Applicable release versions: AP
|Description||a subsystem designed to write file system updates to another device.
The changes are written to an internal queue. This queue is then written to a device, tape, or network by a dequeuing process run on a phantom line.
If the dequeuing process can keep up with the enqueuing of items by the users, then up to the second crash protection can be accomplished. Used with a file-save tape, all updates will have been recorded for restoration.
If used with another machine it can provide a "hot backup".
See the "tape-socket" menu to setup a Unix pipe on both machines for hot backups.
"Startlog" on the primary machine and "tlog-restore" on the secondary machine will provide the basic functionality for hot backups. See "tape-socket" to setup the proper pipes across the network.
"Txlog" is a menu available to help manage the transaction logger. It can start and stop the dequeuing process as well as filter data going into the queue. All files may be logged or only files with an "l" in attribute one.
"set-dptr" is a verb that can change a dptr or all dptrs in an account to add or remove the "l" from attribute one. If only "dl" type files are being logged then a normal create-file will not cause a create-file on the backup machine. So, changing the d-pointer to "dl" later will not cause a create-file either. This is part of the design and should be noted.
A device must be attached to the port that is starting the dequeuing process. The transaction logger will "steal" the device and begin dequeueing to it. The logger runs on a phantom process, usually the last one, right before the scheduler.
When a "stoplog" is entered, the current reel on the dequeuing device is terminated with a file mark and a "t-det" is executed by the dequeuing process. It will remember which tape device it was using, but now this device is free. The next "startlog" entered will re-attach the tape and increment the reel number.
Each reel in a transaction log dequeue session is independent and can be restored from tcl one after the other or separately.
On AP 6.1 multi-user tape releases a list of devices is available to chose from. To cause the startlog command to display this list just detach all the tape devices prior to invoking startlog.
set-dptr +l invoices (f invoices : D -> DL invoices : D -> DL set-sct Block size: 16384  Tape device is assigned to med density (150M) quarter inch tape (SCT). startlog Activate transaction logger (y/n)?y  Transaction logger started. The above sequence will allow all updates to the invoices file to be enqueued for writing to the SCT drive. stoplog  The transaction logger is disabled. This command will write a file mark on the tape and release it from the transaction logger, t-det. Updates will still be enqueued automatically. This is reel one. startlog  Transaction logger started. This restarts the logger to the SCT drive on behalf of reel two.