HP Integrity NonStop J-Series - Manual (Page 62)

Configuring Automatic Transaction Processing
HP NonStop AutoTMF Software User’s Guide—429952-016
4-14
Unstructured Access
In addition to specifying WAITEDIO, use the WAITTIME option to specify the maximum
number of seconds an operation will wait for record locks to be released.
Considerations:

When AutoTMF performs AWAITIO, it does not know the timeout value that will be
specified in the application call to AWAITIO. Configure the WAITTIME option on a
file basis. To avoid perpetual waits, AutoTMF uses the default wait time of 64
seconds.

AutoTMF does not return file system errors 27 and 28 when a program performs
an I/O operation without calling AWAITIO on the previous operation. Instead,
AutoTMF signals an assertion failure which commits all outstanding transactions
and terminates the program.

Error 26 occurs in the normal manner.

When debugging a program, Inspect shows the completed operation state and
error code as soon as the read or write operation has been executed.

A FILEINFO, or a similar operation called between READ and AWAITIO can return
updated key values that are normally available only after the call to AWAITIO.

If executed between the READ/WRITE and AWAITIO, FILE_GETINFOLIST_ can
return the wrong value for the last error code.

Configuring WAITEDIO normally has a minor or negligible effect on performance.
Overlapped NOWAIT I/O is very useful for non-audited files, where every update
requires a physical disk operation. Since audited file updates are buffered,
NOWAIT I/O is far less useful for audited files.
Unstructured Access
The OPEN and FILE_OPEN_ procedures have an optional parameter to request
unstructured access.
Unstructured access to a structured file (key-sequenced, entry-sequenced, or relative)
allows a program to position to a relative byte address and to read or write a string of
bytes at that location. Interpreting and updating the internal Enscribe block structures
are the responsibility of the programmer.
Unstructured access to either unstructured files or structured files also permits large
transfers to be used if the appropriate BULK I/O interfaces are used.
When a file is audited, some the following rules apply to the use of unstructured
access:
Caution. Not all programs that perform multiple NOWAIT operations will encounter this
problem. Using this feature has some side effects. Users should not use Waited I/O
except in consultation with product support.