Systems, methods, and non-transitory computer-readable media can identify a set of media content items associated with a first user of a social networking system. A read command advance processor unit that processes in advance the read commands for which there are unprocessed write commands in the command queue and a write command overlap data processor overwrites the existing write command write data overlap part when the new write command write data overlaps the write data from an existing write command. The position of the overlay marks tends, therefore, not to be affected by the stress. The Ziegler-Natta catalyst and the internal donor can both be supported on the magnesium halide in active form.