Subject Re: [ib-support] Why gbak hangs without G option ? (back to old problem)
Author Ann W. Harrison
At 10:30 PM 9/1/2002 +0200, =?iso-8859-2?Q?Bogus=B3aw_Brandys?= wrote:

> > I have big database (over 2GB) with only one simple table
> > ... Firebird 1.0 server WI-V6.2.794 version of gbak. Database is OK
> > verified with gfix -validate.... populated with almost the same data
> > in each record (about 20 records are different)
> > ... backup this database without G option hangs gbak about 800000
> > row and server memory usage grows to 125 MB.
> > but when using [the G option] all works fine.

The G option controls garbage collection, so my guess is that you've
got a dead record version and an index with lots of duplicates. Dead
record versions are created by updates, deletions, and transactions
that roll back.

> > 1 . Can this happen in good performed production database just becouse is
> > huge ?


> > 2 . Is it a bug or just becouse database is bad constructed ?

Unless I miss my guess, you've an index with several million duplicate
values. I'd drop that index and all should be well again. If you
don't have an index, write back - there may be a bug. As far as I
know, multi-gigabyte databases containing primarily duplicate values
are rare and you may have found some problem.

> > 3. How reliable gbak is ?

Generally, it is very reliable.

> > Is there a procedure to test if backup is reliable ,
> > some of course different that just restore (this is too time consuming)

No, unfortunately, there isn't. Some problems with backups really aren't
easy to diagnose (e.g. duplicates in a unique field) unless you actually
build a database.

> > 4.Which are the advantages gbak has over simple SQL copy data and metadata

1) A copy to text works badly with binary data (e.g. blobs that
contain images).
2) Gbak is probably faster and the output is smaller.

> > 5 .And the last (a little off topic) question about gbak : why backup is
> > named
> > "compressed" ? I don't see any compression in backup files ,I can even
> > compress them with rar or zip to very small sizes

The data portion of records is compressed in a very simple way - tar and
zip use more sophisticated compression and get a lot more space out.


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