Re: [ZODB-Dev] Undo differences between Z2 and Z3

2006-05-19 Thread Chris Withers
Jim Fulton wrote: Chris Withers wrote: Jim Fulton wrote: Even if you did track reads, how would you distinguish an unsafe read as above from a normal read that shouldn't cause a conflict? A write (or the undo of a write) would conflict with any reads in later transactions. Wouldn't that,

Re: [ZODB-Dev] Undo differences between Z2 and Z3

2006-05-19 Thread Jim Fulton
Chris Withers wrote: Jim Fulton wrote: Chris Withers wrote: Jim Fulton wrote: Even if you did track reads, how would you distinguish an unsafe read as above from a normal read that shouldn't cause a conflict? A write (or the undo of a write) would conflict with any reads in later

Re: [ZODB-Dev] Undo differences between Z2 and Z3

2006-05-18 Thread Chris Withers
Jim Fulton wrote: Logical inconsistencies. Consider two transactions, T1 and T2 that run the same code: def f(): if 'x' not in somefolder: somefolder['x'] = 42 The postcondition of the transaction is that somefolder has an item named 'x' with the value 42. Now, when T2

Re: [ZODB-Dev] Undo differences between Z2 and Z3

2006-05-18 Thread Jim Fulton
Chris Withers wrote: Jim Fulton wrote: ... Even if you did track reads, how would you distinguish an unsafe read as above from a normal read that shouldn't cause a conflict? A write (or the undo of a write) would conflict with any reads in later transactions. Jim -- Jim Fulton

Re: [ZODB-Dev] Undo differences between Z2 and Z3

2006-05-17 Thread Chris Withers
Hi Jim, Jim Fulton wrote: BTW, I strongly discourage use of Undo except in emergencies. Sadly, except when undoing the last (non-undo) transactions in a database can lead to inconsistency. What sort of inconsistencies are you referring to? Undo can be a very attractive feature although

Re: [ZODB-Dev] Undo differences between Z2 and Z3

2006-05-17 Thread Russ Ferriday
And undo is prominently exposed in Plone, and its use is not discouraged.Do you think, Jim, that we should reconsider that?--rOn 17 May 2006, at 08:18, Chris Withers wrote:Hi Jim,Jim Fulton wrote: BTW, I strongly discourage use of Undo except in emergencies.Sadly, except when undoing the last

Re: [ZODB-Dev] Undo differences between Z2 and Z3

2006-05-17 Thread Jim Fulton
Chris Withers wrote: Hi Jim, Jim Fulton wrote: BTW, I strongly discourage use of Undo except in emergencies. Sadly, except when undoing the last (non-undo) transactions in a database can lead to inconsistency. What sort of inconsistencies are you referring to? Logical inconsistencies.

Re: [ZODB-Dev] Undo differences between Z2 and Z3

2006-05-17 Thread David Binger
On May 17, 2006, at 6:54 AM, Jim Fulton wrote: It was claimed earlier in this thread, that plone only lets you undo the most recent transactions. If this is true, then that should not be a problem. A facility that let you only undo last transactions would be safe. It would also be useful,

Re: [ZODB-Dev] Undo differences between Z2 and Z3

2006-05-16 Thread Jim Fulton
David Pratt wrote: There seems to be enough of a difference between Z2 and Z3 undo to have an effect on a backend like PGStorage from working on Z3. I believe the objective in the storage api is that it should not matter to the backend whether you are connected to Z2 or Z3. Can someone more

Re: [ZODB-Dev] Undo differences between Z2 and Z3

2006-05-16 Thread David Pratt
Jim Fulton wrote: David Pratt wrote: There seems to be enough of a difference between Z2 and Z3 undo to have an effect on a backend like PGStorage from working on Z3. I believe the objective in the storage api is that it should not matter to the backend whether you are connected to Z2 or Z3.

Re: [ZODB-Dev] Undo differences between Z2 and Z3

2006-05-16 Thread David Pratt
Hi Jim. I managed to fix this by modifying the storage but it seems to me strange to differentiate in a storage whether it is a backend to a z2 or z3 app. Regards, David ___ For more information about ZODB, see the ZODB Wiki: