The SPD Engine does not support user-specified compression. If you are migrating a
default Base
SAS engine data set that is both compressed and encrypted, the encryption is retained,
but the compression is dropped.
The CONTENTS procedure
identifies the compress setting. If the data set is compressed, PROC
CONTENTS prints information about the compression. The following example
explains the Compressed Info fields in the CONTENTS procedure output:
In general, COMPRESS=CHAR
provides good compression when single bytes repeat; COMPRESS=BINARY
provides good compression when strings of bytes repeat. At the same
time, it is more costly to look for strings of bytes that repeat,
than to look for single bytes that repeat. For examples, see
COMPRESS=CHAR and COMPRESS=BINARY.
PROC CONTENTS Compressed Section
Number of compressed blocks
number of compressed
blocks that are required to store data.
Raw data blocksize
compressed
block size in bytes calculated from the size specified in the IOBLOCKSIZE= data set option.
It is the largest multiple of the observation length that gets in the block size.
Number of blocks with overflow
number of compressed blocks that needed more space. When data is updated and the compressed
new block is larger than the compressed old block, an overflow block fragment is created.
Max overflow chain length
largest number of overflows for a single block. For example, the maximum overflow
chain length would be 2 if a compressed block
was updated and became larger, and then updated again to a larger size.
Block number for max chain
number of the block containing the largest number of overflow blocks.
Min overflow area
minimum amount of disk
space that an overflow requires.
Max overflow area
maximum amount of disk
space that an overflow requires.
Accessing compressed
files usually requires more processing time. The files have to be
decompressed before reading them and, if updating, they have to be
compressed again when written to disk.