HP NonStop G-Series - Manual (Page 59)

Configuring Automatic Transaction Processing
HP NonStop AutoTMF Software User’s Guide—429952-014
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Considerations
used to lock records that are not already locked, READUPDATELOCK may be
used with RECORDTX.
Considerations
As mentioned above, record-level transactions increase transactional activity and
processing complexity, and they are useful only in very specific situations. Users
should configure record-level transactions when a careful analysis of a program’s
locking behavior leaves no other option or after being instructed to do so by product
support.
Changing Nowait IO to Waited IO
To commit automatic transactions, AutoTMF must find a point where no records are
locked by the application program. Most programs have such points, but others have
complex algorithms that lock records on some files before unlocking records on other
files, leaving no commit opportunity. The configuration options SEPARATETX and,
rarely, RECORDTX can be used in most cases to provide the necessary commit
points.
However, a program may still be too complex to be managed using these methods.
The WAITEDIO feature handles these rare cases, where a program opens a file
multiple times for NOWAIT processing, and performs concurrent I/O to the same file. If
the I/Os are performed under a common transaction, an I/O may be in progress at all
times, preventing the transaction from being committed. If the I/Os are performed
under separate transactions, operations that need to lock the same record on different
opens may cause an internal deadlock.
If the WAITEDIO option is enabled for a NOWAIT file open, AutoTMF performs the
following operations:
•
Issues an AWAITIO immediately after the read, write, or update operation.
•
Following the AWAITIO, AutoTMF commits any outstanding transaction using its
usual algorithms, as directed by the configuration.
•
Saves the values returned by AWAITIO, and returns control to the program as if
the READ or WRITE operation were still in progress. After a READ, the data buffer
contains the input data.
FILEINFO and FILE_GETINFO_ return the error code for the last READ or WRITE
operation (instead of AWAITIO). Any error returned by the AutoTMF generated
AWAITIO is not visible to the application until the application calls AWAITIO. When the
program calls AWAITIO, AutoTMF returns the saved values and makes the operation
error visible to the application.