow requiredPos=0, totalRows=1; query: SELECT substr(testblob,1,2818047) AS testblob FROM tcw LIMIT 1
2022-08-29 10:58:06.829 D/DEBUG: Iteration is 23. Retrieve Size is 2752512
2022-08-29 10:58:06.832 W/CursorWindow: Window is full: requested allocation 2752511 bytes, free space 2096720 bytes, window size 2097152 bytes
2022-08-29 10:58:06.832 E/SQLiteQuery: exception: Row too big to fit into CursorWindow requiredPos=0, totalRows=1; query: SELECT substr(testblob,1,2752511) AS testblob FROM tcw LIMIT 1
2022-08-29 10:58:06.832 D/DEBUG: Iteration is 24. Retrieve Size is 2686976
2022-08-29 10:58:06.837 W/CursorWindow: Window is full: requested allocation 2686975 bytes, free space 2096720 bytes, window size 2097152 bytes
2022-08-29 10:58:06.838 E/SQLiteQuery: exception: Row too big to fit into CursorWindow requiredPos=0, totalRows=1; query: SELECT substr(testblob,1,2686975) AS testblob FROM tcw LIMIT 1
2022-08-29 10:58:06.838 D/DEBUG: Iteration is 25. Retrieve Size is 2621440
2022-08-29 10:58:06.842 W/CursorWindow: Window is full: requested allocation 2621439 bytes, free space 2096720 bytes, window size 2097152 bytes
2022-08-29 10:58:06.842 E/SQLiteQuery: exception: Row too big to fit into CursorWindow requiredPos=0, totalRows=1; query: SELECT substr(testblob,1,2621439) AS testblob FROM tcw LIMIT 1
2022-08-29 10:58:06.842 D/DEBUG: Iteration is 26. Retrieve Size is 2555904
2022-08-29 10:58:06.846 W/CursorWindow: Window is full: requested allocation 2555903 bytes, free space 2096720 bytes, window size 2097152 bytes
2022-08-29 10:58:06.846 E/SQLiteQuery: exception: Row too big to fit into CursorWindow requiredPos=0, totalRows=1; query: SELECT substr(testblob,1,2555903) AS testblob FROM tcw LIMIT 1
2022-08-29 10:58:06.846 D/DEBUG: Iteration is 27. Retrieve Size is 2490368
2022-08-29 10:58:06.849 W/CursorWindow: Window is full: requested allocation 2490367 bytes, free space 2096720 bytes, window size 2097152 bytes
2022-08-29 10:58:06.849 E/SQLiteQuery: exception: Row too big to fit into CursorWindow requiredPos=0, totalRows=1; query: SELECT substr(testblob,1,2490367) AS testblob FROM tcw LIMIT 1
2022-08-29 10:58:06.849 D/DEBUG: Iteration is 28. Retrieve Size is 2424832
2022-08-29 10:58:06.853 W/CursorWindow: Window is full: requested allocation 2424831 bytes, free space 2096720 bytes, window size 2097152 bytes
2022-08-29 10:58:06.853 E/SQLiteQuery: exception: Row too big to fit into CursorWindow requiredPos=0, totalRows=1; query: SELECT substr(testblob,1,2424831) AS testblob FROM tcw LIMIT 1
2022-08-29 10:58:06.854 D/DEBUG: Iteration is 29. Retrieve Size is 2359296
2022-08-29 10:58:06.857 W/CursorWindow: Window is full: requested allocation 2359295 bytes, free space 2096720 bytes, window size 2097152 bytes
2022-08-29 10:58:06.858 E/SQLiteQuery: exception: Row too big to fit into CursorWindow requiredPos=0, totalRows=1; query: SELECT substr(testblob,1,2359295) AS testblob FROM tcw LIMIT 1
2022-08-29 10:58:06.858 D/DEBUG: Iteration is 30. Retrieve Size is 2293760
2022-08-29 10:58:06.862 W/CursorWindow: Window is full: requested allocation 2293759 bytes, free space 2096720 bytes, window size 2097152 bytes
2022-08-29 10:58:06.862 E/SQLiteQuery: exception: Row too big to fit into CursorWindow requiredPos=0, totalRows=1; query: SELECT substr(testblob,1,2293759) AS testblob FROM tcw LIMIT 1
2022-08-29 10:58:06.862 D/DEBUG: Iteration is 31. Retrieve Size is 2228224
2022-08-29 10:58:06.865 W/CursorWindow: Window is full: requested allocation 2228223 bytes, free space 2096720 bytes, window size 2097152 bytes
2022-08-29 10:58:06.865 E/SQLiteQuery: exception: Row too big to fit into CursorWindow requiredPos=0, totalRows=1; query: SELECT substr(testblob,1,2228223) AS testblob FROM tcw LIMIT 1
2022-08-29 10:58:06.865 D/DEBUG: Iteration is 32. Retrieve Size is 2162688
2022-08-29 10:58:06.870 W/CursorWindow: Window is full: requested allocation 2162687 bytes, free space 2096720 bytes, window size 2097152 bytes
2022-08-29 10:58:06.870 E/SQLiteQuery: exception: Row too big to fit into CursorWindow requiredPos=0, totalRows=1; query: SELECT substr(testblob,1,2162687) AS testblob FROM tcw LIMIT 1

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