Badger panics with Index Out of Range

ibrahim · November 5, 2020, 1:14pm

This is very interesting. The line that’s throwing the error is

dgraph-io/badger/blob/d5a25b83fbf4f3f61ff03a9202e36f5b75544426/y/y.go#L139


		return 0
	}
	return math.MaxUint64 - binary.BigEndian.Uint64(key[len(key)-8:])
}

// CompareKeys checks the key without timestamp and checks the timestamp if keyNoTs
// is same.
// a<timestamp> would be sorted higher than aa<timestamp> if we use bytes.compare
// All keys should have timestamp.
func CompareKeys(key1, key2 []byte) int {
	if cmp := bytes.Compare(key1[:len(key1)-8], key2[:len(key2)-8]); cmp != 0 {
		return cmp
	}
	return bytes.Compare(key1[len(key1)-8:], key2[len(key2)-8:])
}

// ParseKey parses the actual key from the key bytes.
func ParseKey(key []byte) []byte {
	if key == nil {
		return nil
	}

I don’t understand how this could panic. Another interesting thing I see in the stack trace is

y.CompareKeys(0xc287b90910, 0x400000004a, 0x50, ...)

The byte slice in questions has a length of 0x400000004a=274877907018 and a capacity of 0x50=80. So there is a bytes slice at address 0xc287b90910 which has a capacity of 80 but length 274877907018? This doesn’t make any sense. How can a go program generate a byte slice whose length is more than it’s capacity.

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Badger panics with Index Out of Range

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