[ZODB-Dev] replicated ZEO idea

[sean.upton@uniontrib.com]

I like the idea of an iterator style transaction copier, using ZEO itself.

Months back, I was thinking about doing something similar (but at a much
higher level, using something like a deepcopy or the Zope import/export
mechanism) using a dedicated ZEO client to do this kind of thing.  This
seems like a much more appropriate way to do this.  Right now my likely
approach for replication has swung the pendulum to the other end and I'm
thinking of replicating the underlying storage, using Directory Storage
snapshots 8) and find+cpio+nfs.  Something in-between seems a bit more
graceful because of the ability to be storage agnostic.

Sean

-----Original Message-----
From: Toby Dickenson [mailto:tdickenson@geminidataloggers.com]
Sent: Sunday, September 15, 2002 6:25 AM
To: zodb-dev@zope.org
Subject: [ZODB-Dev] replicated ZEO idea


I have been thinking about the storages 'copyTransactionsFrom' method, which

uses another storages 'iterator' method to copy all of the transactions from

one storage to another. This is usually used for transferring data between 
different storage implementations, but I think this technique could also be 
used as the basis for a lightweight replication option.... Given two ZEO 
servers, an external process could perform the following operations using
the 
ZEO protocol:

1. connect to ZEO server B and determine his most recent transaction id.
2. connect to ZEO server A, and use the 'iterator' method to learn about all
   transactions more recent than B
3. copy those recent transactions from A to B.

That would be trivially easy, except that the 'iterator' method isnt exposed

by the ZEO server.

Is there any good reason why it isnt? Any objections to adding it for some 
later release? Has anyone looked at this before?


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