The SPD Engine uses
blocks in memory to collect the observations to be written to or read
from a data component file. IOBLOCKSIZE= specifies the size of these
blocks. (The actual size is computed to accommodate the largest number
of observations that fit in the specified size of
n bytes. Therefore, the actual size is a multiple
of the observation length).
The block size specified
in IOBLOCKSIZE= also applies to compressed data sets.
Once a data set is created,
you cannot change its block size. To resize the block, you must copy
the data set to a new data set, setting IOBLOCKSIZE= to the appropriate
block size for the output data set.
The default value and
the IOBLOCKSIZE= smallest value is 32,768 bytes. You specify an IOBLOCKSIZE=
value that complements the data to be accessed. Access to data that
is randomly distributed favors a smaller block size, such as 32,768
bytes, because accessing smaller blocks is faster than accessing larger
blocks. In contrast, access to data that is uniformly or sequentially
distributed or that requires a full data set scan should have a large
block size, such as 131,072 bytes.