Data compression symmetry

Symmetry and assymetry, in the context of data compression, refer to the time relation between compression and decompression for a given compression algorithm.

If an algorithm takes the same time to decompress a data archive as it does to decompress it, it is considered symmetrical. Note that compression and decompression, even for a symmetric algorithm, may not be perfectly symmetric in practice, depending on the devices the data it being copied to and from, and other factors such as latency and the fragmentation on the device.

In turn, if the compression and decompression times of an algorithm are vastly different, it is considered asymmetrical.

Examples

Symmetric algorithms are typically used for media streaming protocols, as either the server taking too long to compress the data, or the client taking too long to decompress, would lead to delays in the viewing of the data.

Assymetrical algorithms wherein the compression is faster than the decompression can be useful for archiving data, as archives are typically more often backed up to than they are restored from.