TurboIMAGE/XL Database Management System Reference Manual (30391-90012)

326 Chapter7
Logging and Recovery
Logging Preparation
Step 4--Building a Log File for Logging to Disk
This step is required only when logging to disk. You must build the new file and allocate
space for it on disk by using the MPE/iX BUILD command below.
Syntax
:BUILD
logfile ;CODE=LOG;DISC= [ numrec ] [, [ numextents ] [, initial loc ]]
[;DEV= [
device ]]
Parameters
logfile is the name of the log file being built, as specified in the MPE/iX GETLOG
command. If you specify the AUTO option with the GETLOG command, the
log file name must end with 001 to designate the first file in the log file set.
NOTE If you are using roll-back recovery, the log file and the database must be in
the same volume set. To accomplish this, use the device parameter of the
MPE/iX BUILD command and then create the log file in the appropriate group
and account.
numrec is the maximum number of logical records. Maximum value allowed is
2,147,483,647. Default is 1023.
numextents is the maximum number of disk extents (from 1 to 32, inclusive). Default is
8.
initialloc is the number of extents to be initially allocated to the file at the time it is
opened. Default is 1.
device is the class of the device on which the log file and database are to reside.
This parameter puts the log file and database in the same volume set.
Required for roll-back recovery; is not used for roll-forward recovery.
If the default NOAUTO option is used in the GETLOG command, disk log files must be of
sufficient size to prevent the end-of-file from being reached, because MPE/iX causes the
associated log process to terminate when the log file is filled to capacity. Therefore,
subsequent calls to TurboIMAGE/XL intrinsics that require log records to be written to the
log file will fail. If this occurs in the middle of a transaction, the database is left in an
inconsistent state. It then becomes necessary to recover transactions with roll-forward or
roll-back recovery. Because reaching the end of a disk log file is similar in effect to a system
failure, disk log files should be built with a total capacity far exceeding their required size
and consisting of as many extents of contiguous disk sectors as needed to meet the capacity
requirements of the file, subject to the constraints of the MPE/iX file system; of these
extents only enough to satisfy the expected capacity should be allocated initially.
NOTE When the NOAUTO option is used, the MPE/iX SHOWLOGSTATUS command
can be used to determine the space usage of the existing log file and when to
create a new log file using an MPE/iX CHANGELOG command.