Communicator e3000 MPE/iX Release 6.5 (Non-Platform Software Release C.65.00 (30216-90291)

128 Chapter5
Internet and Interoperability
Large Transactions for IMAGE Users
message is written onto the console.
One can also truncate the userlog after expansion if there are any disk space or
performance issues. The volutil interface is same for this operation too.
One can backdate the OS to an earlier version with the userlog in the expanded state.
The expansion of the userlog may fail due to one or more reasons. In that case, the system
reports it through a warning message on the console.
If it fails due to lack of disk space, make sure that there is sufficient contiguous space on
the master that would fit the need for the increment in the userlog size. Then reboot the
system so as to enable it to complete the expansion of userlog. You must ensure that
memory beyond 256 MB is available on the system, before increasing the userlog through
VOLUTIL.
NOTE The userlog size gets scaled between 32 MB and 64 MB if the memory size
available on the system is > 64 MB and < 256 MB.
The current log size can be seen through the command SHOWUSERLOG.
>From VOLUTIL,
SHOWUSERLOG <volset-name>
This command accepts a valid MPE volume set name and shows the current size of the XM
userlog in sectors.
It has to be noted that, a single transaction can grow up to 32 MB now and if the size of
userlog is 64 MB, total size of all active transactions on that volume set can be 32 MB (half
log size). If the total size of all active transaction exceeds half log size, all the processes
which are actively logging into the same userlog are aborted. So, a large transaction may
result in all processes getting aborted, if the userlog size is not expanded appropriately.
The downside of having a larger userlog is that the XM checkpoint process has more data
to write to disk at reaching the end of each userlog half. This can have effect on response
time to on-line users.
TurboIMAGE
Support for Large Transaction Size: Image has been enhanced to support the new 32 MB
transaction size provided by XM. This means, without doing anything special, one can
have approximately more than 8 times the number of extended transactions in a dynamic
transaction than possible today (including the XM optimization available with XM patch
MPEKXG8, which has been rolled into this solution).
User Control of Transactions: In addition to the benefit of transaction sizes up to 32 MB,
available across the board to all IMAGE and IMAGE/SQL users, direct IMAGE
applications benefit from a new feature. This feature helps a user to judiciously
control/manage large transactions. User application can avail of an early warning message
feature through which the application can have virtually a full control over the
transaction. To avail this facility, a new mode (mode 18) has been added to DBCONTROL
intrinsic. If the application makes a call to DBCONTROL mode 18 before the start of a
transaction, it sets a flag in IMAGE, to trap the softlimit warning message from XM, and
inhibits all new transactions. Now the user application have two options: