public static long genKey(long segmentId, int columnId, int packId) {
        assert segmentId <= MAX_SEGMENT_ID;
        assert columnId < StorageSegment.MAX_COLUMN_COUNT;
        assert packId < StorageSegment.MAX_PACK_COUNT;

        return (segmentId << 32) | ((columnId & StorageSegment.COLUMN_ID_MASK) << 16) | (packId & StorageSegment.PACK_ID_MASK);
    }
The capacity of this cache, in bytes.
indexr-segment/src/main/java/io/indexr/segment/cache/MemCache.java