Content that is uploaded to a storage area is compressed if content compression has been enabled for the storage area and if the content can be compressed below the content compression threshold that is specified for the storage area.
Content compression uses blocked-compression technology that separates uploaded content into identical, size-controlled blocks. Compression takes place on an efficient block-by-block basis, in contrast to the uncompressed block size that is variable and based on the chunk size at upload.
If both compression and encryption are enabled, compression is applied before encryption. Each compressed block is encrypted independently.
Retrieval of compressed content takes place on a block-by-block basis. Header information in the first block of data indicates the number of bytes of compressed data to retrieve. If necessary, the compressed data is decrypted. The data is then extracted into a buffer and delivered.
In some cases, using content compression might not be appropriate and can impact overall system performance.
Certain data formats, such as JPEG and compressed files, do not compress significantly and content compression offers only a marginal savings in terms of storage space. In order to avoid inefficiencies during both upload and download, you can specify a content compression threshold that applies to the storage area. During content upload, the compression ratio of the first block of data is compared to the content compression threshold. If the first block is not compressed sufficiently, the entire content stream is written uncompressed and is equivalent to the case where compression is not enabled for the storage area. You can use the content compression threshold to define the threshold at which data is not compressed.