[Zope-dev] Distributed ZODB-Transactions

[Shane Hathaway]

Heine Gregor wrote:
> I want to write an Product that mirrors every ZODB-Transaction to a
> Backup-Server.
> The idea was to trap every transaction (i.e. creation, change, deletion of
> zope-objects) and transfer a copy of the object to another server (via
> XML-RPC?!?) after the transaction got commited.
> I've been debugging through various zope-classes (esp. transaction.py,
> connection.py) but couldn't understand the way, zope manages the
> transactions.
> The creation and deletion process always seems to trigger a transaction for
> the parent object.
> Has anybody an idea?

Data.fs is essentially a log file that is appended with binary data. 
The only time the data is changed rather than appended is when you pack
the database.  Therefore, it may be easier to write a script that
catches the data that is appended and appends it to the backup file. 
When the script detects the file has shortened (after a packing
operation), it should copy the whole file over.

The simple fact that data is appended rather than changed makes Data.fs
quite reliable.  It can withstand most kinds of failure.  And the Zope
undo mechanism is very effective.

So I would suggest that the backup you intend to perform does not need
to be an integral part of Zope.  Rather, it is appropriate that it be a
background process run periodically.

Shane