Andrew Thompson wrote:
I've been using the ZODB pretty intensively for a few weeks now, and
suddenly have started getting intermittent Database conflict errors, after
which calling conn.sync() makes no difference, and I cannot get back to the
pre-exception state in one of my ZEO clients, although all the others
continue quite happily.

I believe you're looking for:

from transaction import get
t = get()

The error is :
database conflict error (oid 0x029b, class btreelist.BTreeQueue, serial this
txn started with 0x03750b64c9cf1f00 2008-04-11 08:36:47.299000, serial
currently committed 0x03750b64ca57a788 2008-04-11 08:36:47.424000)

So, reading this more verbosely:
- the object with oid 0x029b was modified simultaneously on two
  different zeo clients
- when the transaction started on the zeo client where this error was
  raised, the object at 0x029b was committed at
  2008-04-11 08:36:47.299000
- when an attempt to commit this transaction was made, it was found this
  this committed time had changed to 2008-04-11 08:36:47.424000

As such, if this commit were to succeed, it would replace the data committed at 2008-04-11 08:36:47.424000, which would probably be a bad thing ;-)

(Imagine two people working on a text file over a network share: one saves, then the other saves, the changes made by the first person are lost, resulting in unhappiness allround ;-) )

Question : What does the "conflict error" actually mean ?

See above...

Question : All my other ZEO clients continue happily  -- and even this
process works ***most*** of the time.  Short of dropping the ZEO connection
and rejoining is there a way of resetting the ZEO session?

The "standard" way of dealing with conflict errors is to:

- abort the current transaction
- redo all the changes you'd made to objects in that transaction
- commit again

Pick an arbitary number of times to repeat this process (3 is often the magic number [1]) and if it still fails, let the conflict error percolate up...




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