Online Backups

C

coredump

New Member
Hi

Could someone perhaps tell me on what factors have an impact on the suspension during an online backup? How long does it on average take before users are able to perform reads and writes to the database.

Assuming I have 500 users active on the database when the Online backup is kicked off.

One other question which also comes to mind. How does the online backup deal with transactions in programs. If I am in the process of creating an invoice and the invoice consists of a header and detail line how does the Online backup handle this situation? Or will that active transaction not be part of the online backup?

Will it roll back the current transaction, will it partly backup and what happens when I restore the online backup to another database? Will I be sitting with a partial record?

Thanks in advance.
 
When you start an online backup the whole system "freezes" for as long as it takes to copy the whole BI file to the backup. That will be from a few seconds - up to a couple of minutes - depending on the size of the BI file and the performance of your system.

Then the database itself is copied to the backup - and all your users can access the database normally while that happens - although there will be some performance degradation because of the backup.

The "as at" time of the backup is the instant that Progress starts copying the BI file to the backup. In other words it is as-at the moment the backup commences - not when it finishes. Progress deals with updates during the backup to ensure that the backup is "clean".

When you restore the backup it will be, as I said, as-at the moment when the original backup started. When you start up the broker it will do a "crash recovery". That means that any transactions that were "open" at the moment when the backup started will be rolled-back out of the database.

Is that the info you were after??

Ron.
 
Thanks Ron

I disconnected from the wired world for a while thus not being able to respond to you're reply. Yes you comment makes sense to me. May I ask another question to this.

"A transaction is either completely committed or completely aborted to ensure integrity". On this basis, could a program/s hypothectically break this principle? Within a logical transaction can the BI file be updated physically even though the logical transaction has not been completed yet? (logical in this sense as to how one would perceive a complete transaction to be). At the point of "as-is" where the BI file has been updated and the Online backup is initiated, can the backup contain data that is out of sync. At no fault of the DBMS of course
 
The backup is always a snapshot as of the start of the backup. If a program goes to modify something in the database while the backup is running, Progress takes a snapshot of the records before the change and that is what goes to the backup. Any transactions which were not complete as of the start of the backup, whether they were already in flight or were started after the start of the backup will not be in that backup.
 
No, the BI and DB can't get out-of-sync. Progress goes to a lot of trouble to ensure that.

Of course, however, Progress is not a mind-reader. It is always possible -- on any database -- for a program to be badly written such that transactions are not scoped correctly. But Progress's default behaviour makes that difficult. It usually makes "very safe" presumptions in working-out the transaction scope.

Ron.
 
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