TurboIMAGE/XL Database Management System Reference Manual MPE/iX V6.5 (30391-90011)

356 Chapter7
Logging and Recovery
Roll-Back Recovery
For recovery to succeed, you must have access to the log file. This implies either knowing
the maintenance word and having system manager (SM) or operator (OP) capability, or
being the creator of the log identifier with read access to the log file if it resides in a
different logon group and account. If the log file is on tape, you must know the volume
identifier.
NOTE If the operator is unsure of the volume identifier, it is displayed on the console
when the tape is mounted.
If the database creator and the creator of the log identifier are not the same, and if the disk
log file and the database are in two separate accounts, follow the steps listed below for
recovery to proceed:
1. Assign a maintenance word to the database.
2. Logon as the creator of the log identifier.
3. Fully qualify the database name when issuing the >ROLLBACK command.
4. Specify the maintenance word.
MPE/iX Cleanup Mode and Roll-Back Recovery
In the event of a system failure and subsequent start recovery operation, MPE/iX attempts
to clean up any user log files that were open at the time of the failure. The cleanup
procedure involves writing any records left in the system log file disk buffer to the user log
file. Note that for roll-back recovery without this cleanup, transactions are not lost during
a start recovery operation because they are not held in the memory buffer. You should not
cancel (from the console) this cleanup procedure if the log file is on tape. Canceling the
start recovery operation for tape log files will cause rollback recovery to fail.
The advantage of the cleanup procedure is that fewer user log records written just prior to
the failure are lost. For tape files, the disadvantage is the time it takes for the tape to be
rewound and sequentially scanned until the end-of-file is detected so that the remaining
records can be appended to the end.
The TurboIMAGE/XL recovery program DBRECOV does not require the cleanup to be
performed. If it is not performed, however, DBRECOV most likely will report a sequence or
checksum error when the discrepancy caused by the failure is encountered. This would
cause DBRECOV to assume the end-of-file has been reached.
DBRECOV Abort Message
If DBRECOV aborts before recovery completes, the following information is printed:
Abort occurred on database: dbname dbgroup dbaccount
Total database open count: #open Current open count: #open
Process user is: dbuser dbgroup dbaccount Running program: progname
Log file name: logfilename Logging ID: logid
Log file record number: nnnnnnnn Transaction type: xx
Transaction date/time from log record: day, month, dd, year, time
Last successful transaction #: nn
First log record # of last successful transaction: nn
Record the information, set the log file, locate the database store, and contact your HP
support representative.