Addressing OLTP Solutions with CICS: The Transaction Server ... - Ibm

80 CICS for AIX as the Transaction Server
The data component of a file and its indexes can reside on different volumes,
and thus on different disks. This independence gives administrators greater
flexibility in controlling availability and performance.
• Import/export capability.
SFS files can be stored and retrieved from a file, disk, or tape device and
can be transferred between SFSs.
The SFS is a nonhierarchical file system. SFS files are independent of the
operating system file system. Administrators access SFS files through sfsadmin
commands.
To organize record-oriented data, the SFS offers multiple file layouts:
entry-sequenced (also known as sequential), relative, and B-tree clustering.
The records of entry-sequenced files are stored in the order in which they were
inserted into the files; that is, each new record is appended to the end of the file.
This type of file is useful for keeping time-sequenced event records, such as
audit trails.
The records of relative files are stored in an array of fixed-length slots; a new
record can be inserted into a specific slot, into the first free slot in the file, or at
the end of the file. Relative files are useful for direct access by slot number.
The records of clustered files are organized in a tree structure. Clustered files
are useful for records that are to be accessed by a field or combination of fields
as specified by the creator of the file.
Each SFS file has a primary index, which defines the key to be used to physically
order the records. A key is a sequence of one or more fields to be used as a
basis for retrieving a record. Each SFS file can have zero or more secondary
indexes. A secondary index specifies one or more alternative fields to be used
to retrieve a record. A secondary index does not change the physical order of a
file′s records. Instead, it creates an alternative sequence in which the records of
a file can be accessed according to values of certain fields. If a file′s secondary
index is based on fields whose values are most frequently accessed by an
application, use of the index can minimize the time needed to access a record.
Each SFS file has a primary area that contains user data and the primary index.
A file can also have zero or more secondary areas, one for each secondary
index. A file′s areas can reside on the same or on different volumes, and thus
on different disks or partitions. Note that while a volume can contain many
areas, a single area cannot span more than one volume. The flexibility of file
area storage allows administrators to easily control availability and performance.
For instance, administrators may want to mirror only the volume on which the
primary index resides, since secondary indexes can easily regenerated. This
avoids the cost of mirroring the entire file.
To prevent unauthorized access, Encina SFS takes advantage of the
authentication tools embedded in DCE. It provides access control list (ACL)
protection for services including its administrative interfaces (for example, file
creation, file deletion, and file listing). Through the use of the ACL feature, it is
possible to protect SFS operations such as read, insert, and update operations,
as well as grant exclusive file access to a client.