Enscribe Programmer's Guide

number and record number, external to the data record, specifying the record's storage location
within the file. For relative files, the primary key is an ordinal number, again external to the data
record, denoting the record's position within the file.
In addition to access by primary key, you can specify alternate keys for key-sequenced,
entry-sequenced, and relative files. Queue files cannot have alternate keys.
Several HP NonStop software products, such as Enform and Enable, are available to help you
define and access Enscribe structured files.
Partitioned (Multiple-Volume) Files
When you create a file, you can designate it to reside entirely on a single volume or you can have
it partitioned over several volumes. Moreover, the separate volumes need not reside on the same
system; you can partition a file across network nodes.
Enhanced key-sequenced files can have 17 to 64 parts. For enhanced key-sequenced files with
increased limits, 17 to 128 partitions are permitted. Up to 16 partitions are permitted for all other
Enscribe file types. Queue files cannot be partitioned. The primary partition of an enhanced
key-sequenced file cannot contain user data and is instead used to store a portion of the file’s
label.
After a partitioned file is created, the fact that it resides on more than one volume and perhaps on
more than one node is transparent to the application program. The entire file is opened for access
by supplying the name of the primary partition to the FILE_OPEN_ procedure. Unless you specify
unstructured access, the file system rejects any attempt to open a secondary partition of a file.
Partitioned files can be valuable for a number of reasons. The most obvious one is that a file can
be created whose size is not limited by the capacity of a physical disk drive. In addition, by
spreading a file across more than one volume, you can increase the concurrency of access to
records in separate partitions of the file.
If the file is located on multiple volumes on the same controller, the operating system takes advantage
of the controller's overlapped seek capability; that is, many drives can be seeking while one is
transferring. If the file spans volumes connected to different controllers on the same processor,
overlapping transfers will occur up to the limit of the I/O channel's bandwidth. If the file resides
on volumes connected to controllers on different processors, the system performs overlapped
processing of requests and overlapped transfers not limited by the bandwidth of a single I/O
channel.
Partitioned files can also accommodate more locks, because the locking limit applies to each
partition rather than the whole file.
Partitioned file records can also reside in multiple caches, which can result in fewer disk accesses.
File Identifiers
Each partition has a directory entry on the volume on which it resides. The file names for all
partitions are identical except for the different volume names.
Few Differences Among Partitions
All the partitions of a file must be either audited by TMF or not audited; they cannot be mixed.
Primary and secondary extent sizes can differ from one partition to another within the same
partitioned file. In addition, the MAXEXTENTS value can differ from one partition to another within
a key-sequenced file. These and the volume names are the only file attributes on which partitions
can differ.
File Directory
A disk volume's file directory holds information about all the files on that volume. You govern the
size of this directory, either during system generation or when using the Subsystem Control Facility
Partitioned (Multiple-Volume) Files 21